Differential rebuild

[steve redway]

I'm about to start a differential rebuild on my Grinnall. It's a Rover SD1 back axle which essential is the same as the TR7/8. The backlash of the Crown Wheel Pinion is over 20 thou, the sun and planet gears are not separating and the differential clonks like a good un. 

I was thinking of putting a new diff in (RTC2061) from T.D.Fitchett Ltd., https://www.ebay.co.uk/itm/116189349705?chn=ps&_ul=GB&mkevt=1&mkcid=28&google_free_listing_action=view_item plus a new set of Timken bearings.

Has anyone used this guy?

This would then necessitate re-setting the pinion/crown-wheel mesh to get the required 0.006" backlash so I would need a set of suitable shims. Can anyone advise where I might get these?

Can anyone assist or am I in hyper space territory?

[dblenk]

Steve

i just asked a question regarding a TR6 diff in parts and resources

worth keeping an eye as a general view of diff rebuilds

David

[steve redway]

OK thank you David. Differential rebuilding seems to be quite a black art if the number of replies I have received is anything to go on

[Chilliman]

Steve, I've done a number of live axle TR4 diffs & I can honestly say that the gearbox/overdrive rebuild is a walk in the park compared to the back axle, not so much a black art, just very very difficult to secure the accurate measurements that are required to end up with a reliable, quiet & long life unit. I hasten to add I have no experience of your type of car but suspect it's not a task for the faint hearted. Good luck...

[steve redway]

Thank you John. I did one quite a few years ago. More of a pinion, crown wheel and bearing change and apart from setting the pre load of the pinion at 12'/lb instead of 12"/lb I dont remember it being too much of a problem. A few various shims, a dial gauge, big pinion spanner and some engineers blue and I was there.....sort of.

My difficulty at this very moment is getting a second opinion as to exactly what the issue is and if my chosen rectification route will solve it. 

Anyway I will update this Forum as to how I progress but I would like to hear from someone who has used a new diff (RTC2061) from T.D.Fitchett Ltd.,

 

Edited June 21, 2025 by steve redway
spelling

[Chilliman]

Steve, I have to admit that despite all my measurements the acid test is the engineers blue which shows the true contact zones. Hopefully someone will be able to answer your question re the diff you are considering.....

[steve redway]

I am now investigating the rebuild option, that is if I can get the parts. I need some copper cup thrust washers that go on the small planet wheels. They are in the part number range UKC964 to UKC971 with their thickness from 1.17mm to 1.65mm.

 

Has anyone a few knocking about from a past TR7/8 axle rebuild?

 

[BlueTR3A-5EKT]

Are you just doing an reshim, not replacing CW&P?   Do an engineers blue check of the pinion running on the CW before you strip it so you know what to expect when it goes back together.

How will you get the taper roller bearings off the diff carrier?    You will need to do it a few times to get the CW to Pinion backlash set.  

Inspect all taper roller bearings and their tracks for wear, indentations surface break up. Renew as required.

Inspect the teeth of the differential gears for any pitting, indentations or wear.   Reject if the tooth faces are starting to break up.   Measure the thickness of both the sun gear thrust washers.  They need to be the same   Are they metal or fibre?   TR2-6 started metal and went to fibre.   I find fibre is more durable and stable for some odd reason.  

Check the sun gear’s running clearance and fit in the carrier.   If they are sloppy you will need either a pair of gears (if you are lucky and it is they that are worn, not the carrier) or buy the RTC2061 assembly.

Check the planet gear spindle for wear, slide the gears on and feel for sideways play.   If sloppy….new pin or buy the RTC2061 assy.

Build up……Fit new sun wheel thrust washers first if they are required..   Adjust the planet gear backlash second.  The gears need to be a tight but running mesh.
 

Now you are into setting the CW carrier bearing preload.  Then remove same.

Fit pinion and set bearing preload without the seal.  Fit seal and tighten big nut as required.   Fit seal once you are not likely to be belting the pinion back out again.

Fit CW assy and check and set  teeth backlash   Don’t mess up the bearing preload!   Very fiddly and frustrating task.   Blue up the pinion and check tooth markings on the CW.  In both drive and overrun.  As your axle was working and the CW&P have not been changed we can hope the pinion height is correct.   Not always true on TR6 as the factory had a + or- 0.003” tolerance for Pinions.  See markings on the pinion head.

Once you are pleased with the blue markings fit the pinion seal, rear cover and shafts etc ready for refit in the car. 
 

This is all detailed in the factory workshop manual.   The TR4/6 book is very helpful but the dimensions will be wrong.

Edited July 2, 2025 by BlueTR3A-5EKT

[steve redway]

Thank you for all the help here.

I am pleased to report that I completed the job. Differential shims came from Chris Witor, you have to be a bit creative as part numbers don't always match. I think the copper shims came from Triumph 2000 diffs, the brass and nylon larger shims from TR7s. I won't bore you with part numbers. With a new diff pin, Timken differential bearings and shims up a few thou from the ones taken out, the differential lost the backlash and became firm again. I didn't remove the pinion. At the end the pinion backlash was within recommended factory specs.

This has overall improved the play in the prop/torque tube/differential by about 50%. The remainder of the play is in the worn splines of the torque tube fitted to the Rover SD1 axle.

Anyone have a spare torque tube knocking about this good splines?