Differential Failure

[rgh0]

I am building a 3.55 differential from scratch. I'm starting with an alloy housing and 3.55 ring and pinion from Burtons. Their housing is marked with the required pinion shim. In this case .1405". There was no correction marked on the pinion, so I installed the shim and bearing and installed it in the housing. I measured pinion depth and came up with 3.243" which is .047" short of the standard (3.290"). I have a good used 3.77 setup to compare with and I got very similar measurements. The head pinion bearing was only resting in its race, I have not installed the tail bearing or set the preload.

My question is: Will installing both bearings and setting the preload move the pinion away from the crown wheel getting me closer to the desired measurement? Since the bearings were supplied with the races already installed, I assume the supplier was able to check the required pinion height and that the shim dimension is correct.

Thanks
Chris

Preloading the pinion bearings will certainly move the pinion gear face a little further away from the ring gear centre line. How much I don't know but its hard to seat a taper roller correctly without preload and rotation so how good your current measurement is hard to tell. In the end its about the correct contact pattern being achieved with the right bearing preload.

cheers
Rohan

[2cams70]

One other point is that you do need a special tool or make one up in order to be able to tighten the carrier bearing end caps. It does take a fair amount of torque on the caps to set the cap spread correctly.

I was fortunate enough to purchase one from MKF engineering in the UK before Mark Kinman met his sad demise. His death was a great loss. He was a very talented machinist.

Good to have a go. Rear axle rebuilds aren't as mysterious as people make them out to be!

[pharriso]

I was fortunate enough to purchase one from MKF engineering in the UK before Mark Kinman met his sad demise. His death was a great loss. He was a very talented machinist.

A bit too talented from what I have just read...

[seniorchristo]

I installed the pinion bearings and set the preload. I am still .040" short of the 3.290 dimension even after double checking my measurements. I will have to continue the assembly and then check the pattern.

That's a good point 2cams about aluminum having different properties. I'm sure thermal expansion will change some clearances etc.

[seniorchristo]

I discovered my error in calculating the pinion depth. I failed to factor in the step on the pinion where the shim sits.
After recalculating I came up with the correct 3.290 measurement! Amazing!
Next, I set the cap spread (.007) and CWP backlash (.005) then checked the pattern. It was centered on the teeth both drive and coast but I didn't expect it to wipe almost the whole tooth clean. Maybe that's not unusual for a new ring and pinion?

[Hawksfield]

Seniorchristo
You need to thin out the engineers blue to stop it wiping out completely.
I had same problem with yellow ochre
Try again good luck
All the best for the new year

[seniorchristo]

Thank you Hawksfield. I last checked the pattern using straight layout blue and I'm happy with the results.

[Davidb]

I only just saw this thread (been away) and I haven't read all of it I confess. I just wanted to add that ARP flywheel bolts intended for the BMC 'A' series engine can be used to replace the diff bolts in 'our' diffs and are cheaper, and possibly more available, than the designated diff bolt from ARP. I have had them in my diff for 4 years or so-1720cc and 150-160 bhp.

Edit: If you want to find these on Ebay motors enter "BMC flywheel bolts" in the search box-there is quite a list of potential sources and prices!

[ill_will]

Great thread thanks.

I've been going through it in conjunction with the workshop manual, trying to figure out how much of the process is required to swap over a standard open diff to a Quaife ATB ("LSD") unit (using the same bearing, seals, CWP etc) and whether it is feasible as a DIY job and if so what tools are needed.

I had the 3.55 diff off the car rebuilt about ten years ago but it has not been used since. It was rebuilt by a chap Sue Miller recommended, iirc an ex Ford guy perhaps a Brian(?) somewhere up near Thetford. I remember he had a lovely white S3 FHC himself. I haven't had the diff apart but hopefully he has done a nice job of it. It is stock except for the 4 bolt TTR output shafts. At the time I couldn't stretch to some form of locking diff but having had a standard car as my daily driver since, this was one thing which I wanted as spinning inside wheels are no fun.

Am I right in thinking that if it has been set up correctly that I can swap over the Quaife gubbins without removing/adjusting the pinion? And that I will need some longer ARP or std flywheel bolts; a tool to adjust and measure the cap spread (is a 5" or 6" micrometer adequate for measuring, as I have these already)? And a pin drive spanner for the caps.

Is it possible to get a visual check on whether the collapsible spacer has collapsed or is this hidden, and in this case are there any checks I can do to give confidence that the pinion bearing preload is correct?

Many thanks in advance!

[rgh0]

I used a 150 mm micrometer to measure the bearing cap spread.

The pinion bearing preload does not change on dismantling the nose from the rear casing and removing the diff itself. It is checked by measuring the torque to turn the pinion as the collapsable spacer cannot be seen once assembled.

Your other things listed are all good. On reassembly with the quaiffe diff centre you need to check the crown wheel engagement with the pinion using engineering blue as you centre it and preload the bearings measuring the bearing spread.

cheers
Rohan

[ill_will]

Thanks Rohan, I'll give that a try.

[ill_will]

8mm pins required for anyone getting tools together to tackle this

[2cams70]

8mm pins required for anyone getting tools together to tackle this

Or you can purchase one of these

https://www.burtonpower.com/side-adjust ... sDm0XYEPaP

[h20hamelan]

One of you Australian's (CeeJay?) used shims as opposed to the crush washer.