I've been noticing that the rpms fluctuate when the cruise control is set and I'm driving on level roadway. I would expect a change when going up or down hill. I'm not sure if this is normal for 2005 XJ8 Vanden Plas models or not. Never had this problem with other euro vehicles or American made vehicles either. Any suggestions?

 

Hi DeaconHull,

It's possible that the Transmission Control Module (TCM) is simply changing gears to smoothly maintain road speed. The ZF 6HP26 transmission has a special gear map that is supposed to reduce the number of gear changes during Cruise Mode, but perhaps even though the road surfaces seem level to you, there are slight inclines or declines that prompt a change in gear ratio. Do you always set your Cruise Control at the same speed? If so, perhaps that speed falls into the overlap range between two gears, prompting more frequent gear changes than might occur at a different speed.

Have you had the transmission fluid, pan/filter and connector sleeve changed? Or have you at least had the fluid level checked?

You might search the forum for reports from members who have had issues with rpm "hunting" that ultimately indicated a problem with the torque converter. I don't think your symptoms sound the same, but you might want to rule it out just in case.

Cheers,

Don

 

Hello Don, thanks for the info. I was wondering if there might be slight changes in the road surface incline. I haven't had the tranny fluid changed yet. I believe it was serviced on schedule by the previous owner per the maintenance report. Still, I think it wouldbe good insurance for now. Thanks again, this forum is so much more helpful than the Benz forum I belong to.

 

Hi Deacon,

Since both Jaguar and the tranmission manufacturer, ZF, initially claimed the 6HP26 gearbox was "Sealed for Life," or "Filled for Life," even if the previous owner followed the Jaguar service regimen religiously the transmission would not have been serviced with a new pan/filter, connector sleeve and the correct fluid (ZF specifies LifeGuard 6 only, but some members have used other fluids. Please do your homework before you decide because it's a complicated subject, and the highest authority I know of is ZF.).


I've been involved in Jaguar forums since the mid-90s and have found Jaguar owners to be unusually knowledgeable about their cars and amazingly generous in sharing their knowledge with others.

Cheers,

Don

 

I agree and will venture further with caution. The folks on this forum are outstanding!

Thanks,
Deacon

 

Jag & ZF claimed the tranny is sealed for life, and thus they did not specify any regular fluid change. However, the tranny pan gasket and tranny cooler lines have undoubtedly started seeping over the years. Changing the gasket means a new pan, filter and fluid.

 

Thanks for the response rhankey. From the research I've done it seems that the work is expensive since a mechanic would have to know what he's doing . Am I wrong in my deduction?
R/S,
Deacon

 

The hard part is getting the old screws out, changing the sleeve and refilling to spec as per the manual.
Changing the screws for new type are recommended (I can't remember the specific ones but they can be ordered along with the filter, pan and sleeve from CTC in Cali?).
You can order the complete package including oil in one place.
I have watched a dealer mechanic do it once, felt like poking my eyes out because it was as hard as an engine oil change and I paid him $330 to do it... Never again.

 

Hi Deacon,

Whether or not your transmission pan is leaking, the fluid is 10 years old. ZF now recommends that the fluid be changed every 8 years at the most.

For the record, the filter is built into the pan, so you have to replace the entire plastic pan to replace the filter.

The parts source trosty referenced is California Transmission Supply Co. (The CTSC - ZF Parts). They offer all the parts you need in a kit for $258.19, but don't hesitate to shop around. The ZF 6HP26 transmission was used on vehicles made by BMW, Audi, Maserati, Land Rover, Bentley, Hyundai, Kia, Ford, Lincoln and Rolls Royce, so parts are widely available at widely varying prices.

Many of our forum members have changed the pan and fluid themselves, so as long as a mechanic follows the service manual procedures, it's doable. The most common reported problems are difficulty loosening the fill plug, difficulty removing pan screws or one or more screws breaking during removal, and difficulty getting the electrical connector sleeve fully seated. The most critical part of the job is carefully following the procedure to get the fluid level correct at the specified temperature.

Cheers,

Don