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MG Midget and Sprite Technical - Differentials

I have a diff I want to build back up how do you set the end float / dash back lash ?. Richard
rj woolley

Norms the man for this he wrote a good guide and even pictures of tools you can make to help...
Andy Phillips (frankenfrog)

Be wary of one issue Richard. There has been a lot of discussion about "preloading" the pinion bearings. Figures of a min 6lb inches are suggested. From my limited experience of "used" diffs, in both cases there was no preload so I set about creating one. I was subsequently advised by a man who professionally rebuilds diffs and gearboxes that this was not a good idea. His view was that the original pre-load would have eased off throught general bearing wear. Re-loading it was going to force the partially worm rollers against partially worn tracks and would cause rapid bearing wear and subsequent failure.
G Williams (Graeme)

would one put a diff back together or rebuild it without using new bearings?
David Smith

You'd be surprised what people will do when performing mechanical work. Of course, you're aware of just how stupid an average person can be? Well, stop and consider, that being just an average, half of all people are even stupider that that!
Stephen Strange


I don't agree with that advice from the diff guy as if the bearing races were worn enough for that to be an issue then they should be binned anyway. I have seen advice from Ford to tighten the pinion bearing to re-establish the preload if it has been lost and resulting in a noisy diff.
David Billington

David S: that assumes it's been apart. This was intended to be a straight drop in replacement without going to the trouble and expense of a rebuild.

David B: That was my understanding but the chap in question has an excellent reputation and I bow to his experience on this one. THe bearings "unloaded" felt ok.
G Williams (Graeme)

Graeme, Richard's diff IS apart, he talks about building it back up.
David Smith


I don't know who the expert you refer to is but over the years have seen the work of a few experts and either by word or deed they have proven themselves to be anything but experts. Of course I don't mean to imply yours isn't he may well be and so his recommendation may stand up.

The last one was a Morgan "expert" that supplied the crown wheel and pinion for my neighbours rear axle rebuild. I was helping with moral support and technical understanding and slip gauges for reference dimensions. My neighbour did struggle for a while trying to understand how you could do the pinion nut to 140ft lbs and measure the small torque to rotate the assembly at the desired preload but I got it across to him in the end and all was good. He is technical but around 72 but sometimes ones mind takes a stance on things and needs a different viewpoint to bring it round to the correct one. When we started to set the pinion up we assumed the reference surface of the pinion was the precision ground one rather than the rough turned surface but on checking with the supplier we were wrong. The supplying expert gave himself away as not being an expert as he said that he didn't bother with the numbers etched on the pinion and crown wheel by their maker, who would have marked them for best running, as they only pertained to a theoretically perfectly machined axle housing which didn't exist and so he just went by the patterns left by the marking blue. He obviously, to me anyway, from his statement didn't understand what the purpose of the shims and set-up gauges were for when building a final drive unit. My neighbour and I finished the final drive rebuild and all is well.
David Billington

This thread was discussed between 16/05/2013 and 17/05/2013

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.