M-20 case front repair

[Patrick H.]

Hello all,

I will be removing my 4 speed from the 71 this winter to have it rebuilt. I'm leaking plenty of oil from the front of the case in the area of the output shaft, and after 127,000 miles it's time to have it fixed.

I know that this will likely need a bushing installed in the front to bring it "back to round" and avoid further leaking (per many previous threads). Is this a procedure that is commonly done, and the guy at the local transmission shop will understand and be able to perform? Or should I send it somewhere in particular? I only want to do this once, but if I don't have to ship it, that would be nice. I'll do whatever I need to do, though.

Thanks for any suggestions you might have.

Patrick

[Richard D.]

Re: M-20 case front repair

Check out this link.

Lots of pretty good info on Muncie rebuilds.

Rich

http://members.rogers.com/mlvd/muncie_rebuild.htm

[Joe L.]

Re: M-20 case front repair

Patrick-----

This repair is not one that I would expect a standard machine shop to know anything about. Also, most transmission shops probably won't, either. I'd contact Ed Hartnett in Lansdowne, PA. His phone number is 610-623-9381. You could trust Ed with your case and shipping the bare case is no problem.

First, make sure that the cause of the leaks is the cluster shaft orifice. The thing that usually causes this to leak is multiple transmission disassemblies and assemblies. So, if yours is "first run", it's not real likely that this is the cause. If the transmission was formerly "run hard", though, the cluster shaft orifice in the case can get "elongated" and, consequently, leak

A real common source for leaks from the front of a Muncie is the front bearing retainer bolt threads becoming worn. If the bolts holding the retainer loosen a little bit, as they often do, the threads in the case get worn quickly and leak. You can fix these yourself with a Heli-Coil or Thread-Sert. Use Locktite to secure and seal the insert you use.

[Patrick H.]

Re: M-20 case front repair

Joe,

I don't think it was run that hard previously, and it has never been apart. I have a LOT of oil coming out of the front of the trans, though (a nice "inverse skunk" stripe under the car). I replaced the oil pan gasket and rear main seal previously, and they're not the problem. I'll have to look at it closer when I remove it. I also lose oil from the side cover where the shift rods insert through.

Patrick

[John H.]

Re: M-20 case front repair

Patrick -

Make sure the oil drainback hole in the front of the case isn't clogged or blocked by gasket sealer - that's the only path back into the case for lube that comes through the front bearing, which has no seal. The side cover shifter shaft leaks can be cured by replacing the O-ring seals on the shafts.

[Kevin #38315]

Re: M-20 case front repair

I've often wondered why there wasn't a seal on the front end of the trans, so it would not leak if parked on an incline. Would you also get leakage if you frequently spike the brakes?

Kevin

[Joe L.]

Re: M-20 case front repair

Kevin---

It's not possible for a lot of oil to get past the front bearing regardless of how the car is driven. This is 75-90 wt gear oil, to begin with. What oil does get by the bearing goes into the "resevoir" in the rear of the bearing retainer and flows back to the transmission through the "trough" in the retainer which leads to the hole in the case.

As John mentioned, gasket sealer can get into this hole and plug it. That's why I NEVER recommend the use of gasket sealer on the bearing retainer gasket. The gasket material used for this gasket has sufficient compression and "sealability" without the need for gasket sealer. If gasket sealer must be used because "you just can't sleep at night otherwise", then a VERY small amount of a sealer like Permatex #2 can be used. Keep in mind, though, that the folks in Muncie, IN who originally built these things didn't use any sealer on the gaskets they installed.

[Patrick H.]

Re: M-20 case front repair

The way it's sounding, I may just look at it hard and take it apart myself. I know there's now a good video on it, and I may purchase that. I can always send it out or get advice as I go along.

Patrick

[Clem Z.]

Re: M-20 case front repair

make sure it is not over filled if the fluid runs out when you take out the plug it is too full,you should have to stick your finger into the trans to feel the fluid. i have see people check the fluid and if it runs out they quickly put the plug back.

[William C.]

Re: M-20 case front repair

The later Muncies also use a "Slinger" between the input gear and the front bearing to deflect oil away from the bearing. I support Joe's recommendation of Ed Hartnett if you need the cluster shaft rebushed. The seals on the shifter arms are standard items, included in some but not all kits, readily available at our local bearing'seal supplier. Just manke sure the shifter shafts don't have too much corrosion (rust) on the surface where the seal lip runs.

[frank mccracken]

Re: M-20 case front repair

If the leak seems to be coming from the front and all return passages are clear then my experience is that the the pin hole in the case is distorted. To rebush the hole is the correct repair, but to find a shop willing, send the case away and spend big bucks and hope they do it right made me think of what alternatives might work. I devised a permanent altho sleazy sounding repair many years ago which I have used with great success to this day and don't install one of these old 4spd's without doing so. Make a gasket to go between the the bellhousing surface and the front surface of the trans. Because transmission alignment is critical, it must be full gasket with a center hole for the bearing support in the trans, and follow the outside dimension for the 'ears'. For a little insurance, a dab of Permatex black sillicone at the pin area may be applied. I have seen many try to do a quick fix by just applying sillicone sealer to the pin area and then installing the trans but that never works. Unless the distortion of the hole is such that the trans does not work right, which I have never seen, this repair will seal your leak and is almost completely undetectable.