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MG MGB GT V8 Factory Originals Technical - Can I mix C/B running gear with R/B car?

Guys, started out planning to V8 my 67BGT but have just been offered a bare (but rusty) r/b GT shell for peanuts! Would it be possible to use the running gear and bolt on panels from the 67 but build up using the r/b shell (set up for V8 isn't it?). I would like to use the c/b front end or should I try for a r/b x-member? Comments please
regards
mark
mark mathiesen

Mark,
Anything's possible but if you go with the c/b crossmember you'll have to change the steering rack mounts because the angle will be different.

The c/b crossmember gives you the benefit of being able to lower the car without running out of suspension travel.(the r/b crossmember lowered to the same height will give you one inch less suspension travel).

I believe also that the rear spring hangers on the r/b are one inch longer than the c/b car as well. This would be easy enough to get around as you can just get lowered springs to suit. HTH

Stainzy
Stainzy

I just finished swapping cross members on my '76 B. The c/b cross member had to be modified by cutting the rack mounts lowering them 0.250" notching the cross member to allow for rotation of the rack housing and shortening the steering shaft, i did have interferance of the shock absorbers towers with the inner fenders where they bulge out i had to bump them a little bit imagine this on a fresh painted and detailed engine bay oh well we have to do what we have to do !!
Romney
Romney

I think if you did this the best way to go would be to use a C/B steering rack. The pinion will of course be a bit short; you can just swap in the R/B pinion. Doubtless there will be some fiddling, but I've always thought the R/B offset steering rack mounts were theoretically impure.
Niles

Niles,

I'm not sure, but I think if you swap the pinions over you might get the wrong angle for the UJ at the top.
IE. Swapping the pinion effectively lengthens your c/b pinion shaft which would mean that the shaft will be too high to meet the r/b UJ attached to the upper steering shaft.

Stainzy
Stainzy

Stainzy, you are certainly right ... you have to grind the steering rack mounts at a slight angle in order for the upper column and the pinion to have a happy meeting at the U-joint. I forget the angle but maybe I have it lying around ... it's a known quantity, anyhow. This is how some of the US guys do conversions and I like the way it works.
Niles

Niles,
Sounds like a good idea, I might give it a go myself. I have a chrome bumper car but was going to try and fit the new r/b rack that I bought.

Stainzy
Stainzy

Stainzy, I hope you give it a whirl. I can't find where I wrote it down. I believe Glen Towery in the US does it the way I stated; presumably you could contact him and figure out the right angle to grind the rack mounts. Putting the R/B mounts on a C/B x-member really seems to me like going backwards.
Niles

Occasionally Glenn Towery adds comments, but he must not check often, so in his absents I’ll tell you what he does and why based on phone conversations and his video.

He would encourage the use of the older car to avoid running afoul of the emission laws and to get improved handling from the original ride height. However the smaller transmission tunnel and older style steering system would complicate the use of pre ’68 MGBs.

The following parts are used from a rubber bumper MGB, the rack and pinion unit, the steering column and the portion of the firewall that the mounts to and the U-joint.

The upper end of the steering column bolts in to the same brackets as the ’68 through ’74, but is two inches (25mm) shorter where it connects to the firewall above the driver’s feet. That is the reason that portion of the firewall needs to be salvaged from the newer car and welded to the older car. For a pre ’68 car, the upper steering column would also need to be moved over, but it will not bolt on without adding some captive nuts. The fatter collapsible column will require the latter dash and therefore gauges.

None of the proceeding paragraph needs to be done if you use the rubber bumper MGB with the ’67 cross member and rack and pinion unit and the lower ride height will be restored in the front.

Whether you go through the long process listed above or use the rubber bumper car, you will now have the shorter column and smaller U-joint located farther back as in the factory V8s. With the chrome bumpered car’s cross member the older rack’s pinion shaft will be too short and the new one will be too long. Towery’s method is to shorten the long one, but this will leave it pointing to where the larger U-joint was when mounted to the longer steering column. The final step is to modify the rack housing by shaving the lower mounting edge where the two back bolts go through. Glenn Towery sells rack housings that have been modified the proper amount.

So the short answer is yes, you can mount a cross member from an MGB with chrome bumpers to an MGB with rubber bumpers by shortening the pinion shaft and modifying or replacing the rack housing to lower the upper end of the pinion shaft to join the smaller U-joint in the rearward V8 position.
George Champion

Hi Mark

I just finished all the front stuff with my RB to CB conversion, and now have a RB steering box with a shortened pinion shaft mounted on new brackets welded to a CB cross member. ( I didnt quite like the idea of grinding the steering box mounts)

The rear spring mounts are pretty well converted to CB mounts as well. I did this instead of using lowering blocks.
The work is fairly straight forward, as hidden underneath the RB stuff, there is CB stuff trying to get out. However there no way I would attempt it without the car being on a spit, but with the car upside down its not too difficult.

I can send details and some photos if you want to go this path.

Cheers Ian F

Ian Fraser

This thread was discussed between 23/07/2001 and 26/07/2001

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