Ok...official road test today on the 97 Land Rover Discovery after replacing the valve body assy due to a shifting problem..... and.....no difference in the transmission. The initial shifting problem is still there!!!!

Tha trans is a ZF4HP22 4sp manual (The valve body is not controlled by the ECU)automatic.


Will not upshift into 4th (hangs in 3rd)unless its cold. As it gets hot, it then begins to hang in 2nd. In both cases I can slide the gearbox into Neutral and pump the accelerator and drop back into Drive to prompt the upshift, but as soon as I come to a neutral throttle position or let off the accellerator, it will immediately and somethimes abruptly downshift back into 3rd, or 2nd .

Questions...there is some type of a tourque converter or clutch pack lock up mechanism is there not??


Is there some type of TPS or electronic modulation of input to the transmission that could be malfunctioning when it gets hot?.

Or could the transmission oil pump be bad...(hence the revving to build pressure prompts the upshift) ?

Could Vaccum leaks or dirty lines may be causing a pressure problem?

So far.. fresh fluid and filter, new valve control block assy. >


Hell...I think I'll just get one from a breaker...Any transmission Mechanics out there with ideas
__________________
"The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants".
...Thomas Jefferson.....

 

check the kick down linkage from the throttle body. The rpm change may make enough of a difference to cause the problem of down shifting. The other thing i can think of you already have and that is a bad pump. or maybe a pump pressure switch, relay that is giving the wrong info to your vehicle for the right gear to be in. I don't know about that one. I am just trying to follow the dots, and the road less traveled. hope it helps, gotta love a rover. duboff

 

you could have a number of problems but, im with the pump or internall clearences have gone out of spec and the pump cant catch up, but always check the easy stuff first sometimes you can get lucky

 

Because this seems to be temperature sensitive, and experienced land rover trans mech thinks it may be a malfunctioning Governor...worn seals, clogged screen etc.....Again...easy to get to...and not too expensive

 

Ive built many, when the tranny is cold the fluid is thicker and will not be as prone to leaks (internally) i am thinking pump or a clutch leaks through the shaft seals (cast iron or nylon seals) its time for a BMW or ROVER trans shop HP22 R4 , HP24 R4 make sure they replace the stator shaft with a hardened one and use nylon rings on the a clutch and converter seal set when rebuilding I have learned this one the hard way the build isnt that bad though