My '71 has exhibited a clunk when changing gear ever since I bought it three years ago. There are obviously several possible sources of play in the drive train but one likely one is the differential front mount snubber. This comprises two rubber bushings that limit and damp the up and down motion of the front of the diff under driving loads.The snubber assembly is circled in this pic...
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The active components are rubber and I doubt they've been changed in the cars 50 year life, so even if they're not the source of my problem they're almost certainly worth changing. A problem in this area is readily detectable on automatics but less so on manuals (like mine) where it is easier for the driver to minimise a clunk by careful feathering of the gearchange. I arm myself with an overhaul kit ( in rubber rather than polyurethane; this is one pair of bushes that are better having the greater compliance of rubber ).....
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....hoist the car in the air on my trusty QuickJack....
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......and squirm underneath. The diff area is a bit damp (that's a problem for another day) but I locate the snubber nut - arrowed red ....
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.....and attempt removal. I need to get a 5/8" spanner on the bolt head to react the nut torque but the very limited access beats any of my spanners so I give a good haul on the nut anyway to see if anything comes loose. Nothing does so I revert to my impact wrench and eventually both nut and bolt break free and rotate. I cut the nut off with a grinder and extract the bolt upwards, rotating the propshaft by hand to optimise clearance. With the bolt out I need to prise the the diff mount bracket down to extract the lower bush. Unfortunately The ideal place to react a lever is right on top of a brake line - arrowed yellow, so I remove the securing clip - arrowed green, gently ease the brake line clear and with leverage applied with a robust tyre iron, winkle out the bush. The upper bush parts I extract through the small clearance between the bracket and the prop shaft.
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Upper row is the old parts, lower the new ones
The lower bush is in reasonable condition but the upper - arrowed red, is toast - in two parts - so providing no restraint on upward movement of the diff nose. This seems to bear out the possibility of this being the source of the clunk. In forward gear the drive torque reaction applies a downward thrust to the front of the diff. During a gear change the torque is momentarily released and the diff nose will lift. The degraded upper bush provides no resistance - hence a clunk.
So, levering down the bracket again I squeeze the new lower rubber in place. Fitting the new upper is more of a problem. Try as I might I cannot find a way to squeeze the rubber fitted to it's metal 'top hat' bush through the gap between the frame bracket and the prop shaft. The bush and the 'top hat' will go through separately but his gives me the problem of how to reassemble them in a blind space with very limited finger access, not helped by the rubber being a tight fit on the 'top hat'.
There is actually a large clearance between the mounting bolt and the top hat and rubbers, so I drill a small hole in the end of the bolt and after fitting the top washer, attach a length of cable. I lube the bore of the top rubber and the shank of the top hat with silicone grease and slide them over the cable (still assembled together in this shot)......
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With the free end of the cable fed down and through the lower bush and bracket, I pull the parts into position and as the end of the bolt appears through the bracket, a tug on the cable slides the top hat into the bush....
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The cable removed, I can get my finger on the head of the bolt enough to prevent rotation while I fit the large clamp washer (I re-used the original - arrowed yellow in the row of parts - as it's far more robust than the replacement), spring washer and nut. With the nut screwed up above the hole in the bolt I can stick an appropriate rod ( in this case an Allen key).....
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...... to hold the bolt while I tighten the nut. Just need to ease the brake line back into position and replace the clamp -
et voila - job done!
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Down off the QuickJack and off for a test drive. Immediate improvement! Gear changes - even relatively clumsy ones - are now clunk free and even a judder when letting out the clutch from stationary ( that I'd mentally attributed to a misaligned clutch) is reduced.
The whole process was a bit of a pain - more than it should have been according to the clever-cuts on the internet - but it's turned out to be one of the more rewarding jobs I've done so far.
