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Will a little gear oil affect fresh RTV


SamC777

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94 Ranger 3.0. Just resealed my diff cover, but there was still a little gear oil dripping out. I'd let it drain for about 30 min already while I was cleaning the surfaces. It was at a very slow, but noticeable drip.

I put the RTV on the cover and did my best to wipe the oil away and keep more from coming out before I placed the cover on. I placed it and tightened the bolts down, but I think I still see oil coming through.

Will this affect the seal? Should I have waited longer to let it drain? Do I gotta redo this?
 


Shran

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Clean = a good seal with RTV... it will not stick to oil. Best way I've found to drain axles is to drive it & get the fluid hot, then immediately pull the cover and let it drain for a couple hours. There is a little trough in the bottom where oil will accumulate - scoop that out after it's drained for a while and any oil left in the diff will drip into that and not run out onto the surface that the cover mounts on.

You need the diff cover mounting surface and its mounting surface on the diff to be very clean. Red brake cleaner cuts the oil off best. You also need to remove any remnants of old gaskets or RTV from both surfaces... as clean as possible for a good seal.

I run a bead on the cover, put it on and tighten the bolts finger tight. Let it sit for about 20-30 minutes and then snug them up. Let it sit for a minimum of a few hours, preferably overnight before filling it. You just risk a leak if you deviate from that process.
 

SamC777

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Clean = a good seal with RTV... it will not stick to oil. Best way I've found to drain axles is to drive it & get the fluid hot, then immediately pull the cover and let it drain for a couple hours. There is a little trough in the bottom where oil will accumulate - scoop that out after it's drained for a while and any oil left in the diff will drip into that and not run out onto the surface that the cover mounts on.

You need the diff cover mounting surface and its mounting surface on the diff to be very clean. Red brake cleaner cuts the oil off best. You also need to remove any remnants of old gaskets or RTV from both surfaces... as clean as possible for a good seal.

I run a bead on the cover, put it on and tighten the bolts finger tight. Let it sit for about 20-30 minutes and then snug them up. Let it sit for a minimum of a few hours, preferably overnight before filling it. You just risk a leak if you deviate from that process.
So in other words, I'm pulling it off and redoing it. If it won't stick to oil and some got in between, then it's probably not going to mate to the surface. Better safe than sorry, I suppose.

Thank you for your insight!
 

cbxer55

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Technically, RTV needs to set for 24 hours untouched by anything, in order to work properly. Works for me, I use it on everything.

So yeah, you're redoing it. Take cfover off, let it drain overnight. Wipe it inside with something before you put the RTV on, make sure there is nothing that can drip out for 24 hours.

My Lightning, the trans pan and diff cover have o-rings and drain plugs. Just put a little oil on them and install. Does anyone make a diff cover for the Ford 7.5 that has a drain plug?

I think TA Performance may make a cover for the 7.5. It will have a drain plug on it. Also a fill plug.
 
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Shran

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Yep I would redo it. I know that kinda sucks but now you know.

LubeLocker makes a reusable gasket for the 7.5" diff, not sure how they work with the thin metal or plastic factory covers but they work really well with aftermarket (ie, thick, non-flexible) covers. I've used them on D44's, D35, 9".... excellent product and way easier & faster than RTV.
 

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Personally I'd run it and see. If it leaks then fix it. I would run a smooth bead on the clean cover and let it harden overnight, then install. Even if there is a bit of oil on the diff it should seal.
 

SamC777

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Got it. Took it off, recleaned the surfaces, waited til it stopped dripping, and laid a new bead. She'll sit overnight. Thanks, y'all
 

cbxer55

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Personally I'd run it and see. If it leaks then fix it. I would run a smooth bead on the clean cover and let it harden overnight, then install. Even if there is a bit of oil on the diff it should seal.
You're using it like an o-ring that way. Suppose it would work. I lay a bead and install it, wait 24 hours then fill it. Never had a leak.
 

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