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4T80e Fix for leaky driver's CV shaft / output shaft bearing

40851 Views 52 Replies 26 Participants Last post by  brmurph
I had some interesting transmission issues when I first got my Deville and I had to pull the transmission out twice in the middle of winter. So once my new transmission developed the dreaded driver’s side output shaft leak I decide I was going to come up with a fix that didn’t involve pulling the transmission again. Hopefully what I figured out can help out a few people.

Doing a bunch of internet searches gave me the root cause of this issue. The output shaft bearing inside the transmission gets worn down and as it does the output shaft starts moving. Once it moves enough the output shaft seal cannot hold the fluid. The output shaft pulls the seal out of round and you start to get a gap where fluid will drip out of.

So the solution is simple, just replace the output shaft bearing to keep the shaft from moving. Unfortunately this requires the transmission to be removed and a costly rebuild to take place. So we need to use a substitute bearing that will take the function of the output shaft bearing.

When you look at the output shaft seal it is actually recessed inside the transmission a good amount. There is a center plate that will actually pull out. Once this plate is out there is a nice recess for a bearing to sit in.

By the way, most of these pictures were taken on the old broken transmission that I have sitting on my garage floor.

Of course you need a properly sized bearing that will fit inside this hole, but be large enough to fit around the CV shaft. Such a bearing does not exist. To solve this I had to have something made. I chose a bearing that fits just inside the opening in the seal housing. I had the inside diameter of the bearing machined out by a guy that I know so that it will slip over the CV shaft. He had to come up with an interesting method to put the bearing in the lathe since you can’t grip the outside if you are working on the inside because it will just spin. I can give you my guy’s contact info if you want him to make you up a bearing. By the way, the bearing that I chose is a wheel bearing for a motorcycle, so it should be able to take the side loading of a CV shaft and have no issues with the RPM. The over all size was a 40x62x12mm bearing.

With the proper diameter on the inside I was able to work on the outside. The overall diameter is just a tad too small for the opening. It is maybe a half mm shy of a good snug fit. So I took the center plate from the seal and fit it around the bearing. The thickness of the center plate is just enough to make the bearing fit snug in the hole. I also cut out the center of the plate so that it would not rub on the bearing part that does move.

Now comes the fun part, since the bearing is 12mm deep it will stick out of the side of the transmission case(as seen above) and interfere with the CV shaft from locking into place. I measured the CV shaft end and there is plenty of metal to do some clearancing without having to worry about weakening the CV shaft. That being said I am not drag racing my Cadillac, if you are then you may want to rethink modifying the CV shaft. The key here is to try and keep the CV shaft balanced. Ideally you would want to do this on a heavy duty lathe, but I was stuck with my angle grinder. I took my time and was careful and it turned out well. It needs to be ground until the curved transition between the shaft cover and the larger diameter piece is gone. When in doubt try putting it on and see if the CV shaft snaps into place. I would try this without the outer shim on the bearing so it is easier to get things on and off. You will also have to clean up the shaft itself if there is some kind of build up(rust).

Here is the modified shaft next to a stock one. If you are good you won't have to pull the CV shaft apart, but I found it easier to do the grinding this way.

Once the CV shaft is to the correct dimensions it is just a matter of putting it all together. I used some locktite red on the shim/center plate on both the bearing side and the seal holder side. That way it should stay in there pretty well. Once the CV shaft is locked into place there really is no way that it can come out though. It may wiggle out a bit, but not enough to go anywhere. There is too much of the bearing inside the seal holder to go anywhere.

Oh and always remember to start this by replacing the output shaft seal, the old one is most likely damaged from the output shaft movement. Not all auto parts stores seem to carry them, I have had good luck getting the seals from Autozone.

I have a few thousand miles on my car since I put this fix in and I haven’t had any issues with it. I do a lot of highway driving at 70-80mph. So if you are having this problem it may be worth trying this out, especially if your alternative is a transmission rebuild.
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Took my '04 to the dealer last week for an oil change. The advisor has me walk back and look at the car on the lift which in my case means the news isn't good. Was told the car was leaking tranny fluid from drivers side axle. Was first advised to replace just the seal and then came online and found out what this really means. Took the car to a transmission only shop yesterday and was told it was fine even though it had just left a long trail of transmission fluid about 20 minutes earlier. It's now back at the dealer and the 3rd clutch housing is being replaced. Cost will be $1400... I can't swing the rebuild or a new transmission. No other issues other than leaking fluid. Should be back to me tomorrow or Monday.
I have to say this is pretty interesting.

I tip my hat for your efforts, I guarantee you will perfect this with enough time to find bearings to suitable size.
There is a "saver" or stabilizer seal for the TH125's & 440's.

I've never seen one for a 4T80E, though.
Let us know how it holds up.
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F.Y.I. Post #1 was copied to Tech Tips. Nice job.
I have several cars in for repair with the same issue. I've been working on a more OEM style repair. I have a prototype made, so hopefully I can report back good news.
I'm really interested in how it turns out. I might need one in the near future, but I have no luxury of having access to any of the tooling that's needed to make one of those, not to mention the knowledge. It sounds like it'll save thousands of dollars. If you ever get to make more than one, please let me know, I am interested.
That's clever!

Just be aware that the worn bushing material doesn't disappear - at the very least, drop the pan and clean the metal particles when you do something like this. If you've got the transmission out to do this, also replace the side cover main fillter.
I will be selling these, but since I'm not currently a supporting vendor, I'll keep the details brief. I plan on selling the complete kit, axle and stabilizer bearing for 349. I'm not ready just yet, so I'm not taking orders. When that times comes, I'll pay the vendor fee to advertise it for sale on here. I was just wanting to let everyone know there is finally a solid repair that is pretty much plug and play. Also I commend the original author on his creativity.

Just as an FYI this can be done very easily in the car in about an hour, so there is no need to pull the transmission. Doing a fluid change is always a good idea, so I can't argue with that.


When you start selling these, will you be willing to sell just the bearing or is the axle required for it to work. And about how far out are you from having these for sale?
The axle is required since the factory axle is too large for a standard bearing. You run in to the issue like the original post stated and simply put, no one manufactures a bearing thin enough at that size. That's the reason he had to grind down the collar of his axle to accomodate. The axle that I will include has been machined to perfectly match the stabilizer bearing. I have to check the status at the machine shop doing the fabrication, but I expect to have some available in about a week.

mn_vette you are THE MAN!!!

My 03 deville was leaking bad from the output shaft seal. Bad like i was going through a gallon of fluid a week. I really wasn't looking forward to pulling the tranny or paying someone thousands of dollars to fix it. I saw mn_vettes' post on how to fix it so I thought I'd give it a try.

I pretty much followed his procedure pretty closely, but with a few small changes. I couldn't find a machine shop that would machine the inside of the bearing, so I ended up getting the CV shaft machined down to fit inside the bearing. The diameter of the cv shaft is about 40.75mm and the diameter of the inside of the bearing is 40mm. The diameter of the seal is between 38-39mm so it still fit pretty snuggly.

I drew this and gave it to the machine shop along with the CV shaft and bearing, don't mind the marks and dirt:
View attachment 186401

The machine shop didn't want to lathe the CV shaft into the lip at the base of the shaft, so I ground it down using a bench grinder and then a square edged file to get a nice 90 degree angle at the base of the shaft. I tried to clearance it only enough to get the shaft to lock in to the tranny. I didn't want any extra clearance so the bearing in the transmission seal would be pretty much sandwiched between the transmission and the hub of the CV shaft without any wiggle room. Also, I had to take the axle apart, the machine shop said they couldn't put it on the lathe assembled. Taking it apart also made it easier to grind and file it. Once I had the majority of the lip ground away with the bench grinder, I used a file to "fine tune" the clearance so I wouldn't remove more material than needed. Like mn_vette suggested, I filed a bit, then tried it on, if it didn't lock, I filed a little more then tried again.

The bearing and inner seal ring assemble fit pretty tightly in the transmission seal and I used this to drive the seal into the tranny as well as the bearing/inner seal ring into the seal
View attachment 186417

I just finished this the other day, and it's working pretty good. No more leak. I also drove the care twice 75 miles straight highway and didn't notice any weird noises or vibrations.

I broke the clamp taking apart the CV shaft so I used this from autozone as a replacement, no special tools required: Motormite/2 pcs. universal CV joint clamp kit, Part Number: 03644

I hope this helps and my bad for not taking photos of the actual install.
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It took a little while to set up the lathe, etc. but they are finally completed. For anyone interested in this repair, as soon as I update my account, I will let everyone know how to purchase.

Ebay item number 301110819072, or search for 4t80e axle stabilizer.

Just curious... has anyone tried the actual kit sold on ebay? that is listed here. I am faced with the leaky seal issue right now and must make a decision as to try the kit or bite the bullet and have the tranny dropped... Is the bearing included meaty enough to hold up? What if it ever needs replaced? or the seal needs replaced? Just want to find out if anyone has had any experience yet?
The seal can be replaced without removing the carrier assembly and is a standard off the shelf seal. As for the bearing, it isn't exposed to extreme loads and has proven reliable. It can also be replaced; however, you would have to remove the carrier since it's pressed in from the rear.

I'll add to this. Mike's fix works. It was a bitch to get in right cause the bearing assembly got slightly crooked but works like a charm after I got it straight.

And truthfully, neither the seal or bearing should ever need replacing.
I thought I would give a quick update. Since I put the bearing fix on my car(now my brothers car) we've put on over 10,000 miles without any issues. No leaks or noises. Things seem to be working great with it.
mikelawson is the part your referring to is it still on Ebay I could not find it I have that same problem in my 2004 DTS and would like to purchase your product instead of replacing my transmission/rebuilding it.If you could reply back that would be great thank you.
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