Superaquarama Posted March 1, 2013 Report Share Posted March 1, 2013 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 Quote Link to post Share on other sites
Motorsport Mickey Posted March 1, 2013 Report Share Posted March 1, 2013 Anti vibration damper, try scratching it it ain't rubber ! Helps iron out certain frequencies in the resonances. Mick Richards Quote Link to post Share on other sites
Paul Harvey Posted March 1, 2013 Report Share Posted March 1, 2013 it's the 'lump' - beware Quote Link to post Share on other sites
TR 2100 Posted March 2, 2013 Report Share Posted March 2, 2013 Most people bin them so they are becoming a collectors item! (it's an anti-vibration device) AlanR Quote Link to post Share on other sites
AlanT Posted March 2, 2013 Report Share Posted March 2, 2013 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. Quote Link to post Share on other sites
stuart Posted March 2, 2013 Report Share Posted March 2, 2013 It was fitted to eliminate a vibration at around 2400 RPM but it doesnt always work, dont bin it though just in case. Stuart. Quote Link to post Share on other sites
Superaquarama Posted March 2, 2013 Author Report Share Posted March 2, 2013 Ah, right - many thanks, everyone, rather obscure and not something I'd have guessed ! So may as well leave it where it is and let it continue fulfilling its purpose. Quote Link to post Share on other sites
AlanT Posted March 2, 2013 Report Share Posted March 2, 2013 Is this 2400 RPM in ANY gear or just in top-gear? Al. Quote Link to post Share on other sites
Superaquarama Posted March 2, 2013 Author Report Share Posted March 2, 2013 (edited) Presumably it's a prolonged period at 2400, so would most likely only apply to top gear. But that's only about 48 mph with a non o/d car, I thought the crankshaft breaking resonance was much higher than that - is this a different problem ? Edited March 2, 2013 by Superaquarama Quote Link to post Share on other sites
AlanT Posted March 2, 2013 Report Share Posted March 2, 2013 The "lump" is too isolated from the engine to damp any crank resonances. This must be to do with transmission resonance. Most likely propshaft whirling. Al. Quote Link to post Share on other sites
BrianC Posted March 3, 2013 Report Share Posted March 3, 2013 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, Quote Link to post Share on other sites
Superaquarama Posted March 3, 2013 Author Report Share Posted March 3, 2013 Balancing is a complete mystery to me, other than something like wheel balancing. I mean, how did you know where to put the circlip,or was it just trial & error ? Quote Link to post Share on other sites
BrianC Posted March 4, 2013 Report Share Posted March 4, 2013 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. Quote Link to post Share on other sites
Ade-TR4 Posted March 4, 2013 Report Share Posted March 4, 2013 (edited) 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 March 4, 2013 by Ade-TR4 Quote Link to post Share on other sites
RAHTR4 Posted March 4, 2013 Report Share Posted March 4, 2013 Anthony, What the Factory said about the balance weight : The installation : Regards, Richard Quote Link to post Share on other sites
Davepowderblue Posted March 5, 2013 Report Share Posted March 5, 2013 Putting gearbox back in friend said you do not need it . Works fine without one on my car . Did that , took car out terrible vibrations . Straight back doughnut back on car David Quote Link to post Share on other sites
mdave Posted March 13, 2013 Report Share Posted March 13, 2013 (edited) 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 March 13, 2013 by mdave Quote Link to post Share on other sites
Badfrog Posted March 13, 2013 Report Share Posted March 13, 2013 (edited) 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 March 13, 2013 by Badfrog Quote Link to post Share on other sites
RAHTR4 Posted March 13, 2013 Report Share Posted March 13, 2013 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 Quote Link to post Share on other sites
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