Rear lca recommendations

Enfield

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After replacing front control arms and upper rear control arm rear bushing, and installing new shocks, wheels, and tires, I went for a test drive. The car handled overall much better, but on turn-in about half the time it felt like the front and rear axles were fighting each other. Stringing revealed that the passenger rear is toed in about 2mm, while driver rear is toed out a similar amount. Fronts are just where I want them: toed in about 1/16". Side-to-side rear toe is 0, as one would expect. Wheelbase is about 3/8" longer on driver's side. There is also a buzzing vibration that suggests a binding driveshaft at about 35mph and again at about 70.

These symptoms suggest a problem with rear lca's. The car came with J&M nonadjustable rears; I haven't checked the condition of their bushings and don't know whether I need to, or should just replace the arms with something adjustable. Should I bother with having an alignment tech check the whole chassis for kinks or bends first? Given the rather consistent nature of my measurements, I'm leaning toward just installing the lca's and having a tech set the rear toe and pinion angle afterwards.

No drag racing or hard launches contemplated, so I guess that arms with somewhat stiffer rubber bushings would best serve.

All suggestions welcomed, tia

Enfield
 

1950StangJump$

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Even with adjustable lower LCAs, I don't *think* that rear toe is adjustable. Am I missing something?

The LCAs will affect pinion and thrust angle. In my experience, you use them to get the wheel more or less centered in the wheel well, then insure thrust angle is good. Then use the adjustable upper to finalize pinion.
 

OX1

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Even with adjustable lower LCAs, I don't *think* that rear toe is adjustable. Am I missing something?

The LCAs will affect pinion and thrust angle. In my experience, you use them to get the wheel more or less centered in the wheel well, then insure thrust angle is good. Then use the adjustable upper to finalize pinion.

It's not in relation to the axle tube, but I think what he is saying is the entire rear might be skewed in relation to perpendicular, of the body center.
 

Racer47

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Rear toe isn't adjustable, you have to heat up the axle housing to do it. But he doesn't have a toe problem. The real problem is that the rear axle is not square in the car. So yes, you do need adjustable lower control arms.

Since you have already measured everything, get adjustable arms, adjust accordingly, remeasure / readjust until the rear end is square and you should be good.

It wouldn't hurt to look around to see if anything is bent while you're under there. Plus remember that the bushings are offset. So it is possible that the current lca's are not installed correctly.

I use these and like them
https://www.bmrsuspension.com/?page=products&productid=158&superpro=0
 

1950StangJump$

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That makes sense.

I wonder if the driver's side wheel base is 3/8" longer, than correcting that with adjustable LCAs could easily fix the 2mm of "toe" that he is seeing.

3/8" of thrust angle variance really isn't that much though. BMR says -.5 to +.5 degrees, and I would have thought 3/8" which fall within that, but maybe I'm wrong.
 

Norm Peterson

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1/8" difference in rear wheel longitudinal location is more than enough to show up at the steering wheel. This isn't quite the same thing as "different wheelbase measurements", as those could include differences in front wheel longitudinal location (and likely with different caster values showing up).

1/8" over a roughly 62" track amounts to about 0.12° thrust angle. IIRC, that's about one full thread on an adjustable LCA (adjusting one side only here).


Norm
 

JEWC_Motorsports

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J&M is a junk brand, my bet is they are not equal in length. This is what happens when one company tries to copy another brand and half asses the quality. You could pull them and measure them to be sure.
 

Enfield

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You're all correct. The axle is straight, but it's not positioned perfectly perpendicular to the direction of travel. Took out the control arms and compared their lengths, which are very close. They do have an offset at the rear, and those appeared to be correctly installed. As a final check I swapped them side to side. Before driving the car I rechecked wheelbase, and the result was much the same: driver's side is now 5/16" longer.

A visit to the local alignment tech confirmed that [with adjustable lca's] he could easily make the axle perpendicular and also set the pinion angle; I'm hoping that the buzzing from the driveshaft at certain speeds can thus be removed. Tech checked the rubber in my J&M bushings and pronounced it no better or worse than the stuff he works with every day. Finally, he observed that most factory specs allow for up to 1/8" variance in rear toe. Even though I'm not racing anymore, I like for my cars to have alignment as close to perfect as can be achieved.

Not sure how to check the fronts to confirm that their control arm bushings are identically placed in their respective sockets, but when installing I tried to make them as close to identical as I could. Further, when I set the strings parallel to the front wheels there was a quite noticeable difference in the angle of the rears relative to the fronts. To be fair, I must mention that the car is slightly lowered on Bullitt spec springs - which are apparently what Roush sold back in '07 as well. Measuring for horizontal offset relative to the fenders, the fronts are dead even and the rear sits about 1/8" to the driver's side. It is my hope that truing things up with adjustable rear lca's will eliminate the need to add an adjustable PHR as well.
 

DieHarder

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If the rear is lowered you need an adjustable panhard bar to center the rear end. There's no other good way to center it other than spending a grand for a watts link.
 

Enfield

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If the rear is lowered you need an adjustable panhard bar to center the rear end. There's no other good way to center it other than spending a grand for a watts link.
Will an adjustable PHR fix the rear toe problem? Right now, it appears that the rear axle is slightly offset, but it also tracks in a plane that is measurably not parallel to that of the car in motion. Double trouble?
 

Norm Peterson

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Will an adjustable PHR fix the rear toe problem? Right now, it appears that the rear axle is slightly offset, but it also tracks in a plane that is measurably not parallel to that of the car in motion. Double trouble?
There is a little crosstalk between lateral centering and thrust angle (courtesy of the LCAs not being precisely parallel to the vehicle centerline as seen in plan view). But it's not enough to where fixing centering that might be off by only 1/8" or so will also fix the thrust angle.

To fix both, I think you'd want to start with thrust angle (adjustable LCAs) and only after that consider centering the axle (adjustable PHB).


I'm not a fan of LCAs with polyurethane bushings at both ends, and I'm not aware of any adjustable-length LCAs that use OE rubber-style bushings. Better than poly/poly is if one end uses a spherical joint, which does not have to be a metal-on-metal rod end.

Rear Lower Control Arms w/ Poly Del-Sphere | 2005-2014 Ford Mustang (spohn.net)

UMI has a similar LCA that's probably using the same joint under a different name, but I like the location of the Spohn's adjustment better (it's structurally a bit better by not being located mid-length on the LCA).

I'm running LCAs from Currie that are generally similar to the Spohn, but I'm not at all sure that Currie is still making them. Mark Savitske at SCandC.com (mainly a GM shop with a few Ford parts last I looked) can source them if you want to try that. They did not introduce any noticeable amount of NVH, and that's with the OE exhaust in place.


Norm
 

Norm Peterson

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No idea. All I'm seeing is poly/poly, and FWIW you're not likely to get new poly/spherical LCAs for $90/pair.

Full disclosure - I don't use e-bay at least partly because I find it too hard to tell what I would be getting.


Norm
 
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Juice

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I used the 2013 stock LCAs that came with my 8.8 from Ebay. Only because they were lighter than the stock v6 LCAs. Works fine for road course duty. I do have an adjustable upper, qa1, spherical bearing on chassis side, and uses stock bushing in the diff. W/adjustable panhard bar.
 

JEWC_Motorsports

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I would not use any no name brand on my car. Id be afraid of a cheap part breaking causing a lot more damage than just spending the extra money up front and having a dependable part.
 

Enfield

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The Whiteline video on AM's site was very enjoyable, especially Stephanie. Looks like my linked eBay specials are a knockoff of this KTA-195 piece. I'm tempted to get the copies just to have a look at the design, the welds, and the quality of the components. If they fail the eyeball test, I'll send 'em back and order the pricier ones.

In some racing applications the rear control arms are designed to be the weak link in the suspension - saving damage to more expensive components by bending to absorb a lot of the energy in a minor crash. Been there, done that, got back on track for the next session with straight corners; this was after the other guy tried a silly pass on the last lap of open qualifying, locked up, and hit a rear wheel on my car.

Nothing against drag racing - watch it all the time on YouTube, and more of the local car guys are into drags than into dirt tracks. The GT is plenty enjoyable without testing its launch capabilities. My goals with adjustable lca's are fixing thrust angle [for better turn-in and high-speed stability] and eliminating driveshaft vibration [if caused by improper pinion angle].
 

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