Rear Torsion Bars Not Equal Strength???

[leadrsa729]

Hi -

I recently lowered both the front and rear of my car. I measured the ride height of the rear of my car. I used the floor to center of torsion bar cover, then floor to center of wheel and subtracted the amount. I found that I am 1/16" lower on the driver side than the passenger side. The car is not professionally aligned yet and I did the lowering myself.

I drove the car a little to get it to settle and it seems that I am getting more suspension travel on the driver side then the passenger side. I see a slight rub on the driver-side tire sidewall. Do I need to adjust the spring plate angle on the driver side to correct this? If I move one inner torsion bar spline in one direction and then one outer spline in the reverse direction will it only move 1/16" or can I not make adjustments this small? I have the pre-SC non adjustable spring plates so I have no room to play.

Since the difference in height between the two sides is so small, and one side is rubbing while the other is not, is it safe to assume that the tensil strength of the driver side torsion bar is weaker than the passenger side?

Both eccentric bolts are set to the same settings on both sides. I marked the side of the bolt head where the lobes are so I know where they are positioned. I am using the stock torsion bars, 19mm in front and 23mm in rear.

Any info is appreciated, thanks!

[mpetry]

Others will jump in here with more info but let me see if I can explain this simply. The inner and outer splines on the rear torsion bars are different. One has 40 splines, the other 44. By "clocking" the torsion bars with various positions on the inner and outer splines, a means of adjusting ride height is provided.

Since you already marked the outer spline's position on the spring plate, here is what I'd do: Take the side that is NOT where you want it (too high or too low) and make an adjustment on the inner spline, moving it exactly ONE click (360/40 or 0.9 degrees) in the direction you desire, up or down.

You can calculate what that converts to in ride height with some simple trig.

Are you any closer to even, left to right?

Both splines interact to give you very fine adjustment in ride height. HOwever it takes some trial and error to get it set right if you don't measure with a protractor before you take it apart!

[leadrsa729]

So you think that I can make adjustments in ride height as small as 1/16" by reindexing the torsion bar?

[wildcat077]

You really have to be on a level surface to take precise measurements for ride height ...
Depending where i park my car in my garage the rear tire to fender clearance varies where i can slip the top my hand up to the knuckles over the top of the tire and not touch the fender on one side and if i park in another spot it's the other side ...

I spent a whole day fighting with the R/H side torsion bar for 1/4 inch just so that i could leave my eccentric adjuster in the middle position.
I wouldn't worry about a 1/16 difference but if your rear tires are rubbing it's most likely a wheel offset situation or your car is simply Too low !

What type/size, wheels/tires are on there ?

Cheers!
Phil

[80-911SC]

are you really 1/16" off from left to right ???? I would guess that you are as close or better than when it was born .... i am off by 1/8 or better and figured thats pretty close ....

Just my opinion ....

Steve

[Richard Burns]

Get the car on level ground and measure from the underside of the wheel arch (ie the guard) to the botom 0f the wheel on both sides that will tell you the difference in ride height.
If you are really pedantic about it get someone of the same weight as yourself to sit in the drivers seat and then do the measurement to see what the difference is when you are driving.

Richard

[pete3799]

I wouldn't bother with 1/6" difference.
Whats your camber on the rears?
Perhaps the one that's rubbing needs more negative camber.

[DRACO A5OG]

Originally Posted by 80-911SC

are you really 1/16" off from left to right ???? I would guess that you are as close or better than when it was born .... i am off by 1/8 or better and figured thats pretty close ....

Just my opinion ....

Steve

+1 on level ground to insure no false readings.

Hell, I am off .25" side to side, Very Happy since it was .75" off before I corner balanced. Got new 27MM Rears.

Jim

[911pcars]

If you're car is shod with "standard size" Porsche wheels and tires (you don't say), there should be no clearance issues at all in the rear unless the rear ride height is excessively low.

The rear will typically rub if using wider or more offset wheels and/or larger tires than recommended.

What year 911, then what size wheels and tires and the ride height (ground to top of wheel well opening)?

Sherwood

[leadrsa729]

Hi Everyone -

Thanks for all the comments so far! I'm running Fuch 15x6 wheels shod with Khumo Ecsta 205/60 R15 tires. I am also running a 6mm spacer in ther rear.

I've checked the level of the floor and there is a slight downwards grade from the front of the garage to the rear, but the side to side is level. I just can't understand why the driver side rubs while the passenger side is fine when both sides are adjusted almost absolutely identical.

Thanks!

[911pcars]

A few possibilities:

- Vehicle build from factory results in slight L-R fender clearance difference. It happens.
- Previous collision damage and repair

As a temporary/permanent cure until this is resolved, remove the wheel spacer to gain needed clearance. Research future tire purchase with narrower tread or cross section, same size.

The rear shouldn't rub at any reasonable ride height, thus these workaround suggestions are not recommended:
- Increase rear spring rate
- Raise ride height

Sherwood

[Trackrash]

1/16 inch is negligible.

With 205s in the rear you are going to have a tight fit with out the spacers. Why do you have spacers?

I would check to see if both the torsion arms are at the same angle. Make SURE the floor is perfectly LEVEL. IMO even torsion angles are what is important, not ride height.

If you plan on playing with your torsions again, you may want to consider instaling the newer style adjustable torsion arms. They can save a ton of time.

Also, you need to check your camber. A little more negative camber will make the difference in rubbing or not.

[Flieger]

+1

The SC adjustable spring plates are a must for corner-balance.

[Richard Burns]

If you are measuring from ground to car you could get 1/16" just from different tire pressures left to right or even by uneven tire wear or tire sidewall strength (subject to the age of your tires).
By measuring from car to metal on your wheel you cut out these possibilities.
Richard.

[KTL]

Measuring for equal relative heights at the corners is not going to get you a well-balanced ride, even if you are on level ground. I diddled with my ride height years ago on the '87 to get it lowered a bit (but not slammed to the ground) for a better stance. I used the often-quoted fender arch measurement of 24.5" or 25", whatever it is. Car never really handled that great, despite having a nice attitude/appearance. When I finally got it on some scales, the right rear was extremely light and that explained why i'd lock up the right rear under heavy braking. Instead of going through a complete corner balance, I just lowered the left front to help the excessively light right rear. Doing so made a substantial difference. Point being is, eyeballing the ride height, even by taking detailed measurements, is not going to get the car well balanced. You need to respect what the scales tell you.

That said, for street driving, I agree a 1/16" difference is splitting hairs. You're not checking toe here. 1/16" is definitely close enough. Heck, when you corner weight the car, you have to be diligent to get repeatable results. Often times the changes you make to fine-tune it are much greater than 1/16".

Also consider how other variables affect the height- tire pressure & wear, fuel load (always varying), suspension bind (old bushings, tired shocks). Speaking of suspension bind, you're creating some when you're setting the heights. Because factory sway bars are non-adjustable and they will therefore be fighting whatever adjustments you make, if the car itself is not level side-to-side.

[Tim L]

I think you're going to need to corner balance the car after adjusting the front and rear ride heights. The car could be good for ride height and be way off as far as balance.

[JP911]

Have a friend take the ride height measurement with you sitting in the driver's seat. You may find that the car is going lower in the left rear than you think. Also, you mention that you lowered the car yourself but have not had it aligned, so it is possible that the rear camber is out of whack (not enough negative).

[jurhip]

+1 on Tim L,
Corner balance tells you what you need to know. Ride height measurements may be slightly off due to exact CG of the car and car loading during the corner balance, as KTL mentioned.

BTW - Measurements taken from the ground to the fenders are not an accurate way to "level" a car. They vary from the factory.
Measurement taken to the fenders can be used as a delta reference only after a corner balance is performed.