The Stovebolt Site Forums The Shop Area Driveline front transmission seal 1939 4 speed

I think I'm losing oil out the front of my 1939 4 speed transmission 3/4 ton pickup. I can't find a seal in the schematic. What keeps the oil from escaping out the front? If there is a seal for the front, where is it located? I don't want to fight the transmission out and back in without some idea up front.

Thanks.

If I am remembering correctly, there isn't a seal in the older 4 speeds at the front. There is instead a spiral groove in the input shaft that helps to draw the oil back into the case from around the input shaft during operation. These transmissions are somewhat sensitive to oil level, with the correct level being slightly below the fill plug. Even with the correct level there is usually some seepage at the input shaft, especially if you park on a downhill.

2ton

I thought that was the case, but I couldn't remember. I've had the transmission out a few times, but I didn't take pics of it. I should have. The various schematics that I found are hard to read closely. I also have to check the differential to see if any oil is escaping down the tube. That has an oakie bushing, but one never knows for sure. I've stepped up to 140 weight from 90 weight. That might help a little. Tomorrow, I have to measure the dip stick on the crankcase to make sure I have that set up correctly. Lots of little kinks and turns with the old truck. I'll get a little deeper into it, tomorrow. Thanks for the response.

I think I located the problem. The front bearing retainer has a hole in it. I had that installed with the hole on the bottom side. After pondering things a bit, I think the hole is suppose to be on the upper side, and is there for venting as oppose to oil release. There are threads on the interior of the bearing retainer. I assume those are for the purpose of gravitating escaping oil back into the transmission. With the hole on the bottom, the oil was encouraged to escape towards the clutch. I will try it with the hole on the upper side, and see what happens.

The hole in the bearing retainer is supposed to be on the bottom so that excess gear oil can spill out onto your throw out bearing instead of your clutch disk.


The 4 speed vents through the shifter.

...which puts me back to square-one. The transmission is losing fluid, and it isn't gravitating down the torque tube. All fresh gaskets. Is it possible that something is amiss in the front of the box but behind the bearing retainer?

Ok, next possible dumb mistake by me. The last time I put the transmission together, I fashioned a gasket between the front bearing retainer and the case. I just check tolerances a bit closer. The retainer will fit fine without the gasket. With the gasket, the bearing, gear, and oil slinger all sit slightly forward. Perhaps that lets the slinger too far forward, thereby letting excessive oil gravitate out the front. Do you recon that's possible, or am I again flogging a dead horse?

I just found a schematic indicating that there is to be a gasket between the bearing retainer and the case, but it's still possible that I made one of material that was too thick.

I would suggest that the cold oil level in the tranny should be about 1/2" below the fill hole. That can make a difference.

OK, that was on my list. The book says 6.5 pints. I was going to fill with just six. On the last go-around, it appeared that the box was about 1/2 down, though. Lots of oil under it in the garage. I'll have to also try to look at all the seals/gaskets. I did find the gasket for the retainer on the master parts list, but it doesn't give the thickness. Still searching.

thanks

I believe the gasket thickness is supposed to be the thinner of the two available thicknesses on the market (0.015).

Getting the non-syncro 4-speed to stop dribbling from the many unsealed orifices is problematic. My truck was leaking out of the bearing retainer weep hole whenever I drove down a steep slope. It has reached somewhat of an "eqalibruim" with fewer leaks when the oil is about 1/2 inch below the fill plug when cold (@ ~50 degrees F). Your issue may be no more than that.

When you get driving your truck, and when operated at speed, oil will most likely seep out of the top cover shift shaft rails, and even out of the shifter base. Before you started cleaning up your project, you do remember the thick accumulation of greasy road grime in that area don't you? I almost think GM engineered the process of utilizing grime to seal low pressure joints, definitely not as tight as modern engineering.

Are you using a gear oil that is okay for yellow metals? There are a few bronze bushings in these transmissions. I am using a GL-1 straight 90 weight in mine.

Paul,

I did have the wrong (modern) oil in it, but just managed to find a five gallon pail of the correct stuff on line. Yes, the whole underside of the truck was bathed in residue. I bought the truck in '61, so I have a pretty good idea of the history from that point forward. Prior to that, it was a county truck, and the county wasn't nice to it. I just spent about 4 years bring it back to pretty good condition. I rebuilt and installed a '58 235, but I might have erred on the rear main seal. That or a miss-calibrated dip stick might be reason for some of the oil residue, but I still think I lost too much out of the transmission. I have a sneaking suspicion this isn't the last time I will pull the tranny. Today, I'm going to try to engineer the cross-member to make it easier to remove. One step at a time. I will run the fill at least half an inch under the filler hole.

Thanks,

Gary

Ok, re-engineering the cross member for easy removal is out. I didn't realize that it's sandwiched between the frame members in a fashion that makes removal almost impossible. I know the box can be installed without doing it, because I did it before, but the process is more difficult.

I decided to fill it with oil before installing. That doesn't work as the front lower mount holes are open to the interior of the box. The oil comes out those holes. I have found that putting a plumbing "L" in the fill hole makes things a bit easier, but the 140 weight fluid is still a slow go when filling.

Too many lessons and not enough time.

Gary,

Wow, I guess since you have owned the truck since 1961 you certainly do know its history pretty well. Most of us don't have such a clear provenance, but then you are limited in blaming past owners for things that are messed up.

The torque tube transmissions look much more difficult to install than open driveshaft versions.

Have you ever taken out your shifter lever? It is very easy and makes filling the transmission with oil a breeze. The 140 GL-1 should help some with the leaks but shifting will be difficult at first when cold. I would still fill to a level approximately 1/2 below the fill plug. I hope it works for you.

Paul

Yeah, I take the blame for much that is wrong, but I've had the truck in both Canada and Mexico, and from the Pacific to the Atlantic and back all under it's own power, and it's still running, I must have done a few things right along the way. Apropos of not much, I "found" the truck dead in a pasture when I was in high school. I paid the guy the princely sum of $100, which was a princely sum in the days of yore.

I'm slapping myself on the forehead. Yes, I've had the top off, but...I didn't think about doing it to fill the box with oil. It also will be much easier to install that way.

It shall be done...after lunch and a nap. I will also cut out a crude cover for it, and put it aside for future action. Piece of cake, right?

Thanks for the swift kick in the...awareness.

Gary

Question! For those transmissions that don't have seals and just slingers on the front bearing, is it possible to replace the front bearing with one that is sealed on the side that is pointed out and no seal on the side that points into the transmission case? I plan on replacing all the bearings in my 39's 3 speed this winter.

Rick

Rick, I don't know definitively but it sounds like a great idea. I cant think of any harm. The reason that that type of bearing was not used in "the day" was that it wasn't invented yet.

I would like to hear from some other folks.

Gary, I trust you know these old beasts better than I would claim, I wasn't even a thought in 1961.

Paul

Rick,

An interesting thought on the sealed bearing (or bearing with seal?). A bearing is a bearing, if the dimensions are correct. It would have to be thinner to accommodate a seal. Paul did mention earlier that the throw-out bearing gets it's lube from the weeping, but...I don't know if a throw-out bearing needs much lube. Interesting thought. I remember having a booklet from something like "Chicago Bearing" that had all kinds of dimensions and sizes available, and I also remember replacing a bearing in a Shop Smith multi-tool with a much cheaper better bearing from an Arctic Cat Snow Machine. The guy at the Napa store spent a lot of time digging to find the right dimensions. I guess the worst that could happen would be a growling throw-out bearing.

I was pondering why a seal wasn't placed in the bearing retainer. I guess if someone could get really cute in a machine shop, it might be possible to cobble that together. Food for thought. I gotta' go sit cross-legged with my tongue in just the right place and ponder some more on this.

Paul, I don't know if I know the beast better than you, but I have been with it for a few years.

Gary,

Let me clarify, the throw out bearing does not get any lubrication from the transmission gear oil. The weep hole will drip onto it, but there is no benefit or apparent harm either. My point was that in the absence of the weep hole in the bearing retainer would lead to weepage much farther forward on the input shaft which would be close to leaking on the clutch disk (definitely a bad thing).

Paul

OK, that makes more sense. That's the logic that I used when I first re-installed the front bearing cap. So...there should be no damage if the output side is sealed. This needs to be examined a bit closer. I did a lot of digging, and didn't find the printed specs on the actual dimensions of the bearing, but I can measure it, and then search a bit more for something that would comply with Rick's suggestion.

Again, thanks,

Gary

Take a look at the condition of the bearing nut/oil slinger and the inside surface of the bearing retainer where the two match up. If one or both are worn excessively it could cause the problem you are having. The gap between the two components is about all that keeps the oil from working it's way out the front.
Fred

The is a bit of rust on the slinger itself. That indicates that there is probably more rust in the lower parts, but the tranny works fine, so I'm not going beyond that. I'll have to dig a bit more deeply on the matching surfaces.

I did notice, however, that I might have the clutch not perfectly adjusted, and that could let the bearing retainer block the weep hole almost continuously. That would mean much of the oil is being forced down the shaft and closer to the clutch surface. I do have some indication of a contaminated clutch surface. That could be part of the cause. I don't think there is any oil coming out the rear main on the engine as that side of the fly wheel is completely dry.

I will pay more attention to the clutch adjustment, and I will check the mating surfaces on the slinger/bearing.

Back to the shop.

Thanks

Gary

The transmission front main shaft bearing is GM part number 903209, or New Departure 3209.

This part interchange link may help with your quest:

http://www.kakapart.com/oem/partscrossinterchange/new-departure-3209.html

The bearings all appear to be OK. The box works well when together, so I'm not really worried about the bearings, but I will squirrel-hole the numbers that you, Paul, sent. All info is good info.

I did go out and press off the out-shaft bearing. For those who might want to try it, I did need a large press and some degree of finesse to get it off (in about a 1/16 or 1/32 first, and then out). I did that because the oil slinger was loose with play. I pulled all apart, cleaned the parts well, and put on a bead of silicone gasket maker, and then pressed it all back together. That should stop any seepage around the center of the slinger and the shaft. I will work on reassembly after lunch...and a nap. I will also pay closer attention to the clutch adjustment.

If all of this works, the old truck will be as good as new and ready for another 75 years on the road.

Again, I do appreciate all the input. These old beast are
sometimes hard to parse.

Many thanks,

Gary