Troubleshooting Low Governor Pressure

[dtool242]

I recently rebuilt my automatic transmission, and it worked fine for about the first 150 miles. But then it was becoming reluctant to up shift into 4th and then even into 3rd.

I hooked up a gauge to measure the governor pressure and it was low, never got above 5 psi no matter what speed I was going. I tried swapping out the governor, still the same low pressure.

I pulled out the valve body to inspect thoroughly. I had done this before on the rebuild but the only valves I opened up were the ones behind the bolted on plates. This time armed with a more detailed manual on the transmission, I noticed a few valves I overlooked on the rebuild. One of them was a bit 'sticky' (circled in red below) and I got it moving more smoothly.



You'll notice its name is the 'shift control pressure valve', could be the problem?

Before I installed the valve body back in the tranny, I decided while I was in there to pull out the lower cover (the part that the filter bolts to) and check it out. One of the screens was clogged with metal shavings to the point that it was crushed inward. This screen is a wire mesh screen that is the shape of a thimble and about 1/10th the size of one. I guess the flow of fluid goes from the outside-in since the shavings were on the outside and the screen was crushed inward. I cleaned it off and bent it back out to its original shape and re-installed. It's circled in red below.



Could this have been the problem with low governor pressure? I'm thinking it's quite likely. I would looooove to have a diagram that shows the flow of fluid through the tranny to get a clue of the cause and effect of things like this.

One thing I didn't do on the rebuild was to flush the cooler and lines (thinking I probably should have now). So hopefully these shavings are old stuff and not new wear. Time will tell.

So I got the tranny buttoned back up and guess what? Governor pressures were right on and car seems to be shifting fine. It's sort of hard assessing the quality of shifts when you are measuring transmission pressures since you have to unplug the vacuum line from the pressure modulator to measure the pressures and this in itself causes funny-feeling shifts.

My job for tonight is to remove the pressure gauge line, install the plug and reconnect the vacuum to the pressure modulator. Then a little test driving and tweaking of the bowden cable, and hopefully (fingers crossed) it will be all good.

I know how you guys like 'real world' pictures, but I'm not good about stopping, cleaning the ATF off my hands and taking pictures. Besides, I think the drawings in the manual show things more clearly.

Anyway here's one for the people who like the real world pictures. I had to take a picture of this as it was completely different than what I was looking at in the manual.

Picture:


Manual:


You can see that the parts circled in red (kind of hard to see the red circle in the picture) are not even close to being the same. In the manual its a shift valve and spring, in my valve body its a solid aluminum dowel. WTF? And gee, that part is labeled as the Governor Pressure Shift Valve!

I am aware that they made changes to this transmission over the years so what I see in a manual may be outdated (or what I have is outdated). Anyway, if anyone has some insight as to why these are different, please let me know.

[aluminum]

Great Post Thank You > Good Job > Yes I agree to Flush everything out would have been Good .
What % of the Shavings where magnetic do you think ? just a Guess ? or mostly Aluminum ?
a Magnetic Drain Plug would be good perhaps I bet . I have seen how well they work on many Cars.

[dtool242]

Ya I had the same thought after I cleaned all the metal bits off the screen. Just a guess, but they looked to be aluminum. Yes a magnet in the pan would be a good thing, perhaps the next time I pull the pan off I'll put one in there.

Speaking of which... in the WSM it tells you to unbolt the expansion tank from the pan and then undo the coupling between the tank and the pan and leave the tank dangling from the trans by the vent hose. I have found it is much simpler to leave the tank attached to the pan and just pull the vent hose from the trans.