MTFCA Forum

I went to do a spring service on my '27 Touring. When I unscrewed the plug to check the differential grease, about half a quart of 'oil' flowed out. This must be engine oil. What seal has failed, and how do I fix this? Thanks.

It is leakage past the 4th main. It may or may not be due to wear. Having an oil screen inside the trans cover seems to cause much more oil to get past the fourth main. The benefits of the oil screen outweigh the potential leakage issue in my opinion. Several years ago I started installing a drain in the rear axle housing on my axle rebuilds to counteract this very issue. Axle oil mixed with engine oil is a poor axle lubricant. I also think that changing axle oil once a season might do a lot to prolong its life. You can use a suction gun with a metal tube on the end (to allow you to get to the absolute bottom of the housing). Get as much axle oil out as you can, then re-fill. If the differential is warm from an extended period of driving beforehand, it is easier to remove the old oil.

The axle has to be completely apart to install a drain.

Thanks. The engine was recently professionally rebuilt, and seems to run well. I do have a a transmission oil screen with magnet. J.R.

Probably nothing to worry about. Just keep an eye on the level and change the diff oil every time its over full.

You only have to fill the diff this much:

If you are getting that much engine oil into the rear end, most likely there is no plug in the transmission driven plate output shaft. There should be a concave type freeze plug in the transmission output shaft just in front of the square that the u-joint fits into. That plug is to prevent engine oil from going out past the u joint and down the driveshaft. Has your transmission been rebuilt in the past? Also, you will also find that there is no grease in your u-joint as the engine oil has diluted it.

When the engine was out we replaced the reverse drum, which was scored, and installed new "Jackrabbit' clutch plates.
Not sure what the driven plate is.

Driven plate plug placement.



Driven plate

That makes it clear. We re-installed the old component during the engine swap. If it is missing the plug, it must have been for a while. I suppose you can't check if the plug is there unless you drop the drive shaft?.

Thanks.

So assuming that the plug is not missing from the output shaft, and I have added, and possibly over filled engine oil a few times, is this accumulated 'oil' a problem? I guess I'll check the rear end more often and drain off excess. I do have a oil screen which may aggravate the condition.