# Transmission sealant ?



## ridgetop (Sep 13, 2007)

I recently changed the oil in my transmission and now it's leaking and it looks like around the seals. I wonder if the new "thinner' oil is escaping though the seals in the case. Is this a common thing in older trucks to leak like this after new tranny oil is put in?
Anyway, is there a good or better type of additive I could use to try and seal the leak? 
Right now it's about a drop/drip an hour type of leak.


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## taxidermist (Sep 11, 2007)

What type of gasket did you use? My old 78 F-250 I use the cork and haven't had any issues. The rubber gaskets wont "swell" and if your surface (pan, etc.) isn't flat and clean they can leak. Also, if you overtighten the bolts it can create a small void between the mating surfaces and leak a little.


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## ridgetop (Sep 13, 2007)

I should clarify, I had a shop change the oil and filter. I thought they only had to drop a drain plug and replace an external filter like they do on motor oil. Am I wrong?


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## Buckfinder (May 23, 2009)

When I’ve done it in the past you have to drop the whole pan and replace the gasket.


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## brisket (Mar 3, 2015)

I'd take it back in. If it's a decent shop, they should fix their mistake for free.


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## Critter (Mar 20, 2010)

I agree with brisket on taking it back into them. 

If you want to keep the vehicle putting sealants or something else in the fluid is just a bandage and will need to be fixed sooner or later. And most of them don't work anyway no matter what it says on the bottle.


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## weaversamuel76 (Feb 16, 2017)

ridgetop said:


> I should clarify, I had a shop change the oil and filter. I thought they only had to drop a drain plug and replace an external filter like they do on motor oil. Am I wrong?


Yes like was already posted above. The shop would have to remove the transmission oil pan to change the filter.

Sent from my moto z3 using Tapatalk


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## ridgetop (Sep 13, 2007)

Thanks for the input guys. That really helps. I'll be taking it back in to the shop.


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## DallanC (Jan 13, 2009)

I had a shop change my tranny oil about every 40k miles.... last time in for a change they said refused and said "dont F### with it, at a certain point on a tired transmission oil changes will start doing more harm than good". 

That was 30k miles ago lol...


-DallanC


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## taxidermist (Sep 11, 2007)

One more reason I like a stick tranny on the older trucks.


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## muddydogs (Oct 7, 2007)

DallanC said:


> I had a shop change my tranny oil about every 40k miles.... last time in for a change they said refused and said "dont F### with it, at a certain point on a tired transmission oil changes will start doing more harm than good".
> 
> That was 30k miles ago lol...
> 
> -DallanC


Never heard of this and I have been a fleet manager for 20 years. especially if your changing every 40, most guys don't take that good of care of there tranny.


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## DallanC (Jan 13, 2009)

muddydogs said:


> Never heard of this and I have been a fleet manager for 20 years. especially if your changing every 40, most guys don't take that good of care of there tranny.


Oh I've heard it off and on for many years. The theory is when your clutch plates (auto tranny) get really worn down, they are getting some additional friction from contaminants from the dirty oil. Replacing the oil with nice clean oil, can cause increased slippage without the prior additional fiction.

At this point though, its extending the life of the tranny by a small amount. It really needs a rebuild. I can feel a little slipping occasionally when trailering... so I know I'm on the edge of a rebuild, no sense tempting fate at this point.

-DallanC


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## ridgetop (Sep 13, 2007)

I took the truck back in and the leak was actually coming from the seal where the gear shaft goes from the transmission to the transfer case. Since they were replacing that one, I went ahead and had them replace the others.


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