Gear box mounting bushes

Technical MGB discussion
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David Witham
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Gear box mounting bushes

Post by David Witham » Tue Nov 17, 2020 11:27 am

I currently have the engine and gearbox out of the car to deal with the speedo worm drive gear replacement.

While I am at it I have stripped down the gearbox cross member to paint it. My car was made in Feb'74 and has to metalastic type mountings, which do most of the work, plus a pair of top hat brackets with rubber bushes that are connected by a long bolt. One top hat bracket being mounted on the cross member and the other on the gearbox.

I assume the purpose of these brackets, bushes and the bolt are to restrain the gearbox in the event of the metalastic mountings failing. They don't seem to have any other function that I can see.

Owing to oil contamination the bushes had deteriorated. When I replaced the other mountings 20 or more years ago I didn't change them. So I have bought new ones to fit. The bushes are waisted and need to be squeezed in their holes. However, the rubber seems rather hard for doing that. So I may have to trim one end of each bush to make it possible. Given the way they work trimming the sides that face each other should have little impact on their function.

Over the years I have had similar problems with oil cooler hose grommets and the rubber bad that is supposed to go between the heater and the bulkhead. Is there a general problem with some rubber parts being made from too hard a grade rubber?

These bushes came from Leacy but I think many of the parts vendors source a lot from the same suppliers so I doubt that shopping around will help.

Ian Fozzard
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Re: Gear box mounting bushes

Post by Ian Fozzard » Tue Nov 17, 2020 12:53 pm

Hi David. I think you are correct, for reasons unknown to me, many black rubber components available now are extremely hard and inflexible. This makes fitting a bit of a problem. I would mention engine mountings and the black rubber seal in the heater system you mention.
Could be a forced change in ingredients perhaps, or just cost related?

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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Peter Cresswell
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Re: Gear box mounting bushes

Post by Peter Cresswell » Tue Nov 17, 2020 2:02 pm

I had exactly the same problem and resorted to the same butchery to fit these rubber bushes through the holes in the upper and lower brackets! I am not convinced this pin and bush arrangement does anything really useful. The fore and aft movement is also restricted by the restraint plate fitted to the left hand engine mount, and so long as this is in place and the engine mounts are in good condition, the engine moving will not move forward enough to put the fan through the radiator. Additionally the MGC which uses a similar gearbox to the MGB but with a different gearbox crossmember, doesn't have anything on the crossmember to restrict movement like the MGB does. As the MGC engine is much heavier than the MGB engine I would have expected it to have greater restraint not less.
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965

David Witham
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Re: Gear box mounting bushes

Post by David Witham » Mon Nov 23, 2020 10:04 pm

I had forgotten about the plate on the left engine mount. When I used to compete in sprint and hill climb I removed that lump of metal to save weight!

It must be under the bench somewhere and it would fit in my powder coating oven.

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Peter Cresswell
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Re: Gear box mounting bushes

Post by Peter Cresswell » Mon Nov 23, 2020 10:11 pm

Hi David,
If you were sprints and hillclimbs you needed that plate to be in place even more!!!
Pete
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965

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