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Fox body 3-link suspension

24K views 31 replies 15 participants last post by  DMassey 
#1 ·
I have done some extensive searching for a 3-link rear suspension kit for the fox body, and have only come up with a couple people that make them for ford, and there all pre 1973-ish. A buddy of mine found one but they had since gone out of company according to the website. If anybody knows of a company that manufactures them please let me know. Any help would be greatly appreciated.

Rich.
 
#6 · (Edited)
How many of ya'll are auto-x'ing fox bodies with a PM3L? Thoughts?

After a handful of events, especially after today's, I'm not sure I want to stick with the trak-link as a TA setup that I currently have. On a grippy concrete surface today with decent tires (F1 Supercars, 295 rear, 265 front) and a co-driver to help keep them warm, my car just didn't feel grippy at all. I was 5 seconds behind (on a 70 second tight ass course) a really good driver and his stock 3rd gen FS car on old R compounds, which to me is ridiculous. I don't think I've ever been that far behind that ever guy before (2 seconds is normal if he is on R compounds and I am not).

Also, I let a bunch of other people drive the car during fun runs and I drove their cars; none of their cars so much as twitched when driving through the dirtiest portions of the course, areas where I felt like I was driving on ice. Granted, I drove an E30 on Direzzas, an M3 on decent tires, and a turbo miata, so I may just be suffering from the delusion that a fox body can be made to turn AND put power down. Those three cars were sick; if I lifted, the car turned, no matter how hot I came into a corner. The brakes on the Bimmers were redonkulous, btw way. ZOMG. I have 98 cobra brakes on my <3000 lbs notchback and they suck in comparison.

Anyhow, I think the short trak-link is providing WAY too much anti-squat (using Bill Shope's calculators, I calculated anti-squat to be 187%), which is making the car go into rear roll oversteer everywhere. Does that sound right to you engineering types? It feels great on the street but it's really really twitchy when auto-x'ing. I'm contemplating going with a PM3L for the last event of the semester just to see if I like it.

Or am I just describing something that gets fixed with a proper K-member? Could I have too much rear roll stiffness from the springs and big rear sway bar given my high anti-squat values?

TIA,

Casey

The car:
92 notchback
Front: 300# coil overs (koni yellow SAs), ~-2.5 camber, ~+5 caster, SN95 control arms, stock 33mm sway bar (had a 28.5 mm bar on it but the car turned in so hard the ass end couldn't keep up at all. The car understeered a lot more today with the bigger bar), 94-95 spindles, bumpsteer kit, 17*9s with 265s, stock v8 k-member.
Rear: 350-390 conventional springs, koni reds, stock LCAs, SN95 axles, 18*9s with 295s, GW trak-link, Griggs adjustable PHB (bar set parallel to ground as high as I can get it, which is just below the seam of the gas tank, ~3/4 of the way up the pumpkin), 98 cobra 27mm hollow rear sway bar.
 
#9 ·
My friend has a shop and we made mine. I am very happy with it. I roadrace my Mustang and it is amazing much better the car handles bumps and uneven surfaces. There is also a big difference with how stable the car is under threshold braking and corner exit. Our design is not street car friendly because we used the backseat seatbelt holes to mount the chassis side of the link. I did a search on 3-links and came up with a design that mostley borrows from the Evolution Tri-Link.
 
#10 ·
By-tor, would you be willing to share your design? I deleted my back seat years ago. Would it work in a notchback?

Terryr: Yeah, I know of only 3 or 4 people who have used the trak-link as a TA (i.e., without UCAs). Most who tried it made the mistake of using the UCAs as well. I think there is hope for the concept, it's just tough to figure out spring rates for the combo. Re: the floor pan, I added a brace from the chassis mount to the sub-frame connector on the driver's side to help distribute the force load away from the sheet metal of the floor. That is working great so far.
 
#11 · (Edited)
By-Tor I'd also like to see your design if you're willing to share. Don't worry no plans to ever go wheel to wheel for real. I'm in the process of designing one up with a link going up to just behind the seats attaching to a down tube from my cage. I might reconsider based on seeing your design.

....I actually can't believe I'm considering cutting a hole in my 36k mile rust free body!!!
 
#13 · (Edited)
Let me contact my friend and see if he still has the pics. Right now all I have are the pics I found on the internet. Let me get some stuff together and I will post what I got.

In short for right now I can try to explain a little bit what we did. For the rear housing we pretty much copied the Evolution Tri-Link. We used a 1x2" square tube that spans across the upper control arm mounts. We made big spacers to replace the housing bushings and pressed them into the rear. Then we welded tabs on the square tube for mounting it to the upper control arm mounts as well as added tabs in the center for a heim joint. There are also 1" square tubes going forward and down that bolt to the holes in the rear housing that used to hold the rear dampner.
On the chassis we took another 1x2" square tube and bolted it to the chassis with bolts running through the 2 center seatbelt holes. With the bar bolted in place we welded hollow spacers that are about an inch or so long to the bar. These reach the upper control arm mounts on the chassis. We then made spacers to fill the gap where the bushings used to be and bolted it all together. By doing this the chassis mount is solid and there is no way to rip or tear anything in the floor or trans tunnel.
As for the link itself we got a solid bar that I think has a 11/16" hex cut the length of it. Not sure of the exact wrench size but it is pretty big. We right and left hand threaded it for the heim joints. I think the link itself is something like 6" long without the heim's.

Like I said I will get pics asap. And if any of you are interested we still have the dummy rear end mocked up to make another housing bracket. And if you are REALLY interested I can get my car to his shop to copy the chassis bracket and link. As we made mine we took notes and measurements the whole way so we could reproduce it in the future.

Also you will need to run a panhard bar with this set up things could get spooky without one.
 
#14 ·
if any of you are interested we still have the dummy rear end mocked up to make another housing bracket. And if you are REALLY interested I can get my car to his shop to copy the chassis bracket and link. As we made mine we took notes and measurements the whole way so we could reproduce it in the future.
I can't speak for the others, but count me as REALLY interested!
 
#17 ·
Yep, same with Lateral-g.net, but most are 1st gen Camaro's. Love those cars! Might have to be my next project.
 
#19 ·
Argh ,can't post pics on here. E-mail me addys and I will get out pics I have of our working prototype that is on my car now. I only have the rear brace pics right now. Final customer version will look alot cleaner and will have a powdercoat finish.
 
#22 ·
EVM parts...

If anybody is interested, I've got the chassis bracket, spacers and 3rd link from the EVM setup that I don't need. Make an offer and it's yours. You'd have to fab up the axle mount similar to that picked above, and buy some u-bolts, but that's about all. Oh, you'd also need to make some of the reinforcement pieces that bolt around the driveshaft tunnel, these are basically some 1/8" metal plates that are bent to fit. Wouldn't be difficult to make either. I can send pics if anyone's interested, as well as the EVM PDF file. I used the setup on a AI car, but changed the chassis 3 link mount to improve AS and SVSA length. Now the 3rd link ties into my cage....
 
#23 ·
Ed, I'd really like to see how you did your chassis mount. I'm planning for something similar it sounds like.
 
#24 ·
Toys: Heres a interior pic of my car... I welded a 1.75" square tube between the main hoop bars, bent to fit the shape of the floor. Its welded to the main hoop, the main hoop mounting plates, and the floor at the center hump. The vertical bar was added, at the bottom is a 4 hole bracket that my upper 3rd link attaches to. Per AI rules all linkages have to be covered, so I made the aluminum cover you see in the pic. Its easily removable so the 3rd link can be adjusted. If I had it to do over again I would just use a sliding type link attachment to the vertical bar to have a more adjustable link.



In this pic from under the car you can see how I changed my RLCA chassis and axle attachment points. I dropped the axle mounts 1", and cut out the torque boxes, moving my LCA attachment points forward. I started with a 3" (maybe 4"?) steel channel, cut out one side, then cut it to fit between my frame rails and the rocker panel. Its welded in place and through-bolted to my main hoop mounting plates. There are two holes in the channel that the LCA can be bolted to - one is 1" lateral to the hole occupied, if you wanted to change the convergent angle of the LCA's in plan view. The front mounts can be raised or lowered by changing the spacer stack - this will change your AS and roll steer a bit. Now all 3 of my rear links are adjustable... Also in the top L of the pic you can see my 3rd link attached to the roll cage...



Another pic of the LCA mods on the other side. The hoop is a tiedown point. The zip ties hold my flexible brake lines that run along the lca... You can see the hard lines in the first pic above...



Finally,two pics taken a couple of weeks ago... the car is getting very close to being completed, hope to run it Sunday at Summit Point for an easy break-in session! :joy:



 
#25 ·
Ed, nice work and thanks for taking the time to share. Did you do any anti-squat and roll steer calculations? Curious where you were able to get for both. I can't seem to get much above 51% AS attaching to the cage like you did. I'm also sitting at a 1/2 of a degree of roll oversteer. I'd like to be able to adjust AS from 50-90% and get to roll understeer or at least neutral. To be honest I'm not sure how much roll steer I need or how a 1/2 degree is out on the track. I'm also playing with moving the lower arms around like you did.
 
#27 ·
Did you do any anti-squat and roll steer calculations? Curious where you were able to get for both. I can't seem to get much above 51% AS attaching to the cage like you did. I'm also sitting at a 1/2 of a degree of roll oversteer. I'd like to be able to adjust AS from 50-90% and get to roll understeer or at least neutral.
Mike: I did some calculations using a neat x-cel spreadsheet I found somewhere, probably on the CC site. If you PM me your email I'll send it to you. Just plug in the measurements of link heights, lengths, etc. and it'll calculate the numbers for you. With the EVM setup, my AS was around 110%... I was trying to go lower. Per the Mathis book, a RR mustang should have a AS of no greater than 50%. I don't know, but that's the direction I was shooting for. As it is, my AS now is around 48%. My SVSA is around 95" I think, and my rollsteer is around 1/2 -1%; with the EVM it was around 3%. I have no idea how noticeable this will be once it gets on track, but it can't be worse than it was. Changing the SVSA should eliminate any brake hopping - I broke a tranny that way. The car has never sat on all 4 wheels under normal load yet, so the settings will change once the ride ht is set. Lowering the axle RLCA mounts should keep the rear LCA level at ride height - before it angled down if I dropped the car too much. I just got the engine installed this past weekend, hope to fire the new engine for the first time tomorrow, and take it to the track on Sunday. There are so many changes since the last time I drove it that it'll be a whole new experience...
 
#28 ·
Ed - I'm using 3 Link Calculator v1.0 by Dan Barcroft which is excel based, is that what you used?

Let us know how it performs Sunday.
 
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