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MG MGB Technical - Rear Damper Replacement poser

I have a bit of a non standard mgb roadster.
It is a rubber bumper 1975 version with chrome bumpers fitted, and a pair of old Spax shockers.
I have chrome bumper springs which are nearly new.
I am trying to fit a pair of new Koni shocks which are suitable for MGA,B,C and V8.
Looking at the axle position I noted that at rest the check straps are nearly tight.
Does this mean that they stretch as the weight comes off the wheels?
I fitted the dampers and the only warning that came with the dampers was to ensure the standard MGB bump stops are not removed. I assume this means that if the dampers go to the end of their travel in compression they will get damaged, but no mention of the fully extended limit. The reason I mention this is that the dampers come to their end of travel before the check strap is tight. This does not seem correct to me.
I tried to turn the lower damper mounts upside down to reduce the extended length but I found that they would be fully compressed before the bump stop is reached.
Am I correct in assuming that as the wheels rarely come off the ground during driving, the dampers being fully extended when removing the wheel etc, would be OK.
Whilst working of the car yesterday one of the check straps broke. Luckily I was not near but it seems a lot of weight to be supported only by a rubber band.
I have tried Rubber bumper straps but they are longer than the Chrome versions and only make things worse for damper travel.
I would appreciate any comments.
Regards
David Tetlow
D M Tetlow

Does your car sit at rubber bumper, or chrome bumper height? It sounds like the shocks you have are designed for the crome bumper, and require the use of CB limiter straps.

Did you measure the difference in length between your Spax and Koni shocks? Fully extended are they the same?
Jeff Schlemmer

Hi Jeff
The spax shocks were longer than the Koni, but they have completely different monunting plates. The new Koni use the old original lower shocker plate as the Spax had a plate that protruded down 2 inches below the axle, and the upper plates are different too.
I do not know what height the car sits at but the shocks state clearly that they will fit all MGA, MGB, MGC, V8, Chrome or Rubber bumper models!!
Regards
Dave
D M Tetlow

I'm sure the instructions that came with my spax said to remove the straps, as well as leave the bump stops. So I did.

I have a very high sitting chrome bumper CB. No way would the straps have reached.

The springs are supposed the sit almost flat under normal load - mine are nowhere near, but it is still mainly a rolling shell.

It may be the new springs - what is your wheel centre to lip of wing measurement? We can compare.

Liam
Liam

Hi Liam
The centre of my wheels to the top of the lip is 380mm.
Bearing in mind my car is missing doors, boot lid,roof,seats, carpets,windscreen,front wings and Bonnet. It also has only a bit of fuel in the tank.
If you are removing the straps then isn't the whole weight of the axle on the fully extended shocker?
In your case it may be possible to fit Rubber Bumper straps. thay are 3/4" longer than the Chrome versions.
My springs have AHH7080 stamped on and have the interleaves.
Regards
Dave
D M Tetlow

For some time now springs have been supplied which are either too hard or too arched or both, first on the American side of the Atlantic and more recently in the UK. It is right that correct springs will be almost flat on a car with all components fitted but no occupants, and the shackles almost vertical. It should be easy to fit the rebound rubbers just by jacking the axle up towards the body, way before the body starts to lift off its supports. Although note that rubber bumper cars may have to have the shackles levered away from the chassis rails to start with, due to the lower position of their upper mounts.

My V8 came with Spax and it still had the rebound rubbers. Can't see what harm they do, or what benefit there is in letting the axle hang lower if the Spax lets it hang lower and it does no harm for the Spax to take the shock of the rebound. However anything that lets the axle hang lower is going to put more stress on the rear brake flex pipe, which I would have thought is definitely best avoided.

You may not need the bump stops or rebound straps very often, but it may not take many shocks to damage the dampers if they are taking the shokc and not the rubbers/straps.

Centre of the wheel to the bottom of the bright trim strip is the usual measurement, 380mm equates to nearly 15.5" which is very high, 14" to 14.5" is more typical.
Paul Hunt 2

Mine is, like yours, a 75 that has been converted to chrome bumpers, and to chrome bumper height. Exact Chrome Ride height was achieved by fitting one inch blocks and redrilling the front (rear spring) hangers and moving the hole up about 45mm. It has been fitted with chrome bumper straps and about one inch cut from the bump stops.
All of this to tell you that from ride height until the strap starts to tension is 4 inches, from ride height to (cut)bump stop is 2.5 inches. You will have to get those springs reset by a spring maker I think.
Peter

The rear bump stop on the rubber bumper models is also lowered, which will reduce your rear axle travel. I can be cut out or the rubber bumper cut back.

It is instructive to compare a chrome bumper car and rubber bumper suspension car, side by side. You will see all the work the factory went to, to make the car handle like an overloaded 74 Chevy station wagon.

Converting front and rear suspension specs to chrome bumper from rubber bumper, is complex. If you look in the archives there is lots of stuff on this over the years.

Barry
Barry Parkinson

The measurement I gave was the distance from the centre of the wheel to the top of the wheel arch. The actual distance to the bottom on the trim strip is 17.5" or 444mm!!!!!
There is about 3" clear above the wheel.
The springs are almost flat, only dip obout 1" in the centre.
I suppose I could fit 20" wheels!!!
Regards
Dave
D M Tetlow

Dave
There are lots of questions and comments in the archives regarding aftermarket springs that are too high.
barry
Barry Parkinson

If it is any comfort Dave, my '77 RB measures 16" from wheel centre to the bottom of the strip. The springs look flat to me.

Martin
M Layton

I have looked at photo's of the car before the rebuid and the gap was similar.
I have noted that the car is definitely too high but I have a similar gap above the front wheel and the car looks level.
To drop the rear to esthetic levels would mean dropping the front too.
I will finish the build and re-assess.
Thanks for all your help Chaps.
Regards
Dave.
D M Tetlow

17.5"? Yikes! That is off the scale on my graph of 30-odd cars from around the world. Mind you, chrome bumpers weigh quite a bit less than the original rubber bumpers with the very heavy armature, Clausager reckons they were lightened subsequently. My 75 V8 is only about 15" and that is with the harder V8 springs, which still show some curvature.
Paul Hunt 2

This thread was discussed between 20/08/2006 and 26/08/2006

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