I just recently, less than 100 miles ago, replaced my M5R2 with a remanufactured unit. It just started leaking fluid out the front seal. I'm worried that this may be from a venting problem. Can anyone describe exactly how this transmission vents? I saw online it is through the shifter, but I just don't see how. The transmission also has viton plugs installed at the back, i don't know if they work to vent the transmission either.

Just to give you an idea of how things are around here, it has been much colder than usual, constantly below freezing. I was told by the reman. company to run ATF+4 in it (chrysler fluid). I have noticed slight grinding on the 1-2 shift on the first couple shifts when the trans is cold...when it's warm it shifts fine. I'm wondering if the fluid could be part of the problem as well.

 

The M5r2 is splash lubricated. I've never heard or read of anyone
complaining about any pressure build up inside the transmission
causing external leaks or seals to blow out.

The front input shaft cover is bolted to the front of the transmission and
holds the front input shaft seal. The front cover and the six
bolts that hold the front cover to the case are sealed using silicone
sealant.

The service manual calls for Dexron II. Since Dexron II is no
longer available, people use Dexron III.

I'd say the transmission you purchased was a repaired unit that
was cleaned up and sold as a remanufactured unit.

The 3 rubber plugs on the back of the shifter cover should have been
replaced with steel/brass 5/8 freeze plugs. (Replacement plugs
Dorman 108-555).

The 3 plugs allow access to the shift rails.

The factory rubber plugs would harden over time and fluid would
leak past them. Eventually the bearings would fail due to the low
fluid level.

Two very common problems with that transmission are the two
plastic shifter bushings on the bottom of the shifter lever cracking
and worn pivot pins in the shifter cover that the shifter pivots on.

 

From what I can tell from the outside, it has been cleaned up. I didn't take it apart to verify that everything has been replaced. This leak did just happen recently though. At first it was bone dry, then just started with a steady drip when running. It does run very smooth...like a rebuilt box. From the outside, the input shaft and output shaft had no surface rust or anything like they would if they had sat out for a while. The rubber plugs were brand new. I was told they are viton, but I can't verify for sure. Viton is supposed to last much longer than standard rubber...I've used it for other applications. Yes it is possible to clean up and make it look nice on the outside, but I do believe it is a reman. box.

I always thought these transmissions ran Mercon fluid standard, since that is a standard Ford fluid..where Dexron is GM...but I know aftermarket fluid manufacturers sell a single fluid that works for Dexron and Mercon applications..DexMerc or whatever. I was going to run Mercon but then I saw the reman. shop recommended ATF+4. Maybe I'll switch to DexMerc and see what happens.

Also, I'm wondering if maybe the transfer case is backfeeding into the transmission causing an overfilled condition. I didn't change the seal on the t-case, although I probably should have. Or maybe even the vent on the T-case could be plugged causing problems? Maybe I should give that a look