I went for another 10 mile test drive this morning, filled it up with gas for her and grabbed a sandwich. Still drove great.

Tonight, she took her car back for the first time since I worked on it. She has been driving my XJR and had said "I was afraid of this, I'm jealous" the first time she drove it. Her car is much smoother and more refined, it's just not quite as fast as mine. Anyway...

She went into town for an hour for errands and to pick up some dinner. She said "I'm not jealous anymore, I love my car." She put it to the test and came back smiling. She said "It drives wonderful, I can drive it like I want to now!, Thanks.". Plus it appears I saved us about $800, so I was a good husband today.

With regard to the re-flash, the shop assured me it would be necessary after the seal was replaced, even if I did it myself. The car drives and shifts wonderful though. Should I be worried about a software re-flash?

 

That's awesome!

I have to get to mine hopefully this weekend but I'm very encouraged!

I wouldn't worry about the TCM reflash at this point...

Congrats!!

 

Fantastic news. Very happy for you.

 

Thanks for being happy for me guys, I appreciate it. I'll offer this last (hopefully) update.

She drove the car again and reported that it still drove great but I noticed a spot under the transmission about the size of a nickel. I was concerned that I over torqued the plastic drain pan plug, but it "appeared" to be leaking a little from the seal on the drain plug end of the pan. I checked those bolts and two of them seemed loose, so I torqued them again. When putting transmission or oil pans on our Jaguars I usually err on the side of under torque rather than over torque. I guess I didn't get those two tight enough.

Today she drove a 60 mile round trip through some curvy roads up to Winston Salem and again came home glowing about how much fun her car is to drive. She detailed a few close call passing situations with great enthusiasm which frankly made me a little nervous that we got her a Jaguar, haha. But, apparently the car accelerates and shifts like it's supposed to; she still has not been able to duplicate the slip. I got home from work a couple of hours after her and when I checked, the floor under her Jaguar was dry.

I am optimistic that we are done with her transmission for a while. But, frankly if it WAS leaking hey, that's a much better problem than a SLIPPING transmission, just to keep things in perspective.

 

Over a week and a couple hundred miles later, still no slips and no leaks either. Thanks again for all the help.

 

Good job and thanks for posting back your fix. Really helps others looking repair their cars.
.
.
.

 

I regret that I must re-visit this issue, but I have an update.

The car performed flawlessly for well over 1,000 miles without re-flashing the TCM. It has recently started the same "slip" again from what I think is 4th to 5th gear. It's only under aggressive acceleration and it's not as bad as before, but it has started happening again.

The shop that diagnosed the car said if the new seals didn't work then it would need a new valve body. In fact they gave me two quotes, one to replace the seals and one to install a new valve body. They recommended the seals first and if that didn't work, the new valve body. The cost of the two repairs together was roughly equal to the price of a re-built transmission, but I digress.

I don't mind buying and installing a new valve body; I've sourced what I feel is a quality product at a decent price. I am not pleased to be spending more money on the car (the discussion has come up to sell it), but overall we still think the car is worth the trouble and expense. Here are my questions:

1) Is it possible that all the car needs is the recommended re-flash and adaptive driving sequence and the issue will go away?

2) Is it possible that I under-torqued the valve body screws and it has loosened a bit causing pressure issues? The torque rating on those screws was very low. I feel confident I torqued them properly, but with the low torque rating it makes me wonder.

3) The valve body I have priced claims to come already fully programmed, not needing to be flashed. Does that sound correct? Am I reading that right?

Even if I have to install the new valve body, my total invested cost so far will only be about $500 higher than the quote I got to ONLY replace the seal. Yes, I am trying to look at the bright side. lol

 

Update (if anyone is following, haha).

I have been reading accounts of people having transmission problems that were caused by bad spark plugs. I was "told" the plugs were fairly new in this car, but of course I have no way of knowing. I decided to change them.

Two of the ones in the car were not even the same plug as the other six, they weren't even the same electrode material! One of them was a BEAR to get out. I had to use PB Blaster and work it out over a about three hours time. When I did get it out, the electrode was pretty much gone. I'm pretty sure we were lied to about the "recently" changed spark plugs.

With 8 new (and matching) spark plugs I took it for a test drive. I know exactly what to do to make it slip, so I put it to the test. The first time I tried it DID slip, but just a little. Then I tried about 10 more times and could not get the transmission to slip. I did full throttle 0 to 80 mph, smooth as silk. 70 to 90 passing at full throttle, nice and smooth. I did the jump back and forth from 50 to 60 (which usually causes the worst slip) and it shifted perfectly.

As with any "victory", they can turn out to be short lived. I'm going to change the oil and filter tomorrow and we'll see how it performs for my wife over the next few weeks. It would be nice if the plugs were the cause of the transmission issue.

 

A few thoughts.

Nice move changing the plugs. I also heard coils going south can cause shifting issues. Might be worth getting them tested. (You would need a COP tester) depending on mileage one or more coils might be working at less than 100%

You would have to swap in your TCM from the old valve body to the replacement valve body to retain programming to your cars PCM.

You could indeed try a TCM reflash and adaption clear. You should have the PCM flashed also before meddling with a TCM reflash. You will need SDD/IDS to handle.

Just my thoughts at this late hour on the East Coast. If your near NJ I would be able to help you test your coils and I have SDD and VCM, no clones.

Thanks and wishing you forward progress.

Anthony

 

I am cautiously optimistic. No benefit in being pessimistic, right?

I rotated the tires and changed the oil and filter this morning. I went out to fill up the gas tank for her and took the car on another 15 mile abusive test drive. I still could not get the transmission to slip. Last time I "repaired" it the slip came back after about 1,000 miles, so we'll see.

I have a couple of x350 observations though, and I posted these observations in the x308 forum as well. That engine was always smooth, but with the new plugs it's like a sewing machine. That is the quietest and smoothest idling engine I have ever heard. My daily driver is a 2003 XJR (x308), which I love. But, my wife's 2004 XJ8 (x350) has 27,000 more miles on it yet idles and runs much smoother. It also rides infinitely better and it's darn near as fast! I'm always impressed when I drive her car, it's a fantastic driving machine. I can only imagine what the XJR version of her car drives like.

I am still partial to my x308 XJR's body style, and it is still a bit faster than her car, and the transmission is better....so, I think I'll hang on to it.

 

Yes, another update! I hope in years to come this steady updating will prove useful to someone.

My wife just drove her and the kids to a school event out of town. A little over a 100 miles round trip. She texted me several times throughout the evening just to tell me how much she loves her car. Apparently she put it to the test and it drives better than ever. She drove it VERY hard and did all of the passing and on-ramp maneuvers that normally caused slipping (it had gotten to where she could not even pass people on the highway).

She said the car has not driven or shifted that well since we've owned it. She was actually giddy with excitement because she had so much fun driving the car. She doesn't have to "drive it easy" now because of the transmission slip.

Ok, so I have to admit it's encouraging to think a relatively inexpensive set of spark plugs was all it took to fix the transmission. I had quotes from specialists for thousands of dollars for valve body replacement. This is after they did a full diagnostic ($95) to determine the cause of the shifting problem. If in fact it was only the spark plugs from the beginning, then I would have been REALLY sad to spend thousands on the transmission and STILL have the problem.

Again, it's only been a couple of hundred miles. It was slipping EVERY time she drove it before I changed the plugs, and now it shifts perfectly. I can't know for sure, but I hope this is the last update!! lol

 

Great news indeed. I just ordered a new set of OEM spec plugs and going to try that as my car is at 120K miles as the previous owners clearly didn't think of proper maintenance (case and point they had their mechanic install tire stems and manually filled each front air strut one of which was a new unit instead of taking care of the compressor - clearly I rectified with $50 worth of proper parts and zero air suspension issues!), and I'm also going to test each coil with my COP tester and clear adaptations and reflash my TCM/PCM to see if my 3/4 shift issue goes away.

If that doesn't work I have a 20K mile valve body and seals that's going into my trans and ZF6 lifeguard and filter and T40 bolts are brand spanking new.

It shifts like butter until that up shift to 4th and she acts up..

On another note I think you did a great thing by dropping the valve body and increased/restored line pressures with the bridge seal and those other round seals.

Great, great news indeed...

 

A couple thousand miles later, still seems to be operating fine. The transmission is almost at 150,000 miles so longevity is anyone's guess, but for now it seems the new spark plugs got rid of the harsh 3 to 4 shift.