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MG MGB Technical - Lowering my 74 1/2 MGB GT

I have a question most American's can't answer. I have a 74.5 (11/74) MGB GT with rubber bumpers. They are extremly rare in the U.S. I want to lower it approx. 1 inch to the specs of a chrome bumper GT Nobody can tell me which coil spring to use to lower the front. Moss ect. sells lowered coil springs but they can't tell me which one to buy because they have no applications for a Rubber Bumper GT. Can anyone help me in locating the proper kit for lowering a Rubber Bumper MGB GT. You guys are much more knowledgable on this. Thank You. Dan
D.E.C Cramp

I have a 74.5 (11/74)mgb roadster.
I replaced the front springs with springs from a CB and ended up with the heights as listed below. I had the rear springs re-arched from @ 16 to what is listed below


DF 14
PF 14 3/8
DR 14
PR 14
I believe the front springs are Up rated Road springs 480# part #Aht21.

Lowering the car sure helped to reduce the body roll.

I have a Rover 3.5 which is about 50# lighter than the 4 cylinder, so I might sit a little higher than you would.


Have fun

Bruce
Bruce Mills

Dan
There are lots of posts on suspension modifications for the rubber bumper MGB. Check the archives. Problem 1: The front cross member is raised more than an inch. Lowering the front changes your suspension travel. Changing to an early model cross member has it's own issues as to mounting the steering/rack & pinion.

The rear axle has higher mounting points front and rear and a lowered bump stop. You can go to flatter springs or lowering blocks, but you have less suspension travel with the lowered bump stop.

For best handling you install the early front cross member and adapt the mounts to allow use of the late rack and pinion.

For the rear you can get flatter springs. The front and rear mounts could be raised to pre rubber bumper heights but that is a lot of work. Either way, you then have the issue of the length of the rod to the rear shocks. Also unless you cut out the crescent addition at the top of the frame axle arch, you will have less suspension travel.

Parabolic or fiberglass rear springs will substantially improve your ride and can be used to lower the rear of the car.

Once the car is lowered to pre rubber bumper, you do not need the rear sway bar.

In short, getting a rubber bumper to handle like a chrome bumper is doable but is a project.

Welcome to the club. If you research the archives you will find there is a wealth of information.
Barry
Barry Parkinson

Thanks Barry, I think what I'm going to do is buy the lowered springs from Moss.
the thing is they did not know which ones I should order. They think it is 264-395 but I think it is 264-385. Can you steer me in the right directin. I tried the Archives but could not find the part # for a 74.5 GT. Thanks, Dan
Daniel Cramp

To the best of my knowledge, the suspension components for the rubber bumper cars are all about the same. The 74.5 handled very poorly. The later addition of a rear sway bar helped a lot. I would expect the parts no. for the rubber bumper cars would all be the same.
Barry
Barry Parkinson

I Finally found my answer. It was on tech. (MGB 14) from British Automotive. Now I can sleep!
Daniel Cramp

The original factory specs show the front springs for a rubber bumbered GT were the same as for the rubber bumpered roadster and indeed the 1973-on chrome bumper roadster, that is, BHH 1225. Front spring rates are quoted as 100lb per inch for a 73 GT. Rear spring loads are quoted as 400lb for early roadsters, 450lb for 63-on CB roadsters, 510lb for both CB and RB GTs.

From Moss's figures I do find it surprising that the same spring lowers a chrome bumpered car 1", a rubber bumpered car (roadster?) 2", and a GT (chrome?) 3/4". Other factory figures show a CB GT as variously 50lb or 100lb heavier than a CB roadster, and a RB GT about 50lb heavier than a CB GT. If the springs are that sensitive to weight surely a CB GT should be lowered more than a CB roadster, and if they are referring to an RB GT then that should be lowered even more.
Paul Hunt

This thread was discussed between 16/03/2005 and 17/03/2005

MG MGB Technical index

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