Bought a super nice looking 2004 XK8, which I love, but have been dealing with "Gearbox Fault" issues since I got it 18 months ago. The TL/DR version of this question is: Has anyone else had leaking fluid from the transmission bell housing? If so how did you deal with it?

Detailed description of the issue:
Ever since I got the car I've had these problems: When "Gearbox Fault" appears on the dash (about 10% of the time I take the car out) it prevents up or down shifting until it is cleared by restarting the car. When parked a few drops of transmission fluid leaks under the car after being driven. After checking for codes the "Transmission Control Module CAN" reports "P0783 3-4 Shift Malfunction".

Had the transmission fluid replaced professionally which resulted in a slow leak totaling about one or two cups of trans fluid over 48 hours while the car was parked. The fluid was then topped up, and again leaked about the same amount and rate. Since then the car has gone back to leaking a few drops when parked after being driven. Looking under the car it seems like there is not much fluid leaking while the car is driving as the underside of the car shows no oil build up.

Looking at this ZF Trans troubleshooting guide indicates that the fault I am getting could be caused by low fluid from a leak. The leak is from a 2" diameter hole in the bottom of the bell housing. The hole has a loose fitting rubber cap on it and the fluid leaks around it before messing up my garage floor. When the car was in the shop I could look up in there and saw the fluid leaking in a straight line from the center of the bell housing behind the torque converter.

I'm guessing I need to replace the seal between the shaft in the bell housing and the rest of the transmission. Which I also assume means pulling the transmission. Has anyone had any experience with fixing this? Any help is greatly appreciated.

 

For the error code, start by checking the condition of all the wheel bearings, especially the driver side rear. They need to be fairly tight. Next, check the condition of the ABS reluctor rings, and make sure they are SOLID to the axle. If they slip somehow, the car thinks the vehicle speed changed and the trans is in the wrong ratio. Next, read up and double check that the fill procedure was done correctly. It is temperature-based and needs to be done properly. Your "leak" is likely a sign the trans is over filled. I would not start by assuming the trans has to come off.

From a larger perspective, you might want to do an extended maintenance to replace the fluid, pan/filter, bolts, and also pull the valve body to get to the tube seals and that bridge seal. Also do the connector sleeve at this time. This is all done from under the car, and there are kits on eBay, so this is not terribly expensive. Mercon SP is a good alternative fluid, way cheaper and matches the spec. It comes into play when you do another fluid flush later to get more of the old fluid out as the torque converter does not drain. Of course check the big pan magnets for sign of metal shavings, a sure bet of internal problems.

Next step is to validate you have the last software update (TCM reflash) and then do a reset of the adaptations (software/diagnostics procedure). This will trigger the "learning" mode for 100 miles so the solenoid can adapt to the new fluid.

Once all of that is done, you can re-assess. Next step would be to focus on the valve body. Cheaper procedure is to get a replacement solenoid or a full kit and swap them all out. Of course, there is the risk of throwing good money after bad, so maybe getting a complete rebuilt valve body might be best at that point if ti comes to that.

FWIW, folks have called the ZF tech support line (Ericson industries?) and have received great advice from experienced techs. You can try that too.

Best of luck, keep us posted.

 

Transmission vents are often routed into the bell housing area. An overfilled transmission will then relieve itself through the vent, right where you are seeing a leak.

The other options for the leak are unpleasant

 

The vent is on the upper left near the front, does not drain into the bell housing.

 

The only experience I've had of a failed transmission input shaft seal was on an XJ40 but it dumped the fluid out through the bottom of the bellhousing at an alarming rate. I think (and hope) fmertz is correct in suggesting your issue is an overfill.

Graham

 

Thanks everyone for your input.

I just checked the bearings by jacking the wheels up and trying to rock them side to side and top to bottom and they seem good. There was a little rocking top to bottom in the back but not side to side at all, so I'm guessing that play is in the mounting parts and not the bearing.

When I had the transmission fluid replaced I talked with the shop to be sure they knew about the procedure I found here, including running the engine but not too hot or cold etc. So I'm pretty sure they did it correctly. They also installed a new pan and seals as well as replacing the bridge gasket. So I'm running out of options on what would cause this leak.

Since the leak is only after driving and has persisted for 18 months it seems to rule out an overfilling issue.

I'll take it to a transmission shop today, see what they say and update this post.

 

What fluid did you use?

 

I'm not sure. Seems I recall asking about this and was assured they knew what they were doing by adding the correct fluid. But the specific fluid I don't recall. This was one year ago.

 

So I just got the XK8 back from the transmission shop. They pulled the transmission to reseal the front pump which they said was leaking. They also replaced the rear main oil seal. Bill was $1090 labor and $96 in parts for total of $1256. They said the engine still has a leak but from the other parts of the engine. I took a few photographs and it looks like a green fluid is leaking from between the bell housing and the engine. So I'm going to take it back in to see if they can tell me why it still seems to be leaking from that location.

On the plus side after a few trips it has not had the dreaded "Gearbox Fault" message yet.
Here is a pic of the leak:

 

The only greenish fluid I can think of would be washer fluid leaking from around the scuttle.

 

So I took it back to the transmission shop and they said the fluid pictured above is excess shaft lubricant that should clear up in a few days. This makes sense as the consistency of it is grease like (at room temperature) and not like transmission fluid or motor oil.

However the dreaded "Gearbox Fault" returned on the 6th or 7th start. Again no detectable slippage or roughness in shifting, just the fault. I left it in the shop which will diagnose it again. My fear is that this is due to some "gremlin" that is either hard to find or otherwise just not able for a transmission shop to profitably fix and sell the fix to customers. They did do as I asked and fixed the leaks, as far as I can tell, but there is apparently something else going on. Will keep this thread updated.

 

I got the car back from the Transmission shop and they recommend flashing the Transmission Control Module (TCM) and resetting the adaptations. This is also recommended after fixing a leak by the trouble shooting guide linked above in my original post. After doing that, see if codes re-log and if so they recommend rebuilding the valve body. As I am going to be away from the car for two months I will have to wait to do any of this. I'll update this thread or maybe start another if the code re-logs. However since this thread is about the leaks in the bell housing, it seems this part of the issue has been resolved. I thought I had one leak but actually had two.

One leak was coming from the transmission front pump. This showed itself as a leak of about half a quart of transmission fluid after the fluid was topped up. The fluid dripped out very slowly over a 48 hour period. The transmission had to be pulled to fix this leak but the parts were relatively inexpensive.

The other leak was in the engine rear main seal. This showed itself as a few drops of motor oil leaking from the bell housing after each trip in the car. Again the transmission had to be pulled to fix this leak.

 

TLDR: Resetting the transmission adaptations at the dealer seems to have fixed the issue.

Update: I followed the Transmission troubleshooting guide referenced in the original post and it seems the P0783 code is fixed (fingers crossed).

After fixing the leak in the trans, the code continued to appear for several months. Each time it appeared I restarted the car, sometimes while still moving by shifting to neutral. Was quite a pain.

I finally took it to the dealer to have the software in the Transmission Control Module (TCM) updated. They were following the checklist, just like I was, and took a look at the Transmission Air Intake Hose (really a manifold) and found groupings of small holes where the manifold was exposed to heat and bubbled up a bit. The holes were only visible when shining a flashlight through. This may not of needed to be replaced, but I went along with them and did it for $280. When the code came back I returned to the dealer to re-flash the TCM. They said their software said there is no update they have available to the TCM. They also said, based on experience, the trans would likely need to be replaced for ~$6000. After practically pleading with them to reset the Transmission Adaptations using the dealer tool, they did it, reluctantly, for $179.

When leaving the dealer, first thing, the code reappeared. Dang! The transmission was also very choppy and going through some fits, especially when stopping and starting. I continued to drive and by the time I got home the transmission was feeling good and has been good ever since (about a week). So, so far so good. If the code reappears I'll post another update.