Differential parts

If you have a stock of knackered diffs, is it worth stripping one or two for their shims?

A very long shot, but if they're a similar size to Triumph ones, this place in the US still claims to stock parts:

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Asolepius" saying something like:

I suspect the rebuilders have been in contact with the makers of the original parts (or the owners of suitable tooling) and arranged their own supply on a batch basis. Talking to them nicely might free one up, but it might not.

Thanks - also I heard about another possible US source. Odd that - why do we have to go there for British parts? Actually, the shims are not the problem, as I can work around that. The crush spacer is though, because it can only be used once.

"Asolepius" realised it was Mon, 08 Aug

Possibly

Not that odd if you consider that over half of the production of some popular British sports cars were sold in the US.

Actually this could be less of a problem than you think. The collapsible spacer only "collapses" a few thou so you either lengthen the old one by roughly that amount or add a spacer and crush it a few thou more. To lengthen it, slide it over a piece of solid bar and tap the ridge with a hammer all around the circumference as evenly as possible. Obviously measuring before, then after a bit of tapping until you gain something. Then it's trial and measure fitting. I don't profess to be an expert but I did have a go at it on my TR7 V8 conversion here:

After posting this question your answer occurred to me, but it seemed too obvious to be feasible! Thanks, I'll give it a try.

This is a terrible idea. It will give entirely the wrong pre-load value.

How? The preload is measured with the pinion assembled in the casing. You tighten up the nut until you get the correct preload. That is the method used by people who do it for a living and charge you for the privilege. I had two people who used to assemble axles for a living advising me when I did mine.

You didn't quote this bit:

How many summers do you think I've got before it goes bang?

"Pete W" realised it was Tue, 9 Aug 2005 21:31:54 +0100 and decided it was time to write:

This 'summer' doesn't count - the weather's been terrible!

Yes, and the 25 year old glass sun roof leaks but I suffer a wet arse for the cause!

Provided you arrive at the correct preload, surely it doesn't matter how you do it - either using a new collapsing whatsit or a solid spacer with shims. The collapsing whatsit is just a handy way of not holding up the production line when the things are being built.

Ron Robinson

For vehicles of this age, I've seen two main ways of getting the pre-load right. One is to put a spring balance and a string (or a light torque gauge) onto the pinion or diff and measure the torque to rotate it. Adjust a screwed ring until the torque is right. This is usually used for dif carriers, or older pinion shafts.

The other way is the collapsible spacer, used on more recent pinion shafts. An easy process, but it relies on the spacer having a known crush behaviour and a known relationship between applied stress and resultant strain. Once you've crushed it once, this won't be the same next time.

It's years since I assembled an axle for money. But if you have a Rover, the machine that assembled the diffs for that and measured the pre-loads and the bearing asssembly loads was running my software.

I used a spring bar type torque wrench on the pinion nut to measure the preload. Point taken about the stress; it won't be the same but it will be f*cking close. So close as to make no difference and besides, as you can't get the spacer new, the alternative is to rebuild the back end to accept a completely different axle. Most of us in the real World accept it.

There are 2 sequential processes here (according to the BL manual):

1. Assemble the pinion in the carrier without the crush spacer, set the preload and measure the pinion height (I am doing this using marking blue). Repeat using different shims until correct.
2. Take it all apart, put back together with the crush spacer and tighten the nut to 140 lb/in.

I agree that hammering the spacer to lengthen it will work harden it and change its properties. But in the absence of a new one I have no option. Again, the rebuild guys can get them, why can't I?

Mind you, all this would be even more interesting if I could get the bearing off the pinion - I have broken my puller and no sign of it moving.

Used also to set the layshaft bearings pre-load on Rover P6 3500 manual boxes. So if you got a figure off a good diff, shouldn't be too hard to copy. Things like collapsable washers are for quick and cheap factory assembly, but not the only way to do it.

Assuming you're fitting new bearings, grind a slot and split with a cold chisel.

Are you sure they can get them? The suppliers I tried all carefully word their info, "..these are no longer available, we can get the work done for you."

If you are replacing the bearings, for heaven's sake measure how far into mesh the pinion is before you destroy anything, otherwise you will have nowhere to start from when it comes to getting the cw & p to mesh properly. BTDT - GTTS (covered in marking blue)

Ron Robinson

"R.N. Robinson" wrote in message news:ddqdm4$o7m$ snipped-for-privacy@news8.svr.pol.co.uk...

Actually the pinion bearings are OK and I was planning to keep them. In any case if I'm using the marking blue method I will have to get them on and off a couple of times before I've got it right. But it looks like I'll need a