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· 1st RFM/FFR Legacy Winner
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Discussion Starter · #1 ·
Please respond if you utilized brake components from 1987 - 2000+ Mustangs. Recently I have experienced several scary braking incidents so I want to warn others and solicit feedback from anyone experiencing the same thing, particularly from those who have remedied this:

My setup is per the donor brake installation in the manual- SN95 Mustang GT PBR dual piston calipers and new stock pads/dics on the front. SN95 Mustang GT new stock rear calipers, discs and pads on the rear. SN95 Hydroboost (cut spring mod) and a FMS proportioning valve in the rear circuit adjusted to provide full pressure to the rear.

Under mild to moderate braking (which is 99% of the time), I don't notice any abnormal stopping. During "abnormal" braking (sudden or moderately hard braking, braking on damp roads, in turns, on sand or gravel covered roads) I have experienced three recent events that caused the front wheels to lock up unexpectedly resulting in loss of corning and steering ability.

Additionally, after inspecting the tread wear on the front tires, a pattern of angled wear on the ridges consistent with tire wear from heavy braking force is visible. The car is never raced and driven only as a pleasure vehicle.

Please chime in if you have a similar front brake over-bias situation and if you have remedied this.

Thanks,
Greg
 

· Speed-crazed and Confused
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Greg,
That has pretty much been a common theme with these cars, every one that I have driven or been around. Thus the old debate about a proportioning valve in the front circuit (which, from what I understand has some potential for bad outcomes also due to non-linearity). These brakes are designed for cars that are heavier and have a different front-to-rear weight ratio and likely the same size tires on front and rear.

On wet pavement, mine does the same thing (thus no wet driving). In reverse, if you hit the brakes hard, the same thing (weight is transferred to the rear). Gravel, same thing.

I have ruminated over solutions to this and came up with the following.
1. Same size tires all around? (would look stoopid for what these cars are)
2. Install the anti-lock system? (most sensical)
3. Use the wilwood box and the proportioning bar with manual brakes? (I like my hydroboost)
4. Different master cylinder with a different F:R bias? (wouldnt know where to start)
5. Know thy car (working on this, thus no gravel or wet drives)
6. Start Auto-x to accomplish #5 (want to, but dont want to thrash the car)
7. Sell the car (Not likely)
8. Try a front prop valve and see if the aforementioned issues are really issues.

I have driven Hydroboost cars and manual brake cars and they both have this issue. In fact, the manual brake car locked on dry pavement under hard braking. The tech behind good braking is very in-depth and this system is NOT designed for these cars. FWIW, if I had to go back to the start and do it again, I would put in ABS and call it done.
 

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· FFCobra Craftsman
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Typical .......

Very common problem (Spec Racers even w/ the smaller front brakes) ...... most install a proportioning valve on the front brakes to stablize the system ....... Myself, decided to go another route and am in the process of fitting dual piston PBR's w/ 13" rotors to the rear w/ matching masters on my CNC to balance the system ...... Boosted or not I suspect the issue will manifest itself the same, just easier ......... Pat
 

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Here's my set up:
Front Fox standard calipers, ss lines and carbon metallic pads
Rear 93 Cobra discs, new rubber lines and EBS greenstuff pads
M/C: Mitsubishi Eclipse/Porsche 911 remote reservoir

Why the Mitsubishi Eclipse M/C perfect 50/50 split front to rear. Oe application uses same piston volume as my setup. It require a little more work because the fittings are metric and the use of a tapered and adjustable pushrod. Bolt pattern on M/C is so close it bolted up to fox footbox. They come in 3/4",7/8" and 1" sizes. How do I know the f/r ratio is 50/50. 1. I have a book that yields m/c specs and 2. The m/c is plumbed L/R then split f/r. So it has to 50/50 or the L/R split wouldn't work.

I use no shuttle valve or proportioning valve.

I get good rear brake grab. If I hit the brakes real hard and fast i can get a 4 wheel initial skid then the rears start to roll. What would happen on gravel or sand is anyone's guess as I haven't tried that and for the most part I avoid the wet. I suspect that I would spin because of the un-adjustable rear braking force. This is good for dry and that's why I like it.

Anyway food for thought and I bet this thread goes into the hundreds...

Michael S.
 

· FFCobra Craftsman
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26,220 Posts
Since you have the hydroboost you don't have an effort problem.So the easiest fix is grabbier rear pads/less grabby fronts.i struck out trying to find someone to recommend a 'harder' pad for the front when i had vac assist. So i went w/ better rears. Along the way i went to manual brakes and now i have experience some stock pads and w/ hawk pads only. The hawk HPS definately grip better than stockers so i recommend you try them.The Hawk HP plus grip even better than the HPS but dust a LOT and groan some. Currently i have HPS in the front and Plus's in the rear and this is working well w/ my dual MC adjusted almost perfectly centered so would be a good step for you. Some of my friends like Carbotech pads also but i have no way to compare them.
 

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Actually, it sounds like your brakes are working as they're supposed to. You always want the fronts to lock up before the rears. If the rears lock up first, then the potential for a spin is extremly high. If the fronts only lock up when traction is poor, then you have plenty of braking force.

If you remove the fuses from your DD's ABS system, it will perform the same way.

If your tires are showing wear from heavy braking (a pattern I'm not familier with), then you're using your brakes a lot on the street. That's your personal driving style, not an equipment malfunction.
 

· Senior Member
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Greg: It is working good! Time for some good race shoes and feel the peddle baby! Mine did the same thing and it freaked me out.

I have the same issue and agree that when the braking forces are balanced against available traction, the system is operating as it should. The front wheel lock up and subsequent push are just part of the deal. A rear lock as the primary point of lock up would be a much more unstable event.

I took the car out in our business park on a Sunday when it was abandoned and pushed it to its traction limits so I would know what and where were the indicators were and what they felt like. The slightest bit of sand or particulate debris on the road surface, decreases the traction aids by a huge margin. By that I mean to say at least 50%. I think our cars operate on the edge, at best, if you will. I have zero idea about rain and wet traction.

Hint. I can rotate my cold front tires on my smooth shop floor with a 28" breaker bar on one of the lugs with the car bearing its full weight on the floor. That would indicate that there is not a surplus of traction resistance there. I run a pretty sticky tire.

The good part is that with the slightest lift of whatever input is being offensive, brakes, throttle, wheel, I find the car to be extremely forgiving in that it will get back into shape very quickly. Some folks find this offensive as the car CAN snap. One just needs to stay ahead of the car.
 

· FFCobra Fanatic
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Most every vehicle I have owned, including 3 sports cars, the front wheels locked up before the back. thats the way it should work, you get as much balance as you can, but definitly don't want the backs locking up first.
 

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Your fronts should lock up first, the question is how much... The issue is probably your proportioning valve. My understanding is even when adjusted for full pressure to the rear they will still restrict pressure to the rear. (they may not be ever be fully open)

Another issue with the prop valves, is the pressure curve has a knee. So they wont restrict the pressure much during mild braking, so your bias will more favor the back. When jumping on the brakes the pressure will spike and the prop valve will really restrict pressure... so the bias goes way to the front.

Your options are to remove it entirely. If so, please be very careful with the car until you understand how it will brake. Do emergency braking manuvers in a safe locations.

The other options are to put the Cobra brakes in the back to get some more diameter on the rotor or put a more agressive pad out back with a higher COF. Beyond that, putting a CNC dual setup with proper sized masters for front and rear. Not sure this will fit with the hydroboost or not.

My guess is your issue is with the prop valve causing changes in brake bias depending on the pressure presented to the system.(due to the knee in the curve)

...or put ABS on the car :D

David
 

· Senior Member
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David:

Is the ABS worth the endeavor? I know this has been beat to death. But from your personal perspective?

I dumped my Proportioning valve because I did not care for the break over (knee) that it produced. I switched to the Whitby power system, sans any additional valving. I have the same PBR set up that Greg does.
 

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The other options are to put the Cobra brakes in the back to get some more diameter on the rotor ...
This is what I did and seems to work OK for me. (hydroboosted) SN95 GT front discs (11", vented), SN95 Cobra rear discs (11.65", vented). The oem GT setup used 10.8", non-vented discs in the rear.

I have an adjustable rear proportioning valve almost full open (maybe closed 3/4-1 turn) and my brake balance appears good on dry, level asphalt in warm weather. The way the proportioning valve operates isn't likely to allow the rear wheels to lock before the fronts.

I would be cautious about being too balanced, especially without any proportioning valve on the rear. Seems to me there are plenty of varying driving conditions and circumstances that could make a controlled, (parking lot) environment test irrelevant.

Sean
 

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David:

Is the ABS worth the endeavor? I know this has been beat to death. But from your personal perspective?

I dumped my Proportioning valve because I did not care for the break over (knee) that it produced. I switched to the Whitby power system, sans any additional valving. I have the same PBR set up that Greg does.
My thoughts are based on what others have told me... but I do respect their opinion. Dave Smith, Jim and others told me that the Brakes (ABS, hydroboost) on Yespers car was unbelievable. I agree they were not tuned to the roadster and that the tuning of the ABS unit is probably not ideal but my assumption is the system has a way of adapting.

I certainly dont think its needed but in the case of hitting gravel or some sort of emergency manuver it might be a nice to have. Im thinking about putting them on my new car if I can find a place to hide the pump away. On my old car, Ive flat spotted more than my share of $250 Hoosiers... :D

What do you think of your brakes now with the Whitby power system?

David
 

· Junior Charter Member
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Similar to CraigS, I have HPS pads on the front and HP+ pads on the rear. Jeep manual MC, 13" 1996 PBR cobra brakes on the front, 13" Alcon disk kit on the rear with stock 1996 cobra calipers. Seems to work great.
 

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Thank you for the input David. I hold your opinion in high regard.

I love the brakes with the Whitby system. It has the right amount of take up and they are very progressive. There is still great feel to the system, but the peddle effort is much easier on the linkage etc. I am not a fan of having to really mash any input devise to get it to work. This cured my wish list perfectly.
 

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Most every vehicle I have owned, including 3 sports cars, the front wheels locked up before the back. thats the way it should work, you get as much balance as you can, but definitly don't want the backs locking up first.
I have no reason to believe this not to be true, but I feel certain that if I put you in my car you would come away saying, "man those brakes suck."

I'm not looking for another debate or fight over this issue, but I really think some people that have never experienced the problem don't understand how bad the problem is for some people.
 

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I have no reason to believe this to be true, but I feel certain that if I put you in my car you would come away saying, "man those brakes suck."

I'm not looking for another debate or fight over this issue, but I really think some people that have never experienced the problem don't understand how bad the problem is for some people.
I don't think anyone is looking for a fight. This is just the result of using brakes designed for a long nose heavy car in a short tail heavy car. Then aggravate the problem by putting wide tires in the rear when the system was designed for equal tire sizes.

I understand the frustration many are feeling trying to get these combinations to work but until the brakes are properly set up, they will never work well in a wide range of conditions. Without a well engineered system, the best anyone will do is to get them to work well in a narrow range of conditions. Even the best OE brakes had a difficult time going beyond this before anti-locks.

Not saying it hasn't happened, but I have yet to see a post where someone said that they had too much rear brake and had to dial them down with a proportioning valve. What does that tell you about the brakes for almost every car on this forum?
 

· FFCobra Fanatic
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I've gone through multiple brake variations over the past 10yrs. I've constantly battled with the lack of rear bias in the car. I think I've currently got things pretty darn good with Baer/pbr dual piston front calipers 13" disc and using hawk hps pads and cobra real calipers with baer 13"discs in the rear using Porterfield r4s pads and a dual master with 3/4" front and 5/8" rear cylinders. I can achieve enough rear bias this way without losing mechanical advantage on the front's. The last incarnation of by system was the same as above but I was running portifield r4i pads. I had great rear braking and it allowed me to dial in the fronts a whole lot more but after 3000 miles of cleaning dust daily off of my nice polished PSE wheels I found that I had completely eaten through the slots on my rear discs.( the down side of running race pads on the street is that some of them have a very hungry rotor appitite. )
In summary the one thing to think about to fix your problem is good pads and potentially bigger discs in back to give you more friction and or leverage to work the rear brakes.
The one other thing that has helped my cars brakes more than anything is good tires which is probably the most important and most overlooked part of your braking system.
 

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I don't think anyone is looking for a fight. This is just the result of using brakes designed for a long nose heavy car in a short tail heavy car. Then aggravate the problem by putting wide tires in the rear when the system was designed for equal tire sizes.

I understand the frustration many are feeling trying to get these combinations to work but until the brakes are properly set up, they will never work well in a wide range of conditions. Without a well engineered system, the best anyone will do is to get them to work well in a narrow range of conditions. Even the best OE brakes had a difficult time going beyond this before anti-locks.

Not saying it hasn't happened, but I have yet to see a post where someone said that they had too much rear brake and had to dial them down with a proportioning valve. What does that tell you about the brakes for almost every car on this forum?
Great points Mike...

I've gone through multiple brake variations over the past 10yrs. I've constantly battled with the lack of rear bias in the car. I think I've currently got things pretty darn good with Baer/pbr dual piston front calipers 13" disc and using hawk hps pads and cobra real calipers with baer 13"discs in the rear using Porterfield r4s pads and a dual master with 3/4" front and 5/8" rear cylinders. I can achieve enough rear bias this way without losing mechanical advantage on the front's. The last incarnation of by system was the same as above but I was running portifield r4i pads. I had great rear braking and it allowed me to dial in the fronts a whole lot more but after 3000 miles of cleaning dust daily off of my nice polished PSE wheels I found that I had completely eaten through the slots on my rear discs.( the down side of running race pads on the street is that some of them have a very hungry rotor appitite. )
In summary the one thing to think about to fix your problem is good pads and potentially bigger discs in back to give you more friction and or leverage to work the rear brakes.
The one other thing that has helped my cars brakes more than anything is good tires which is probably the most important and most overlooked part of your braking system.
Also good points... Similiar to you, I got perfect balance using the CNC setup for my racecar with stock 99+ front brakes and Cobra rear brakes and I believe the same size masters as you. I ran the same pads as front and rear though(more agressive pads for autocross)

I could dial in the bias bar so the car car would rotate perfectly entering a corner allowing me to rotate the car while trail braking.

The challenge is finding a brake setup that will give the same sort of bias but using a power booster of some sort... or pads that have enough COF but work when cold and wont dust the poo out of your rotors.

My GTM has very very good brakes and they were manual using the wilwood pedal setup which is similiar to what is provided with the complete kit. I used Axis pads which seemed to be pretty good and had almost no dust.

David
 

· Senior Member
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I think it is a lot about getting to the know the limits as long as it is built the way it was intended.

I have IRS , with rear disks and Mustang GT fronts. Use a good Road Race pad on fronts (forget which one). Rears are just std TBird.

On road driving I have to hammer the brakes to get a skid, on track can often have one wheel up front lock up when pushing it hard (the unloaded wheel) , and car behaves exactly as I expect. I have never felt I was not in control.

During my build I decided to keep the manual brakes even though Whitby were pioneering the Booster Master Cylinder at the time, and I still enjoy them as I can "feel" the braking on track. I also did quite a lot of work getting the pedal to swing correctly, including changing the pivot position and the length of the arm (Whitby) , in early days a few people had issues with the arm scrubbing the side of the master cylinder wall, thus hanging.

I have only once locked up in wet weather , and just regulated the pedal with some pumping and stopped easily enough,
With such large tires , the car is not fun in wet anyway, not unless you want to be sliding all over the place. Been there done that.

Good luck
 
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