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Fixing the rear differential oil leak – resealing with RTV silicone

The rear diff has been leaking ever since I got the van but it has got worse. I removed the rear cover, cleaned it up and used RTV silicone to make a new gasket, and that’s what this post will cover.


Loosen bolts

I had to spray a bit of WD40 around the bolts to get them off. A couple of the bolts where really corroded so I had to get a bolt grip socket (I bought a set for £14 here) and they came off easily. I put a bowl beneath incase the oil started coming out right away – it didn’t.


Prize open case

With the bolts still in but loosened I carefully used a big flat screw driver on the edge of the case.


Drain oil

I let all the oil drain with the case still half on, just so it’s more controlled.


Scrape off old gasket sealant with a plastic scraper

I removed all the old gasket sealant (although I think this might have just been standard silicone) with an old plastic card. I did this on both mating surfaces: on the diff housing and the cover.


Clean cover plate

I cleaned the cover plate in the same way as above but I also used some brake cleaner spray.


Apply sealant (gasket maker or RTV silicone)

I made one clean bead of RTV silicone sealant around the cover plate inside lip making sure the bead goes inside of the bolt holes. I used ProSeal Red Silicone Gasket Maker – See it on Amazon


Place cover back on and hand tighten

With all the bolts about evenly hand tightened I left this it one hour (as instructions say) for the silicone to slightly set. Some silicone will squeeze out the sides, that’s alright.


Fully tighten and leave for 24 hours before filling with oil

I went round in a star pattern making sure I tightened each bolt evenly bit by bit. A little bit more sealant came out at this point but it was a thicker consistency as expected.


I did a separate post on checking the rear differential oil level and topping it up – see Checking rear differential oil level and filling it up

I’ve just driven 300 miles and it has held up well – totally dry.

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