most common cause of leak in front of 68 muncie

[r bridge]

I just installed my new motor and 68 muncie that I rebuilt myself. After 150 miles there is a leak from the front of the trans into the bellhousing and has a drip every 10 seconds. It didn't do it the first 100 miles or so. I used synthetic 75-90. I have the level about 1/2" below filler. What would be the most common causes of this and any fixes before I take it out. I thought of switching back to regular 90 weight gear lube. I was sure the drain back hole was clear on rebuild. I suppose some sealer that I used could have gotten into the hole. thanks bob

[Joe L.]

Re: most common cause of leak in front of 68 munci

Bob-----

First of all, are you SURE that the oil is coming from the transmission and not the engine? I realize, of course, that transmission oil is a much higher viscosity than engine oil, but sometimes in a situation like this it can be a little difficult to tell for sure. Rear main seals are MUCH more likely to cause leaks into the bellhousing than manual transmissions.

In any event, assuming that it is the transmission which is leaking, there are several possibilities. First is the one that you already mentioned. If the oil drain-back hole is plugged, that could be a potential cause of a leak. Excessive application of silicone sealer is a very easy way to cause this to occur. Either the hole OR the passage in the retainer could be plugged. Either will have the same effect.

Second, the Muncie main case front retainer bolt holes are notorious for becoming "thread worn" and leaking. Although they often "tighten", they don't always SEAL.

Third, original Muncie transmission input shafts had an oil slinger installed on them. Later replacement inputs usually do not and the seperately sold slinger has been discontinued for years. The slinger is not essential, but, without it, there is more liklihood of a front leak since most of the oil is not deflected.

Fourth, the counter gear (cluster gear) shaft hole on the front of the transmission is also notorious for leakage. This hole often becomes enlarged causing the shaft to fit loosely in the main case. Sometimes, folks "knurl" or "centerpunch" the circumference of the hole to "tighten it up". Either way, unless silicone sealer is properly applied to this area, the case will leak. Usually, however, this will not cause leakage into the INSIDE of the bellhousing.

[R Bridge]

Re: most common cause of leak in front of 68 munci

Thanks Joe I have made sure it is the trans fluid rather than engine and that is good as I would rather do the trans pull than the engine. I hadn't really given much thought to the bolts as the trouble, so will look for that also. While I have you on the line, the speedo gear you recommended works super. bob

[Patrick T.]

Re: most common cause of leak in front of 68 munci

I had the same problem when I rebuilt a '72 M-22. The leak was coming from the countershaft hole in the front of the main case. I cut a round piece of sheet gasket material, coated 1 side with Loctite blue silicone and attached it up against the hole, let it cure, reinstalled the transmission and had no more leaks.