3-Link - The missing link!

13524 Views 65 Replies 33 Participants Last post by William Mapstone, Jan 20, 2009

dv/dt

Discussion Starter · Jun 4, 2006

6

I went out the other day to weld the banana bracket to my axle. As I was welding it I was thinkingg it would be a pain if I didn't have a welder. Would be nice if there was a bolt in solution for transmitting the torque into the axle. Well here's what I came up with. Puts a link directly from the 3rd link bolt to the unused four link upper bushing mount on the axle. Still needs to be trimmed to length and the forward bolt changed out for a grade 8 bolt. The forward bolt may seem small but a 3/8" grade 8 is good for 10,000 lbs in shear. The link is put in compression under acceleration. I have talked to William at VPM and he would be willing to make up a kit if the interest was there. We have discussed and alternative that would be a straight bolt in and would not require any drilling. It would be very strong but would be more expensive since it would involve some machining work on his part rather than just off-the-shelf parts. Let us know what you think.

And here is the concept drawing for the bolt in kit.

Cheers, Rod

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NAGA

· #2 · Jun 4, 2006

Typical engineer!!

You don't really want to finish that car do you Rod?

Another nice mod buddy. Only question I have is why do you think that link's in compression? The third member is trying to move forward in relation to the body. That would put the link in tension, but only if the banana bracket broke. Otherwise, there's probably no load on it.
The FFR link? It would be in compression as the rear end is trying to drive it forward into the frame.

Here's a challenge for you. IF you can figure out how to statically preload your new strut into tension, it would preload the banana into compression which would offset some of the live load tension. Maybe add a turnbuckle into the new link?

d

dv/dt

Discussion Starter · #3 · Jun 4, 2006

Hi Don,
Under load the front of the differential is rotated up as the pinion tries to climb the ring gear. This means the axle is trying to rotate the banana bracket rearward not forward. This puts the new link in compression since it would be pushing back on the banana bracket. The upper link is in tension and tries to lift the front of the car remember.

If you look at the bottom drawing of the production variation it is essentially a turnbuckle and would allow you to preload it (in compression) as you state.

Actually I'm waiting for an order from Summit so I can finish up the engine, etc. Besides, if I finish this what the heck am I going to do for fun!!

Cheers, Rod

CraigS

· #4 · Jun 4, 2006

I like your solution as is.The rod end one is pretty but, like the other one you developed,those rod ends increase the cost about 10 times.I'd use the square tubing and weld on a plate at the forward end like the one at the other end.Drill the hole so the owner uses it as a guide for the hole in the big ear on the diff housing.Good job

dv/dt

Discussion Starter · #5 · Jun 4, 2006

Hi Craig,
One of the problems with the first setup is that drilling the hole in the 4-link ring can be tricky if the car is already together. It has to be centered and square on the ring for best strength. You would need to use an angle drill from the passenger side wheel well if the trunk sheet metal is already done. So the installer would need some special equipment and a level of skill above the second solution. But it is possible and does provide better mechanical advantage for the link.

The price difference for the rod ends isn't really that clear cut if you factor in the time to manufacture the parts. Throw in a couple of hours labour to make up the pieces/weld them up and it adds up. The rod end solution also gives you the added benifit of adjustability to fit variations between cars. Even slight variations in the banana bracket and it's installation will affect the bars length and angles. So even if William goes with the first version I think he would use a rod end set up. The other benifit of using the rod ends is that you could pre-load the rod slightly as NAGA pointed out.

Cheers, Rod

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Stinson Pilot

· #6 · Jun 4, 2006

Wow, and you think a lot of engineering thought goes into a production car...

You guys are awesome. Keep it up.

Do most guys with 3-link do some spot welds to transfer torque to the banana bracket or just leave it clamped as is? Will the clamp slip on the axel if you don't?

Always seems the simplest solutions are the best.

thebicman

· #7 · Jun 4, 2006

Rod, get to work on finishing car. You know I'm way behind you in the build and I need to live the dream by driving in yours. Now come on, get cracking. Bert.

Jim_Miller

· #8 · Jun 4, 2006

Originally posted by Stinson Pilot:
Do most guys with 3-link do some spot welds to transfer torque to the banana bracket or just leave it clamped as is? Will the clamp slip on the axel if you don't?

Not speaking from experiance with a FF5 but from experiance with a 69 fastback stang and stock spring pads and also from what I can tell from page 3-4 of this Collegiate.pdf weld it. Add a Posi and some good tires and the rotation on an axel housing can be extreem.
Spun my rear housing up 90 degrees inside the leaf springs years ago. messy

MJN

· #9 · Jun 4, 2006

Another effective and simple solution. Nice job

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dv/dt

Discussion Starter · #10 · Jun 4, 2006

Doug,
Here's a post from last year discussing a failure and the welding issue. http://www.ffcars.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/58/t/011653.html?

Currently the banana bracket relies on the clamping force in the main mount and the forward 3/4" tube that is in pure bending. Neither is a very efficient means of transferring the torque from the axle to the banana bracket. Not saying they don't work, just that they are not efficient and are subject to several variables (correct torque and clamping force, layers of paint or corrosion on the axle).

Bert, As soon as the Summit order comes in I plan to go nuts and get er done. Time to cut some grass!

Thanks Mike!

Cheers, Rod

KevinM

· #11 · Jun 4, 2006

I still think you should be charging FF a consulting fee for all of this.

Very good solution.

Kevin

quicksand

· #12 · Jun 4, 2006

rod, step way from the welder and get some sleep..nice innovation especially considering you're likely living in sleep depravation

CraigS

· #13 · Jun 4, 2006

Rod-Ok, you convinced me. I keep thinking about your prototype which I could make up myself from bits in the garage and, of course my time is at no cost.But to do this as a business, and allow some adjustability, you are right.Once again-good work! Some day when I get good tires I'll definately need one.
Craig

Vegas

· #14 · Jun 4, 2006

Rod,

How many Afco rods are you going to have me install before you are done?

ONEBADSN8K

· #15 · Jun 5, 2006

It seems that everyone is worried about the three link. I have roasted the rear tires off and have seen no stress cracks or any sign of either twist or any thing else.It seems that most of the things I have seen are geared for the MKII as the MKIII is very well enginered. Have not seen any one even post about a MKIII breakage. I have built stock cars both dirt and asphalt for years that use a 3 link that is just as strong as the FFR with no failure.So much of this seems like overkill and over enginering. Remember this is just my opinion.

AC4ME

· #16 · Jun 5, 2006

Rod, I did mine the way the drawing shows, except I used a aluminum rod turned down to fit in the ear hole, with bolt and washer to hold it in, but it was 1 1/4" long out on the pass. side. Then I milled that on a angle so the rod end could bolt straight in the side.
Can you tell me how to put drawings, either from AutoCad or hand drawings on the posts so I can show you what I did? Thanks
I have a little concern about the twisting or rotating force that these links will cause at the top of the banana bracket. What do you think?

[ June 05, 2006, 08:29 AM: Message edited by: AC4ME ]

stroked

· #17 · Jun 5, 2006

ONEBADSN8K

Later MKII and the MKIII have the same 3 link setup. Earlier 3-link setups lacked a cross brace on the upper link bracket that helped reduce breakage at that point. In this discussion, the strenghtening is at the bannana bracket on the axle tube, which is the same design as it has always been. So in this case, the discussion applies to anyone with a FFR 3- link, including MKIII's. Do a search and you will find people with MKIII's with 3-link issues. Reality is that high HP + wide sticky tires + unmodified 3-link = broken parts. The 3-link upgrades are not hard and should make the setup more able to handle the high HP sticky tire combo.

ChrisH

· #18 · Jun 5, 2006

Depends on the cost for me Rod. I liked the first upgrade, and this one looks promising as well. Let's see how much.

I think you would have a lot more interest if suddenly a bunch or banana brackets started to fail. I think it will take time to see if this upgrade is overkill or actually a needed component of the whole 3-link upgrade package. However, depending on the cost I would be interested in some "cheap insurance".

dv/dt

Discussion Starter · #19 · Jun 5, 2006

AC4ME,
I get what you are saying. To post drawing from AutoCAD I take a screen pic of the AutoCAD window (select the window and then hit Alt+"PrintScreen". You can then paste it into MS Image Editor (Paste as new image) or any other image tool and save it as a JPEG. Then crop it so just the stuff you want shows and you can post it here as you would any other pic. For hand drawing (like mine above) I took a digital pic of it but you could also scan it.

As for twisting, this link will only come into play if the loads exceed what the banana bracket can take or partial loads even if you pre-load it a bit. Either way the combination should be able to take more than the banana bracket by itself before failing.

Cheers, Rod

dv/dt

Discussion Starter · #20 · Jun 5, 2006

ChrisH,
Pricing will be determined by William. I see this as an alternative to welding. Not everyone has a welder and there are some risks (bent axle housing) if you don't do it right.

Cheers, Rod

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