We have a C6 rebuilt transmission in an 1977 econoline chassis motorhome. When it was put in last year, the fluid was replaced and it ran fine. It was a good, strong transmission. We noticed it started to leak while it was sitting this summer. We changed the fluid once, didn't have any problems with shifting but heard a loud squeal. We changed the fluid again the same day and lost all gears but reverse and it still had the squealing, but not as bad. We were told the bearings in the valve body might be sticking so we changed the fluid AGAIN with an additive and got our gears back, but it is slipping badly and it still has a squeal, but the sound has decreased. We have checked the modulator, vacuum line and diaghram, but don't believe any of these are the problems. We were told the vacuum pump is probably bad because when you change the fluid it will clean out the pump of contaminants that were creating friction or whatever. That doesn't make sense to me since we changed the fluid when we put it in 1,000 miles ago with no problems. Why would a fluid change bother it now? Do we need to adjust the bands? I'm not ready to give up quite yet, but we're pretty baffled. We were told there is a screw in the filter that shouldn't be tightened but don't remember anything like that when we took it off. HELP!!!!!!

 

I would put a pressure gage on it first & see what it has in each gear.

 

There is another filter on the C6 transmission that nobody told me about either, I found it while I was rebuilding it myself. If you drop the valve body down, 8 bolts 3/8" socket, you will find a wire screen filter on the top side. It will pop out with some finess, and if you clean and dry it well, you can use it again, as long as it's not tore up/broken. I don't know if you can purchase them or not but I can sure tell you it can and will get clogged.