Replacing diff pinion seal

[Divano Veloce]

My diff is a bit leaky from the pinion seal.

Any advice doing this job? What size seal is required? Special tools (for the nut)?

Thanks!

[1750GTV]

One of these is handy. I bought this one when I rebuilt the diff in my 50s Giulietta and because the nut is the same (part number 2120.16425) it will also fit the 105 series cars.

I got it from -

http://www.okp.de/xtc2/105/115-Bertone/25-Rear-axle/Differential/Tool-for-differential-nut-2000cc-105::18874.html

Chris

[Paul Byrne]

Hi Matt,
I sent you a pm, but I have a home made socket tool for the nut and you are welcome to borrow it. Replacing the seal is straightforward and this is a good chance to see if the nut was tight! They are often loose. Tightening torque is 70 to 100 ft lb. Need to check that the pinion drag (preload) is somewhere near right when the nut is tightened again.
Cheers,
Paul

[Paul Byrne]

Diff pinion seal size is 45 x 74.5 x 12

[LaStregaNera]

1300/1600/1750 diffs have a smaller nut and seal.

[Divano Veloce]

Thanks guys, sourcing a seal now. According to Classic Alfa website the 2l diff uses the following seal dimensions:

ID 45mm OD 74.50mm T12mm.

[Divano Veloce]

I have finally got around to this job....

Turns out the leak was not the oil seal but via the pinion shaft splines and under the diff pinion nut; it was not very tight.

So i have replaced the oil seal, fitted the flange and nut. When torqued the pinion shaft feels like its binding... Could it be that the nut has been used to set the preload instead of shims? The nut has been staked in position.

The diff was quiet prior to this work.

[Colin Byrne]

book says 56 - 100 lb ft

very unlikely that the pre-load was set with the nut, if anything, over time the preload should reduce as the bearings bed in.

It's usually very hard to determine the pre-load of just the pinion bearings whilst the entire rear axle is together (including wheels, brakes ect?), there is just to much drag with everything else, so if you can notice a difference by hand, there is something very wrong

when you do the pinion nut up, is there still some backlash between the pinion and CW?

[Divano Veloce]

Thanks Colin, Great news about your new car, condolences for the old one.

the wrist-o-torque gauge says there is a big difference between when the nut is nipped up and when it is tightened.

To check the backlash i will pop the fill plug out and lock the crownwheel. I suspect that the primary issue is pinion bearings preload.

[Colin Byrne]

thanks for that, looking forward to building the new car now.

You shouldn't need to lock up the CW, just the mass of the CW is enough, basically if you can feel any backlash on a 2L diff, you've got enough

That is very strange, can't think of why that would be it's almost as if you've lost a shim on the pinion shaft, did you pull out the front bearing when you changed the seal?

[Divano Veloce]

no i didnt... i could attempt to pull the seal but will probably destroy it.

i have done some reading online and it seems that with the correct preload on the pinion bearings there should be a reasobable amount of torque required to turn the crownwheel and pinion (16.5-24.5 kg.cm). Maybe this is what i am feeling... 2.35 nm??

I will have another look at this tonight... Thanks colin for your advice, and to Paul for loaning me the special tool.

[Divano Veloce]

I torqued the nut and the amount of torque required to rotate the pinion shaft didnt feel too bad but i had no piece of mind so i pulled the seal and destroyed it.... thats two good seals mangled now!

heres what i found. a single thin shim


The drive flange was a bit flogged



there didnt appear to be much wear on the parts that affect bearing preload.

alas, i wont be at broadford on sunday. if anyone is interested in a last minute spot contact Neil