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Just fitting the engine & gearbox to our TR4A chassis.

 

Right at the aft end of the o/d box where the propshaft attaches is a collar round the neck of the mainshaft housing which holds a large downwards facing 3" to 4" rubber doughnut. I assumed was the rear gearbox mounting until I realised this is further forward on the box and a different thing entirely.

 

So what is this doughnut that now hangs in space and doesn't seem to be in any parts diagrams ?

 

Thanks,

 

Anthony

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Anti vibration damper, try scratching it it ain't rubber ! Helps iron out certain frequencies in the resonances.

 

Mick Richards

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DONT BIN THIS!

 

This kind of thing is fitted at a vibration node.

 

Its a production bodge when you find that you are getting field-failures.

Usually is cracks in castings due to vibration.

 

In this case I would guess the problem was the gbox tail housing cracking. But hopefully some body will tell us exactly.

 

Of course you could bin it and, especially if you didn't go far, proabably get away with it, for a while.

 

Al.

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It was fitted to eliminate a vibration at around 2400 RPM but it doesnt always work, dont bin it though just in case.

Stuart.

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This must be to do with transmission resonance. Most likely propshaft whirling.

Oh, that stirs up some ancient memories. As a student I had a summer placement working at the National Physical Laboratory, Feltham. I was put in the Ship Division, developing software to calculate whirling speeds, frequencies, amplitudes, etc., of ships' propshafts. It's quite frightening to see what happens when one of these gets up to speed, even assuming it is fully balanced. I'm glad the TR propshaft is a bit shorter. However, the knowledge was useful when a few years later I had a Spitfire and was able to eliminate the transmission vibration by balancing the propshaft with a strategically placed jubilee clip, :D

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Trial and error - easy enough to get an improvement, but probably not optimal! I suspect my propshaft wasn't too badly out of balance, so one jubliee clip was sufficient. If it was seriously out of balance, then two clips might have been needed at opposite ends, but if it was that bad it would be better to have it off and reconditioned/balanced properly.

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Try it with and then without.

It made a difference (positive) on mine when fitted, but others have reported no change.

If it's working, don't fix it :)

There's a tech service bulletin about it that someone may have a PDF version of. There's some Meccano-style bracketry arrangement to tie it in to the gear-shift housing steady-bar, which is pictured in the TSB.

Cheers

Ade

Edited by Ade-TR4
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I have been looking to get data on one of these, ie how much does it weigh, and how stiff is the rubber? I want to fit one to my TR4, as I have a bad vibration, RPM related, at about 2700 - 3000rpm, highway cruising speed range...

I have a copy of the service bulletin reproduced above, which is how I knew of the fix.

Can anyone help with the data? Or better yet, if someone has one they don't want, I am happy to buy it and pay shipping to Australia....

cheers

Dave

Edited by mdave
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From experience AND reading memory, it's the 2700 rpm resonance that is targeted. Quite a nuisance in some cars.The lump works. The other option is shaft balancing and gearbox rebuilding with balanced shafts again. A bit expensive for the result tho. I would only consider keeping the lump and balancing the propshaft, which I had done years ago.

 

The other killer is the 5200 rpm harmonic ( some at 5800 too) but that's crank and damper business.

 

Badfrog

Edited by Badfrog
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I have been looking to get data on one of these, ie how much does it weigh, and how stiff is the rubber? I want to fit one to my TR4, as I have a bad vibration, RPM related, at about 2700 - 3000rpm, highway cruising speed range...

I have a copy of the service bulletin reproduced above, which is how I knew of the fix.

Can anyone help with the data? Or better yet, if someone has one they don't want, I am happy to buy it and pay shipping to Australia....

cheers

Dave

 

Dave,

 

The lump - steel casting - weighs 1.37kg.

 

The suspension part is a Silentbloc bush.

 

Mine needed a new one and the nearest match I could find came off a Rootes car, it just needed the outer diameter reducing slightly to get it to fit.

 

Regards, Richard

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