Differential overhaul

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ndevans
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Re: Differential overhaul

Post by ndevans »

Wow. That's no small difference.
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
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Declan_Burns
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Re: Differential overhaul

Post by Declan_Burns »

If that solid spacer is the correct part then there must be an additional spacer in there. Something wrong somewhere!
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ndevans
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Re: Differential overhaul

Post by ndevans »

There is. Think this photo may explain.
IMG_20191031_090317~2.jpg
IMG_20191031_090317~2.jpg (563.42 KiB) Viewed 1915 times
This is the pinion from my 3.9:1 diff. Between the crush spacer and the pinion inner bearing is another spacer. The crush spacer has been crushed to approx.19mm, and the two combined measure just under 41mm.
The solid spacer is marked 10/39 and BTA1225.

Cheers N
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
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Re: Differential overhaul

Post by Banned User »

An additional spacer if you use a crush spacer? Surely someone must have had one apart, I can’t be alone in this? The distance between the bearing ‘seats’ is obviously fixed.

Edit. Mr Evans may have solved it.
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ndevans
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Re: Differential overhaul

Post by ndevans »

PoolGuy wrote: Thu Oct 31, 2019 9:47 am Edit. Mr Evans may have solved it.
That'll be a first!

I haven't actually had them apart yet, but it looks like there may be a shim under the solid spacer. Will report later today.

cheers N
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
oliver90owner
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Re: Differential overhaul

Post by oliver90owner »

Post deleted. Something went wrong!
Last edited by oliver90owner on Thu Oct 31, 2019 2:07 pm, edited 1 time in total.
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Re: Differential overhaul

Post by oliver90owner »

oliver90owner wrote: Thu Oct 31, 2019 12:03 pm
ndevans wrote: Thu Oct 31, 2019 10:09 am
PoolGuy wrote: Thu Oct 31, 2019 9:47 am Edit. Mr Evans may have solved it.
That'll be a first!

I haven't actually had them apart yet, but it looks like there may be a shim under the solid spacer. Will report later today.

cheers N
Think about it. If the builder went slightly over the required crush, would he use a new crush washer/spacer if the current one could still be used? Shims are cheaper than crush washers.
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ndevans
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Re: Differential overhaul

Post by ndevans »

The BMC manual does talk about using a washer of "known thickness" when reassembling. You then use the dial indicator reading & the markings on the pinion head to increase or decrease the washer thickness, in order to set the pinion height correctly.
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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
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ndevans
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Re: Differential overhaul

Post by ndevans »

Interestingly, the diagram in the the BMC manual, section HH, page 2, suggests that there is no shim between the solid spacer and the inner bearing, only a thrust washer between the inner bearing and the pinion head. Which is right?

Cheers N
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
Declan_Burns
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Re: Differential overhaul

Post by Declan_Burns »

Neil,
Look at item 29 on that page. It does show a shim.
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Re: Differential overhaul

Post by Banned User »

This is how mine was, between the pinion head and the bearing, it’s 3.12mm thick and the inside edge against the pinion head has a chamfer on it.
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Declan_Burns
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Re: Differential overhaul

Post by Declan_Burns »

The pinion head thrust washer (item 25) is between the pinion head and the inner bearing. Item 29 is the shim between the spacer and the outer bearing. The manual shows both.
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philthehill
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Re: Differential overhaul

Post by philthehill »

Item No: 25 Washer Pinion Thrust is supplied in different thickness and dependent upon the thickness is given a specific BMC Pt No: ATA7048 to ATA7055. The shim item No: 25 determines the fore and aft meshing of the pinion to crown wheel,

Item No: 29 Shim Outer Bearing is also supplied in different thicknesses and dependent upon the thickness is given a specific BMC Pt No: 1G7261 to ATB7107. The thickness of these shims determines the amount of preload on the pinion bearings when a solid spacer (Pt No: ATA7046) is used between the inner and outer pinion bearings.

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ndevans
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Re: Differential overhaul

Post by ndevans »

Right, I see now. Confusingly, my hardcopy of the manual shows the shim between spacer and outer bearing as item 27, but my electronic copy shows it as item 29!

Back to the spacers. I am a little unsure now. What I thought was a 21mm spacer and a shim between the crush washer and the pinion head, now on closer examination, appears to be just a change in shaft diameter. It is not shiny like the area under the spacer, and there is no discernible gap between the minor diameter of the shaft and the stepped area.
This implies to me that there are two types of pinion-one which has a step in diameter, like mine, and is intended for a crush spacer and shim, and one which is intended to take a solid spacer of approx. 40mm, plus a shim.
IMG_20191031_223500~2.jpg
IMG_20191031_223500~2.jpg (492.45 KiB) Viewed 1837 times

Either way, I don't appear to have a separate shim between my crush spacer and the outer bearing. Should there be a shim between the outer bearing and a crush spacer, or is the shim for solid spacers only?

(This is the 3.9 diff, not the 4.22, which I have tried to set the pre- load on. The 4.22 pinion is still intact in the carrier).

Edit:-new and old crush spacers side by side. The new one is 21.7mm, the old 18.9mm.
IMG_20191031_223431~2.jpg
IMG_20191031_223431~2.jpg (490.16 KiB) Viewed 1837 times
Cheers N
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
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Re: Differential overhaul

Post by Banned User »

Just checked my box of bits and sure enough there’s a 5thou shim.
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ndevans
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Re: Differential overhaul

Post by ndevans »

Where was it fitted? Did you have a solid spacer?
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
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Re: Differential overhaul

Post by Banned User »

Between the thrust washer and bearing, it’s the one that Declan mentioned that sets the pinion height. Yes, solid spacer.
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ndevans
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Re: Differential overhaul

Post by ndevans »

Ok thanks. So, the question is, am I missing a shim, or do crush spacers not need shims?
cheers N

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33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
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Re: Differential overhaul

Post by Banned User »

My assumption would be that the nature of the crush washer means that it doesn’t need a shim. But one of the learned members will give you a definitive answer.
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ndevans
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Re: Differential overhaul

Post by ndevans »

It's annoying that the BMC manual only covers the solid spacer type. Well mine does, anyway.
cheers N

Image
33063, Eridge, Sept 2021 by Neil Evans, on Flickr
'69 Traveller, 1275, discs.
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