Diff set up

[Bobbieslandy]

Hi all,

The manual is relatively straightforward on how to get the pinion / crown wheel mesh correct, adding shims where necessary but something has left me slightly confused... When i pulled out the old diff, there were no shims yet there were huge gaps between the carrier bearings and sides of the diff casing. To all intents and purposes, lateral movement was stopped purely by the friction of the bearing caps. Surely that's not right? It showed no signs of wear and was quiet as you like.

Rob.

[FI Spyder]

Are you talking 4 speed diff or 5 speed diff?

[Stag76]

Setting up a CWP can be testing, using bearing blue to achieve the correct contact
pattern in the correct position of the tooth. It's more of an art than a science.
What you've got doesn't sound correct, but, as you say, is working OK.
Basic rule is:
Heel and Toe - Adjust the throw.
Hip and Flank - Adjust the crank.

There are plenty of articles on the net.

[Steve @ SandS]

It needs shims. They set the position of the diff assy which in turn sets the mesh between the crown wheel and pinion.

You cannot and should not do it without the shims.

[Bobbieslandy]

Steve, completely agree and would never of reassembled it without them. I'm just puzzled as to how there were none in there yet it performed faultlessly.

Stag76, i've got the blue at the ready. I've pressed all the bearings on and going to measure it all up at the weekend, ordering whatever shims i need.

FI Spyder, 5 speed axle with quaife diff and new 3.45 crown / pinion.

Thanks chaps

Rob.

[john 215]

Hi,

New one on me, never seen one with no shims whatsoever

How you planning on setting pinion preload ? You managed to get hold of the ' Holy Grail ' of a new collapsible spacer ? Or is it a reshape of the old one ?

Cheers John

[FI Spyder]

A friend had a Spitfire diff with no shims (they had worn to nothing) but it was pretty noisy which is why he had taken it apart.

[Bobbieslandy]

erm... I found a shim under the bench I was going through my photos and saw two shims on the bearings so set about dragging my bench out and crawling through god-knows-what to search for them. I found one, the other has disappeared. Sorry about that!

There is more bad news, i took the collapsable spacer, found some round bar the right size to avoid distorting it and proceeded to tap the ridge down. It's now a bigger I/D then when it left the factory and completely wrecked. Idiot. I have a spare axle and along with some spare shims, i should also have a spare collapsable spacer which will be returned to it's original length, not "hammered flat" like i read somewhere. Not a proud day.

[FI Spyder]

Have you read the set up instructions for setting up the differential in the OEM manual? If you can understand them on first reading, NASA wants you to help plan the trajectory on their first manned mission to Mars. Now if you do it all the time (or before even) I'm sure it's much simpler than first appears but it's one job I'd like to be peering over some ones shoulder before doing it myself.

[sheetsofsound]

I echo FI Spider's sentiments on that. Faced with a similar issue, I was dithering: Should I spend $200 and pick up a used rear axle, or try my hand at the task without an experienced guide? A mechanic friend said he would outsource it if I brought it to his shop rather than work on it himself. That was all I needed to hear. Spent the $200.

[john 215]

Hi,

IF you have access to a lathe and can turn a piece of metal then in theory you could use a solid spacer, make it slightly longer that the spacer that came out and start from there, its easier to take metal off than put back on.

Set them up myself years ago BUT that was with a box of Churchill special tools, which made life so much easier. We had a tool which fitted over the pinion splines, at a right angle to this was a long rod with a weight sliding along it, by moving the weight along the rod, preload was shown as when the pinion would just move, to little it wouldn't move and too much it swung down at speed, just a case of getting that sweet spot. Guess a very good spring balance and a fine touch the same could be achieved. You also have to flap around with a ' dummy pinion ' this is for a selective spacer that sits on top of the collapsible spacer that control pinion depth.

Two wishes are that I should have brought a box of those collapsible spacers and the other rescued the box of special tools ( which also had loads of ' spare ' shims in it ) from being thrown in the skip when they shut down


Cheers John

[Stag76]

Is there any collapsible spacer available that can be adapted?
There are plenty of other pinion bearings that are pre-set using a collapsible spacer - Ford is one.
If you can find one with the same internal diameter and equal or greater length it may be able to
be adapted. If the bearings are similar, the preload is probably also similar. The turning torque
would give you an indication.

Is the pinion turning torque setting available. If so, you could make up a solid spacer, as long as you can
measure the turning torque. Most pinion turning torque settings are between 15 and 30 inch pounds,
but you would need a good torque wrench to measure this...most start at about 40 in/lbs or higher.
You could make a tool like John described if you know the weight of the rod.
eg. A rod 15" long weighing 2lb pivoted horizontally at one end will exert 15 inch/lbs at the pivot point.

[Stag76]

I talked to a Diff rebuilder and he told me he re-uses the crushed spacer, and shims it using
.020" shims. He said the shims were originally developed for the local Holdens.
He's recently changed the CWP from 3.9 to 3.08 for a friend using this shim kit, and it is
smooth and quiet.

[Bobbieslandy]

I'm ashamed to admit i'm going to farm this one out. Firstly because i don't have the confidence to do it (seems a lot more complex than the machine gearboxes i've rebuilt in the past) and secondly, now the rear arms are polybushed and everything's that bit harder, more noise will be transmitted into the cabin. My brain won't know the difference between 'normal' and 'diff not set up correctly' so if i do it, i may end up chasing a problem that doesn't exist. If a 'man who knows' rebuilds it i can put up with any extra noise knowing that if it does become a problem, it won't be my problem. Thanks for the messages though, allfood for thought.

Rob.

[Hasbeen]

Don't be ashamed Rob. There is nothing shameful in using common sense.

I set up the diffs in Hewland transaxles a dozen or more times, back in the day. With all that experience you would expect to become good & fairly quick at it. No way, the last one took me 4 nights to get right.

Believe me I would have farmed them out to someone, if I had been able to find anyone I trusted who would do the damn things.

Hasbeen