I have a 2004 XJ8. I had a transmission leak, but I fixed that right away and the Jag mechanic added more fluid. Once in awhile when I put the pedal to the floor, the car will accelerate but once it's ready to shift to the higher gear it just revs and wont shift. I let go of the gas and then it decides to shift at a higher gear (when it shouldnt) and the car transmission hits hard. It's happened twice to me already and i'm not sure if it's just a glitch or if I have a serious problem with the transmission. Anyone have any ideas what's going on or any thoughts?

 

Try a TCM software reload first, (called a 'reflash'). Most problems on these cars trannys are normally software. Very rare for a tranny to fail mechanically, (cue here for all owners whose tranny has failed !!!)

 

"Most problems on these cars trannys are normally software."

That just looks wrong in print. In theory it's more correct than this old school mind wants to hear. Cheaper to fix as well!

 

Thanks for the info! I'm taking it to the mechanic asap and see if they can diagnose it. I'm going to tell them if they can re-flash the TCM and see if it that solves the problem. My car reacted the same way today when I accelerated on the freeway and it's not shifting like it used to. It's not being efficient on the shifts and causing it to feel underpowered. I'm still praying it's nothing mechanical.

 

Was it doing this before the repair? The wrong fluid can cause this as well as low fluid level. Slipping and missing shifts is normally a rebuild situation unless the fluid type or level is wrong.

 

Actually it NEVER did this before the repair. I took it to a well known Jag mechanic in my area, but it still may be possible they put the wrong fluid. It took 6 quartz to fill-up the fluid so I'm not sure if it's possible it could be low again. I'm going to have to take it in soon this week and find out what they did in order to narrow-down the problem. If it is a major problem, can these transmissions even be rebuilt? I heard these are lifetime transmissions and they cant rebuild them.

 

Not many people are changing fluid and filter pans in these units due to their advertised "filled for life" and it is very possible that a local Jag guy may not be in tune with the procedures and parts to do it right. This sounds like your problem. You may need to redo your steps with someone who knows the right products and procedures. This fluid and filter pan change should have cost about $400-$500. If it didn't, be suspicious. You will need the ZF filter pan and Lifeguard 6 fluid at about $250 from thectsc.com. its also a good idea to replace the electronics sleeve at the same time as they often start leaking at about 60K and cannot be changed unless the pan is removed.

 

Yes, I need to talk to the mechanic to see what he did to be sure. I was charged about $580 for the whole thing and about half of that charge was for that expensive fluid. He also did replace the sleeve as well. I'm pretty sure he did the job correctly, but it's always good to find out since I have a warranty on the work he performed. With this in mind, I think the TCM reflash may be the answer (I'm hoping). Just out of curiousity, How much is it for a new or used transmission for this vehicle?

 

Ok, so I took the car back to the mechanic and he went over what he did to the car and he did it correctly and used the proper fluid and treatment. Since the car is still not shifting properly when accelerating and no warning or fault codes pop up; I'm thinking it needs the transmission reflash of TCM. I really hope this solves the problem and hopefully it won't cost too much.

 

BTW, the shift cable can work loose where it enters the gearbox. Don't know if this would give your symptoms though.

 

My 1998 xj8 VDP did the slow to shift then hard bump into gear with Transmission fault warning on the dash. I was 300 miles from home so I took it to an AAMCO trans place, they dropped the pan and showed me some real fine metal stuck to the magnets and a couple small shiny metal chips no larger than a grain of salt. The estimate to rebuild it was $2800+ with the car barely worth $5000 I asked them to replace the pan and fill it with oil and I'll take my chances getting home. Success! I made it home 300 miles, it seemed to slip getting started but drove fine at 60 mph. I kept an eye on the revs and the mpg and the temp to make sure it wasn't getting worse. Checked the codes this morning and got: P1637, 1722, 1730,1797, and 1637. Is it time for rebuild or can I hope it's computer control related. I hate to put $3000 or more into a car I'd be lucky to get $5000 for. Any suggestions? BTW, you gotta love Jag engineers if they can design a trans that will get you home with tis many issues.
T

 

I don't remember where I got this link, so please excuse me if it is a duplicate.


It's a 28-minute video is a guy changing the fluid in his XK8 (also ZF 6HP26).

 

Ok, so I found a solution that fixed my problem. My mechanic told me to disconnect the negative wire for about 5 minutes and then connect it back. This reset the computer controls of the car. After a day of regular driving I tried accelerating fast and the transmission was smooth and responsive again. It's been 3 days and not a problem so far. I hope this really did do the trick and it stays like this.

 

I disconnect the battery once a month to keep issues like this at bay. Thank you for the confirmation!

 

If I am not mistaken, disconnecting the battery has absolutely no effect on the TCM or transmission. It will however clear ECM fuel adaptations.

 

Really? But once I had done this, the car has been driving normal with no problems with the transmission shifts. Is there something else I should be aware of that caused my transmission problem in the first place?