I have a 98 xj8 and sometimes when I am crusing along and I throttle up for passing gear the transamission downshifts so hard that you think It will tear something up. this happens once in a while, it dosn't seem to matter wheather you are in cruise control, sport or manualy throttling up, other times it shifts normaly. the throttle seems to back off and give the drive train as much slack as possible and then slames it into the lower gear. I am a hot rodder and a fair mechanic but in my 68 years I have never ran into anything like this. please help this old fool. ha, ha

 

Maybe an A-drum in your near future. Has the transmission been rebuilt in the 190K mile history?

 

I had exactly the same issue except it extended to anytime the ECM/TCM called for a downshift. Worked fine on J gate shifts when you let off the throttle. Jaguar dealer said 'new TCM . . . that will be $2050 please'. I don't really remember hearing the 'please' part. I was not going to lay out that kind of money to verify that the TCM was the problem. Thanks to H2Oboy who loaned me his test equipment I was able to see that the TCM was not releasing the torque converter lock-up solenoid on down-shifts. An used TCM fixed it that I found for less than $100. In hindsight perhaps disabling the TC lock up might have identified the problem. That might involve clipping a wire at the TCM or transmission connector.

Either would be better than blindly replacing the TCM.

 

what is an a-drum and i have no history on the car

 

ZF 5HP24 Heavy Duty Input A Clutch Drum

Here is a picture- it's inside the transmission right under the Bellhousing.

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