C6 auto shift fine but no manual shift

C6 auto shift fine but no manual shift

Joined: March 9th, 2012, 1:47 am

March 9th, 2012, 1:52 am #1

I have a 80 Mustang with a 460 and a C6. It's a early model C6 with a Hastings shift kit installed. Long story short is it shifts fine in drive but I can't manually shift it. It just stays in 1st. what am I doing wrong. I've checked the linkage, and have 17 inches of vacuum at the modulator. It does not have a kick down lever or cable. Help !
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Joined: November 18th, 2004, 4:20 am

March 9th, 2012, 6:23 pm #2

How early is early?
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Joined: March 9th, 2012, 1:47 am

March 9th, 2012, 11:25 pm #3

OK you got me ! All I know is I bought a rebuild kit for an 1980 C6 but all the rubbers were too big. When I took it back to the place the counter help said " you dummy, you've got an early model transmission"
so I guess it's a 60s model, like maybe a 68 or 70. It didn't have the servo tag on it and there are no casting numbers on the case. It does have a screw in type modulator and the detent for the linkage is on the valve body not a rooster comb bolted to the inside of the case if that helps.

Thanks for the reply .
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Joined: November 18th, 2004, 4:20 am

March 10th, 2012, 11:47 am #4

Ok. If it has PRND2L on the shift quadrant it is the select shift version.

Earlier ones had what is known as green dot.

If it shifts fine in drive but can't select 2nd manually there is a problem in the valve body.

Did you compare the separator plate gaskets?

Perhaps you have valves mixed up.
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Joined: March 9th, 2012, 1:47 am

March 10th, 2012, 1:07 pm #5

I did not compare the gasket because the kit instructions were to remove it. As for the valves, I was very careful to keep them in place. Looks like I bit off more than I could chew.

Thanks again for your reply
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Joined: November 18th, 2004, 4:20 am

March 10th, 2012, 2:00 pm #6

That could be the problem.

I rebuilt perhaps 10's of 1000's transmissions in my lifetime and never once had good results from omitting a gasket.
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Joined: March 9th, 2012, 1:47 am

March 10th, 2012, 11:45 pm #7

Stuart,

I pulled this thing down again to check to make sure all the valves were not sticking. I also did some more research on my valve body..On the TransGo sight I found that a valve body with a C8 casting on it will not shift in manual mode. If you start in 1st it stays in first, start in second it stays in 2nd.

I not sure if that's correct or not but it really doesn't matter right now cause the car chucked a rod in the burn out box.

Thanks for your help.
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Joined: November 18th, 2004, 4:20 am

March 11th, 2012, 12:27 am #8

That's how it should work.

Upshift in D position only.
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