Engine oil leaking into differential?

[mbowen]

I haven’t driven the ‘24 touring I bought last October in several months, due to having the front axle out for rebuild. I’m close to getting the front axle back in so I decided to check the oil in the differential. Upon removing the plug, oil gushed out and continued to run for a while (fortunately I had a bucket at the ready). My first thought was that it was simply over filled, but I don’t see how it would be possible to fill it above the bottom of plug hole (I do have the later housing with the plug below the level of the axle). I also noticed that the oil that came out seemed a bit thin for gear oil, especially at the 50-55 degrees I keep it at. Is it likely that oil from the engine/transmission has leaked down the drive shaft housing?

[TXGOAT2]

That's almost certainly what has happened, assuming the car has not been in a flood. I can think of a couple of reasons this might happen: 1. Too much oil in engine pan. 2. Water in oil pan due to leaking gasket, raising oil level. 3. Running car with problems in 4th main/u-joint/driveshaft bushing. 4. Parked on steep incline with front of car up, or jacked up.

[Henry K. Lee]

Pat nailed it!!!!!!!!

[67pontiac]

Another thing to check is the "plug" inside the transmission out-put shaft. Its a bit hard to describe, but there should be a "disc type freeze plug" inside the transmission just in front of the U-joint. If its not there, there will be a tremendous amount of engine oil running down the torque tube and ending up in the differential assembly. A lot of folks don't know about the plug, but it IS important!! Just one more thing to look for! Wight Kind Regards, Bill

[mbowen]

That's almost certainly what has happened, assuming the car has not been in a flood. I can think of a couple of reasons this might happen: 1. Too much oil in engine pan. 2. Water in oil pan due to leaking gasket, raising oil level. 3. Running car with problems in 4th main/u-joint/driveshaft bushing. 4. Parked on steep incline with front of car up, or jacked up.

Thank you Pat. I have jack stands under the frame about even with the flywheel but the car is in a fairly level attitude. The last time I checked the engine oil it was between the two petcocks. Are there any in-car checks I can do on the 4th main/u-joint/driveshaft bushing? In the little bit of driving I’ve done in it I didn’t notice any unusual drivetrain noise, even up to about 40 mph.

[Scott_Conger]

Engine life is inversely proportional to road speed. Your car was not designed to hold up to very much 40MPH driving when new, and 100 years later, unless your car is prepped and built for it, it will hold up even more poorly to very much 40MPH driving. For starters, rethink your driving needs.

As mentioned by others, you either have a missing plug on the output shaft or a completely beat-out 4th main (giving you all the more reason to take it easy on the speed).

[MichaelPawelek]

[mbowen]

Don’t worry yourself Scott, I only got it up TO 40, but didn’t sustain it for any amount of time. Where I was driving I only have a half-mile straight and I was surprised to see it go that fast and immediately backed off.

[mbowen]

Another thing to check is the "plug" inside the transmission out-put shaft. Its a bit hard to describe, but there should be a "disc type freeze plug" inside the transmission just in front of the U-joint. If its not there, there will be a tremendous amount of engine oil running down the torque tube and ending up in the differential assembly. A lot of folks don't know about the plug, but it IS important!! Just one more thing to look for! Wight Kind Regards, Bill

Thanks for this info Bill, that’s the next think I’ll check. Is it accessible through the transmission cover?

[DHort]

I think the only way you can check it is by removing the rear axle. This is not difficult. You just need to raise the car high enough to slide it out and have the frame well supported while you do it.

[Norman Kling]

I will add a few things. If our 4th main is a bit loose, and you have the accessory oil screen at the top of the transmission, you could have a bit more oil at the top back of the transmission. If you turn the 4th main 1/4 turn the oil hole will be turned to the side and since the bearing is a bit loose, it should get enough oil. If it is a snug bearing, then the oil hole should be at the top. Also fully packing the U joint and the oil cup behind it on the front of the driveshaft will help stop some of the oil from running down the shaft.
Those are two things you can do without spending a lot of money. Also check the engine oil. If it keeps getting low and the differential keeps getting full, you might need to replace the 4th main.
Norm

[MichaelPawelek]

[mbowen]

Thank you David, Norm, and Michael. Since my last post I’ve perused my copy of the MTFCA’s “THE MODEL T FORD TRANSMISSION” and found where the plug goes. I can see why the drive shaft would have to be dropped to check for the presence or absence of the plug. If it’s missing it looks like the transmission would have to come apart to install it.

[JTT3]

So if you do find that oil is leaking out through the tail shaft and you don’t have a wallowed out 4th main a simple fix so you don’t have to pull the engine, though that’s probably the best solution. First if it is your forth main being bad, measure the OD of the shaft and contact Gene French and he will machine you a repoured 4th main to replace it for a very low cost. I say that because the simple fix will require you to loosen the rear axle to remove the drive shaft/ universal anyway and while your there you can replace the 4th if needed. The advice on filling the universal with grease is right on target too. That said, the simple solution is to drive an over size rubber plug into the tail shaft deep enough that it doesn’t interfere with the depth the universal needs to go inside the tail shaft. The rubber plug needs to be driven in so that it conforms to the walls of the shaft tightly. I’ve seen this done with a friends motor he rebuilt and forgot to put the metal plug in the tail shaft. That’s been years ago and it stopped the oil flow into the rear axle. It’s still working. Sure beat pulling the engine and taking the tranny out to put the metal plug in. Just a suggestion from a shade tree fix, remember the rubber plug must be oversized and forced in with a big flat rod or punch and a BFH. The rod / punch needs to be large enough that it covers most of the opening but not so big that it can get jammed in the square hole as you drive the plug in but not so small that you could punch through the plug. You can find the rubber plugs at Lowes. Your mileage my vary. Good luck.

[Craig Leach]

Hi Miles,
Had you checked the Diff. oil before or was this the first time? Was there a puddle under the U/joint? Could this be a issue that you got with the car when you purechased it. May have been a build up from a long on going problem. Engine oil should not fill the rear end but a small leak over years before you purchased the car could be a explanation. The oil level in a not running T should not be so high that it will run out of the engine into the drive shaft and the rear end unless it has a extra gallon of oil in it. I know people that have not seen a leak under the rear end and have not checked it for years.
All of the reasons offered are very good possibilities for the over full rear end and should be checked but unless the rear end fills up rapidly with motor oil it may not be a real critical problem. change the the gear oil & watch it to see how fast it fills up. To many new ouners loose intrest by being overwelmed by little issues that can be delt with while enjoying the hobby. J.M.H.O.
Craig.

[Steve Jelf]

If you want to pull the rear axle so you can look inside the square hole, here's a video. Note that this method doesn't require a spring spreader. https://www.youtube.com/watch?v=8mZzAt9Q_4k&t=310s

[dykker5502]

oups! i think I have to check this before my engine goes back in the car!! Thanks for reminding!!

[MichaelPawelek]

My 19’ Touring might have had this problem at one time in the past but I rebuilt the engine after I bought it so I will never know. The previous owner had drilled a drain hole on both sides of the rear axle housings just inboard of the backing plates and just let excess oil drain onto the ground.

[Jerry VanOoteghem]

Miles,

All of the above advice is great. However, since the car is new to you, I'd suggest a wait & see approach to your problem. Unless you checked the differential oil level since you've owned the car, you don't know how long it took to accumulate that much oil in the diff, or how high an engine oil level the previous owner maintained, or even how the car may have been loaded for transport to you, (e.g. was it ever loaded onto flat bed car hauler that pulls the car up a steep incline?).

I would try to suck out whatever oil is in there now, fill with the proper lube, at the proper level, and check it every so often for changes.

[henryford2]

I agree with Jerry, my suggestion would be to drain the rear end and replace with 600W, hard to tell if someone had earlier replaced the 600W with a "modern" 90W or 140W. The match up between axle halves is not the greatest to begin with, with or without the thin paper gasket. A lot less work that tearing everything apart. JMHO. Enjoy

[TRDxB2]

I think Jerry, above, has a good point. It could be that some previous owner used some heavy weight motor oil to lube the rear axle too , you never know . I wonder too, if it is a serious issue, wouldn't there be signs (a huge mess) of leakage at the ball cap end of the drive shaft as well?

[Rosenfelder]

I've had the same issue with my '27. The plug in the u-joint was OK. The engine was recently professionally rebuilt, and has not had other problems. I just keep a close eye on engine oil level before each run.

[TXGOAT2]

Maintain engine oil level halfway between upper and lower petcocks and be sure that the oil filler cap is not restricted. It has some limited ventilation function, and if it is restricted, It might increase crankcase pressure which would tend to increase oil leakage at all points.

[mbowen]

Miles,

All of the above advice is great. However, since the car is new to you, I'd suggest a wait & see approach to your problem. Unless you checked the differential oil level since you've owned the car, you don't know how long it took to accumulate that much oil in the diff, or how high an engine oil level the previous owner maintained, or even how the car may have been loaded for transport to you, (e.g. was it ever loaded onto flat bed car hauler that pulls the car up a steep incline?).

I would try to suck out whatever oil is in there now, fill with the proper lube, at the proper level, and check it every so often for changes.

Jerry, that is exactly my plan; thank you for confirming. The car was picked up from the previous owner and delivered to me in an enclosed trailer with a shallow ramp door. This was the first time I’ve pulled the differential plug since I’ve had the car. I’ve checked the engine oil several times and it has always been between the petcocks. It’s been sitting for several months now, and there are small drips under car but no major puddles. There is some oil under the left rear wheel hub, but I suspect that is from the differential being overfilled. I do plan to suck out the remaining oil, probe around with my borescope to make sure it has bronze thrust bearings, refill with 600W, and keep an eye on it. I’ll also pack some grease in the 4th main and u-joint just because I haven’t yet done that on this car.

[Oldav8tor]

Miles,
Boy! Did you get some great advice! I'll add one little thing - if the brass (originally Babbitt) bushing at the end of the drive shaft near the universal is badly worn it will let any oil that makes it that far easily enter the drive shaft tube.