If someone who knows their stuff could help me out on this difficult problem, I would appreciate it. I am a student at a Technical College for auto technician, and not even the instructor can figure this out.
92 Chevy Z71 350 4L-60 not electronically control.
Problem: High Line pressure (180 psi)

Things tried to fix it: Pulled pan off, and check the T.V. modulator valve that normal sticks in the valve body, it wasn't stuck.
Pulled valve body off, and check all valves for sticking or binding, nothing wrong. Put in a bigger boost valve in the pump, and check the pressure regulator valve for binding. Nothing binding. When I put the valve body in the last time, I left out the copper checkball and that was no help either.

I have had the valve body down 2 times, and the pan off 5 times trying to figure this out. T.V. cable is adjusted properly, and when pulled, line pressure does not increase. Werid thing is that when I am driving, if I put in N and then back into OD, tranny will shift to second or third, and not have to be red lined to shift.

Fluid is pretty much new, along with filter. Old oil from tranny was not burned.
The story was that a trailer was pulled in D, and after that is when it started not shifting right.

 

If the Throttle Valve is not sticking, and the Pressure Regulator valve is not sticking, then perhaps the pump slide is jammed or maybe the housing is cracked or warped allowing "decrease" fluid to bleed off.

 

If the slide on the pump wasn't functioning properly, would there still be a rise in line pressure when reverse is selected? When I put it in reverse, the pressure goes down to 60, and then rapidly climbs up to 300 or so. Is this decrease just from filling the reverse clutch with fluid or the regulator working properly?

One other thing I noticed was that the gauge pulses very frequently, as if the regulator valve can't make up its mind where to run at. It is about a 10-15 psi range that the guage moves between at a very rapid pace.

Thanks for your help, and any ideas are appreciated


Justin

 

Its normal for a momentary drop when put into reverse because the Reverse input housing has to fill up with fluid, and the reverse piston has a large air bleed, that will allow fluid to bleed off as well, untill the clutches apply enough to collapse the belville sping enough to block the air bleed off.
However, since the pressure raises even more when in reverse, then I think your pump slide is not jammed, but something is sticking in the valvbody. I know you said you checked it, but if the reverse boost valve is capable of increasing line pressure, then that tells you that the pump is capable of changing ouput volume/pressure, so its not the pump slide. That also tells you that the regulator valve is not sticking either (because it too will move to vary pressure). Now the fact that you cannot get a line rise from pulling on the TV cable, would almost have to mean something with the Throttle Valve circuit is stuck. Personally, I would install the TransGo kit, and remove all the valves for cleaning/inspection.

 

I put in a new/used valve body that was known to be good today. Line pressure went back down to normal readings. Went on a test drive, first worked fine but it didn't have 4th gear until I turned around to come back.
Then it worked fine from then on. Parked it for 45 minutes, and then went to drive again. Worked good again. Shifts a little high going into 2nd. (2500 to 3000) On my way to work it started doing what it was doing before. (Late shift into 2nd) and no 4th. As I drove for 15 miles or so, it began to work occasionally and then not.
So do you think I have a valve body problem still or possibly govenor problem? This is probably going to be harder to find since it is currently not a all the time problem.
I'll know more tomorrow when I put the pressure gauge on it again.
Thanks

Justin

 

I have found that everytime I worked on a 700R-4 in stock form, the Throttle Valve would stick causing these symptoms. It did not matter how well I cleaned the valvebody or what, it always acted up. It usually cleared up after a while, but initially, it would always act up. Now, I will not do a 700-R4 without installing a Transgo. The TransGo kit includes a new TV lineup that will prevent this problem. I don't know if the valve gets cocked in the bore, or "hydrolocked" or what, but it always used to happen. Ever since using transgo, NEVER had a problem. And even though the valve moves freely in the bore, it can act differently when installed and has fluid pressure on both ends of the valve.