4L80E w/ Transmission Drum E-brake Leaking

[jcwren]

I recently acquired a '99 C3500 HD, and it's got the 4L80E with the drum brake. It's leaking a fair amount of ATF from what appears to be the extension housing tail shaft, into the drum brake housing. It's hard to tell for sure since there's so much fluid all over the bottom of the truck. The previous owner told me they had swapped the 4L80E (don't know what happened to the original), and they got frustrated when it started blowing ATF. It's from a tree cutting service, and has a chip box on it, and they didn't have time to mess with it.

I've pulled the driveshaft and the extension housing. It has two bearings in it, and they appear to be lubricated by a passage from the transmission that puts ATF into the bearing housing closest to the transmission, and then I assume just fills the housing with fluid. I don't see where there's a return passage, so maybe it's not circulated, or maybe I just don't know what I'm looking at. This is my first experience with the 4L80E.

The output shaft seal looked OK, but it was hard to get a good look at it, and frankly I had to wreck it to get it out. The O-ring between the transmission and extension housing looks fine. After removing the extension housing, it looks like the output seal on the transmission is weeping (maybe a lot more when the transmission is turning), but if the extension housing does fill with fluid, would that even be an issue? The bearings seem OK. I cleaned up the housing in the parts washer then hosed out the bearings, and they turn freely with very little wobble.

The yoke does have a rough area on it, as you can see in the picture. I'm not sure if taking that down with emery paper may end up removing too much material. Perhaps I should have it welded up and turned down to spec if need be (trying to find a replacement yoke seems next to impossible and the one I did find the person wanted waaay too much for. If you have one you don't want that's in better shape, I'd cheerfully pay shipping and some beer money ).

I am going to replace the transmission output seal unless the wise people here say there's no need, and of course replace the housing o-ring (because I already bought one) and the extension housing output seal. Is there anything else I should look for that may be causing the leak, like the extension housing getting pressurized? I have not yet checked the vent line, it started raining before I could get to that.

Hoping that someone here has some experience with these, and maybe knows of a common issue or a simple fix.

Thanks!

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[stutaeng]

Yes, the 2wd version of the tail housing is pressure lubricated. The bushing at the yoke has holes where the oil comes out. From there you can see the bottom of the housing is sloped. The oil goes down to the pan.

Can you post a photo of the rear seal? Seems like that's what I would replace too.

I've never messed with the 4L80e that have that drum brake, just the regular ones. Is the yoke a bolt-on style?

That surface looks pretty rough. I'd like to see what the bushing on that tail housing looks like. Maybe it's worn and allows the yoke to have too much play, allowing fluid to seep out of the seal under pressure and rotation?

 

[jcwren]

Yes, the 2wd version of the tail housing is pressure lubricated. The bushing at the yoke has holes where the oil comes out. From there you can see the bottom of the housing is sloped. The oil goes down to the pan.

Can you post a photo of the rear seal? Seems like that's what I would replace too.

I've never messed with the 4L80e that have that drum brake, just the regular ones. Is the yoke a bolt-on style?

That surface looks pretty rough. I'd like to see what the bushing on that tail housing looks like. Maybe it's worn and allows the yoke to have too much play, allowing fluid to seep out of the seal under pressure and rotation?

Do you mean a picture of the rear seal on the transmissions, or the one on the extension housing? Hopefully the former, because the latter is metal shards after the removal process. It did not yield willingly If it's not raining here tomorrow, I can get a picture of the rear seal.

The yoke is a bolt-on style, although the yahoos that did the swap did not bolt it on. I had to buy a used bolt on eBay, and I'm waiting for it to arrive. I'm sure I could have found a bolt at the hardware store or maybe McMaster Carr, but those thick washers are hard to find.

There is no bushing on the extension housing. Maybe there's supposed to be, but there's not one there. I do have a non-drum brake housing the guy gave me, and I know the bushing you're talking about. Here's a picture of the drum brake extension housing.

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[stutaeng]

Yeah, the regular ones just have a bushing. You can see the groove and hole for lubrication. Almost looks like an engine main bearing.

That looks like a roller bearing on yours. That makes sense, given the extra weight back there from that massive drum.

Does the roller bearing have an play in it? How is the feel when you insert the yoke? Any slop?

That set up for that transmission is not common at all. Only the C3500HDs and the RVs have them. It had to do with the internal parking pawl having a limit; the vehicles with GVWR of 15k lbs got the drum.

l've seen some drum setup transmission for sale here, but I've never messed around with them because I read you have to swap output shaft to use them in a regular truck.

On the first photo you posted, there was a seal there? You already removed it, right?

 

[jcwren]

Yeah, the regular ones just have a bushing. You can see the groove and hole for lubrication. Almost looks like an engine main bearing.

That looks like a roller bearing on yours. That makes sense, given the extra weight back there from that massive drum.

Does the roller bearing have an play in it? How is the feel when you insert the yoke? Any slop?

That set up for that transmission is not common at all. Only the C3500HDs and the RVs have them. It had to do with the internal parking pawl having a limit; the vehicles with GVWR of 15k lbs got the drum.

l've seen some drum setup transmission for sale here, but I've never messed around with them because I read you have to swap output shaft to use them in a regular truck.

On the first photo you posted, there was a seal there? You already removed it, right?

It is a roller bearing in the drum brake extension housing. Actually, two of them. And correct, there was a seal there. No play that I can detect when the yoke is the bearings. I need to take a picture of the back of the transmission to confirm with y'all how the extension housing drains back. I don't remember seeing a hole near the bottom, but there is an O-ring with some kind of fitting that's to the upper right of the output shaft (as you look at it from the back). So either the fluid is unable to drain back and it's getting puked out, or the yoke just isn't sealing in the bearing because of the roughness.

I have confirmed that it's true, that if you try to swap this to a conventional housing, or a conventional housing to an extended housing that you will need to replace the front section of the drive shaft for a 2 or 3 piece drive shaft, or modify the length of a 1 piece drive shaft. That's what the previous owner was going to do, but in my mind that's pretty stupid, as it completely relies on the parking pawl to keep it from rolling. And, as you mentioned, the parking pawls do have a limit.

 

[stutaeng]

It is a roller bearing in the drum brake extension housing. Actually, two of them. And correct, there was a seal there. No play that I can detect when the yoke is the bearings. I need to take a picture of the back of the transmission to confirm with y'all how the extension housing drains back. I don't remember seeing a hole near the bottom, but there is an O-ring with some kind of fitting that's to the upper right of the output shaft (as you look at it from the back). So either the fluid is unable to drain back and it's getting puked out, or the yoke just isn't sealing in the bearing because of the roughness.

I have confirmed that it's true, that if you try to swap this to a conventional housing, or a conventional housing to an extended housing that you will need to replace the front section of the drive shaft for a 2 or 3 piece drive shaft, or modify the length of a 1 piece drive shaft. That's what the previous owner was going to do, but in my mind that's pretty stupid, as it completely relies on the parking pawl to keep it from rolling. And, as you mentioned, the parking pawls do have a limit.

Actually some of those transmissions configured like that don't even have parking pawl! You see by dropping the pan, but not recommended anyways.

Since you mentioned they swapped the transmission (and I mentioned the output shafts are different for the regular truck transmissions...) I wonder if the output shaft is the correct one? They didn't rebuild the original transmission, right? It got swapped?

You can do a search: Performancetruck.net has a thread on the different output shafts available. May be worth a look.

 

[jcwren]

Wow, I'm surprised some transmission don't have a parking pawl. I'd figure that be some sort of liability issue with not having one in an automatic, given the way drivers are conditioned.

I'm not how the swap was handled, e.g., if it was just a completely different transmission, if they swapped output shafts, or what. I'll see if I can find out, but I'm not confident on getting a good answer.

Unless the difference in output shafts is just the length, and it's on the order of a few millimeters, I think this is likely the correct shaft. The yoke engages fully on the splines, and the end of the output shaft seems to be about flush with the end of the yoke (maybe 1/4" shorter when the yoke is seated). But I'll definitely check the link you mentioned. Hopefully that can be verified without having to pull the output shaft for a measurement.

 

[stutaeng]

What I meant to say is that some of the transmissions with the brake drum don't have the parking pawl...at least that's what I've read.

Here's the link I was thinking about. It's actually a different website:

4L80E output shaft variants - LS1TECH - Camaro and Firebird Forum Discussion

Automatic Transmission - 4L80E output shaft variants - Are there just 5 different output shafts styles on the 4L80E? https://www.pirate4x4.com/forum/attachments/general-4x4-discussion/318842d1186591194-4l80e-th400-behind-496bbc-dsc00132.jpeg I've read that yoke selection for the 4L80E depends on...

ls1tech.com

 

[jcwren]

So it looks like I have the slip yoke output shaft. I can't tell how well this will work, as I suppose it could allow the yoke to slip out of the seal. What I don't understand is where there's any slip if bolt-on yoke is used. The stub shaft universal would bolt to the yoke, and the back of the stub shaft has no play as it's bolted to the frame. It seems like any front-to-back flex in the engine/transmission is going to yank on the stub shaft pretty hard. There is, of course, the slip joint between the stub shaft and the propeller (long) shaft for any movement in the rear end.

I also haven't found how to remove the sleeve (can looking thing). The service manual illustrates it being there, but doesn't say if it should pull off or not, or if it's even used with the long heavy duty fixed yoke (2nd picture, which is the correct output shaft for the drum brake).

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[stutaeng]

So you don't have that longest output shaft then? Um. The other difference of the transmissions with the drum brake setup is that they (or some?) had straight cut gears on the output carrier gear set. Although it was once thought those are stronger for drag racing and stuff like that, I think the consensus now is they had those due to some thrust loading...

Speaking of which since you mentioned you don't seem to have any slip: can you see how much end play you have on the output shaft. Should be very little. With a dial indicator on a rebuild, somewhere around 9 thousands. By "feel" it should be minimal.

I believe the slip occurs on the 2 piece driveshaft, if that's what I'm understanding you have.

That sleeve you can gently tap out with a hammer, but usually needs to be replaced once it's removed...I really don't know if that sleeve should be used on your yoke or not.

There's a member on the LS1tech website that's a former Hydramatic GM engineer part of the team that worked on the 4L80e.

I posted a thread here a long time ago about a very interesting thread on that website. I'll see if I can find it. Maybe you can reach to him and ask. Edit: his username is vorteciroc https://ls1tech.com/forums/automati...9-can-i-get-my-6l80e-shift-like-my-4l60e.html

Another guy who probably knows is Jake's Performance. They specialize in TH400/4L80e. They are in Bridgeport, Texas.
Edit: http://www.jakesperformance.com/