leaky M5OD...solutions?

[5spdman]

The truck might not be stock anymore, but the tranny is...

To make a long story real short, my 91 XLT got a new transmission last year. Between then, it got gear oil like the guy at NAPA had told me to use (oops), and while it was out again to replace the slave cylinder, I sealed the leak at the extension housing with blue Permatex since there doesn't seem to be a gasket out there. Even with the Permatex, the transmission still leaked a bit, but it wasn't enough for me to feel concerned.

I switched the fluid back to ATF a few weeks ago and it seems to be dripping even more than before...I'd rather not start losing all of the $50/gal Amsoil I poured in there, and wondered if maybe any of you knew of a gasket or another kind of sealant that I should use.

Or you can just tell me I didn't do it right haha!

 

[2stroke]

Are you talking about that piece between the tranny and transfer case? That should not have fluid in it. I use ultra black RTV for oil, but a mechanic friend of mine recently recommended ultra grey. He says it is oil resistant, and seals better. I was looking at that extension, and to me it looks like it is designed to leak if you look at the grooves. Maybe some day you can catch all the fluid in a clean bucket and fix the leak properly? I've done it with anti freeze coolant plenty of times.

 

[Anime]

If you bought a brand new transmission and it leaked, I'd say you should have taken up the issue with the company that sold you the transmission so they could either give you a new one, or at least the parts to fix it.

The ATF is held in with the metal ring/rubber lip type of seals, at least around the output shafts, so if it's leaking, you probably need a new seal. Could be that the company used cheap seals that didn't last, that rear seal just wasn't seated correctly, or it was never lubed so the rubber lip was damaged the first time it was engaged, with a dry shaft turning on a dry seal.

 

[5spdman]

I'll make the short story a little longer...if you want the even longer story, see 5spdman's slow and cheap XLT build...

I was in possession of a 93 Sport that wasn't worth the time or money to fix the blown head gaskets. I had found a 91 XLT for $200 that needed a transmission, and since it was a 5 speed also, it was an easy choice; throw the Sport's tranny into the XLT.

While the tranny was out of the Sport, I drained the fluids and filled it back up with the gear oil. After a few months of being in the XLT, the slave cylinder went out and I had to replace it. Since it was still leaking, I decided to reseal the extension housing to the transmission.

It still leaked, but it was a very slow leak, so I thought nothing else of it...but when I finally got around to switching back to ATF, it's started to leak even more.

That housing does not have fluid in it, but between the transmission itself and the housing is where I'm getting the leak...can't find any kind of gasket anywhere, so I was just curious if there was a gasket out there somewhere, if I need to make my own, or if I should use a certain type of RTV.

Guess I should ask for torque specs too on that extension...

 

[2stroke]

Oh, that's an easy recommendation. I have ultra gray on mine right now with no leaks at all. Not even a seep. Ultra black would do fine as well. Just make sure you get the surfaces nice and clean.

 

[Anime]

Okay, well, THAT gasket between the transmission and the extension DOES keep fluid in, it just keeps it in the transmission, not contained in the housing, obviously.

The factory Powertrain/Drivetrain manual specs silicone rubber sealant to be used to seal the extension to the transmission, hence why no gasket is available.

I'd guess that the reason it's leaking is that the Blue RTV silicone isn't up to the task of sealing gear oil/ATF. Ultra Grey/Black might be better, but really, I'd just say use the Ultra Copper since it's high-temperature. Permatex also makes an Automatic Transmission sealant (which would obviously work good on transmissions in general), but the Copper may be where it's at since it's not just sealing a transmission pan. From what I have seen of tearing apart the Explorer, Ford used the Copper RTV (or something very similar in color, at least) to seal the differentials and transmission surfaces.

I haven't taken the extension apart since the vehicle was new and it hasn't leaked in 220,000+ miles.


You may also need to be more precise in surface prep, application, and putting the surfaces together to get the best seal. All it takes is one spot to get messed up to allow a leak, then fluid gets everywhere. You can also get a poor seal if you just stick the parts together too fast, the RTV should cure for a few minutes at least to get 'tacky', THEN you slowly put the parts together, letting it cure a little more, then finally you push them all the way together and bolt them lightly, then tighten them to spec later still. If you just squirt on the sealant and bolt the parts together, you just wind up with a thin film between them rather than a gasket-like seal that is compressed between the two.

 

[5spdman]

So Ultra grey, black or copper, got it....would it be worth a try to make a gasket, like cork or rubber? I have a roll of cork and an old tractor inner tube, not really sure cork would do the trick, but thought it might be worth a shot......

Any ideas on the torque specs? I had followed the instructions for the ultra blue to the letter, and I'm just wondering if I may have just over tightened the bolts...

 

[Anime]

You would be creating problems trying to use cork (very bad idea) or rubber (especially from an inner tube, also a bad idea), or any kind of fabricated gasket here. It WILL leak and you will have to re-do the job AGAIN.

I think a fancy metal-with-adhesive/sealant type gasket like the super expensive head gaskets would do the trick, but they don't make one like that for this application.

RTV is used for a reason - it's effective (when the right type is properly used for the right application and it's properly applied) and inexpensive. You can do the front and rear differential plus this transmission/extension seal from one tube, that would cost 10-20+ times as much if you had to buy fancy gaskets for all 3. (they actually do make differential gaskets, but RTV is way better)


Factory manual says 32-46 N-m or 23-34 lb-ft for the Extension Housing Retaining Bolts.

I would aim for 30-35 lb-ft on a torque wrench.

 

[5spdman]

You would be creating problems trying to use cork (very bad idea) or rubber (especially from an inner tube, also a bad idea), or any kind of fabricated gasket here. It WILL leak and you will have to re-do the job AGAIN.

I kinda figured, but just wanted to make sure...looks like I'll be going into Flagstaff tomorrow, so I'll be sure to grab something to get this done....not sure what happened to my tube of ultra grey from doing the diff's, but with the rear cover leaking very slightly (had to patch a hole in the cover) I'll need some more anyway....doesn't hurt to be prepared either!