MG Sports Cars

Does anyone know if the front suspension cross member for a chrome bumper (1970) is the same as a rubber bumper car? If they are different how do you tell the difference?

Thanks Mark



Edited 1 time(s). Last edit at 02/06/2012 10:01AM by coolmgcma.

No, it is not.

There are "risers" welded onto the rb x-member where it attaches to the car to give it the additional height that was required....sorry, no pictures to post.

So if I grind off the risers then I have a chrome bumper cross member, correct?

I beleive the steering rack mounts not in the same location.

Dave

I could be wrong about this but if you grind the risers you would probably induce more bump steering than desired and the amount of clearance between the rack and engine would be less causing the motor to be higher. Is that correct?


Paul

I wish I had more suitable photos at hand.

Here's a "chrome bumper" crossmember (viewed from the rear)... disregard all the extra holes that were cut in it to lighten it up for racing:



Here's a picture of a rubber bumper crossmember (viewed from the front), courtesy of Pete Mantell... disregard the motor mounts Pete has added to suit a Ford V8 engine installation:



As Rick mentioned, MG welded risers onto the crossmember to space the body higher relative to the suspension (to meet Federally mandated bumper height requirements).

Steering rack mounting pads are similarly spaced, but they're tilted at two different angles.

Thanks guys guess I will go a different route. Mark

Raising or lowering it will not affect bump steer since none of the wheel/steering angles changes. What will change is the steering rack angle, as Rick mentioned, in two aspects. It will change in rotation. This can be resolved with shims under the mount, as almost everyone who has moved the firewall cone downwards has done. The other aspect is the angle of the rack across the car. The later rack does not sit exactly horizontal. But this has a minimal effect and cannot be felt. Carl might have some valuable input here.

Also something to look for is any change in caster. I doubt you'll see that but you should check it. The use of caster wedges has been fairly common but I'm seeing less of it with the wider tires.

If it is desired to lower the rack on the crossmember, shaft collars, muffler clamps, and a 1/4" plate makes a simple and rigid mount which is adjustable for pinion angle. See the Roadmaster and 340 threads for full details.

Jim

Why not look for a earlier crossmember?

You’re right Jim, If I’d really put my brain in gear I’d have noticed all that stuff is bolted to the cross member and changing the relationship to the frame wouldn’t have an effect. I was wondering, as I’ve never had my cross member off, are the bolts that attach the cross member to the frame tapered and are they different for rubber and metal bumper cars?


Paul

They are tapered so that they lock into the frame of the car. I'd think the RB ones would be an inch or so longer.

Jim

Was it common for the bump stop mounts to be cut off the chrome bumper crossmember? I've got a used chrome bumper crossmember that I am trying to swap into a RB car and it looks like my mounting tabs are missing.




Edited 1 time(s). Last edit at 07/15/2022 09:04AM by gstock.

Never seen that. Looks like they removed both the upper & lower parts where the bump stops would fasten. Would love to know what was being done to the front suspension that required that.

Thanks Carl. Looks like I've got a welding task this weekend.