Reverse/Low servo
Glacier,
Thank you for all the useful information in your transmission diary. I have a 4R70W transmission that works great until it heats up. Once it is hot I have no reverse. This is the first automatic transmission problem that I have had to deal with and I would like to fix it myself.
From what I can gather I think the problem lies within the valve body or the solenoids (I believe it is a pressure issue caused by a bad seal??). Am I on the right track? What would you suggest replacing on this transmission. I plan on selling the truck in the near future and would like to keep the cost to a minimum. FYI it is tough finding parking spots when you have no reverse!
Thanks,
David
Ok I have procrastinated long enough and today I decided enough was enough. I took out the valve body for another inspection and to replace some parts. I have done some more research and looked over the diary again. Before I consider taking the transmission out I want to replace the parts I can access in the pan.
I popped the metal O-ring out for the reverse servo and ATF went everywhere (so did the piston/servo and spring)! Is this normal or have I located the problem, the seal is leaking on the piston/servo. It seems to make some sense considering the seal clearance and force required to push the piston (temperature change and worn seals could make a huge difference). Anyways I was planning to replace the piston/servo and seal today, but my lack of planning and not making sure the transmission shop was open has cost me a couple days. So meanwhile I am looking it over and have come up with a list of possible problems and parts to replace. Here is what I have done.
Checked the shift cable and tried replacing the TR sensor for the shifter, no change.
Replaced the valve body gaskets, no change (torqued bolts to specs). Separator Plate looked ok. Replaced Boost valve, no change.
I think I will change the manual valve on the VB. It moves slides back and forth just by rotating the VB. I have considered replacing the entire VB, but only as a last resort before I disassemble the entire transmission.
If all these fail to fix the problem, it must either be the pump assembly bolts, the reverse band, center support seal, or the mechanical diode. Any of these mean rebuild time for me, lets hope it doesn't come down to that, but crap I'll fix anything thats fixable.
Shopping List:
Reverse Servo/Piston w/ Cover Seal +(Spring and O-ring)-its a 3 grove piston.
Manual valve
Any other ideas? Thoughts? Suggestions?
Thanks,
David