RIGHT Pull after suspension rebuild

[mmasse]

I disassembled my front suspension to install ER PolyBronce bushings.

I took the car to do the alignment today in order to complete the job and the guy was not able to set it. I get a strong right pull.

Initially, he set both R and L caster to 6 degress. And the car pulled to the right, I took it back and he tried to solve it by giving less caster to the left. Final setup was 6 degrees on the right and 5 on the left, but the car keeps pulling to the right.

Could I have srew something when I assembled the suspension (A arms)?

The car had no problem with alignment before this suspension work.

Thanks for you help

[Chuck Moreland]

Very likely your corner balance is off.

I will assume this problem did not exist before you took the front suspension apart. Further , I assume you did not touch the rear suspension and it was seemingly correct to begin with.

When you re-set ride height, you dialed more weight into one wheel than the other. It is easy to do this, even though ride height is perfect.

If it's pulling right, you put too much weight on the driver side.

Your best bet is to check corner weights on a proper set of scales, then adjust accordingly. Failing this, try loosening the driver side height adjuster a bit (try 1 full turn) and tightening the passenger side adjuster an equal amount.

Report back.

[mmasse]

Hi Chuck,

No, I didn,t have this problem before.

But yes I did mess with the rear suspension. I also installed your PolyBronce bushings and replaced my old spring plates with OEM adjust ones. Is there anything in the rear that could cause this?

Thanks for your help

[mmasse]

Chuck,

Off course you were right!!

The problem is that in order to get rid of the pull I had to lower (loose) the drivers side a lot. The is almost 1 inch between drivers side and passenger at the fender lip.

I assume I also need to adjust ride high at the rear, but which side should go up and which one down?


I really dont understand how this works. I thought that lowering the driver side meant putting more weight in that corner, but according to your recommendation it seem that lowering will take weight out. Is this right?


Thanks again

[Chuck Moreland]

Corner balance is an issue at the rear as well. At this point you really need to get a proper corner balance performed.

Ride height is not a good indicator of corner balance correctness.

Get the alignmetn done after the corner balance.

[mmasse]

Unfortunately, i was not able to find a shop that does corner balance here where I live. I will try the Porsche dealer this weak.

In the mean time I was playing around with heigths using the diagonal method and I solved the problem. At least the pull issue. Now, I need to see how the weights ended up.

Thanks again for the help Chuck

[mmasse]

Has anyone used this device for corner balance?

I am looking for a economical solution, since scales are too$$$$

http://www.speedwaymotors.com/p/230,234_Wheel-Load-Checker-Hydraulic.html

[Chuck Moreland]

I used to use one of those, prior to buying a set of computer scales.

That device works pretty well, but you MUST learn and use good technique. It requires two people to operate.

Not nearly as easy to use as computer scales, but you can get reasonably repeatable weight measures - within 20 lbs or so. It's worth it for the home shop and can be used to achieve a decent corner balance.

[Walt Fricke]

I've got an earlier version of one of those, and I agree with Chuck - better than nothing, will get you close, and economical. But I always had trouble getting repeatable results. Add a stick-on circular bubble level so you can always measure with the handle level.

For years guys used Ruggles Scales. These were a lever system which pressed on bathroom scales. I forget the factor involved, maybe scales read 1/4th of actual weight.

The "equal diagonals" method is an approximation (except in two special cases). Probably good enough for your needs. But the math for the right method is simple: The front of your car weighs, let us say, 40% of total weight (so rear is 60), as you learn from scales (or this variation of the Wacho Weight Checker). Let's say the car with you in it weighs 2800 lbs. And the left side (with a weight equal to yours in the driver's seat) has 53% of total weight. So the left front should weight 0.4x0.52x2800 = 582.4 lbs is ideal left front weight. Let's say you find it actually weighs 500 lbs. This means that the left front and right rear are light, and the other two correspondingly heavy. So you need to jack up the left front and right rear some until reweighing gets you to 582. Or thereabouts. 20 lbs off shouldn't make any noticeable difference. And even with good scales you are doing well if you get 5 lb repeatability due to all the sources of friction in the suspension (less, nowadays, with your spiffy new bushings, but it is still there).

This is tricky stuff, because it also can affect ride height, so it is apt to take some playing around to get both corner balance and ride height where you want it.

Does Guatamala have any race tracks? Ovals would do. While the roundy rounders purposely bias the corner balancing to promote left turns, they are apt to have scales.

Walt Fricke

[Chuck Moreland]

The manufacturer has added a circular bubble level to the product, it was on mine.

The basic operation is to place a peice of paper beneath the tire. Your helper pulls on the paper as you lever up the wheel. The wheel is "up" when the paper moves, and that is when you take your reading.

It is important that the bubble be level at the exact time you the paper releases from beneath the tire.

It is important that you be on perfectly flat ground - not just flat to the eye, you must measure it and make it flat within about 4mm.

It is important that you place the device in exactly the same position on the wheel everytime.

You will want to make a provision to prevent the device from scratching your wheels, or use an old set you don't care about.

[Steve@Rennsport]

....And make that you disconnect one end of your F & R swaybar's droplinks, otherwise you'll have a crossjacking issue and inaccurate cornerweights.

[Gunter]

Mario:
Good advise here.
Since you replaced parts/bushings all around, you pretty well have to set/adjust everything.
With incorrect settings, the tire-wear will tell the story in the future.
I would not leave the caster uneven per side.
Can you post what specs you want?
Camber front/rear?
Toe front/rear?
Height?

[mmasse]

Gunter, I agree with you I will make caster equal now that I know what the problem was.

I am running 8" wheels with 225/40/18 in the front and 11" with 295/30/18 in the rear.

I am looking at the following settings:

Toe:1/16 F, 1/32 R
Camber: -1.5 degr F ; -2 Rear
Caster 6 deg BOTH sides.

I was looking at 24.5" rear and 25" F. I saw on this board that people are running their cars lower, but with my wheels I am afradi to have rubbing if I lower it more.

What do you think?

[Gunter]

Mario:
Height, Caster and Toe sounds good but..............
With these big tires, excessive cambers will have them run on the inside edge.
18 inch wheels will put quite a torque-stress on the axles, CV's, and transmission, even with the upgrades on the 915.
I cannot see how the ring/pinion and gears in the 915 can stand up to the torque coming from a 3.6.
Time will tell.

[mmasse]

Gunter,

I just bought a pair of 10" BBS for the track and I plan to put 275 on them for the rear in order to decrease stress on the CVs and tranny...and also to solve an understeering problem I am having.

I will keep the 11" 295s for the street to impress people!!!..at least until they wear
Thanks for the advise.