Why is no one Using Mark VIII IRS Rear Brake Calipers with Cobra 11.66” Rear Rotors? - FFCars.com : Factory Five Racing Discussion Forum
FFCars.com Forums Advertisers Build Sites FFR FAQ Gallery

Go Back   FFCars.com : Factory Five Racing Discussion Forum > General Topics > Brake and Suspension Tech
Register Garage iTrader FAQ Members List Calendar Mark Forums Read Auto EscrowAuto Loans


FFcars.com is the premier factory five cars Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 10-29-2007, 02:44 AM   #1 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Question

Many builders are using Mustang GT PBR front calipers and 10.8” front rotors or Cobra PBR front calipers with 13” rotors to improve the front braking on the FFR. The popular rear brake upgrade to go along with this modification seems to be using 11.56” rear Cobra rotors and matching Cobra rear calipers, using North Racecar’s adapter brackets to mount the larger Cobra brakes to the IRS spindle carriers.

Even with these brake upgrades there is a general consensus that there still needs to be additional rear brake bias to optimize braking on the FFR.

To that end…. why is no one using a combination of the Cobra 11.56” rear rotors with the original Mark VIII rear calipers?

The rear Cobra single piston caliper is 1.5” in diameter providing a piston area of 1.767 sq. in.

By contrast, the rear Mark VIII single piston caliper measures 1.78” diameter or a piston area of 2.488 sq. in…. Effectively a 40% increase in piston area!

Both rear calipers would require a purchased or custom fabricated mounting bracket due to the larger rotor diameter.

Because the Cobra rotor has a .200” offset toward the car centerline, compared to the original IRS rotor, a change in caliper spacing would be needed, but this offset would be simple to accommodate in the fabricated mounting bracket.

Both rotors are within .005” of the same nominal width…easily accommodated by the caliper and pad set.

The Mark VIII calipers would also require slight added clearance to accommodate the larger rotor arc, but it would be a very simple modification.

There are only two negatives I can see. One is minor, and the second may be a problem.

The minor issue is that the larger Mark calipers add 1.2 lbs more unsprung weight to each rear wheel, but this is a fair trade-off, especially on the rear, in exchange for the increased braking pressure the large pistons would afford.

The more serious issue is the apparent lack of performance pads for the Mark VIII rear caliper. Hawk for example does not offer a rear pad. I have not researched pad selection very far yet, but this MAY be a stumbling block.

Any comments or thoughts as to why this combination of rear brake components has not already been tried?

Any obvious problems with this combination I may have overlooked?

It certainly seems like a viable option to gain needed rear brake bias and would seem to especially be a good match with 2002-2004 GT front PBR 44.5 x 44.5mm dual piston calipers and 10.8” rotors.

Kerry
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 10-29-2007, 02:57 AM   #2 (permalink)
Senior Member
 
Bob Cowan's Avatar
 
Join Date: Jul 2002
Location: Colorado Springs, CO
Posts: 16,046
Post

As long as you can get performance or semi-performance pad, I don't see why it wouldn't work.

If you can't find a good pad, consider using the stock T-Bird caliper with the larger rotor. Again, you would have to fab your own mounting bracket.

The T-Bird rotor is about 1/4" thicker than the Mustang or Lincoln rotor. That can be an issue. If you let the pads wear enough with the thinner rotor, the piston will pop out of the caliper. Although I'v never experianced that, I suppose it would be a bad thing. But placing a 1/4" spacer behind the outboard pad will fix that issue.
__________________
.boB "Iron Man"
NASA Rocky Mountain TTU #42
Dart 427W, Momar 8 Stack EFI, 600'ish hp, TKO, 3.55 TruTrac, Red with Ghost Flames. More fun than should legally be allowed.
Bob Cowan is online now   Reply With Quote Quick reply to this message
Old 10-29-2007, 03:20 AM   #3 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Post

Bob,

What year T-Bird rotor is 1/4" thicker?

I did a check of the 93 T-Bird IRS and the rear rotor and caliper are the exact same parts as used on the 95 Mark VIII...
???

Kerry
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 03:41 AM   #4 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Post

OK...

Poterfield offers a R-4S or R-4 compound the in the AP599 / D599 rear pad configuration that is common to the Mark VIII and T-Bird IRS.

This same pad is also used on the 2001-2002 Viper 8.0 rear caliper.

Pad availability should not be an issue.

Kerry

[ October 28, 2007, 11:56 PM: Message edited by: Kerry & Kathy ]
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 04:04 AM   #5 (permalink)
Senior Charter Member
FFCars Craftsman
 
mrk3cobra's Avatar
 
Join Date: Mar 2005
Location: san ramon,california
Posts: 529
Post

I have the poterfield R-4s pad on my IRS rear calipers.Let me know what you find I would like to install the cobra 11.56 rear rotors on my cobra if there is a bracket available.
__________________
San Ramon Pete, markIII, IRS,SN95 spindles,AGR custom power rack,non donor,302,VPM swaybars,Mass-flo,AFR 165 heads,Vortech V-2SQ 10 psi supercharger.
mrk3cobra is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 07:56 AM   #6 (permalink)
Big Kahuna
 
bstuke's Avatar
 
Join Date: May 2007
Location: Lawrenceville, GA
Posts: 5,644
Post

Quote:
Originally posted by Kerry & Kathy:
What year T-Bird rotor is 1/4" thicker?
The 1990 used a .945” thick rotor. 1992 and up use a thinner .715” rotor.
__________________
FFR4615 is Sold!! 818 next up.
818R Build Blog
"We don't just build cars, we build friendships and memories" Chip Foose
bstuke is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 11:17 AM   #7 (permalink)
FFCobra Master Craftsman
FFCars Captain
 
John Phillips's Avatar
 
Join Date: Jan 2002
Location: Jupiter, FL
Posts: 3,236
Post

Kerry, thanks for this idea, and the research.

FWIW, if performance brake pads are not available, Carbotech used to bond their various performance pads to your pad plates on an exchange basis. Check with them to see is this service is still available, They're listed in "Vendor Links" on this forum.

If this Mark VIII rear brake concept can be developed further by those with machining skills, I'd be interested in trying it. Vendors, what would a set of brackets cost?
__________________
John Phillips, Jupiter, Florida
#1152; #3422; #1004554 mod 5.0 DOHC, IRS, sold May 2013, pics at http://imageevent.com/jlphil/carstuff/ffr

Smyth G3F Beta-build: 1999.5 Jetta TDI donor, Malone Stage 2 Tune and injectors. Loved my Roadsters; the G3F will be my daily driver. Build details here:http://www.g3f-jlphil.blogspot.com/
John Phillips is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 11:52 AM   #8 (permalink)
ASE Tech & Shop Teacher
FFCars Master Craftsman
 
Cobrabilly's Avatar
 
Join Date: Dec 2006
Location: Upper Peninsula of Michigan
Posts: 1,936
Post

Even though I have a 4-link, I thought I'd add my 2 cents. Go ahead and add the bigger rear rotor set-up, and leave single piston 11" brakes up front.

I read enough posts about the need for more rear brake bite, and the prop valve tricks not helping much, I wondered why everybody was upgrading their front brakes.

Of course the 13" set-up "looks good". But to me it's having the best looking girl in the room, but having to deal with the fact that she's a phsyco!! Just not worth it.

I left the stock single piston calipers, OK, I did buy reman calipers and new rotors and pads, but basically left stock 11" GT brakes on the front, and went with the 11.65" FRPP Cobra rear brake set-up. With the stock hydroboost, master and prop valve, it all works great together.

Predictable, efficient, fairly cheap and easy. I like it.

FRPP sells two kits, cheaper than the one BIG kit. The rotors, brackets, and shields kit was under $200, and the FRPP Cobra caliper kit with pads I found was also under $200.

Prices vary, but I thought it out, had patience when I shopped, and I'm really happy how it turned out.

You might want to try a set-up like that.

Makes me wonder why FFR includes the big fronts, and small non-vented set-up with their new complete kit.

Sooner or later guys will be posting complaints about that I'm sure.

Carry on.
__________________
MkIII #5877
4.6 SOHC, T45, 4-link, 5 lug, 4 disc, SN95 spindles
Harness diet, Diablo-Sport tune, Halibrand Cobra IIIs
Champ pan, King Cobra clutch, brakes and suspension all new
Ford D3 red and HP white.
Pro-built, start to finish, it's all me :)
Sold to a woman who gave it to hubby as suprise B-day gift.
Trophy for new owner, June 09
Cobrabilly is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 12:25 PM   #9 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Post

The plan at this point is to run the 11.66 Cobra rear rotors with the Mark VIII IRS 45.2mm single piston rear calipers and machine a simple mounting bracket to move the caliper radially .750" and inboard .200". This should offer better rear wheel bias than the smaller 38mm single piston Cobra rear caliper.

On the front, I will run the 2002-2004 GT dual piston aluminum caliper with matching GT 10.8" rotor rather than the original cast iron single piston front caliper.

As reported here:
http://www.ffcars.com/ubb/ultimatebb.../1.html#000000

This combination provides 15.6 lbs. less unsprung weight on the front suspension than the more popular 13" Cobra rotors.

By selecting the larger 44.5 x 44.5mm dual piston GT PBR calipers, this front brake combination should be an overall better choice than the Cobra 38x38mm dual piston calipers on 13" rotors.

Just my $.02...

Kerry
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 01:18 PM   #10 (permalink)
Senior Member

 
Richard Oben's Avatar
 
Join Date: Jan 2002
Location: Kansas City MO
Posts: 11,769
Post

We have the prototype for the bracket done and could easily make them. The reason we do not is too many people would take the earlier Super coupe calipers and mount them with the larger Cobra rotor. The big problem raises its head at that point. The piston can come out of the hole if the pads get worn. I have seen it happen. The later rotors are thinner than the earlier units and I assume the caliper is also different.

In short we chose to avoid the liability of a dangerous part.

Billy, depending on what wheels you use the longer axles on your 4 link will lead to problems. HTH, Cheers Richard.
__________________
Richard Oben FFR builder www.northracecars.com

Need help finishing your project we can help here or at your shop.

FFR GTM #34 first GTM with working AC. 400 hp LS1 w/G50
FFR coupe 3617CP 331 Stack EFI T-5 IRS Cobra brakes, AC/heat.
Both cars by NRC, we can build (and have built) any FFR product.
We also make and sell a ton of great parts for the FFR community.
Brake kits, AC systems, #1 supplier of Team III wheels.
Richard Oben is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 01:50 PM   #11 (permalink)
Engimuneer Extraordinaire
 
Join Date: Jan 2007
Location: Blacksburg, VA
Posts: 232
Post

http://public.fotki.com/jhnbrackett/ffr-pics/

This is a common upgrade for some of the guys on the Mark VIII forums. The above link contains 2 pics of the bracket that is being sold by some of the guys on the forum. Flat plate w/ a nut welded on. Purty darn simple & a great upgrade. Soon as I found out the Mark's calipers were bigger I started looking into this. Didn't realize they were 1.2 lbf heavier though.

Kerry, you've definately influenced my build more than anyone else thus far. I've been shopping for Mark VIIIs all around the area and taking notes on what will need to be done. Thanks!
__________________
Current Plans:
93-95 Lincoln Mark VIII donor
96-99 Mustang T45 tranny
SN95 front spindles & brakes
96+ Cobra rear brakes w/ Mark VIII caliper
JhnBrackett is offline   Reply With Quote Quick reply to this message
Old 10-29-2007, 02:44 PM   #12 (permalink)
ASE Tech & Shop Teacher
FFCars Master Craftsman
 
Cobrabilly's Avatar
 
Join Date: Dec 2006
Location: Upper Peninsula of Michigan
Posts: 1,936
Post

Gotta hand it to you Richard for not milking a potential hazardous part just for the sake of a few $$$.

I've been known to turn away customers with similarly scary ideas. One guy wanted me to cut his Yamaha cycle rotor on my lathe, and since I had no minimum spec or adapter, I had to say no. He got all pissed and said, "a GOOD lathe man could turn it". Yeah, insult me, that helps

I was probably the tenth guy to say no, and he was getting frustrated. Maybe he was running a sting operation for Michigan DOT?

Kerry&Kathy, Richard had been around the block here, and is worth listening to. I too would NOT run a "fat" caliper on a "skinny" rotor.

Richard, the FRPP rear brake kit I bought is for the 94-98 rears. My donor was a 98.
I'm running 17x9 Halibrand Cobra IIIs made for the 94-98 Stang. 30mm offset if I recall.

275/40s are tight out back, but look no tighter than 315s with the Fox legth axles that I've seen.

Not quite the classic look of deeper offset wheels, but they're genuine Halibrands direct at $640 shipped. Factored in with the fact that I didn't have to buy shorter axles, was a no-brainer on my budget.

Next time I want to go with the more classic look of the shorter axles, and deeper Cobra II? style wheels.

I'll have to find a buyer for WhiteFang with a healthy checkbook

That would of course require a set of Richard's caliper brackets and shorter axles available from him or others if I want to use the brake package I currently run.

Anyway, 100+ miles on my set-up, in gelcoat and no troubles.



Kerry&Kathy, you might want to rethink the front upgrade until you upgrade the rears and drive the car. These weight 1/2 a ton less than a Stang, (more sensative to changes) and the more front bite you add, the more the rear will need to keep up. Just my 2 cents as a ASE brake and front end tech with 30+ years in.
__________________
MkIII #5877
4.6 SOHC, T45, 4-link, 5 lug, 4 disc, SN95 spindles
Harness diet, Diablo-Sport tune, Halibrand Cobra IIIs
Champ pan, King Cobra clutch, brakes and suspension all new
Ford D3 red and HP white.
Pro-built, start to finish, it's all me :)
Sold to a woman who gave it to hubby as suprise B-day gift.
Trophy for new owner, June 09
Cobrabilly is offline   Reply With Quote Quick reply to this message
Old 10-30-2007, 12:17 AM   #13 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Post

Apparently there needs to be some clarification here as my intent and comments are quickly becoming misinterpreted.

This entire brake exercise began for two reasons.

One… to research a brake rotor / caliper combination that would address the need for added rear brake bias reported by multiple builders while reducing unsprung weight where possible, particularly on the front end.

Two…to better utilize the donor parts available for those of us using Mark VIII donor cars with IRS, Hydroboost and ABS.

Cobrabilly wrote: “Kerry&Kathy, Richard had been around the block here, and is worth listening to. I too would NOT run a "fat" caliper on a "skinny" rotor.”

Billy, I do indeed listen to Richard and respect his expertise, but I NEVER stated I intended to run a “FAT” caliper on a “skinny” rotor as you imply. In fact I never intended to run ANY T-Bird caliper or rotor. As stated in the original thread, I am using a MARK VIII caliper. There has never been a “FAT” caliper used on the Mark VIII series. The only issue of T-bird calipers arose when the question of pad availability was raised and the T-Bird was mentioned as an alternative source for pads. As pointed out earlier, It was determined that Porterfield pads are available for the Mark VIII rear caliper, so…the issue of T-Bird calipers is a mute point.

Richard: I appreciate and agree with your decision to not supply a T-Bird caliper adapter because of the potential liability of someone using the incorrect pre 1992 T-Bird caliper.
In my case, and I believe in the case of any well informed builder, it remains a viable option for the builder to fabricate his own bracket for use ONLY with the correct width 1992 or later T-Bird or 1993 and later Mark VIII rear caliper. As a builder, I can and do assume the responsibility for my own choices. As a vendor however, I understand that the situation is much different.

Cobrabilly wrote: “Go ahead and add the bigger rear rotor set-up, and leave single piston 11" brakes up front.”

Billy, I don’t have a donor with 11” brakes up front. The Mark VIII donor uses 11.56” vented front rotors with heavy cast iron single piston front calipers. My desire to use SMALLER 10.6” diameter 2002-2004 Mustang GT rotors with ALUMINUM dual piston front calipers was to reduce unsprung weight on the front suspension. The smaller front rotor saves 2.0 lbs per rotor. The dual piston aluminum caliper saves 4.0 lbs per caliper. That is a weight savings of 6lbs. per wheel and 12 lbs. of unsprung weight off the front suspension. Compared to the 13” Mustang Cobra front rotors and calipers, the weight savings is even more significant with 7.8 lbs. per wheel or 15.6 lbs total saved. That is a significant unsprung weight savings.

Cobrabilly wrote: “Kerry&Kathy, you might want to rethink the front upgrade until you upgrade the rears and drive the car. These weight 1/2 a ton less than a Stang, (more sensative to changes) and the more front bite you add, the more the rear will need to keep up. Just my 2 cents as a ASE brake and front end tech with 30+ years in.”

Billy, Again, the aluminum GT dual pistons, actuating a smaller diameter rotor, were not considered an ”upgrade” or increase in “front bite” as you imply. It was considered a trade-off, in that the higher clamping force, resulting from the larger piston area, is being offset by the shorter lever of the smaller rotor diameter. I am not expecting any GAIN in front braking. I would be happy if it is just equal. Also, the reduced rotor mass will likely result in reduced cooling capacity, but I consider it a fair trade for the reduction in unsprung weight. That is the primary benefit of this combination. NOT an increase in overall front brake bias.

Because my car is a partial donor with most parts being new or rebuilt, there is no benefit in installing existing front brake parts that I have no intention of using, only to later install parts, that from the beginning, I knew to be better choices.

The “lets try it and see if it works” school of problem solving is not one that is consistently successful in my experience. Sometimes you may get lucky. Most of the time…you don’t. If I learned anything about problem solving as a manufacturing engineer, it was to be as thorough as possible in researching and sorting through the details, to be analytical in evaluating the options, and not to rely on the “shotgun” approach of throwing multiple solutions at a problem, hoping that in doing so…. something will work.

My purpose was to research these details for myself and for other builders using Mark VIII donors, before any commitment was made to a particular set of parts. At this point, I am comfortable that the brake combination described above is a very viable option that when used with IRS, ABS and Hydroboost, can achieve the two goals of improved rear brake bias while reducing unsprung weight on the front suspension.

Just my $02….


Kerry
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Old 10-30-2007, 10:21 AM   #14 (permalink)
Senior Member

 
Richard Oben's Avatar
 
Join Date: Jan 2002
Location: Kansas City MO
Posts: 11,769
Post

I never suggested Kerry was doing anything wrong. I just wanted to point out why we did not make that bracket.

Billy, the different offset 9s are what is saving you from rubbing.

I can make the parts no problem, my concern is the having some other idiot do it and come back at me. I have had people ask some crazy questions and do some crazy things over the years. A perfect example is redrill the Cobra rear rotors for 4 lug.

On a side note, the challenge car racers run the 11 inch fronts and the 10.6 inch rears. I know for a fact one of them is running the Jeep MC and NO prop valve in either end. He just has a more aggressive pad in the rear and it balances out fine.

Everyone relax, the discussion is a good one, HTH, Cheers Richard.
__________________
Richard Oben FFR builder www.northracecars.com

Need help finishing your project we can help here or at your shop.

FFR GTM #34 first GTM with working AC. 400 hp LS1 w/G50
FFR coupe 3617CP 331 Stack EFI T-5 IRS Cobra brakes, AC/heat.
Both cars by NRC, we can build (and have built) any FFR product.
We also make and sell a ton of great parts for the FFR community.
Brake kits, AC systems, #1 supplier of Team III wheels.
Richard Oben is offline   Reply With Quote Quick reply to this message
Old 10-30-2007, 03:07 PM   #15 (permalink)
ASE Tech & Shop Teacher
FFCars Master Craftsman
 
Cobrabilly's Avatar
 
Join Date: Dec 2006
Location: Upper Peninsula of Michigan
Posts: 1,936
Post

Alright, alright, alright. Where's the love?

No offense intended, or implied!!!! [img]smile.gif[/img] [img]smile.gif[/img] [img]smile.gif[/img]

Kerry, your doing the right thing asking questions. I can TOTALLY relate to what you are trying to do. Best of luck to you, sounds like a completely logical quest you are on.

My only intent was to share my ideas, efforts and results. And after Richard brought up the rotor/caliper issue I wanted to keep someone from running a thin rotor in a caliper designed for a thick one.

Please accept my apology if offense was taken.

I have a line on a Mk VIII right now at $700.00, and maxing it out interests me also, that's why I originally read you post, and I'm very interested in your final set-up and results.

As a retired brake and front end man, the brake bias thing, and all the attempts at cures and remedies interests me a great deal. It's been a few years, so excuse me for not being completely up to speed on which cars ran which rotors and which calipers.

If you think I pulled a "try it and see" or "shotgun approach" on my car, that's your opinion, you're intitled to it. I researched it, changed my rears only, then road-tested carefully. Research only gets you so far, sooner or later somebody has got to Just Do It. And no offense, but I think that's where your at at this point.

If the Cobra rears didn't turn out for me, I could always unbolt them and sell them. No problem.

You probably won't paint your car the color I chose, your gauge package may be different, stereo, no stereo, stripes, no stripes, etc.. that's what makes these cars so great.

In the words of Red Green, "I'm pulling for ya', we're all in this together".

[img]smile.gif[/img] [img]smile.gif[/img] [img]smile.gif[/img]

[ October 30, 2007, 11:27 AM: Message edited by: Cobrabilly ]
__________________
MkIII #5877
4.6 SOHC, T45, 4-link, 5 lug, 4 disc, SN95 spindles
Harness diet, Diablo-Sport tune, Halibrand Cobra IIIs
Champ pan, King Cobra clutch, brakes and suspension all new
Ford D3 red and HP white.
Pro-built, start to finish, it's all me :)
Sold to a woman who gave it to hubby as suprise B-day gift.
Trophy for new owner, June 09
Cobrabilly is offline   Reply With Quote Quick reply to this message
Old 10-30-2007, 04:20 PM   #16 (permalink)
Junior Charter Member
FFCars Craftsman
 
Join Date: Aug 2003
Location: Brooklyn Park, MN
Posts: 1,279
Post

How 'bout 12" Corvette rear brakes? I brought this up a few years back but it never caught on...

Topic: IRS with Corvette brakes

I think the piston diameter is 1.6" but I don't know for sure. I'll measure it and try to dig up the pics/dimensions of the adapter plate later tonight.


Greg
__________________

Arachnyd is offline   Reply With Quote Quick reply to this message
Old 10-30-2007, 06:34 PM   #17 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Post

Greg,

I like the idea of the PBR aluminum caliper, although the 1.6" piston is smaller than the Mark VIII 45.2mm (1.78") diameter piston, so clamping force would be less with the Corvette caliper.

The .800" thick 12" rotor would add unwanted unsprung weight compared to the 11.66" diameter .720" thick rear Cobra rotor. Without comparing weights of the aluminum PBR and Mark VIII cast iron calipers, I don't know if the net effect would be a total increase of unsprung weight or not.

Also, it would require a change or adaptation of the emergency brake cable that use of the Mark VIII caliper does not require.

And, it doesn't assist those of us with Mark VIII IRS trying to utilize existing donor components.

For me, the Mark VIII caliper with Cobra rear rotor on the IRS would be a better choice, but I like your effort to find a better alternative.

Kerry

[ October 30, 2007, 11:47 PM: Message edited by: Kerry & Kathy ]
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Old 10-31-2007, 12:36 AM   #18 (permalink)
Junior Charter Member
FFCars Craftsman
 
Join Date: Aug 2003
Location: Brooklyn Park, MN
Posts: 1,279
Post

Pictures of the Corvette setup if anyone is interested...

Don't forget a 12" rotor will give more stopping force for any given clamping force. Plus, more swept area for better heat dissipation. Admittedly, the larger piston with slightly smaller rotor has a slight advantage here, but you can't just compare clamping force straight up.

The aluminum caliper might offset the extra weight of the rotor, possibly making unsprung weight a wash... I can take some measurements if anyone is interested.

Almost no question smaller rotor will have the advantage on rotational inertia.













__________________

Arachnyd is offline   Reply With Quote Quick reply to this message
Old 11-02-2007, 12:24 AM   #19 (permalink)
Senior Member
 
Kerry & Kathy's Avatar
 
Join Date: Mar 2007
Location: Farmington / Viburnum MO
Posts: 736
Post

Greg,

Your work looks very good.

I located some weight comparisons for the Corvette 12” rotors and Cobra rear 11.66” rotors.

Raybestos shows the Cobra rotors at 13.7 lbs. each. The Corvette rotors are shown at 14.5 lbs…a small .8 lb increase. However, the Raybestos caliper weight information was not helpful, as the weight for a Mark VIII rear caliper was shown as 10.8 lbs each…with mounting bracket and loaded with brake pads. The Corvette calipers were listed at 6.4 lbs…without mounting bracket and without brake pads. I could not find a weight for the loaded Corvette calipers with mounting brackets. In any event, it appears the total weight of each combination will likely be very close to one another; so unsprung weight should not be a major issue.

However on other issues, I would like to share some observations…

Quote:
Originally posted by Arachnyd:


Don't forget a 12" rotor will give more stopping force for any given clamping force. Plus, more swept area for better heat dissipation. Admittedly, the larger piston with slightly smaller rotor has a slight advantage here, but you can't just compare clamping force straight up.

The aluminum caliper might offset the extra weight of the rotor, possibly making unsprung weight a wash...

Theoretically, you are correct. A 12 “ rotor should provide more stopping force than a 11.66” rotor…assuming the same caliper is being used. But, in this comparison, obviously the calipers are different. In this case, the calipers differ in piston size allowing the larger Mark VIII piston to generate more total clamping force for the same amount of hydraulic line pressure. However, I don’t think the difference is as “slight” as you might think.

The question is: how much is the rear braking influenced by the rotor size and how does that compare to the clamping force resulting from piston area?

First, the increase in moment arm of the larger 12" rotor by .170" helps the brake pads resist the torsional forces of the rotor, so there is a mechanical advantage to the larger rotor, although slight in this case.

Also, it is important to understand why a larger diameter rotor can potentially be more effective in dissipating energy than a smaller rotor.

Basically, as the rotor diameter increases, the higher the braking surface velocity will be at any given axle speed. The higher this velocity, the greater the friction generated between the rotor and pads, the more heat is generated, effectively dissipating the kinetic energy of the vehicle.

Keep in mind that if a brake pad is contacting the rotor over a 2” wide surface, the velocity at the larger diameter of that contact surface will be greater than the velocity at the smaller diameter of the same contact surface.

As a side note, we also need to realize that the actual rotor maximum diameter is not the “effective” diameter of the rotor. Depending on where the caliper-mounting bracket locates the brake pads, it will be something less than maximum rotor diameter... perhaps .100” less on the radius, making it .200” less on the rotor diameter.

We can calculate this velocity using the formula RPM x Diameter x (3.1416 / 12) .

If the 12” rotor has an effective diameter of 11.8” then the surface velocity at the outer periphery of the brake pad, given an axle speed of 1,000 RPM, would be 3,089 Surface Feet per Minute.

By comparison, if the 11.66” rotor has an effective diameter of 11.44”, then the surface velocity at the outer periphery of the brake pad, given the same axle speed of 1,000 RPM, would be 2,995 Surface Feet per Minute. A velocity difference of only 94 Surface Feet per Minute… or only 3 %…!

By contrast, the Corvette’s 1.6” diameter caliper piston has an area of 2.01 sq. in compared to the 1.78” Mark VIII piston area of 2.49 sq. in. That is an increase in potential clamping pressure of 23.8 %…!

That is why I would prefer caliper piston diameter over rotor diameter.

I think it is one added reason why a valid argument can be made for using the 10.86” diameter Mustang GT front rotors and 44.5mm dual piston PBR calipers over the larger diameter 13” Cobra rotors with smaller 38mm dual piston PBR calipers.

The downside to the Mark VIII caliper's larger piston will be a potential increase in braking compliance, which may require a change in size of the master cylinder.

Greg, I certainly don’t want to discount your efforts using the Corvette rotors and calipers. I appreciate what you have done. The Corvette rear brakes would still be preferable to using the stock Mark VIII rear rotors and calipers. However, for me the larger piston Mark VIII caliper used with the Cobra rear rotor makes a lot of economic sense for IRS users and has the potential to provide even better rear brake performance.

Just my $.02…

Kerry

[ November 03, 2007, 12:55 AM: Message edited by: Kerry & Kathy ]
__________________
4.6 DOHC 4R70W IRS (FFR #6401 RD)

No trees were harmed during the sending of this message, however a large number of electrons were severely inconvenienced

"Andy...when scientists first split da atom, dey found it was made up of four parts: ...protons, electrons, Fig Newtons and morons."
George "Kingfish" Stevens

"The more I learn...the less I know".
Kerry & Kathy is offline   Reply With Quote Quick reply to this message
Old 11-16-2007, 08:13 AM   #20 (permalink)
Junior Charter Member
 
hssss's Avatar
 
Join Date: Jul 2007
Location: VA Mtns
Posts: 21
I'm building a Lotus 7 powered by a 351 and using Mn12 front spindles and Cobra/Mk VIII based IRS kinda a FFR minus the body and about 800 lb. What I came up with is using 00 Mustang 11" rotors/hubs/PB calipers and in the rear MK VIII knuckles using Cobra hubs/11" mustang rotors cut down to 10.25/Mk VIII calipers. I believe this should be sufficent brakes for such a light car and other than having to turn down the rear rotors everything is off the shelf and bolts together.
hssss is offline   Reply With Quote Quick reply to this message
Old 06-29-2008, 04:22 AM   #21 (permalink)
Member
 
rudy t's Avatar
 
Join Date: Nov 2007
Location: Houston, Tx
Posts: 49
Thumbs up Spacers for pads/calipers on thin rotors

Kerry,
I discovered the Mark VIII caliper after purchasing new loaded Cobra calipers, the ones from my donor rear. I plan to use them. In reference to losing the piston out of the bore from pad wear, it is a simple matter of using a spacer/shim like Wilwood has for their calipers to compensate for wear on thick race pads. I have them on my Lightning's brake kit and it allows use of the entire pad. I can supply a photo if need. The shim goes between the pad and the piston.
rudy t is offline   Reply With Quote Quick reply to this message
Old 06-13-2010, 03:56 PM   #22 (permalink)
Administrator
 
David Borden's Avatar
 
Join Date: Jan 2002
Location: El Dorado, CA
Posts: 7,952
Quote:
Originally Posted by Kerry & Kathy View Post
However, for me the larger piston Mark VIII caliper used with the Cobra rear rotor makes a lot of economic sense for IRS users and has the potential to provide even better rear brake performance.
Bringing up an old post... Kerry, excellent work on this! Did end up using this setup? If so, what are your thoughts?

What have you found for brake pads for the Mark VIII calipers?

We have quite a lengthly post on the subject here: http://www.ffcars.com/forums/17-factory-five-roadsters/245120-brake-bias-concern-warning-safety-post2263552.html

Feel free to post your thoughts if so inclined.

David
David Borden is offline   Reply With Quote Quick reply to this message
Old 06-16-2010, 11:31 PM   #23 (permalink)
J67
moved to F5 site
 
Join Date: Nov 2009
Posts: 113
If MN-12 = T-bird and Mark VIII, then hasn't this already been done?

http://www.sccoa.com/forums/showthread.php?t=51055
J67 is offline   Reply With Quote Quick reply to this message
Old 09-24-2010, 05:07 AM   #24 (permalink)
Member
 
Join Date: Dec 2009
Location: Kingston, Ontario, Canada
Posts: 61
Brake Choice and Un-sprung Weight

This is probably a question for Kerry. Following his logic of using the lighter PBR calipers and the smaller 10.6 front rotors to reduce unsprung weight and rotational mass, could the same approach be used with the Brembo 4 pot brakes from the 2000 Cobra R? Would I need to machine a special bracket to move the calipers closer to the smaller diameter rotors? Is there any weight differential between the Brembos and the PBRs. I do like the benefits and looks of the 4 pots plus that's what came with the donor.

My guess is that the 10.6 rotors have more than adequate heat dissipation with the 2200 lb roadster and that this change will improve the brake bias to the rear. Additional bias tuning can then be done with the cobra rear rotors, more aggressive rear pads, or master cylinder tuning for those with that option.

As a pie in the sky thought, does anyone make carbon fibre rotors/pads for our configuration? Are they viable for street use? Do I have to sell body parts to afford them?

Peter
morleidre is offline   Reply With Quote Quick reply to this message
Old 10-20-2011, 02:22 PM   #25 (permalink)
Senior Member
 
Join Date: Dec 2003
Location: Lexington SC
Posts: 152
I found these:

New rear Cobra brake 11.65" brake rotor upgrade kit. - Super Coupe Club of America Forums
ChinhookMech is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Bookmarks

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the FFCars.com : Factory Five Racing Discussion Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT. The time now is 08:11 AM.




The Tire Rack

Intercity Lines

Ford Cobra Engines

Team 3 Wheels:

Midwest Classic Insurance:

FACTORY FIVE ROADSTERS:

ROADSTERS
· Roadster Forum
· 4.6L Roadsters
· Big Block Roadsters
· Non-Ford Powered Roadsters

FACTORY FIVE COUPE/SPYDER:

TYPE 65 COUPES
SPYDER GT

FACTORY FIVE GTM:

GTM SUPERCAR
· GTM Forum
· GTM Classifieds
· GTM FAQ

FACTORY FIVE '33 HOT ROD:

· '33 Hot Rod Forum
· Hot Rod Classifieds

FACTORY FIVE COMPETITION:

· Challenge Cars
· Road Racing
· Autocross / Pro Solo
· Drag Racing

GENERAL FACTORY FIVE DISCUSSIONS:

· Free Photo Hosting
· Tires / Wheels
· Tops & Tonneaus
· Upholstery
· Gallery
· Audio / Electronics
· Car Care
· Insurance / Registration
· Brakes / Suspension
· Ford Big Block Tech
· Ford Small Block Tech
· Forced Induction / NOS
· Fuel Injection Tech

EVENTS:

· National Events
· Southwest
· Northwest
· NorCal
· SoCal
· Southcentral
· Midwest
· Southeast
· Northeast
· Canada

OFF TOPIC:

· Off Topic Discussions
· Other Car Discussions
· Smyth Performance G3F
· Automotive Photography Discussions

CLASSIFIEDS:

· Cobras and Replicas For Sale / Wanted
· Parts For Sale / Wanted
· Donor Cars For Sale / Wanted
· Other Vehicles For Sale / Wanted

NEWS / HELP:

· FFCars.com News
· Forum Help / Test

 


Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
SEO by vBSEO 3.5.1
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.


© 2002 - 2010 FFCars.com


 

Welcome to FFCars! The representations expressed are the representations and opinions of the FFCars.com forum members and do not necessarily reflect the opinions and viewpoints of the site owners, moderators, Factory Five Racing, Inc. or Ford Motor Company. This website has been planned and developed by FFCars.com and its forum members and should not be construed as being endorsed by Factory Five Racing, Inc. or Ford Motor Company for any purpose. "FFR", "Factory Five", "Factory Five Racing", and the Factory Five Racing logo are registered trademarks of Factory Five Racing, Inc. FFCars.com forum members agree not to post any copyrighted material unless the copyrighted material is owned by you. Although we do not and cannot review the messages posted and are not responsible for the content of any of these messages, we reserve the right to delete any message for any reason whatsoever. You remain solely responsible for the content of your messages, and you agree to indemnify and hold us harmless with respect to any claim based upon transmission of your message(s). Thank you for visiting the FFCars.com Forum dedicated to Factory Five.