Hey guys really need some help, I have a 1999 XJ sport 4.0 auto. It seems to be shifting back and forth between gears as I'm driving. It runs great and shifts through the gears fine but when I reach my crushing speed be it 35mph, 70mph doesn't matter it feels like it's bouncing back and forth I can watch my tac go up a little over 100 rpms and hold for a sec then drop back down back and forth back and forth. The only way to stop it is to gas it or get off the gas altogether. It's driving me insane!! Has anyone else had this issue if so please what do I need to do to remedy this. Any info is greatly appreciated

 

If it's only shifting up and down a couple hundred RPM, that's probably the torque converter clutch locking and unlocking.
Check the "disengage" switch on your brake pedal and the TPS.
Do you have oversize tires by chance?

 

This:

 

Yes, I'm running 35" tires, the break switch can cause that? Tps is new also

 

Could you also state the axle gear ratio?

 

Check to see that the BRAKE switch is indeed in adjustment. Takes 10 seconds.

 

4:56 sorry, ok I'll check that out thank you very much. So is it the break switch itself or is it a separate switch that locks and unlocks the torque converter?

 

On a 99 I'm not sure SteveMongr should know. Can't hurt to poke your noggin up there anyway in the meantime............

 

I'm clueless, lol. Just figured that gear ratio was important info for these guys.

 

The gear could be a bit of a problem with a 35" tire mine will still do that a little when I swap from my 33's up to the 35's for a short highway drive and I have 4.56's also. The trans will up/down shift from 3rd to 4th gear a lot more just driving down the road.

 

I pulled the break switch, no adjustments on it. It's just a push pin, a twist lock to hold in the bracket and the box/switch no screws or anything to adjust. Is the there another switch which controls the torque converter separately?

P.s I bought the rig from my brother apparently it has had this problem since it was a bone stock rig so I'm guessing tire size/gear ratio won't have any influence

 

The brake lamp switch on your '99 is non-adjustable. If you think it's faulty (which it could be) change it.


However, What trans fluid are you using and when was the last time it was changed. Is it full? The recommended fluid for the AW4 trans is Dexron III/Mercon (DEX/MERC).


You can check the fluid condition by removing the trans dipstick and sniffing the fluid. If it smells burnt that's bad. Drip some on a white rag or paper towel- see f it looks black. If it is black that's bad.

 

Just want to let y'all know I got it! Thank you all for the info big help! After getting under the dash and looking around I found that the previous owner ( my kid brother) also tried to adjust the break switch which there is no adjustment on this style so he bent the bracket closer to the peddle which wouldn't fly with me. I pulled everything out straightened out the bracket replaced the switch with a new one and everything is great! Thanks again guys as always awesome help!

 

The fluid was good just had the trans filter and fluids done just under a year ago may 6000 miles on it since.

 

Thanks for the update!!