C6 tranny issue? Maybe bad VRV?

[Bullnosefan95]

I know there’s a way to test if the vacuum valve is working properly, but maybe someone can give me a good answer as to help me with my situation. Basically I’m at a light waiting to go, sometimes it will go right ahead and start moving and sometimes I have to rev it a bit to encourage it to want to go into gear, even after I get moving there’s still times where it wants to feel like it’s slipping. It’ll grab that gear after a certain point, it just depends. When I reach 35mph it always debates itself whether or not to shift to third. After it reaches 40mph it shifts into third and I don’t really have any issues. Could this be a bad transmission or bad vrv?

[Gary Lewis]

Actually the VRV wouldn't cause that symptom.  The factory shop manual section on the C6 (Documentation/Driveline/Transmissions/Automatic Transmissions/C6 in the menu) says "Should a malfunction occur in the VRV, the valve will cause a 0 vacuum signal to be sent to the diaphragm which will cause delayed and harsh shifts to occur."

To diagnose the problem you'd need to go to the section called General Automatic Transmission Service (Documentation/Driveline/Transmissions/Automatic Transmissions/General Automatic Transmission Service).  And I think what you are describing is what they call No Drive.  And Page 14 of that document says:

When the selector lever is at 2 (second) a NO DRIVE condition may be caused by an inoperative forward clutch.  A NO DRIVE condition at D (drive) may be caused by an inoperative forward clutch or one-way clutch.  When there is no drive in 1 (low) the difficulty could be caused by improper functioning of the forward clutch or simultaneous malfunction of the low-reverse band and the one-way clutch. Failure to drive in R (Reverse) could be caused by a malfunction of the reverse-high clutch or low-reverse band or clutch.

In other words, I think you have a transmission problem.

[Bullnosefan95]

Well that’s terrific. I had a suspicion that it would be but I didn’t want it to be true. I have reverse no problem but when I put it in any forward gears. It grinds really hard and won’t go over 5 mph. Anyone in California near the Sacramento area have a spare c6 they’d part with? I can’t afford much but I can try to scrape together what I can.

[FuzzFace2]

I dont know if you can pull the trans (R&R) and send it out for a rebuild.
Check with near by shops what they get to rebuild the trans if you bring in just the trans.

Then it is just the $$$ for the parts and the labor to bench rebuild it.
A lot of the $$ is the R&R out of the car / truck.
Dave ----

[ratdude747]

Yep. Since this isn't a transmission with a TV cable that if adjusted wrong will burn the unit (AOD, GM Turbo 700-R4, etc), many shops will do these as a "carryout" unit. Units with TV cables some shops will refuse to do as a carryout (or will do as such with no warranty) due to morons forgetting the cable on reinstallation and then smoking all the clutches and bands due to low line pressure. Seen several teardowns of such... not pretty!

[Bullnosefan95]

Has anyone used the rock auto kit to rebuild the c6? If so was it worth the money?

[red1980F150]

I assume your a smart guy, but still, no one asked the simplest question so I might as well.  

Low transmission fluid can also cause a no drive condition... did you check the fluid level?

Sorry if I missed that somewhere and you already said so.  

[Bullnosefan95]

I’m not per say “dumb” but sometimes I have those moments and think maybe I should of the other possibility. In which case, you were right. I thought 8 quarts was the proper amount for this transmission… but yet again I was wrong and jumped straight to the worst possible reason. Went and picked up another gallon today and put it in, and tada!, she magically drives. So again to comment on your statement, I am dumb sometimes and sometimes I don’t realize that the issue is sometimes simpler. However, U-joints are still bad and going to need to replace those as soon as I can. But for now the bullnose drives on, I’m going to be looking at local scrapyards for another transmission for rebuild as a backup. I know I could have two dozen trucks for parts trucks, but alas, I live in an apartment and don’t have property or money for them, yet!

[Gary Lewis]

Well, at least you figured it out. Well done!

[Bullnosefan95]

Now to just tackle more items on the list.

[red1980F150]

LOL - I've done the same thing.  Unlike you I kept driving and completely ruined the tranny.  So, no worries.  We all do things that make us wonder, at times.  

Definitely glad you got it working before anything really bad happened to the transmission.  

[Machspeed]

red1980F150 wrote

I assume your a smart guy, but still, no one asked the simplest question so I might as well.  

Low transmission fluid can also cause a no drive condition... did you check the fluid level?

Sorry if I missed that somewhere and you already said so.

Funny, I almost asked the same question but did not want to offend....LOL!