Corner Balance issue after suspension rebuild, looking for ideas...

[MysticLlama]

So the car is at the shop, it lives there more than at home.

Anyways, I get a call today, and here are the numbers they have:

647/344
627/917

Total 2,535
Cross weight 971lb - 38.3%
Cross weight 1564lb - 61.7%
Left weight - 50.3%
Right weight - 49.7%

No matter what they do, it's not making a whole lot of progress.

Recently, the suspension was rebuilt.
New 22mm Torsions in front
New ER A-Arm bushings
New Ball Joints
New ER shock tower bushings
New rack spacers
New sway bar bushings
Fresh rebuilt Bilstein shocks (custom-valved by Steve Weiner)
ER Triangulated strut brace (pre-existing)

New 29mm Torsions in rear
New ER spring plate bushings
New ER trailing arm bushings (sport)
New sway bar bushings
New drop links both sides
New shock tower bushings
Fresh rebuilt Bilsteins (also from Steve)

New Bridgestone RE-11s all the way around

Car is taking an alignment to pretty reasonable specs

Other notes:
Front torsion caps were indexed the same way to achieve the correct ride height (so they are at similar adjustment via the screws, not one way down and the other high)

Rear spring plates were adjusted and set the same way via the spring plate calcuator and set to the same angle with a protractor. Spring plate height adjustments are similar side to side.

CB has the sways adjusted as usual, and rear shocks were also unbolted in case one had decided to freeze up or something weird.

The right-rear trailing arm got bent somehow in the rebuild process (long story) but was replaced with a known good one, and had a new bearing installed, etc. (but reused the trailing arm bushings that had <50 miles on the bent arm)

Car was taken in for a re balance after pulling to the left with pretty good force on hard braking.



Shop is baffled. What are the next steps?

[john walker's workshop]

it did have a bent rear arm from some previous encounter, so a laser frame rack check for a tweeked body would be good.

[dad911]

JW must know the car, but why can't they 'raise' RF & LR and 'lower' LF & RR?

Are the sways disconnected?

[MysticLlama]

John - Byron said he measured it when it was in there, and it was fine at that point. Also takes the alignment okay, for whatever that's worth.

The theory is also that it got bent with a jack or something vs. a wreck since it was fine before it was taken apart.

Sways are disconnected, and within the ranges of adjustment it just doesn't make a big difference apparently, that does seem like the obvious answer.

I suppose the one corner could be indexed differently on purpose to get more adjustment, but that just seems wacky and didn't want to start doing anything stupid.

They say it acts like it's pre-loaded or something.

[911pcars]

Originally Posted by dad911

JW must know the car, but why can't they 'raise' RF & LR and 'lower' LF & RR?

Are the sways disconnected?

I'm leaning this direction as well (pun), but that seems too easy a fix. A shop should be able to figure that one out.

If in raising LR and RF to increase weight loads to those opposite corners, the side-to-side ride heights are way off, I'd also suspect a tweaked chassis.

Sherwood

[MysticLlama]

That's what I thought too, it's just that the other shop saying that it measured out fine is throwing me off.

A quote I missed on pasting in the original post from the tech:

All were taken with sway-bars disconnected, scales on floating tables, Tires at 30 psi cold pressure, and the rack was level and ride height was sitting level side to side within 7mm.

[MysticLlama]

Also, I know there is the inevitable take it to another shop, but this one is working to do a realignment on an alignment that's already been paid for, and the last time that happened I spent a fair amount of money and time to have someone else tell me the same thing.

And since that's happened numerous times in this project, I'm kinda done spending money on it and moving it around, it either gets figured out where it is or gets parked for an unknown amount of time.

[burgermeister]

Depending on which ride height (measured ground to torsion bar center) is more off, I'd jack up the RF and / or LR.

The shop technician does know you need the car on some slidey plates or else roll it back & forth a bit if it's been up in the air? Seems silly to ask, but you never know ...

I'll be curious what you think of the RE 11's.

[DanielDudley]

One of the torsion bars is way off.

[MysticLlama]

Originally Posted by DanielDudley

One of the torsion bars is way off.

Could you elaborate on this? This is sorta what they thought too, but I don't understand how it could be if they are indexed the same way? I can see how you could do it with a coilover, just not with a torsion bar.

Basically, on the front, both caps were indexed to be completely at the bottom of crossmember and then adjusted from that point. (They were indexed at the middle before-hand and basically bottomed out to approximate a good ride height, this puts it in the middle of the range)

And on the rear, they were both indexed by rotating both the inner and outer splines as needed to get the same amount of droop according to the spring plate calculator.

[MysticLlama]

Another bit of info, at one point they lifted up the front of the car to try it without the front suspension in the mix.

"when I had the front balanced in the center on the airbag, the rears were.

Left: 617 lbs Right: 792 lbs

Obviously, this won't be exact since it's relying on the factory jack points that aren't perfect, but it's a pretty good estimation of the bias.

I am thinking the rear right is too pre-loaded, but as you said, if it were off, the car should be clearly higher in that corner. I am not sure on why it was a lot less of a difference when measuring just the rear, but I can only assume it has to do with the front of the car not being perfectly level, we aren't really setup to do that kind of a measurement."

[ShakinJoe]

Did you have a roll bar welded in at some point during this process??

[911pcars]

Originally Posted by MysticLlama

Another bit of info, at one point they lifted up the front of the car to try it without the front suspension in the mix.

"when I had the front balanced in the center on the airbag, the rears were.

Left: 617 lbs Right: 792 lbs

Obviously, this won't be exact since it's relying on the factory jack points that aren't perfect, but it's a pretty good estimation of the bias.

I am thinking the rear right is too pre-loaded, but as you said, if it were off, the car should be clearly higher in that corner. I am not sure on why it was a lot less of a difference when measuring just the rear, but I can only assume it has to do with the front of the car not being perfectly level, we aren't really setup to do that kind of a measurement."

That was my next recommendation, to observe each end independently. Sounds like the shop knows what it's doing in an attempt to isolate the issue-end. Repeat to check the front end corners. If they're also relatively close like the rear, I'd suspect a chassis issue, but I hope not.

Sherwood

[MysticLlama]

Joe-
I haven't had a roll bar welded in, but I do have one bolted in, and it's a really tight fit, would unbolting it and getting it loose be good enough to try, or would it have to be pulled entirely? it's a DAS that mounts to the rear seat bolts and rockers / seat belt locations. It wasn't during this process, but it was between the last corner balance / alignment session and all these changes, with very little driving in between, so it is pretty new.

I thought of that and discounted it since it was a bolt in, but it was a pain in the arse to get settled in and lined up, and then it remained in there during an engine/transmission pull where they were out for quite a while, FWIW.

Sherwood-
I figured that 175lbs was pretty substantial? Is that considered pretty close?

I can see if they can do just the rear also, I think the leaning is always towards thinking the rear is the issue because of the trailing arm fiasco.

[ShakinJoe]

I would bet my box of cheerios that the roll cage is pre-stressing the car chassis. Unbolt it with the car on the ground and try the corner balance.

[Scooter]

Originally Posted by ShakinJoe

I would bet my box of cheerios that the roll cage is pre-stressing the car chassis. Unbolt it with the car on the ground and try the corner balance.

This is a very very interesting observation. Especially since ShakinJoe did not even know Rob has a roll bar. Any second opinions out there?

[Flieger]

I had an RSR style front strut brace with the weld-in brackets on the towers. The bar was non-adjustable and bolt in. I am not sure if the car was on the ground when welded in, but when the bar was put in the front would not align. It aligned with it out, though.

Of course, since then I have learned that my front suspension pan was replaced badly because one of my Rebel Racing bearings had to have the hole slotted a little to get smooth kinematics. The other side was in the factory location and the RSR bearings went in fine.

[Joe Bob]

Geez, sumthin is outta whack. Does it sit in the drive on all four wheels?

[joeblow]

It sounds like a bind in one of the bushings, the right front might be binding on the rebound so after jacking it will not settle making that corner very light. Check for bushing bind...

Also the damper might be hung too on the right front not drooping back down.

Had a tight bushing on a 914 once and did the same thing.....

[Walt Fricke]

I would not think a DAS bar (not cage) would do anything at all as far as twisting the chassis (or stiffening it, for that matter).

So I'd look elsewhere.

And given the hard pull you experienced, I would not think the weights are just a result of friction in the joints, so to speak.

Using the equal percentages approach to corner balance (ignores diagonals), you are 149 lbs out of perfection. Ideal would be
LF 498 RF 493
LR 776 RR 768

Because your car is so close to a 50/50 right/left distribution, this doesn't vary much from the equal diagonals approach, so as a practical matter you end up in the same place within the inevitable tolerance of corner balancing.

Unless these weights are without you in the car - which would explain the nice side to side split.

I'd be inclined to take Dad911's approach and get it within 10 or 15 lbs all around and go drive.

And then see where your ride heights are measured from some key suspension points: like a lower bolt where the rear spring plate attaches to the chassis, and the right and left sides of the reinforcing crossmember up front. And, for fun, from bolts holding the front of the A arm on. Doesn't matter what the absolute numbers are, just the side to side differences. That should tell you if the frame is twisted also.

I can see why you are puzzled. I had the front cut off my SC at about the shift lever, and a replacement welded on. I had left the rear suspension in the car for this. When I put the front suspension back on I just screwed the adjusters up equal amounts until the front was at a suitable height. To my amazement the corner balance was just about what it had been before the wreck, and I didn't have to change anything! Gave me a lot of confidence in that body shop's work.

If I had to guess it would be that something went wrong with setting the torsions in the rear - angles which seemed the same weren't somehow.

But, again, when I finally decided to put even bigger rear bars in the SC, measuring the "before" angles and the unloaded angles, calculating the reduction in angle appropriate for a bigger bar, and resetting to those calculated values worked out slick - the Wil Ferch method. Piece of cake, really (other than all the work generally). So no real reason for a huge problem here.

My 1.5 cents