Fine bronze dust in diff oil

[Graham O]

Hi Tony
Sorry if my story seemed a bit cryptic.
The picture shows the old pinion assembly that I discarded.  As you can see, the bearings had completely collapsed and the pinion and crown wheel were in a very bad state.

The torque tube assembly and crown wheel I used seemed in good shape.  However, I was unable to dismantle the torque tube to inspect the bearings and so decided to try it as is. I hope to replace all bearings in the diff and torque tube and set things up again, hopefully with expert advice.
Graham

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Tony
Just to answer your question more clearly, the replacement "new" pinion was in the torque tube.  This assembly I could not disassemble to inspect the bearings and so used as is. Both the pinion and crown wheel had matching numbers and showed little wear.
Cheers
Graham

[Ruairidh Dunford]

I must confess to being confused as to what was going on, my picture comment illustrates this perfectly, my apologies.

[Dave Mann]

In graham's photo it appears that the spacer 1A 7243 appears to have been acting as the outer track for the roller bearing. I trust that the outer track was still in the diff case.

[Graham O]

Thanks Colin for your comments.  
Yes it is clear that I have no mechanical training as I am an electronics engineer. Maybe that explains why my trafficators flash with super bright LEDs, and when I go into reverse a monitor in the cubby hole shows the view from a reversing camera. If you look carefully there are side cameras just below the trafficators as well.  

It has been suggested that I should explain that this is a DIY rebuild, and only the sleeving of the motor and some chrome plating has been done by professionals. The motor has been made up from the best parts from two motors and from swap meets. Other smaller parts have been Nickel plated at home using chemicals made from Nickel and the appropriate acids.  I did the body work over many years and really enjoy gas welding.  Luckily the neighbours did not complain about the smell when I painted the car.
I bought an industrial sewing machine, learnt to sew and the interior is almost finished.  Just not looking forward to doing the head lining though.

I have almost convinced myself that it will be fun doing the rear axle project, and if you know of any experts who can advise, please PM me.

Regards
Graham Ockleston

[Parazine]

The pinion assembly is the usual culprit in A7 diff demise in my experience, very often the lock nut on the thrust bearing is not tight enough, the bearing spacer then wears creating end float.

I agree with Ian that pinion end float is a primary trouble source in 7 axles but the question is: did the nut become loose or did the spacer wear first?

I think that previous drivers lack of skill with the clutch starts the rot, moving the train of bearings and spacers on the pinion. Once they start to move, the soft spacer wears rapidly and terminal end float sets in. This is apparent from the original axles I have stripped, where the nut is still tabbed up from the factory but not actually doing anything.

The same issue appears to afflict Big 7 axles, due to the fact that there is no engine rear oil seal and the crankcase can vent oily fumes into the bell housing. These condense on the clutch plate, causing horrendous juddering when combined with metalastik engine mountings. The back axle is the casualty.....

[Ian Williams]

I think it is a design flaw, the spacer is a machined from mild steel and sandwiched between the hardened ground thrust bearings and retaining nut, it has to deal with some very high forces and shock loads. My personal view is that the minute machining ridges left from the manufacture of the spacer quickly compress, couple that with any give in the retaining nut thread and you introduce a tiny amount of clearance. Once this situation exists,, as Parazine says, the spacer wears, and this wear accelerates the more the clearance increases. I have tried making hardened spacers to see if that helps, the trouble is I have not had any axle come back to me after a high mileage so I can have a look.

[Howard Wright]

Hi Graham

Looking at your pictures of the excellence restoration of your car I think you should be well capable of doing the axle.  

I was a structural engineer pre retirement and have no mechanical engineering or workshop training. I’ve rebuilt several axles and learnt a lot on the way but I’m convinced that luck plays a part in getting one to be quiet!  Be patient (a quality I’m not great with!) and if in doubt consult.

Woodrow, the Companion and this forum are all great sources.

Regarding the comments on the spacer from Ian and Parazine.  I very much agree.  The last axle I built was a bitsa and I had to make up the spacer.  My first attempt lasted less than 100 miles before I noticed backlash. The second using a harder steel seems to be OK at 3000 miles but I regularly check the pinion flange for any movement.

Good luck

Howard

[Dave Wortley]

I vaguely remember using the inner race of a bearing for the spacer. Sorry, cannot be more accurate.