Hi all,

This may belong to the suspension section, but I figure I may get more responses from her.

Story:
Brought the car in for a corner balance and alignment on Sunday. The car was put on the scale to do the initial check. When the car is first dropped onto the scale, it gave a 50.2% cross weight. After we rock the car up and down from the passenger side, the cross weight would drop to 49.1% after it settles. We then rock the car up and down from the driver side, the cross weight would go back up to 50.2%. We repeated this cycle many times, and we would have the same results over and over again....(very consistently wrong!)

The shop spent a good 3-4 hours rechecking the suspension bolts and loosening them to try to find out the issue, but they ran out of idea.

Any idea what could be the issue?

The shocks/struts have just been recently rebuilt. They are the older Ohlins R&T and only have 40 miles or so after the rebuild (literally put them on the car and drove to the shop)

Issues identified that need to be fixed (but not sure if these could be the reason for the strange cross weight changes)
1) Front bearing will need to be replaced
2) The rear of the front control arm bushing appears to be installed incorrectly by the previous shop. The markings do not seem to be in the right place. The front control arms also have the White Line poly urethane bushing at the front bushing. The shop suggests the bushing may be causing some binding.

At this point, I am thinking about replacing the front control arms completely with OEM bushings and the front wheel bearing and hope the issue will be resolved, but the shop is not confident that it will fix the problem. My other option is to give up the car completely and forget about spending any more money on it.

Any thoughts or suggestion on what I check?

 

First thing I would ask is were you sitting in the car the entire time, not getting in and out, no other changes? If you do have front bearing play it will affect the camber usually but not the weight.

Cornering is a huge PITA with non-race cars because they have a whole mystery of parts that could be at fault. However with your results that tells me that your springs are still binding because a bushing isn't going to offset 1-2 whole percent cross weight usually. Most folks need to drive the car for a week and then come back to check it again after any adjustments are made. Most shops ignore this because they know at this point that Evo's are as bad as chic's and change their mood at the sight of scales, so you get "close" but never ever at 50.0 at ANY shop. And even if they do show it to you you'll go drive and it'll be 51.3% next week.

This is why a genius of a person invented hub stands, eliminates the need to account for such crazy factors and is way more accurate. I've been so fed up with the lack of support and precision from said "shop" services that i've embarked to do it myself with my own stands and scales. Once I get my arms from R/T (hopefully SOON poke poke) i'll be doing a write up.

 

Were the swaybars still connected?

 

Thanks for the response. To respond to your comments, nobody was in the car when this happened, all we do was rock the car on each side of the car and let it settle. We haven't even gotten to changing anything yet, as we were obtaining the baseline figures, but failed to repeat the readings.

I can totally relate to your frustration about the shops out there. However, this one is not "just any shop". The guy is a fellow autox-er who is doing all of these in his backyard with proper equipments. Other shops would have just told me the cross weight were close enough and do the rest anyways and charge me $500 for it.

Back to topic, I don't quite understand why the spring would bind when the car is just at rest? My understanding is that binding should only happen when the car turns and the spring is not able to rotate with the strut. If the car's steering is straight and at rest, how would the spring binds? Perhaps, not enough preload?

With regards to the bushing, I guess the rear bushing is a pillow ball type bushing, so if it is not installed correctly, then the control arm is not able to move properly with bumps, wouldn't that be a pretty big issue? Presumably, the markings on the bushing from factory does mean it is quite important to have the orientation of the bushing correct to allow for proper movement.

 

Yup, we disconnected both front and rear sway bar links (all four of them)

 

If your talking about the front's rear caster bushing then there's only one way that goes in, wither it's facing the wrong direction should only involve caster and a little camber but it shouldn't affect how much preload a spring has, that's an upward motion not a sideways motion. If it was in the rear strut arm that'd be different since that can lower/raise the actual strut spring.

 

Correct, I was talking about the front's rear caster bushing. If there is only one way that it can go in, then not sure what the markings are for. As they sit, the markings are not oriented the same way.

Perhaps, it might be a spring binding issue, I will double check the struts as I heard some noises while driving, so maybe they weren't seated properly which causes the binding.

 

When applied to springs, the term "binding" has a specific meaning that has nothing to do with this thread. Much more likely is that the shocks and/or bushings are sticking. We're only talking about 30# here. I'm afraid that I agree with the shops that say that all of this is too close to equal to be worth worrying about.

 

The shocks were just rebuilt, so it's is quite possibly the last thing to check. However, I will check if the springs are seated properly, if not, then rocking the car may cause it slightly unseated and the weight sticks slightly.

I guess when you have three autox-ers scratching their heads about this, that 30# or so matters.

 

steering wheel locked in place when you're doing this?

small steering wheel movements will easily cause this much cross weight change.

 

Good question and I am not positive that it was locked. If that really is the case, then it would be very stupid to overlook this, but i will take it over having to replace parts randomly.

This is going good, keep the suggestions coming. Thank you all!

 

Since you've now been asked about the swaybars and steering wheel, I'll go for the hat-trick of semi-insulting questions by asking if the shocks are set to full soft. The fourth question would be whether there's enough gas in the tank that you aren't sloshing some from one side of the saddle tank to the other, but I'll save that one.

Oops.

ps. that multiple autocrossers obsess over this is not strong evidence that it's important; what don't autocrossers obsess over?

 

Not to get off topic. But I lost it when I read this!

 

Thanks. I'll be here all week. Try the veal.

 

Ha....the shocks were set midway between full/soft. I figured that the single adjustable really don't do anything at the extreme end of the adjustment (other than being out of whack), setting in the middle was ok. Then again, if this causes the issue, then the shocks are not working as they should.

I had about 1/2 tank of gas at the time of this test.