I was seeing if anyone had an opinion about which "color" transmission modulator to buy for a 1984 4x4 6.9L C6. I can't shift out of first, and the modulator is stock, so it probably could use replacing either way and I'm starting there on fixing this problem. Thanks for sharing any experience with different colors.

 

I believe its green or black? Also check for vacuum leaks.. no vacuum = no shift, or VRV out of adjustment/ not working
Mine is green

 

I haven't had a C6 for a while now but I had that vacuum line come off one time and it wouldn't shift. I would start there if it was me. I think it plugs onto a nipple on the top of the trans if I remember right.

 

Okay, thanks. I'll go with green. I am replacing this first because the modulator is a lot cheaper to replace than the VRV, but I will check vacuum as best I can. Will buying new hose to replace old ones also be a cheap/easy place to start on that? Thanks.

 

they make a adjustable modulator I bought one some years a go was easy to tune it right to what I wanted...

 

It seems a lot of them are adjustable, but I guess they use different ranges of MPH or whatever they refer to to change gears. I'm not seeing any in stock at any local auto parts stores, so I may do some more research. I will look for a fully adjustable one. Thanks.

 

I got a lot done yesterday with the transmission. I had the oil pan off, while I had that off I put in a drain plug and replaced the screen. It definitely needed a new gasket also. I then filled it up with fresh ATF. The pan looked pretty good inside and wasn't too dirty.

I took the old modulator out and did the vacuum test on the VRV, and it needed adjustment but held vacuum. I also vacuum checked the line between the VRV and modulator, and it held vacuum. There was dirty ATF in the line at the modulator end on the vacuum hose, so it was probably the modulator that was bad, in conjunction with the VRV needing adjustment. It now has a new (green) modulator . I didn't get to road test it because it needs an alignment, but I'm crossing my fingers that it will shift nicely. Thanks again for the help.

 

The stock ones for diesel engines, are black, but any will work, their just pre set at different settings for different applications.