Diff rebuild - locked up when tight

[AndyPen]

Just reassembling my diff and I've come across a problem I've never had before - if I tighten it down hand tight it all locks up? Loosen it slightly and all is well in terms of movement of the gears.

I am refitting the original type yoke output shafts having taken out the pot joint type that had been fitted. Everything else is the same components apart from the copper shims for the planet gears and 6 new bolts and locking tabs. I have refitted the copper washers behind the output gears where they meet the body of the diff, and am now wondering if they are thicker than the fibre ones for example?

Anyone had this problem before? Am I on the right lines regards the shims?

diff on worktop.jpg

diff open.jpg

[Peter Laidler]

As sooon as I started to read the thread I thought shims. Good move but....... Yep, I'd say shims

[Spider]

You'll find one set of the thrusts are thicker than original.

A simple fix here is to grinding a wee bit off the 'pip' that's in the centre of the inner ends of the output shafts. It does not matter one bit how much end float you might end up with here as these shaft are thrust hard out as soon as the diff cage spins. For many years, in the Metro Boxes, they never fitted the hex centre block, so they had nothing to thrust against in an inward direction.

[Jason]

That will be the output shafts pressing tightly on the thrust block due to mica washers on the back face of the output shafts being too thick. Be careful if re using old mica’s especially the bronze ones as they can leave a raised section which is thicker than the rest of the face.
I have a tub full of the old bronze type mica’s and you will be surprised how much they vary in thickness. I would build it up with 2 standard thickness fibre mica’s(.35 thou)and see how you go from there. If the outputs are sloppy then fit the oversize mica’s(.43 thou) or a mixture of both .
Rgds Jason

[bpirie1000]

Take it all appart and clean it up check tollerances i would say....

[AndyPen]

Thanks everyone, I was wanted to use the old shims for longevity as they seemed ready to again. I'll pull it apart and try again with the fibre type... as well as getting the micrometer out first of course.

Didn't know that about the Metro Spider, learning something new every day

[Jason]

The pot joint output shafts used where the thrust block was deleted in some of the metro’s do not have the raised pip in the centre of the gear face. The diff’s always look odd when stripping them down with no thrust block fitted.

[AndyPen]

Well I solved it in the end - after a bit of head scratching. The older copper colour washers were slightly thinner than the new fibre type ones from mini spares. They were also in superb nick, so that didn't look like the problem.

I then thought about spider's idea of grinding the pip back a little, then saw what was staring me in the face. I had offset the thrust block so that the original face was no longer the one that was sat against the output shafts - see pic for details.

Stripped it, turned it and refitted it. Now fully torqued up and still spinning nicely.

Thanks again for all the ideas, now I will move on to the bearings... in another thread

Thrust block offset.jpg