RTAB preload

[Viren]

So I'm going to replace the RTAB with oem bushes and understand that the bush needs to be preloaded so that is does not twist.

Does anyone know the correct procedure for this without using the "special" bmw tool? Thanks!

 

[chris]

You need the tool imo. You can do powerflex bushes easily, but OEM you need the tool to get it right. Most garages dont charge a lot, and its a ball ache to do. Some places will hire the tool out as well

 

[Viren]

You need the tool imo. You can do powerflex bushes easily, but OEM you need the tool to get it right. Most garages dont charge a lot, and its a ball ache to do. Some places will hire the tool out as well

Thanks, do you know who I could hire the tool from? Struggling to find

 

[chris]

Where abouts are you located?

 

[exdos]

If you can measure the position of the hub against a couple of fixed points on the car whilst the rear wheel is on the ground before starting the job, then you can put the hub in the same position whilst you tighten the bolt for the bush. Easy.

 

[Viren]

Chris, I'm northwest London,

Exdos, so if I take the measurement from the centre of the hub to top of the wheel arch whilst the car in on the ground.

Then when fitting the the bush I jack the rear assembly up to the same height and tighten the bolt to the bush.

1. Will this work?
2. Do I then take a straight edge from the centre of the hub to the bracket and tighten?

I'm thinking if the bracket is tighten here when I push it up in to the pocket, it will twist as I will have to raise it to fit the three bracket bolts, sorry if in sound confused!

 

[exdos]

Chris, I'm northwest London,

Exdos, so if I take the measurement from the centre of the hub to top of the wheel arch whilst the car in on the ground.

Then when fitting the the bush I jack the rear assembly up to the same height and tighten the bolt to the bush.

1. Will this work?
2. Do I then take a straight edge from the centre of the hub to the bracket and tighten?

I'm thinking if the bracket is tighten here when I push it up in to the pocket, it will twist as I will have to raise it to fit the three bracket bolts, sorry if in sound confused!

That'll work.

Provided that the RTAB cage is in position (loosely bolted) and the hub is in the same position as when the car is standing normally, then as long as you tighten the RTAB bolt when in that position, you'll have no preload.

If you want to keep the exact toe value after, as before, put a few blobs of paint onto the edge of the cage and the chassis where it sits on the body before undoing the three bolts, so that when you refit, you simply tighten the bolts where the paint blobs all are completely aligned.

 

[Viren]

Does the angle of the cage matter? Should it be relative to the position when fitted in the pocket?

 

[exdos]

Does the angle of the cage matter? Should it be relative to the position when fitted in the pocket?

As long as the trailing arm is in the same position relative to the cage when in situ on the car normally, at the time you tighten the RTAB bolt, you can remove the whole assembly off the car and tighten the bolt and it will be correct without preload.

 

[Viren]

Does the angle of the cage matter? Should it be relative to the position when fitted in the pocket?

As long as the trailing arm is in the same position relative to the cage when in situ on the car normally, at the time you tighten the RTAB bolt, you can remove the whole assembly off the car and tighten the bolt and it will be correct without preload.

Ok think I've got it now, so the bmw tool essentially puts the cage at the right position/angle when the suspension is not loaded