I just put in a freshly rebuilt C6, I wasn't the one who had it rebuilt, I bought it from a guy that way. he said it had been kitted.

Anyway, I can't get it to go into 3rd gear at all, and it will only go into 1st manually until I touch the throttle, then even with the stick in first it will still drop into 2nd to pull. Also, once I get it up to speed and let off the throttle it seems to slip into neutral until I wind it up to about 3,000 rpm, or until it comes to stop.

getting it to go into gear initially requires patting the throttle, and takes about 1500 rpm to keep it in. once it's in though, it seems to be as tight as it should be.

ive change the modulator valve and the governors both are brand new. the fluid level is a little under halfway between the dots at idle, in park, at 190 degrees. its got a new vacuum line hooked to the intake plenum right behind the carb. do you guys know what I could try next?

 

Here's what I would try FIRST...Getting my money back !!

 

I would if it came from a commercial dealer, but it was in some dudes barn. I don't even want to mess with it

 

I'd find out what kind of kit was installed. Might be a hot rod trans and not "built" for truck use.
He could have also just been saying anything to get it sold...

 

I would first top up the fluid to the top mark and see what happens as they are some of the signs of low level.
If that don't fix it time to pull it and take it to a shop for a proper rebuild or if you have the old one already out send it to the shop.
Most of the cost of a rebuild is the shop having to R&R the transmission.
I would think if they are not too busy drop it off first thing and you may get it back by closing time.
Dave ----

 

You were right on the level part Dave. yesterday when I set the level, I did it in park. after you said that I went out and cycled it from R to D a few times, then left in neutral to check it and it wasn't even on the stick. I got it set now and it is going in gear much easier. still stuck in 2nd though.

I have another complete C6 here and I'm wondering if I were to change the valve body out if you guys think that would change anything, whether it fixes it or not if it gives me a hint at 3rd gear I can buy a new valve body, also I haven't done a pressure check yet, i dont have a guage, but ill be getting one soon if this keeps on.

(EDIT) the guy I bought it from said he had it built at a local shop about 5 years ago and it hasn't been installed in anything since, i asked the shop how to tell if they did it, they put a stamped tag in one of the tailshaft housing bolts. I found the tag, it had their name on it

 

A Google search turned up what I think you have checked, Mod valve leaking, do you have vacuum at the valve with motor running?
Fluid level being low, check in gear hot.
The last I don't think you checked is the kick down linkage. If it is not adjusted right it could be in assing gear" and will never up shift to 3rd.
Dave ----

 

My wife picked up a gauge for me, ill go out and test it in a little while, theoretically there shouldn't be any reason it wouldn't have a vacuum, its a new 3/16" line all the way from the rear port of the intake down to the valve. all 1 piece rubber hose. fluid is good, in gear/hot. I don't have a kick down rod, I lost the one I had, but I do have it tied up about a quarter-inch down

 

It’s got 12 psi of vacuum with the mild cam

 

It's usually futile to try to do surgery on a automatic transmission. The life blood is the fluid. It is used to control it running through all those close tolerance valves in the valve body, and it's also used to lube the larger mechanical parts and to keep it cool. Once something mechanical fails, it sends metal debris throughout the whole thing, including the transmission cooler in the radiator. That may be what happened, the cooler in the radiator wasn't properly flushed and it sent debris into the rebuilt trans, contaminating and sticking various valves in the valve body.

I am a do it yourselfer, but I have never torn down a automatic trans. I went to a local shop and asked them how much to rebuild my trans if I took it out myself and brought it to them, and then put it back in myself. They said they would only cut $100 off the price and there would be no warranty. I asked why no warranty and they said they need to clean the radiator cooler out with their machine to make sure all the bad stuff was out, or they would not warranty the trans.

I have also seen guys buy rebuilt trannys online, and to get the warranty they are required to flush the cooler AND cut the line somewhere and install a included filter in the cooler line. It looks much like a inline fuel filter.

 

I wouldnt give up on it yet.
keep driving it maybe something will unclog or bust loose.

maybe drop the pan and see it the valve body bolts are snug.

who knows what lurks ha ha

 

And there is your problem most likly. Unite the kick down on the trans and just let it fully return to rest.

 

Yep when I saw that last line I said to myself that could be it right there!
You may have it tied back in the wrong direction, kick down, and why it will not up shift.
Dave ----

 

Here’s a few pics. I may get a video later, kick down is untied, still no luck. The fluid on the cross member is from changing the governors, the second pic showing where I’ve got the mod valve hooked up to the intake, also, how big of a difference would the fluid type make? And what would y’all suggest?

 

Just a long shot but is the rod the modulator acts on in place?