Some background first:
1987 BMW 325is
Never in an accident
New BMW suspension bushings everywhere
New Billstein Sport shocks
New H&R race springs
New front wheel bearings
New inner and outer tie rod ends
Calipers rebuilt recently
New brake discs and pads along with all new brake lines
BMW Z3 steering rack
The car pulls to the right quite a bit and it is driving me insane. It has new tires and it was aligned by a well respected shop in south Florida.
The only thing I can think of is the steering rack not being perfectly perpendicular to the front "axle". Would this cause pull even after alignment?
The Z3 rack has thinner mounting points and a spacer has to be added to make up for the lack of material. I cannot remember if the holes on the rack were close in size to the mounting bolts and maybe it is sitting a tad crooked.
I am pretty certain the car did not pull like this before all the suspension refresh.
Any ideas?
I can post a video later tonight, but it pulls quite a bit. It will change lanes in 80 ft.
Also the breaks are not dragging.
Slippery wrote:
The only thing I can think of is the steering rack not being perfectly perpendicular to the front "axle". Would this cause pull even after alignment?
I'm not sure but that would be so wacky, I'd be more surprised if it didn't. It would cause an imbalance of leverage between the front wheels.
I usually suspect caster when a vehicle pulls. What are the results of the alignment?
RedGT
HalfDork
5/23/17 3:21 p.m.
Does it pull the same whether you're on throttle, on brakes or coasting?
Have you tried swapping tires from side to side?
When was the alignment done in relation to when the pull started?
Could be tires. Could be lots of things.
Tires are new and we tried moving them around with the alignment guy.
Caster I will check. I forgot to mention I am using M3 front bushings in order to gain more caster ... maybe this is throwing things off.
NickD
SuperDork
5/23/17 3:34 p.m.
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
NickD wrote:
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
The problem with the caster on the e30 is that it's not adjustable.
NickD
SuperDork
5/23/17 4:04 p.m.
Slippery wrote:
NickD wrote:
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
The problem with the caster on the e30 is that it's not adjustable.
How is caster not adjustable on a RWD car? I can understand on FWD cars where it really doesn't have any bearing on how they drive, but RWD is a big deal
Does it pull coasting with the engine switched off? Power assist in the rack can cause that. Some older Euros had a centering adjustment.
If you have a sensitive wrist, you can tell sitting still whether the power assist is a little more going one direction than the other.
RedGT wrote:
Does it pull the same whether you're on throttle, on brakes or coasting?
I just tested this on the drive home.
It will pull under throttle, coasting in neutral, engine braking and braking.
If I hold the steering straight and start braking before I let go of the wheel it will pull slightly less than if I just start braking while not holding the wheel.
NickD wrote:
Slippery wrote:
NickD wrote:
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
The problem with the caster on the e30 is that it's not adjustable.
How is caster not adjustable on a RWD car? I can understand on FWD cars where it really doesn't have any bearing on how they drive, but RWD is a big deal
e30 through e46 have not caster adjustment from the factory.
See the part that says "Control arm rear mount"? That's what controls your caster, the e30 M3 has an offset bushing to increase caster.
The only way is with adjustable top strut plates or by having a modified bushing.
My suspension has all factory adjustments, all I can adjust is toe on the front.
Streetwiseguy wrote:
Does it pull coasting with the engine switched off? Power assist in the rack can cause that. Some older Euros had a centering adjustment.
If you have a sensitive wrist, you can tell sitting still whether the power assist is a little more going one direction than the other.
I have to check this. I will check tomorrow.
I also have to check on the caster, need to find the invoice from the alignment place.
NickD wrote:
Slippery wrote:
NickD wrote:
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
The problem with the caster on the e30 is that it's not adjustable.
How is caster not adjustable on a RWD car? I can understand on FWD cars where it really doesn't have any bearing on how they drive, but RWD is a big deal
Not true. Caster has as much effect on a FWD as it does on a RWD car.
The ZX2,Escorts had a small adjustment by rotating the strut mount.
I added offset control arm bushings to my ZX2SR and it made a big difference.
NickD wrote:
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
Might still be true if you only ever drive in the far right lane.
NickD
SuperDork
5/23/17 5:51 p.m.
iceracer wrote:
NickD wrote:
Slippery wrote:
NickD wrote:
You should have half a degree more caster on the passenger side than the driver side to account for road crown.
The problem with the caster on the e30 is that it's not adjustable.
How is caster not adjustable on a RWD car? I can understand on FWD cars where it really doesn't have any bearing on how they drive, but RWD is a big deal
Not true. Caster has as much effect on a FWD as it does on a RWD car.
I've driven a number of FWD cars with caster way out and never had an issue. Including a Malibu with 4 degrees more caster on one side than the other that drove perfectly straight down the road.
If caster is a little out you might be able to move it enough by loosening up the strut mount, lolipop, subframe bolts, or some combination of the 3 and use a prybar to move things in the right direction as far as slop in the bolt holes allows. A good alignment guy knows how to do this, but it's time consuming so it probably wasn't done. Or maybe take a die grinder and elongate the holes in the lolipops.
Small update.
I tried it with the engine off. The car still pulls.
I looked all over the place for the alignment numbers to no avail, all I found was the invoice.
After all the suggestions, I feel more and more that caster is the problem. I have a buddy with a caster gauge, will try and measure next week. If its off I will try BrokenYugo's suggestion.
I feel it might be easier to play with the caster at the strut top mount than the lollipop. If I remember correctly the lollipop has locating dowels.
check your trailing arm mounting tabs. if the bolt holes are ovaled out, the car would align fine on the rack but under dynamic load (acceleration, deceleration, road conditions) your rear toe will change and have significant effect on the way the car tracks.
Ask me how I know.
Then I'd say tires. I've had tires that liked to pull one way or another due to the tread pattern, even if the car tracked perfectly straight with different tires on it.
Btw, caster is adjustable by getting the OEM M3 strut tower upper mounts and/or offset lollipops at the rear end of the LCAs. Or camber/caster plates of course.
also, the caster on our rally e30 is all out of whack (and our toe setting are done "by looking at it to see if it looks straight") and that car still tracks perfectly straight an 100+mph. I don't personally think caster is your main issue here, but who knows.
btw, have you verified that your rack is actually "on center" when the steering wheel is straight?
It's possible it was installed slightly off center (i.e. the splined section not centered) and the steering wheel just moved on its own splined section to compensate). Poor explanation, hope you know what I mean.
i.e. When your alignment is good, are both tie-rod ends showing the same amount of threads from the inner tie rods?
