I have a leak from the main cover on the diff for my '85 300TD. I am going to pull the cover, re-seal it, and put in new oil. What products have you had success with in making a good seal for that back cover?
Thanks!

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1985 Euro 300TD Turbo

I just used black permatex. Never a leak --- yet ... fingers crossed.

Permatex RTV has given me constantly good results as have the products from Hylomar. The secret to successful differential cover sealing is getting it really clean and oil free - even but not too generous RTV bead application - fitting the cover as specified by the instructions on the back of the RTV packet. These are usually - fit snug but not tight - torque to manufacturer's specifications after a period of time (usually 30 mins or so) - then leave the differential unfilled for a further 24 hours

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I called the dealer and bought whatever they spec'd for it when I got my axle seals for Dad's 240D. It was around $11 and seems to have worked perfectly.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Permatex RTV is great stuff...
But I use it in a manner which pretty much takes away the need for warning about using too much...
I completely coat whatever gasket I am using with the RED RTV... as thin as possible.. and LET IT CURE overnight.... this will make it oil and water proof.... then the same cleaning process for the metal surface... lacquer thinner or acetone with clean paper towels until no coloring is present when wiped across the surface. Clean wet paper towel only showing.....
Then when applying the gasket to the perfectly clean surface... I again wipe it with as thin a coat as I can with my fingers... really paper thin... and on the gasket surface also...
I have not had a gasket leak in the 40 years since I started doing it this way... and I used to be dealing with VW valve cover gaskets.... held with old spring clips... but a cork gasket treated this way is great because it retains the springiness and seals it from oil...
The most common cause of gasket leak is still over torquing the bolts... or pulling them down unevenly... it is easy to warp the sheet metal involved in some sealing situations...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

http://www.peachparts.com/shopforum/diesel-discussion/106628-any-gasket-300sd-differential.html

Check your shaft and input seals as well.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

I have nothing against the careful use of RTV. However, I think Copper Coat (also a Permantex product) would also work as the surfaces are extremel flat. Copper Coat is a thick cement with Copper Paticles suspended in it (shake the can a lot). Dab it on and let it dry and it will be tacky when you install the Cover.

I can't remember what I used when I had mine off but I had RTV and Copper Coat on hand when I did the Job.

It is a good idea to make sure you can remove the Oil Fill Plug first. With the Differantial Back Plate still on the Car you can exert a lot of leverage on it that cannot be done off of the Car. Also if you cannot get the Plug loose you cannot fill the Differential with Oil.

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84 300D, 82 Volvo 244Gl Diesel

Thanks for all the advice. Ordered a tube of Permatex.

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1985 Euro 300TD Turbo