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MG MGB Technical - RB vs CB Front Crossmember

Anyone tell me what the difference is please?? How to identify and the effect of using a RB one on a CB car!?!?!

Regards,

Andrew
Andrew Walton

I'd say that the most obvious difference is the
height of the shock mounts. They are higher
on the RB version.
Daniel Wong

It will lift the front and you will have to realign the steering column but everything else will change straight over. See the other thread which suggests how to shim the rack and column.
jim soutar

The shock mounts aren't different. It's how it mounts to the car that is. On the RB cross member there is a raised part where it bolts to the car. I am not sure if the brackets for the steering rack are actually different or not but putting a CB cross member on a RB car (or visa-versa) does mean you have to adjust the steering rack alignment.

Simon
Simon Jansen

Brackets for the steering rack are different.

Clifton
Clifton Gordon

Makes sense that they are. If you ever have your cross member out check those steering mounting brackets for cracking.
Simon Jansen

Simon has the right answer. The RB member has 1 inch pads welded onto the top where it attaches to the car chassis rail. If you see a RB and a CB cross member side by side, the difference is obvious.
If you put an RB member on a CB car you will raise it up by that 1" and spoil the handling.
Mike Howlett

And completely cock-up the rack positioning.
Paul Hunt

I stand corrected as to how the shocks mount on
the X-member.

It is the frame rail mounts as well as the steering rack mounts
that are different.
Daniel Wong

Andrew, tried to e mail you. Got bounced!

Do you need a CB xmember?

Colin
Colin Parkinson

Thanks Colin, but I'm o.k - just needed to check differences and have blasted and used original. I'll update my email.
Regards,
Andrew
Andrew Walton

Is it possible to convert a rubber bumper crossmemeber to chrome bumper specification? I've never seen the two together so I don't know how big the difference is. Are there just the 1" pads to take off?

Mike Standring

Major grinding job, and that's if they are just pads welded on to the top of a chrome bumper crossmember. In fact I think it uses a different top plate that is set 1" or so higher under the chassis rails. Which is why the conversion kits all use flatter springs.
Paul Hunt

You would have a lot of grinding to do and you'd need to cut off the rear part of the mounting (the flat bit with the hole in it) and then weld that back on. I have a normal cross member at home and the RB one on the car. Can see if I can get some pictures.

You would also need to reposition the mounting brackets on the front of the cross member that the steering rack bolts to. The best way to do that would be on the car with the steering all in place so you can get the positioning exactly right.

Simon
Simon Jansen

This thread was discussed between 10/02/2009 and 24/02/2009

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