Wednesday, July 8, 2020

To use RTV silicone sealant with the rear differential cover gasket or not? New cover is still leaking!

So the SAME "lube tech" that over filled the transmission by three quarts also did not fix the old rear differential cover leak. So we had paid a huge amount - for a "gasket" replacement - and the rear pinion seal replacement. So then I was not even sure that any work had been done at all - so I bought the NEW rear differential cover to ensure that indeed the rear differential cover would be taken off and new fluid would have to be put it.

The "lube tech" told me he put in a new gasket - while the "service advisor" told me that the "lube tech" had told him that the previous old rear differential cover had the gasket stuck into the metal of the differential via an RTV silicone sealant! This is supposed to be a big no no.
Gasket maker or silicone sealant should never be used as a glue or means of keeping a gasket in position when you reassemble your engine. Mechanics often do this believing, erroneously, that a gasket maker will not only hold the gasket in place, but it will add to the seal.
On Wed, Jul 8, 2020 at 12:12 AM Voidisyinyang Voidisyinyang <voidisyinyang@gmail.com> wrote:
Using RTV on the gaskets with fluoroelastomer coating or silicone sealing beads causes multiple issues: The sealer can chemically attack the rubber sealing beads and degrade them. RTV can act as a lubricant and cause the rubber gasket to slip out of place and split, creating an opportunity for leaks.
The strange this is that I had no record of the rear differential cover having been removed! The fluids had been topped off before - but the cover had not been removed as far as I could tell. And so now that the NEW rear differential cover is STILL LEAKING and the SAME "lube tech" put in way too much transmission fluid then I am very curious as to the state of the "new gasket" behind the new rear differential cover!!
 So this am we are bringing the car to our new local mechanic - and when I said to him on the phone, "You know how the dealer has those 'lube techs'?" He LAUGHED - yeah "lube techs" - he said with great sarcasm. He knew exactly what I meant.
So will the gasket NEED RTV silicone sealant to stop the leak? The PLM differential cover company actually says to not use a gasket at all and just use RTV silicone. The installation vid shows the mechanic REusing the old gasket - and the car owner is very nervous, stating, "any little nick in that old gasket will cause it to leak."
So did the "lube tech" lie to me and reuse the old gasket? Or did he nick it by mistake? Or...
 I use ultra black, or the right stuff on just about everything. I always spread a thin layer on both surfaces with my finger. Then hand tighten, let sit for 20 min, then torque to spec. I have found that I regularly have leks were I don't use it. And never have a leak were I do use it.
  the aluminum gasket surfaces may be pitted or scarred. The rtv helps fill these voids thus creating a better sealing surface. But only on sealing surfaces appropriate for rtv.
 Always have, and always will.
Never had anything leak from this method.

When i do it, i put rtv on the thing the gasket is going onto, stick the gasket onto it, let it tack up and almost dry, then i put rtv on the other side of the gasket, smear it over into a nice layer, then put it onto the other thing that it needs to stick to
 Wow - so against all "theory" -!! but wait...

This is from BigMike over on Marlin's Forum, so you weren't being a paranoid noob. But like I said, experience matters much more than theory.

"Never never never never put silicone over a paper gasket!! The silicone dries hard, and then the gasket absorbs gear oil and expands, the silicone is not able to expand with the gasket and it will leak like crazy.
 wow....

fascinating. It's getting complicated - pits in the surface need sealant... but silicone is not able to expand and the gasket expands from absorbing oil....
 We prefer to install all gaskets dry, but for the sake of holding the gasket in place, we will coat the transmission side with Permatex High Tack gasket sealant (http://www.neverseezproducts.com/gasketseal.htm). That way the gasket will have one sticky side that will stay on the transmission while you get the t/case into place."
 Right - that's the other concern - that the new gasket just "moved" when it was being installed.... and so a little sealant on the engine side... (not the cover side)....

Anyway - the point is it is still leaking and I'm very curious as to what that "lube tech" did since he did such a "great job" on the transmission! haha.

So there was a new leak spot of rear differential oil this am - I was trying to figure it out - and it is right where the Air Vent tube rises up!! So I think that the "lube tech" dude put in too much rear differential gear oil - just like he put in too much transmission fluid!!

thanks for the response and recommendation. Marvel's Mystery Oil. Yeah the car is back at the dealer. Local mechanic says the rear pinion seal is leaking like a sieve and whoever did the job needs to redo it. haha. It was just replaced a couple weeks ago - I thought it was the differential rear cover still leaking.


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