Hey guys, haven't been here in a while...
working on my '77

I have a TRW fiberglass spring, and want to get the rear ride height an inch or two higher. If I turn the nuts on the bolt going to the spring ends - will I need to have the rear re-aligned?

I'm going to be replacing the half shaft u-joints, soon

Might as well replace the old rear shocks ---so looking for recommendations on shocks too

this is a daily driver only car..

thanks in advance
Ronnie

 

You may have to adjust the strut rod cam bolts a bit to get the wheels straight when you get done setting ride height; but you can do that yourself. You should not have to shim the trailing arms again.

 

By changing the rear ride height you will alter the points along the toe-steer and camber gain curves at which your static alignment will be. Depends on where your specs and heights are currently as to whether it may be required, but if either spec ends up out of tolerance then you'll need to have one or both adjusted.

 

TSW

if i lower the rear does the toe-in increase?Yes i think

i would like to lower the rear almost 1" but the 1/2 shafts will become parallel to the ground if i do it. but the increased toe-in could possibly offset the problem of toe-steer

i can't raise the diff...don't want

 

Isn't that the correct setup? With vehicle on the ground, the half shafts should be close to parallel to the ground so as to be easiest on the u-joints. This is a question not a statement.

 

You want the half shafts as close to parallel to the ground as possible. People with slammed cars will run with them pointing up towards the hubs a little which is fine. It just puts a little more stress/wear on the u-joints. Generally speaking, moving the wheel up (ride height down) gives you more negative camber (top of tire in) ... down, positive. Toe will change very slightly but probably not enough to warrant any change.

 

Sorry, but as toe-steer does have its concequences, and while it may not always be avoidable, setting the half shafts parallel to the ground plane on purpose would be a fundamental error in geometry.

In the C2/C3 rear suspension, any bump or squat which moves the half shafts beyond level into an attitude where the outer stub axle ends are above the inner yoke ends will necessarily move toe towards toe-out. Due to the nature of this toe-steer, the further below "level" the suspension travels the more rapidly toe steers towards toe-out. Thus, when the half-shafts are already level at static ride height, the more of this adverse dynamic may come into play. It shouldn't go without mention this toe-steer is also at work in droop, but in that unloaded condition isn't as important as when loaded.

Of course, it is most desirable to avoid this situation if possible. Failing that, one should at least seek to minimize and/or compensate for it, tho 1) increasing rear spring and/or shock firmness may lead to a harsh ride and upset balance, and 2) additional static toe-in increases tire scrub. The only other alternatives are to either live with the adverse effects, live with higher ride heights (), raise the diff, or re-design the suspension.

 

I don't disagree with anything you said with the exception of the first paragraph.

I know where you're coming from. In a nutshell, you're saying to use the subset of suspension travel that yields the most linear toe-change. Correct? And you're absolutely right in that thinking. But the thing is, when I actually measured the toe change years back, I came up with a smaller delta than I could even account for with shims. So I followed the predominant recommendation of this very forum and set them level to minimize joint wear. *shrugs* And that'll work just fine for 99.99% of the cars out there.

 

Believe what you will, but it is a geometric fact that C2/C3 rear toe steer is not linear. No offense, but entering a debate over the finer nuances of vehicle dynamics wasn't the aim of my post, as viewers can decide what that's worth without my doing so.

 

You're right. Maximum toe-in is achieved with the half shafts parallel to the ground. It's also true that GM chose not to set the car to this configuration. Original factory ride height means that the shafts will be higher at their inner ends.

 

I know, but for a section of the total travel the toe change is both minimal and near linear. I think you may have misread me. I really am not trying to disagree with you at all. I just think that in the real world with a street driven car, the difference is negligible.

 

I can agree with you that it's not as critical an issue in a car which isn't going to be pressed hard. For "spirited" driving (track or street) it is, however, an issue worthy of consideration. It is from this latter perspective, as well as for the benefit (I hope) of those who do tend to press hard, that I most often post concerning such technical matters. If you're cool with that, we're cool.






PS: Hey everyone, we've got new smilies!

 

Aldo, amico mio, getting back to your question(s)... Yes, your static rear toe-in will increase as you lower your rear ride height down to the point at which the half-shafts level out. IIRC, you already run a bit more rear toe-in than usual, so you may not need more in compensation. Suggest you lower and get a baseline "reading" (using the instrument on which you sit) to see how it handles without adding more toe-in, then to play with it to see if any more is helpful.

 

TSW
yes i'll do a test drive with parallel 1/2 shafts ( with the related more toe-in ) and i'll see if i like it better.
Now 1/2 shafts are about 1/2" ( slightly more actually) angled and I have about 3/8" toe-in and it's quite fine.I can still push the car with engine off.

when i had the rear toe at about 1/2" the car was really hard to push by hands-legs but absolutely no oversteer. I could slam on the gas pedal out of a corner without any issue.

still searching for the best compromise between ride height, wheels' scrub,no oversteer...but i'm not that far from it

WCSINX

i think the rear toe change is really an issue unless the car is driven just in a straight line. I did a test with close to zero toe-in and the oversteer was terrible. also at low speed and with easy cornering. it seemed a car intended for drifting...

 

I was not suggesting running with 0 toe. I was simply saying that raising the ride height a couple inches is highly unlikely to change your resting toe setting enough to justify realignment assuming it was aligned correctly prior to the change.

The OP's question was, "I have a TRW fiberglass spring, and want to get the rear ride height an inch or two higher. If I turn the nuts on the bolt going to the spring ends - will I need to have the rear re-aligned?"

 

The OP's original question having been asked and answered, the thread evolved towards a different, tho related one. However, you would seem to be missing the subsequent point concerning the very real effects resultant from adverse toe steer when a driver isn't merely cruising around to admire the scenery.

The relevance of elle88's mention of 0* rear toe is due to the possiblity of it's occurance during suspension travel should there be insufficient static toe with the half-shafts level. It may appear such small increments as are in question here are of little or no importance, but when one presses hard their effects can become greatly amplified. Please, try to keep your apples sorted from our oranges.

 

Skunk, you're reading into elle88's post. If that's what he was getting at, fine. But it certainly is not what he said.

Now bear with me please. If we are to assume the OP's car was aligned prior to raising it 2" running 1/8" rear toe-in for example. Then after raising 2" the toe will be virtually unchanged. I know this because I measured it for myself when I last aligned my car. As I said in my second post that delta in ride height produced a smaller toe-change than I could acommodate with shims. Will it change? Yes, of course it will. Will it change enough to matter to anyone that doesn't track their car? Unlikely. Will the granularity of a stock C3's suspension adjustment mechanism be able to accomodate that change? Also unlikely.

Now bear in mind, I'm not suggesting the OP not realign his car. By all means, if you have any doubt go get it aligned or align it yourself. Does it feel squirrely? Are you getting bad tire wear? BUT if you find your settings are out of tolerance after raising the rear 2", then I'll bet you dollar to donuts that it would still be out after dropping it back down 2"

That's all. I'm done. Sorry for pissing you off, Skunk. That was never my intent.