Setting up Eccentric Trailing Arm Bushes

[Grrrmachine]

I think this deserves its own thread, rather than padding out my old one.

I have toe out at the rear: -0.45 degrees left, -0.33 degrees right. I've ordered two sets of Febi eccentric bushes to correct this, so four bushes in total.

I've looked at the relevant page of the Bentley manual, linked here for reference:



I get the idea about rotating the bushes between 0 and 9 to change the toe angle, and that if I set the outer bush at 9 and the inner bush at 0 then I'll get the maximum toe-in angle. But I can't get my head round the last graph - it doesn't help that it talks about toe in mm rather than degrees.

I'm guessing that for the left side I should toe in as much as I can and hope it gives me the half-degree of toe in I need, but I don't want to over-correct the right side. Or is 0.12 degrees difference pretty much naff-all?

[handpaper]

This guide looks incomplete; the eccentrics will alter camber as well.

See here for a better explanation:

http://www.e30m3project.com/e30m3perfor ... c_bush.htm

NOT simple

[Grrrmachine]

Yeah, I'd seen that site but didn't know if these K-Mac polybushes offer more toe than the standard rubber ones. The website also differs compared to the Bentley as to what constitutes the "neutral" position, but I can get my head around that.

The main issue is, basically, how MUCH do I rotate one bush relative to the other to change the toe half a degree?

[Grrrmachine]

Using some calculators, half a degree is around 6mm of toe at the wheel Can't believe eccentric bushes would fix that.

[DanThe]

TBH I wouldnt expect the bushes to stay put, and your going to have a right faff to get them perfect, adjusting them means you have to remove the whole trailing arm

Why not just use the adjuster plates?

[Grrrmachine]

I don't need them perfect, I just need them ball-park close. At the moment I've got a difference of 1.25 degrees in toe at the back - way too much.

It's taken me a while to get my head around degrees, digits, decimal points and millimetre conversions, but I think I've got it sorted now. Based on the KMac charts I should be able to dial in enough toe to even out the camber as well, so I'll let you all know how it goes.

[daimlerman]

Would it not be easier to find the bent component and change it?

With that amount of error,it must be visible to even my untrained eye!

[Grrrmachine]

That's the worry - I've put straight-edges along everything and can't work out where it's gone wonky, and I don't fancy the job of removing the rear beam, diff and everything else on the offchance that another rear beam is straighter than this one. Considering what Polish roads are like, I don't trust any other beams or arms to be straighter than what I've got now.

I'm thinking that if eccentrics don't work then I'll get another beam and slot/weld that one, swap them over, then slot/weld the current one and flog it on to some stance fanatic to cover my costs. But BMW must have made these eccentric bushes for a reason.

[daimlerman]

My thoughts are with the shell/beam mount at the side that's out,TBO.
If,at some time in this car's past,it's been erm 'drifted' into a kerb,that would certainly be enough to bend a trailing arm....given the amount of welding that you have done(cannot remember if you worked in the area of rear cill!)could that be a root cause?

Either way,it's for this kind of thing that BMW made the eccentric bushes.

[Grrrmachine]

I did take metal out of both the sills near the beam but I didn't interfere with the beam mounting points themselves, so that should still be straight. Considering the toe-out is on both sides it would suggest its the beam rather than both trailing arms, but then you never know. The car's got no history prior to 2009 other than miles and miles of bodgework.

The eccentrics were 15 quid a set so I'm not breaking the bank by trying them, just losing a weekend.

[Grrrmachine]

This is turning into a pig of a job. Right-hand outer trailing arm bolt can't slide out fully because of the fuel tank stub pipe. So it's either drop the beam or drop the tank to get the trailing arm off. What a palaver.

[DanThe]

This is turning into a pig of a job. Right-hand outer trailing arm bolt can't slide out fully because of the fuel tank stub pipe. So it's either drop the beam or drop the tank to get the trailing arm off. What a palaver.

You dont need to drop either, just remove the rubber hose from the tank end and the bolt will come past

[Grrrmachine]

Already tried that Dan, the head hits by about 2mm even with some firm yanking on the trailing arm. Maybe this is why I've got this toe-out issue to start with.

[Brianmoooore]

Any sign of twisting on the bracket? As Dan says, it should just clear the stub on the tank.

[DanThe]

Take the inner bolt out first, tilt the arm outwards then the outer bolt will clear the tank stub

[Grrrmachine]

Got it all off, rebuilt and on thanks to you chaps. That stub pipe was a close call, and I'm glad I did it all because one of the bushings was looking mullered.

However, with everything rebuilt and the wheels on I'm still getting 4-5mm of toe out across the rim on each wheel. I haven't let the suspension settle yet so any gains they offer my be offset by the arse sitting high, but it's clear that they're not going to sort out 45 minutes of toe-out.

Looks like I'll need the adjuster plates and bolts after all. Do you still sell them Dan?

[BenHar]

Grrr,

I think someting must be bent.

Why not get another rear beam and trailing arms?

More work, but then it should be straight.

Ben

[Grrrmachine]

Why not get another rear beam and trailing arms?

I've put straight-edges along everything and can't work out where it's gone wonky, and I don't fancy the job of removing the rear beam, diff and everything else on the offchance that another rear beam is straighter than this one. Considering what Polish roads are like, I don't trust any other beams or arms to be straighter than what I've got now.

There's also the added cost and ballache of beam bushings. This beam had new bushes about 18 months/6000 km ago, so they're pretty new. A new beam plus new bushes is more work and more money.