Sierra Diff

[Al04]

Hi All,

 

hoping someone can help, I have a leak on my sierra diff looks like it’s coming from the side screw seal rather than the drive shaft seal on the diff.

Am I right in saying if I remove the side screw seal the backlash will all need setting back up again for the right tolerances? I am running an LSD.

PS Diffs aren’t my strong area - if it does I am Derbyshire based does anyone know of any companies that can do it?

Many thanks

Alasdair

[phaeton]

Not used them myself but heard good things about http://www.all-gears.co.uk/ my son has a couple of mates who run their own garage & they take all their stuff to them

[Al04]

17 hours ago, phaeton said:

Not used them myself but heard good things about http://www.all-gears.co.uk/ my son has a couple of mates who run their own garage & they take all their stuff to them

That’s perfect thank you 

[Sparepart]

I have a copy of the Sierra Owner's Workshop Manual. I'm assuming that you are talking about the pinion oil seal. I have a standard diff on my car and have changed the pinion oil seal following the destructions in this manual. There is no need of any setting of backlash or that sort of thing. You need a good puller and a socket spanner or ring spanner with a long handle because the central flange nut is pretty tight and its easier on the car because you can apply the handbrake to stop the flange turning. Once the flange is off, remove the old, tap in the new, replace flange, and re-tighten the nut to 35-45 Nm with a torque wrench. You can re-use the nut a couple of times, its self locking, otherwise you will need a new nut. I just checked that the same process is covered with a few less photos in the Service and Repair manual which is easier to obtain.

[Al04]

Hey, no it’s not the front piñon seal it’s coming from the side screw driveshaft side but it’s not the drive shaft seal as just above it is dry underneath is wet.

[Sparepart]

Sorry, my mistake, I was too quick to jump to the wrong conclusion, I've not had dealings with the "Side Screw" before, however a bit of digging in our vast wealth of archives which are easily searched and have found that the answer to your question is "yes" the Side Screws do adjust the backlash, so if you remove one to replace the O ring seal then a backlash check would be needed. The whole process of rebuilding a Sierra Diff is/was covered by our member Richard Byrne in 3 articles published in our club magazine. Spring, Summer and Autumn of 2020, these can be downloaded from this website, via the Magazines link under the Useful Sites banner.

[Al04]

Thank you I did search originally but nothing come up that I was looking for. it was only on a YouTube video but it wasn’t English. 

[Bob Tucker]

On 12/1/2025 at 7:32 PM, Al04 said:

it’s not the drive shaft seal as just above it is dry underneath is wet.

That is a classic description for a driveshaft seal leak. They are pretty common, ive never heard of an inner seal leaking.
If it was me, Id change the driveshaft seal in situ & see what happens. It just needs the drive shaft removing.
It possible to do without disturbing the brakes.
To remove the old oil seal, drill a small (1.5mm) hole in the seal face, insert a self tapper, and pull on that.
Make sure to follow the Haynes manual. You dont push the new seal all the way in up to the shoulder inside the casing.