C6 troubles
 

Hello all, I have a C6 which I just installed into my 71 LTD which I took out of a 83 E350 about 2+ years ago which I drove home.


The problem is that the transmission starts out in 3rd gear. Yeah sure with that big 429 pushing it the car still drives but it kind of sucks. Here is what I have done to date. removed the valve body from the transmission, thoroughly disassembled and cleaned the valve body lubed everything and reassembled being careful to properly torque everything properly. Put in a new filter and re-installed the valve body into the tranny. No change. Since I have 4 C6's in my shop I removed a valve body from one of those and installed it into the transmission and still have the same issue.


Does anyone have any idea as to what would cause this issue?


Oh and btw, the transmission will shift nice and strong through all gears if shifted manually.

We would like to think it should be something within the trans itself, but it doesn't have to be.
Two things come to mind and they are; the one way clutch in the trans and then the one way clutch in the converter. I know they both worked in the past , but things can change.

I can rule out the one way clutch because in manual 1st gear the transmission has braking showing that it is working. As for the torque converter, well I finally gave up on this C6 and put another C6 that I had around the shop out of a 72 LTD using the same torque converter and both the transmission and torque converter worked excellent.


Now, when I took the transmission out of the car and pulled the torque converter out I noticed that the input shaft of the transmission pulled out slightly. I pulled the shaft all the way out and there was a 1 inch section approximately in the middle of the shaft that had a severely rough and unevenly warn down. I checked all of my other 3 C6 transmissions in the shop and 2 others had input shafts which just pulled out.

Glad you corrected the problem. It is very easy to check the one way clutch in the converter , stick your finger in to the turbine and you should be able to turn the gear in only one direction.

Like I said the torque converter which was in the problematic transmission it the same one used in the replacement transmission. The problem with the problematic transmission never got fixed. I guess if I decide to tear it down for rebuild I will find the problem.


Andy

Is that the trans that uses a vacuum hose to shift?

Yes, it has a vacuum modulator. I replaced with a new one without any difference to transmission operation.