RTAB alignment tool on reinstallation

[lelandr]

I'm installing all new suspension components on my Z4M track rat. While I am adding JRZ DA coilovers, I did decide to go with factory (Lemförder) bushings in the rear suspension as they are cheap and I always got very good performance out of these style bushings in my previous track car (E30 M3).

Everything appears to be very straight forward (except that I'm ordering new brake lines because I didn't pay attention to the step of loosening the brackets first--oh well, 85k new ones should probably be used for a track build).

However, in the TIS, there appears to be a BMW tool which bolts to the wheel hub and then to the RTAB bracket. I assume that this is to keep everything sort of aligned while you tighten the bracket to the bushing. The TIS does mention that you can use a sufficiently long rod of 18mm dimension, but this appears to be something that probably needs 8 pair of hands.

How critical is this alignment in a practical sense? Should I see if I can find the BMW tool locally, or do I just have to be close enough for horse shoes?

If it matters, I do have a set of the plastic limiters from Condor.

Also, I assume that the upper control arm is going to be considerably easier to replace the bushing and ball joint while the RTA is down. Any reason NOT to do this?

Finally, I assume that everything will go more easily if I use some kind of a lubricant for reinstallation. I see a lot of procedures calling for antisieze, but I suspect that something like dishwashing soap will be preferable?

Thanks!

[filtercoffee]

That rtab bracket is key for the alignment of toe in the rear.

From what I've seen on youtube of e46 rtab jobs, people tend to use paint markers to get the alignment close to before the repair, and then get an alignment once things settle.

I've never seen or heard of the alignment tool. I have seen the RTAB removal tool, a sort of bushing puller, but again, lots get by without it. tldr See e46 rtab videos on youtube.

Update: Idk about the rear upper control arms, getting to the inner mounting point seems kind of a pain in the ***.

[inTgr8r]

lelandr

I haven't seen the tool but I suspect it's for removing the bushing pre-load.

It's VERY important with factory (rubber) RTAB's to remove preload on the bushing.
The BMW tool will do this, but I think it works with stock height.

Instead of the OE tool, the proceedure is.....
- install the RTAB bolt loosly
- put the wheel back on and lower the car back down so that the trailing arm is in a neutral, unloaded position.
- now tighten the RTAB through bolt.

If you can't get to it, measure from hub to the fender wheel arch.
jack it back up, remove the wheel and then jack up under the hub to the proper height.


If you use a spherical RTAB this procedure isn't required.
JMO but sphericals are MUCH better on a track based car as it stops alignment shift under load.

...hope that helps

[lelandr]

Interesting. I thought it was just for centering the bracket with the wheel center.

I used a folding carpenter's ruler to align the new bushing position with marks made on the hub with the old bushing.

I'm not sure how one would tighten the nut with the car on the ground as the opening for the bushing doesn't allow any space for these.

I hope that my effort to align the bracket with the hub and align the bushing as the factory one was in the RTA is sufficient.

Been waiting forever for simple parts, so this damn car is still not yet on the ground.

Thanks.

[filtercoffee]

Not quite sure if this answers the question, nor do I have direct experience with this - but with regards to tightening the bushing, you can use a jack to raise the RTA to the approximate position it would be when on the ground, and tighten the bushing with the RTA in that position.

[inTgr8r]

Originally Posted by filtercoffee

Not quite sure if this answers the question, nor do I have direct experience with this - but with regards to tightening the bushing, you can use a jack to raise the RTA to the approximate position it would be when on the ground, and tighten the bushing with the RTA in that position.

That is the general idea.
You can gain some accuracy if you measure from the hub to the wheel well arch.
Then jack to the same measured position.

[inTgr8r]

Originally Posted by lelandr

Interesting. I thought it was just for centering the bracket with the wheel center.

I used a folding carpenter's ruler to align the new bushing position with marks made on the hub with the old bushing.

I'm not sure how one would tighten the nut with the car on the ground as the opening for the bushing doesn't allow any space for these.

I hope that my effort to align the bracket with the hub and align the bushing as the factory one was in the RTA is sufficient.

Been waiting forever for simple parts, so this damn car is still not yet on the ground.

Thanks.

That will get you in the ball park.