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Discussion Starter #1
I have an 88 Ford Thunderbird that I autox in CP but am wondering about the setup on my torque arm. At some events I have good traction off the line, but at other locations I have little to no bite to get going off of. Can pinion angle make a big difference on a torque arm like the stock style suspension on a drag car?
My current setup
Engine - 2.3T - stock turbo - 250hp/350tq?
Trans - T5 out of turbocoupe
Rear - 8.8 with 3.55 and trutrac
Front springs - 650# 7" coilovers on bilstien HD's
Rear springs - 500# 8" coilovers on MM sport valved bilstiens
Front sway - 1 3/8 solid
No rear sway
Fox front control arms
04 cobra spindles
Front tires - 295/30/18 Hoosier A6
Rear tires - 315/30/18 Hoosier A6
Wheels - 18x10 XXR 521's all the way around
Homemade torque arm and panhard bar - torque arm has slightly different connection at front than I've seen before but I thought it would work better than the others I've seen.
Car weighs right at 2800 without me in it




Any thoughts?
 

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What angle are your rear LCA's relative to horizontal? This has to do with antisquat. The more downward angle (front-to-rear), the more antisquat and the better your grip off the line. Too much angle however could result in rear roll steer, but with 500# rear springs this shouldn't be too bad. A little roll steer helps with the tight turning we see in autocross anyway. Ideally you'd want the rear LCA's about parallel to the ground at full compression.
 

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Well, your spring rates are killing those Bilsteins, for one... The HD's handle about 1/2 your rate, and the Sports up to 300.

I'd either try upping the damper or dropping the rates to something more matched then go from there. I'm not on my up and up for CP stuff, but that seems like alot spring for <3000lb vehicle.

Your fab-work looks good though. Nice.
 

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Discussion Starter #4 (Edited)
I know the fronts have way too much spring on them and will probably put at least sport struts up there too over winter, but the rear I havent really noticed anything detrimental handling wise there. I love the way it drives with these spring rates. Corners nice and flat. It will still occasionally pick the inside front wheel off the ground, but nothing like it did with the 350# in the rear.
The rear LCA's actually raise as they move back toward the axle. I didnt change any of the mounting points for those, but I have fender height at 25 1/4", but I dont remember what the factory height is. I'll try and check that tomorrow off my other car. I wanted to drop the car as much as I could to lower the CG, not realizing that it could mess other stuff up. I didnt think it would matter a whole lot with the torque arm, lol.
Also forgot that my torque arm is roughly 6" longer than the MM mustang torque arm
 

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Discussion Starter #6
Well, that will be moved to the top of my list of mods now! I know the one time I took it to the dragstrip, just because I was curious what kind of power it was making, I couldn't get better than a 1.9 60'.
 

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Well yea, that's a 15" tire with a bit more sidewall. A 30 series is up there in rubber band territory. I'm just saying you're leaving some on the table using that tire. A PepBoys special all season 245/50/15 would probably work better than either of those.
 

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Looks like a leaf spring shackle for the front mount? Has it worked out OK? It seems like this would take care of fore/aft movement of the arm well. Any binding on the side to side movement? Nice looking Torque arm.
 

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Discussion Starter #11
They are poly leaf spring bushings and they seem to work pretty well actually. Rubber would probably allow a little more twist in it, but as it is, if I jack up one side of the car, it sags the one side of the suspension all the way to the limit of the shock. I just didn't like the whole single bolt thing of the MM bar and really didnt like the griggs mounting.
I measured my bars today and the rear of the bar was 2" higher than the front, so I'm going to move the hole down 2 1/2" and see what happens.
 

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Discussion Starter #13
Yeah, I got the pinion angle matched now too.

I ran an event yesterday to find out how much it changed driving wise. It drives somewhat better, but its hard to tell since it was cold and windy. Also the pavement was made up of pea gravel which doesn't grab the greatest anyway. I did notice however that at the event before this one, I got heat in the front tires, but not in the rear. Yesterday I actually had more heat in the rear than the front. It still isn't great, but when I do get both tires to grab, they stay hooked. Unfortunately if one spins, its still spins till it grabs. I think thats just the lacking part of the detroit trutrac I have in it. Thinking I should've bought the locker
 

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As noted, you don't want the rear LCAs to go over center, e.g. pointing up at the back. Bad juju there, running all kinds of angles out into the ether and pissing off the anti's. :)

Pinion angle is also important. 2-5 degrees down works for me. If your axle is cambered, make sure the pinion angle equals the one the camber was set at.

Is your thrust angle correct? .3 degrees was pretty f-ed up on my car based on back to back testing.

I assume you don't have a cambered axle, but have you checked the rear alignment? A little negative camber is your friend, and you also want some toe in. Any toe out is basically fatal to straight line traction.

Have you tried it with the rear bar off?

The TruTrac is a good differential, but not if you are picking up an inside wheel (especially on the non preloaded ones like the 8.8) A locker will fix the symptom, but not the problem. If you switch to that, when you finally fix the rear suspension you will end up with a pushy pig of a car and a ####ty differential (IMO). Been there, done that.

I have been fighting rear traction all year on my new car and I think (hope) finally got a handle on it at Blytheville and started getting over 1.1g accel on course pretty regularly. I am still working on maximizing the lateral grip while under power and will see if my latest changes do any good at Nashville.

It has been an adventure that involved slightly adjusting a lot of things (over time) and making sure the basics were right and stayed right after all of those adjustments.

One last thing, as you noted, some event sites suck in the launch area. And the same site won't always launch the same. I have had superhero grip at Peru in the past at launch, but ran events there this year where I could have spun the tires through all three gears before the lights. Even Toledo, which is my new favorite site in the universe with its great grip, was pretty slick on launch.

Hope all this helps,

DaveW
 

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Discussion Starter #15
As noted, you don't want the rear LCAs to go over center, e.g. pointing up at the back. Bad juju there, running all kinds of angles out into the ether and pissing off the anti's. :)

Pinion angle is also important. 2-5 degrees down works for me. If your axle is cambered, make sure the pinion angle equals the one the camber was set at.
I think it was at roughly 2-3 before, but I set it to zero after lowering the LCA mounts. I will move it back tomorrow

Is your thrust angle correct? .3 degrees was pretty f-ed up on my car based on back to back testing.
I will recheck the alignment, but I don't have access to a good alignment rack so I've been doing string alignments with my dads help(still don't really understand it-I just need more practice lol)

I assume you don't have a cambered axle, but have you checked the rear alignment? A little negative camber is your friend, and you also want some toe in. Any toe out is basically fatal to straight line traction.
You're right, I don't have a cambered axle. I imagine it did move a little when I welded the tubes because I remember it did have a little toe, but don't remember which way. I do think it had a slight negative camber though. If it does have toe out, is there any relatively easy way to fix it?

Have you tried it with the rear bar off?
I took the rear bar off relatively early on in the season before the toledo tour for sure. Really made the car pick the inner front wheel off the ground with the 350# rear coilovers, and still does slightly with 500# rear coilovers.

The TruTrac is a good differential, but not if you are picking up an inside wheel (especially on the non preloaded ones like the 8.8) A locker will fix the symptom, but not the problem. If you switch to that, when you finally fix the rear suspension you will end up with a pushy pig of a car and a ####ty differential (IMO). Been there, done that.
Kinda what I thought too(pushwise), but didn't realize there were different styles of trutrac. I know the 9" one I have in my pickup I can't spin the tires opposite of each other, but the 8.8 spins like an open when jacked up.

I have been fighting rear traction all year on my new car and I think (hope) finally got a handle on it at Blytheville and started getting over 1.1g accel on course pretty regularly. I am still working on maximizing the lateral grip while under power and will see if my latest changes do any good at Nashville.
Unfortunately I don't have any of those nifty data aquisition things, lol. One of my buddies stuck his in my car at toledo express after the tour, but he couldn't get ANY kind of graph off of it, even though it works perfect off his miata

It has been an adventure that involved slightly adjusting a lot of things (over time) and making sure the basics were right and stayed right after all of those adjustments.

One last thing, as you noted, some event sites suck in the launch area. And the same site won't always launch the same. I have had superhero grip at Peru in the past at launch, but ran events there this year where I could have spun the tires through all three gears before the lights. Even Toledo, which is my new favorite site in the universe with its great grip, was pretty slick on launch.

Hope all this helps,

DaveW
I'll make those changes and report back! Dad and I are going back to National trail raceway,where we were at last saturday, this saturday. Also going to try better condition 295/35/17 tires in the rear to replace my worn out 315/30/18's to see what kind of difference there is there. I;m not sure what putting a smaller front bar on will do, but I already changed that out tonite too. I think I went to an 1" or 1 1/16 from the 1 3/8" I had on there before. I figure I haven't changed anything on the suspension most of the year so now is the time to change stuff I guess, lol.
 

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I will recheck the alignment, but I don't have access to a good alignment rack so I've been doing string alignments with my dads help(still don't really understand it-I just need more practice lol)
Nothing wrong with strings IMO.

You're right, I don't have a cambered axle. I imagine it did move a little when I welded the tubes because I remember it did have a little toe, but don't remember which way. I do think it had a slight negative camber though. If it does have toe out, is there any relatively easy way to fix it?
Yes. They can be adjusted with heat. In my case, a friend and I took the axle out, set it up on a level surface on jackstands and used a third stand to set the pinion angle. We then mounted the wheels only and took camber and toe readings.

To adjust, we heated a spot about the size of a quarter either on the top (for more negative camber) or front (more toe in) of the tube to white hot and let it cool. We used an oxypropane torch, but you could probably use a oxy-acetylene with a rosebud tip. Each heat/cool cycle made the exact same adjustment amount, it was very repeatable.

I wouldn't be afraid of 1/16" toe in per side. Toe out is pretty fatal on RWD cars.

Kinda what I thought too(pushwise), but didn't realize there were different styles of trutrac. I know the 9" one I have in my pickup I can't spin the tires opposite of each other, but the 8.8 spins like an open when jacked up.
I am no expert on them, but I know when I bought my 9 inch one, they had a standard one and one with 150lbs of preload. MIne is the same way as the pickup, you can't spin the tires opposite of each other. I don't think they offer the preload one for 8.8, that is a 9 inch only. That shouldn't be a problem in the long term (for autocross, it might suck for drag race:)) once you get both rear wheel to stay on the ground.

HTH,

DaveW
 

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Discussion Starter #18
^yes it is this car


Put the pinion angle back to 3* today - thats as much as I can get without remaking the front mounts.

Also did check the alignment. Rear axle has 1/16-3/32" toe out. Forgot to check camber on it.
 

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Yes. They can be adjusted with heat. In my case, a friend and I took the axle out, set it up on a level surface on jackstands and used a third stand to set the pinion angle. We then mounted the wheels only and took camber and toe readings.

To adjust, we heated a spot about the size of a quarter either on the top (for more negative camber) or front (more toe in) of the tube to white hot and let it cool. We used an oxypropane torch, but you could probably use a oxy-acetylene with a rosebud tip. Each heat/cool cycle made the exact same adjustment amount, it was very repeatable.

I wouldn't be afraid of 1/16" toe in per side. Toe out is pretty fatal on RWD cars.
DaveW
GREAT thread. Seems like a lot of Autocross "Mustangs" are congregating here. T-bird is pretty close IMO.

DaveW, how much neg. camber could one get safely without going to floating components? I assume this was done with std. c-clip axles stock or std. aftermarket differential.

In my quest to improve my Cobra, I've thought about doing PM3L or 5 Link PLUS decambering the rear axle. What will wear out by doing this? My car has seen 5k miles in the last 8 years, so it doesn't get driven much on the street.

Sorry for the hi-jack, looks like we all have some of the same problems.
 

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Nice car. I've been toying the idea of a 87-88 T-coupe with a TA/PHB, 2jz single turbo 5-600hp, and some kind of manual gear box setup.
 
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