I'm puzzled now, for I understood that ZF say the 6HP26 locks up in all forward gears.

 

You do know what's involved in replacing the TC don't you?

 

Especially since the symptoms point away from it.

 

Gentlemen, a respectful word of caution, if I may. Lots of good advice on this thread, but unfortunately the two leading culprits are both expensive to repair. The general consensus has gone one way and then the other, with solid experience and reasoning behind both lines of attack. Unless something is a 100% slam dunk, I'm always leery of suggesting an expensive repair. For other problems, I'd be perfectly fine suggesting inexpensive routine maintenance items such as spark plugs, a fuel filter, etc., as it won't break the bank if that doesn't fix the issue. If I had suggested a $2000 fix and it didn't do any good, I'd feel really bad, even after going back to edit my earlier posts to make it look like I never suggested such a thing <VBSEG>.

With that said, as an honorary Scotsman faced with a potentially big bill, I like to redouble my efforts to rule out the easier stuff first. In this case, if the choices boil down to a driveshaft or the TQ, I'd suggest ruling out the driveshaft as best possible. A visual inspection of the TQ won't accomplish much, but might just find a fault with the driveshaft. For example, I'd check the torque on all the bolts. I'd carefully look over that center carrier bearing. If you see any rust streaks or oily residue, that bearing is kaput. Give both halves a good shake to see if there's any free play. Carefully inspect the center joint and the flex couplings at the end, too. (Thanks for the pic from the manual, BTW)

As far as the lack of vibration when the transmission is selected one gear down from D, that is a big clue but not conclusive proof that the TQ clutch has failed. With the TQ clutch unlocked, this also changes the amount of torque applied to the driveshaft even if the rpm is the same. The engine speeds up a little bit, too. These two changes could be just enough to avoid the resonant combination that create the vibration. Another thing you could try is lots of driving, but without selecting D. Perhaps you could find another speed/rpm combo that causes the fault, which would then rule out the TQ.

Not much help, am I?

 

I've also seen it said that even if it is the TC you can likely drive it many 1000 miles without replacing it.

I'd be hunting for more data and trying to be certain where that leads.

I'm really unconvinced it'll be the trans.

I'm not that fond of letting a problem get worse but in this case that's what I'd do.

 

not wanting to hijack this thread but I have to ask.
being a complete novice with these cars and there known problems, just how often do TQ problems come up?

 

It's actually a TC, or torque converter.

Extremely rare. Far more common is what's covered by TSB S307-14

"This Technical Bulletin has been issued to address a customer concern of a surge in excess of 150rpm during engine warm up, at a temperature of 30°C to 50°C and at a vehicle speed in the region of 40mph (64.3kph) to 60mph (96.5kph)."

But the OP confirms that he has no RPM fluctuation

 

This is TSB S307-14

Link http://www.jagrepair.com/images/TSB/...rge%5B1%5D.pdf

PS Nothing is a slam dunk!

 

I agree with you, I am changing all six coils and plugs along with the ITM o-rings since I will have the intake off. I got in contact with a shop in Chicago that works on Jags and he doesn't believe it is the transmission. He suggested even though there are no engine codes to go ahead and change all the coils and plugs, ruling out the least expensive things first.

 

While you're at it, how about replacing the transmission fluid? If it is indeed the TC clutch (sorry, my phone was previously autocorrecting to TQ for some reason and I didn't catch it), fresh fluid may help.

This falls under the category of reasonable stuff to try that won't bankrupt you. I am reminded of a '96 Lincoln Continental I had that was experiencing some shuddering at cruise speed. The RPM was steady but there was an intermittent light chugging present. After doing some research, fresh transmission fluid fixed that. Just to make it more interesting, the car was also occasionally throwing codes for a #6 misfire, but with a silky smooth V8, that wasn't even noticeable. I eventually isolated that to a hydraulic lifter pumping up. Talk about a headscratcher, with two overlapping problems.

Oh anyways, I remembered that situation and got to thinking fresh transmission fluid may be worth a shot. For what it's worth, humbly presented.

 

Thanks again, I will do that also. Hope to get this resolved soon.

 

I agree with fixing everything else before replacing the torque converter. Even if the other fixes don't solve the problem and it turns out to be the torque converter, those other "fixes" were probably needed anyway.

 

As has been said, it's expensive so +1 to doing other 'fixes' first.

When I presented my car to a ZFspecialist, I was told to drive it until it got worse as they usually get cars in when they are at the 'won't go up a hill without juddering' phase. Mine was a long way from that, but by dropping down a gear, he could make it squawk faintly. He suggested that a fluid change could help, but no promises and said that he would save his money if it was him.

 

If done using the instrument panel tachometer, that can be very difficult to judge.

Data logging using a obd-ii scanner would be much better.

 

Hence the usual prohibition found in JTIS against removing the flex coupling from the driveshaft. It's too bad they don't reveal the reasoning behind it. It would stop people that figure it does not make a difference which way the flex coupling is separated. It would also alert people to the fact that the fasteners need to be marked and replaced accordingly.

It should not be some obscure piece of information posted on the internet.

 

The squawk/squeak is an entirely different problem and not related to the TC.

TSB S307-15v2 addresses this with a fluid change.

"If customers express a concern of a squeal or squeak noise heard during gearshifts whilst accelerating, the transmission needs to be flushed and the fluid replaced"


Gotta love the stiff upper lip usage of 'express a concern' vs. 'complain'.

 

By what he said I took it to mean the two were connected, but I may have been wrong.

 

You're so right!

It was necessary on a car I had some years ago to follow the same procedure but it was documented as to why.

 

I'd rather be wrong and have the documentation

Almost all official paper service manuals from previous decades have this level of information.

Jaguar has moved to digital format for service manuals. You would think that as there is no cost incurred for printing, binding and shipping, limiting content would not be needed. But, they dumbed down the information anyways.

By way of contrast, the current electronic editions of service manuals from BMW, GM, AUDI/VW and Land Rover all contain much more information. BMW publishes many "theory of operation" sections which lay out the considerations underlying a particular system. The Land Rover set publishes this information in a separate volume. Both will give anyone an education in the various versions of ATE ABS systems used by Jaguar.

Jaguar? "Oh, you have ABS ... here's a pretty picture of the exterior casing ... do some pinpoint tests ... replace unit ... end of story".

Sad but true that Jaguar falls flat on its face in this area when the sister company could have been an example of what should have been done and a source of much of the content.

 

Well, I'm more of a "suspect incompetence" type so I suspect they were in too big a hurry to get documentation done so overlooked some things. Plus it looks like they subcontracted it so presumably then failed to check properly what the subcontractor had done. It was probably late, too!

I can't recall if TOPIx is any better (JTIS being a stop-gap now obsolete as you know).