Noisy Diffs

Post by **Matt** » Mon Nov 03, 2008 10:51 pm

Hi Guys

I have 2 1275 sprites... one isnt going to go anywhere again unless I can get hold of a new bodyshell. Its my mums old car and apparently the diff was noisy before the car was taken off the road.

Is it possible to rebuild these diffs at home and is it worthwhile?

Post by **MoggyTech** » Tue Nov 04, 2008 12:03 am

It's possible, but there are pitfalls. Matched crownwheels and pinions are fairly expensive these days. Sourcing the various shims for crownwheel to pinion mesh can be tricky. Ideally you need the various settings jigs as listed in the BMC manual, but can get away with just some engineers blue, and quality dial gauge.

The two things you must get spot on to avoid whine, are mesh and pre load.

Post by **IslipMinor** » Tue Nov 04, 2008 10:23 am

Matt,

I have scanned the pages from the BMC Workshop Manual covering the complete set up of the diff, amd can email them to you if you would like them?

Moss do the shims, but if you get them from there, make sure you check the sizes they send very carefully. What is written on the bag is not always what is supplied!

You will need a good bearing puller to remove the diff carrier bearings, a dial gauge to measure the backlash and a source of good quality bearings at sensible prices. BSL, or Brammer as they are now, will usually supply at trade prices if you ask firmly enough!

Post by **mike.perry** » Tue Nov 04, 2008 10:31 am

My 3.9 diff whines like mad on acceleration but is quiet when decelerating. Is that the gears or just a dodgy bearing?

Post by **MoggyTech** » Tue Nov 04, 2008 11:28 am

mike.perry wrote:My 3.9 diff whines like mad on acceleration but is quiet when decelerating. Is that the gears or just a dodgy bearing?

That will most likely be crown-wheel to pinion mesh, or the leading edge of the teeth on crown wheel and pinion are worn. If oil level kept topped up, they can survive a long time after they start to whine.

Post by **Matt** » Tue Nov 04, 2008 1:33 pm

Yes please IslipMinor

I will pm my email address... or it might be on a little button below, I cant remember!

Post by **bmcecosse** » Tue Nov 04, 2008 8:29 pm

No need for scanning etc of the manual - it's here http://www.morris-1000.co.uk/ free!

Any chance one of the MODS could put this link into a Sticky ???

As for noisy diff on drive etc - it will be the mesh of the crownwheel and pinion - which can go wrong if the nut holding the drive flange has worked loose - allowing the pinion shaft to move. So - possibly worthwhile dropping the propshaft off the diff - and check if that nut is good and tight. Otherwise - you can take the diff apart and have a go at adding/subtracting shims etc to try to improve matters - just don't make it too tight!

Post by **Mogwai** » Tue Nov 04, 2008 9:23 pm

If theres a lot of wear on the teeth it may not be economic to repair but bearings can be changed fairly easily with suitable bearing puller measuring tools etc
Setting the pinion height is the tricky bit without the calibration block if your just changing the bearings ive done them before by measuring the height of the pinion before dismantling to compare after. the original shim should be ok (the pinion shims are NLA anyway) You will also need a collapsable spacer to set & maintain the preload.
Setting the crownwheel preload & backlash is a little easier by the manual as its just a case of a calculation from some numbers stamped on the carrier & cage plus a measurement of the bearings deviation from its standard width to give the required shims. If you have suitable measuring tools you could measure the difference between the carrier & assembled cage to detemine the preload. To adjust the backlash just need to swap shims from one side to the other

All this isn't as difficult as ive just made it sound