Differential pinion bearing preload

[stevelemoir]

Diff is a 4.55:1 ratio 9X41 teeth from a 1961 950cc

I have remove the diff from the car and noticed that it has hardly any pinion bearing preload. It spins quite freely.
Do I assume this is bad and replace the pinion bearings?
Is it ok to use the collapsible bearing spacer even if the diff originally has a non-collapsible bearing spacer?
I haven't stripped the diff yet so don't know what type of spacer is fitted.

The crown wheel play is 0.34mm or 1/64 inches. Is this OK?

What are the numbers on the diff casing in the photo?
They look like 676 and 009.

Any help appreciated

[bmcecosse]

Why are you worrying about it ? Was it leaking oil - or whining horribly ? Is the nut loose? If so - I would tighten it - but otherwise, leave well alone. Hardly worth new bearings.. You would do better to look for a 4.22 final drive as an upgrade for the car.

[philthehill]

Unless you are confident in overhauling the diff and are able to determine the correct pre-load and crown wheel/pinion meshing I would leave well alone.
There are plenty of serviceable 4.55 - 1 diffs out there and at reasonable prices.
On this site alone there are at least two for sale i.e. Kinsley96 is selling a 4.55 - 1 diff for £50 and busguy is selling a 4.22 diff for £30
If you do not mind the lower ratio I would do as bmc says and fit a 4.22 - 1 diff assy.
Happy motoring

[Declan_Burns]

BMC is quite right.
While on the subject-the MGOC is offering brand new CWP`s at reasonable prices:
The 3.9 for £199.75 including VAT !
The 3.7 is £249.95 including VAT !
http://www.mgocspares.co.uk/acatalog/MG ... __159.html
Regards
Declan

[bmcecosse]

Your idea of a 'reasonable price' and mine - are obviously on different planets Declan! I'm glad I bought my 3.7 when I did!!

[Declan_Burns]

Roy,
You think that's bad-Moss charges £349.96 for the 3.9 and £319.96 for the 3.7!!
Regards
Declan

[bmcecosse]

Oh I know - I know.....

[stevelemoir]

Why are you worrying about it ? Was it leaking oil - or whining horribly ? Is the nut loose? If so - I would tighten it - but otherwise, leave well alone. Hardly worth new bearings.. You would do better to look for a 4.22 final drive as an upgrade for the car.

The reason for taking the diff off was that it was getting noisy. The cause was that one of the differential pinion gears has started to break up with a missing tooth and other teeth looking damaged.

I am curious about the pinion bearing preload. Does anyone know the engineering science behind the need for this preload?
Could it be that my differential gears have worn badly because of the lack of pinion bearing preload on my diff?
Can I use the collapsible pinion bearing spacer in my diff if tightening the nut does not give the required preload?

I may look into the upgrade to a 4.22 but I may get a second hand 4.55 to replace the diff bearings.....

[bmcecosse]

The pre-load is just to make sure the pinion is held very securely in place, to mesh correctly with the crown gear. The differential gears only do anything when one wheel is moving at a different speed to the other - so bowling along a straight road - they do nothing. Any damage etc to them is purely down to wear and tear - possibly run short of oil - possibly a 'foreign particle' has gone through the works.

[Declan_Burns]

You can of course use the crush spacer instead of the solid spacer and shim but why? I find the solid spacer and shim are actually better as you can take the differential apart as many times as you want which is often the case when you exchange a CWP for a CWP with different markings to the original. The crush spacer is not supposed to be re-used and costs about £5 a go.
Regards
Declan

[philthehill]

You cannot just take a diff bearing from another diff and fit to another diff even if that bearing is serviceable. You will still need to set the meshing between the pinion and crown wheel. If you do not get it right the diff will moan like h-ll and lead to accelerated wear.
Pre-load is required to keep it altogether as the transmitted loading through the diff tends to push the bearings and gears apart so having the pre-loading keeps the diff altogether and within tolerances when the load is applied.
The non crushable spacer Pt No: BTA532X is currently not available from MOSS and can only find reference to the crushable spacer on the other Minor parts suppliers.
As suggested above the easiest way to get over your problem is to fit a good s/h dii assy.

[Declan_Burns]

Here's a link to one of best descriptions that I know of on how to set up a differential. To me it's a bible and I always refer back to it.
http://www.pirate4x4.com/tech/billavista/Gear_Setup/
This is also very good.
http://www.mgexp.com/article/mg-midget- ... build.html
I would advise anybody who even contimplates touching a differential to read these articles thoroughly. The tip on making a set of set-up bearings is to be noted-it makes life so much easier especially for the carrier bearings.
Regards
Declan

[philthehill]

Declan
Many thanks for the links.
One of the many tasks learnt when undertaking my apprenticeship in the BMC garage was to overhaul differentials and set the meshing using engineers blue. The links brought it all back - though these days it is very rare for the owner/mechanic to overhaul diffs it is usually left to a specialist.

[katy]

I'm not familiar w/the crushable spacer used on the Morris, but in the past we've re-used other make's crushable spacers by stretching them a bit by putting them on a round shaft slightly smaller than their ID, then "massaging" them around and around the middle with a hammer. Was shown this by an "old-timer" many moons ago and have used this method w/success a few times.

[katy]

Forgot to mention to measure the length, before and after.

[smithskids]

Setting up differential pinion on utube by weber auto is quite good but is in "american english"

[MikeNash]

For a full exposition of "doing a diff" see the "The Morris Minor Workshop Manual" at chapter HH; it's all there.
Regards, MikeN.