Hi. Suddenly my gearbox does not change speed and the engine goes up without result. The liquid level is good. kickdown switch on throttle is OK (open or close). Does anyone have any idea about this blackout ?
Do you have drive or is it stuck in neutral?
No, driving is effective and engine speed increases
And it doesn’t downshift, does it shift up very early and stays in 3rd?
it seems to stay in 1st (or 2nd) but downshift seems to work if I no longer accelerate
(sorry for my bad english !)
Does the kickdown inhibitor switch on gearshift have an impact ? I didn’t control it
3-2-1 are downshifts, 1-2-3 upshifts. What are the rough shift speeds (normal driving, full throttle)? Does it seem to think that you are in the kickdown position all the time?
Greetings!
IMHO the first thing to check would be the vacuum modulator, located on the RHS of the transmission, and also the vacuum line to the modulator, which should be connected to the rear of “A” bank intake manifold. The modulator senses engine load, and largely controls the gear changes on the transmission.
Next would be the governor, which can fail if it strips its plastic gears.
only gear 1 is in function whatever speed increases. So I thought it was a kickdown problem. Then thank you for dave answer, I’ll try to process vacuum line (vacuum modulator was alreday changed). I come back after control…
Generally if problem is the vacuum modulator, the transmission will stay in first gear until 45 mph (4500 rpm) then up shift to second; if acceleration is continued in will up shift to third about 70 mph (4500rpm). If it doesn’t upshift at those speeds, and is not slipping, it is most likely a failure in the governor (stripped gear is not unheard of in the TH400.
Also, a shorted to power kick down solenoid will delay shifts to about 5500 rpm, but it will still upshift, accompanied by a very harsh downshift.
Raise the rear wheels and secure on jack stands (jack stands or something very solid). Start your stationary journey and check what RK suggested above. Then you can dig deeper…
Hi. I had control hose of vacuum modulator (both have few kilometers) and everything is OK. However I didn’t control if there’s water inside (recommended test in 44-08 jaguar manual gearbox GM400). Moreover I recently and suddenly had to change the fuse of the turn signals. I noticed on the manual that it is also used for kickdown inhibitor switch…is it related to my breakdown ? where’s power kickdown solénoïd ? Thank you for your advices.
Robert, when you talk about “governor”, what does it mean ?
The bit in your gearbox resposnible for shifting, regulated with centrifugal force of the spinning output shaft or spinning clutch basket.
So it’s a part inside gear box ?
Yes. Google search “TH400 governor” and you will find info on its function, etc.
Yes, it’s a valve with weights that control how far it opens. It sits on the output shaft inside the transmission and tells it how fast the car is going, by adjusting one of the input pressures into the valve body.
The other inputs are pump pressure (engine speed), torque (vacuum), kickdown and shift lever position.
Start from the dry run on jack stands, as indicated earlier, you may have problem with tranny’s offset f.eg vacuum/kickdown rather than with internal components. TH400 was mounted in Hummer H1 for a reason…
I ran with my kickdown switch not working at one point, should make no difference except that flooring it will not kickdown.
Hi. I finaly found governor part on websites (it’s more easy for me to see what is it). Sites also propose “governor inspection aperture cover plate”, then I deduce that’s possible to get a visual control. Is it easy to removing ? At the moment I get under the gearbox but I don’t find location of the governor…