Well after having my tranny rebuilt by the ZF factory rebuilder 2.5 years and 20k it seems my tranny is on the way out. Getting 1798 and 1799 codes. It will hold speed a bit at times and hard downshifts when it is holding speed. Also, got in it today to and it wouldn't go. Stopping and turning it off usually resets it. for a while. Battery is good in fact this morning it had just gotten off a tender trickle charge cycle. Any thoughts?

This will be my last Jag so long as they continue to use ZF trannies. They are simply junk.

 

What is the age and condition of the battery? Even with a tender device, the battery can fail and cause random DTCs to be set. If you do not have at least 12.5 volts across the terminals with the ignition in the off position, the battery must be replaced.

The ZF 6HP26/28 gearbox is used by quite a few other manufacturers due to its ability to handle high torque input. Audi, Bentley, BMW, Ford, Hyundai, Kia and Rolls-Royce all use the 6HP series gearbox.

 

ZF makes most transmissions in performance cars with automatics. They have that market almost all to themselves

 

Battery is just fine, after sitting for days it will read 13.1 or 12.9. Even swapped it with the xjr battery which also is just fine.

Yeah Jag went with zf because the germans used 'em (aside from Mercedes who are smart enough to make their own). I have not had a worse transmission in my life. There is a reason why no one will actually put more than a 12 month warranty on em when they rebuild 'em.

Other symptom it is doing when lightly on the throttle it will seem like it is surging or slipping and quickly go up to 4th/5th.

Oh and it is the zf 5 not the 6.

 

I mention the battery as that is usually the cause instead of condemning the gearbox at the very start.

Similar design, five forward speeds instead of six in the later version 6HP.

 

As I mentioned already. It isn't a battery issue so move on from suggesting that. Have now swapped 3 batteries in all less than 3 years old (Well the one is 3.2 years old) and all pass both load tests. I dont' know of ant 6 speed zfs that fail well under 100k. I know of 1000s 5 speed zfs that have failed under100k. The tranny is simply junk. Wish i would have bought a XKR coupe but couldn't find one locally enough. My mistake already 3k later. In the meantime the XJR has required nothing but fluid changes and the tranny shift properly and doesn't act like it is attached to its wicked step sister.

 

I have a ZF5 in both my Jag & Audi. no problems at all.

 

Then I respectfully suggest you take the vehicle to a competent repair shop that can examine, exchange or repair your gearbox.

 

Have you actually checked what the codes mean?

P1798 CAN TCM/INST Circuit Malfunction
P1799 CAN TCM/ABS Circuit Malfunction.

It more likely its down to cabling/connectors or the control module than the actual gearbox. Get an expert to look at it before slagging ZF or Jag off

 

I hope you knock on wood as you might be one of the few that hasn't had the drum implode at 75k on the odo.

 

What like you who still after I already said the batter had been eliminated continued to offer nothing of substance beyond that? I asked simply because I am probably as good if not a better mechanic then yourself but yet nothing is adding up. Prefer not to take it into my local indie garage as he is quite backed up. Will not take it to a Jag dealer as they hire parts replacers these days who likely haven't seen a XK8 in person. Still looking for ideas. The external connectors have been cleaned and checked now. Codes have been gone since the only time I got them but yet it still shifts horribly. Almost like the engine rpms don't drop. Cleaned the Throttle body and checked the cable action. Still nodda.

 

Yeah, I checked what the codes were when i pulled them. Codes haven't been back since I cleared them but the shifting issues remain. Connections that I can find seem clean and tight.

 

Not sure I can help, but what is the condition of the ECU? Early cars are prone to capacitor leaks and have been known to fail. Folks seem to have them rebuilt with great success. One of the frustrations with a bad ECU is that faults may not be reported or logged as the ECU itself is faulty and incapable of performing diagnostics.

Same with the ABS module. The power posts in the ABS enclosure seem to separate from the board and give major headaches. You do not seem to have a lot of ABS codes to support this theory, though.

Last, I believe there have been a number of TSBs related to the instrument cluster. As you know, the instrument cluster hosts the bridge between the various data buses and could be the cause of these data communication errors you have reported.

Best of luck, keep us posted.

PS: Have you read: 97-xk8-geargox-fault-codes-72181/

 

A caustic and sarcastic tone is not going to get others on this forum to help you. I do not recall questioning your mechanical ability since that is not the issue here. A poorly shifting gearbox is the issue, so let us stay focused on that by eliminating all other possibilities prior to saying the gearbox is the problem.

If you have checked the electrical connectors and wiring loom, you can attempt swapping the control module to see if that makes a difference.

Has anyone checked the fluid level of the gearbox? Was the torque converter replaced when the unit was overhauled?

 

No sarcasm at all, just simply expect anyone with suggestions actually read what was done prior and already eliminated. Fluid level is pretty much spot on (maybe down a 1/2 quart at the best as it didn't come out when opened. I don't have another control module as I'm pretty sure it will be a tough thing to find since mine is one of the early (firth 1000 made). Tranny had to be sent out rather than being exhanged as it didn't match up with the later 97s on. Torque converter was included in the factory rebuild and they also shipped back wet with the proper amount of fluid.

The ECU is pretty much spot on, never really gave any issues, ABS module was rebuilt (ie solderd) 2 years or so ago. It acts so oddly at times. Sometime it is almost as if you are pulsating the gas pedal. Most noticable under light acceleration but it also seems to want to shift more quickly then it should. At speed it almost seems to "hold" the gas when you lift up on the pedal like the rpms aren't dropping quickly enough. Of course though I'm getting zero engine codes and it doesn't do it in park or neutral to have me think it is TPS related.

i do have another Throttle body but it isn't the easiest thing to swap out on a whim.

 

Why don't you get your transmission to the proper level. It my be causing your problrms. And if it isn't causing your problems it is a cheap way to eliminate it as a cause.
How did the rebuilder get it at the proper level. They would have to run the transmission to get it to the proper temperature and check it while it was running. Also if your cooler lines were not completely full they would make the transmission level lower.
There is a thread in the stickies the gives the proper way to check the level.
The way I do it, and it might not exactly be the correct way, is to first to loosen the fill plug while the transmission is cold. I'll have my transmission oil and pump ready in case I need to add oil. Start the car and let it get to operating temperature. Then with the engine running I get under the car and check the level. Add if necessary. Reinstall the plug and wait till exhaust cools to completely tighten.
I believe you are better to have a little too much oil than to be below the level where oil comes out of the transmission.

 

No trannies from my understanding are better lower then over filled. Overfilling leads to foaming which hurts distributing heat. I said it is if anything a little under as I didn't get a bunch out when I opened it. Just a couple drops (which is what I mean by didn't come out). Probably as close as any could be and not worth $20 to have the fluid simply leak out and get recycled.

Since the rebuilder was the North American ZF factory rebuilder I can only assume they know how much to put it and then add for the cooler line (by installer said it came with explict instructions that it was prefilled by the factory and not to adjust the amount of fluid or warranty may be voided. Also that the cooler was to be flushed.

 

It was just a thought. You said it might be a half a quart low and I haven't seen it in any manual that half a quart low is OK. And by over filling I don't mean a half a quart or more it just that I like it to flow out a little when I fill it. I think it would be hard to overfill too much unless you had the car jacked up on the right side only and the transmission would be on an angle.

 

Hi.

I got my car back with a rebuilt transmission from the ZF factory in Germany.
It was installed by a Jaguar dealer. The shifts were harsh and no good.
Checked the fluid level myself at the correct fluid temperature, and it was grossly overfilled.
Adjusted the level, again at the correct fluid temperature, and no problems since.
That dealer in Germany will never see me again.

Now for the codes. They point to communication failure between different modules. The first easy and cheap solution would in my opinion be to open all connectors, spray carefully with electrical cleaner (not WD 40 here) and reconnect.
You will probably need JTIS to find the connectors concerned.

 

Assumption is the mother of all fluck-ups. You are complaining about $20.00 suggestion to resolve your issue, really? So a couple drops of oil came out when you checked. Bend a piece of wire and check the damn level to be sure. You come for advice but are clearly emotional about suggestions?? I bought a new 2000 dodge 3/4 ton pick up and went thru 4 transmissions under warranty pulling nothing. I would still buy a Dodge. Although the next new truck was a Ford. If you follow the advice above you just may find your issue. I've had MANY batteries that test good and are JUNK!! Your tranny sounds like a communication issue to me. We hope nothing but the best for you but it sounds like your mind is already made up when it comes to Jags.