So I have a problem...

[mcgoo26]

So, I am fairly new to C-10s, TH350s and everything, but everything is straight forward...or so it seems. So here is my issue: This last weekend I dropped the transmission to change out the torque converter. Reason being, when driving the truck, the transmission doesn't seem to want to shift at all when in drive. The engine will be at high RPMs, but takes forever to shift. After it is up to 30 mph or so, everything seems fine. So a co-worker who use to work in a garage suggested changing the torque converter. Basically going from least involved and expensive to more involved and expensive. So back to my issue. Over the weekend I swapped out the torque converter and even the modulator. I primed the new converter before install. It took about four quarts of fluid. I checked the transmission fluid level while at idle and it was just above the add line. I pulled it out of the driveway with no issues and took it for a test drive. A little better on the shifting, but not quite. So I parked it for the night in the driveway. Today I decided to try adjusting the modulator. I turned it clockwise about a turn or so and went about a half mile down the road for gas. The truck seemed to function better and actually responded. So I pulled into the drive way (which has an incline) to make about a half turn clockwise adjustment on the modulator. I make the adjustment and start it up for another test drive. Then the problem occurs. I have no reverse or neutral. When I put the truck in reverse, it lunged forward when pressing the gas. I put it in neutral, lunges then stops as if in park. I adjusted the linkage on the trans and on the column. Same result. I am at a lost on what may be the issue. I even backed the modulator off two turns to see (but from what I know, that doesn't affect this problem). Any help on this would be appreciated. Like I said, I am new to working on c10s and everything. Sometimes, things aren't as straight forward as they seem with old vehicles. Thanks in advance for any advice or pointers.

[70']

Doubtful the problem was torque converter related. Probably hardened lip seals in the transmission, had that happen to me in a car once. Once those seals become stiff and hard they can make your trans do all kinds of crazy stuff. The shifting problem could also have been a vacuum leak in the line going to the advance on your distributor. May even be a soft vacuum line on the advance too which will collapse when under vacuum.

[mcgoo26]

Thanks. Ill check those lines out tomorrow. Tell me if this sounds "stock". From the modulator on the trans there is a soft line elbow which connects to a tube (guessing aluminum) that is routed on top of the intake manifold which connects to the vacuum advance line which is a hose. Im going to double check all this tomorrow. See where it leads.

[mcgoo26]

So I checked out the lines, and everything looks good-to-go. I checked it out today and when it is in reverse it starts to move forward then stops as if you would by putting it into park with out coming to a complete stop in the driveway. Neutral isn't neutral, it the truck creeps forward fairly slowly. Checked the fluid, good-to-go. It doesn't smell burnt and as far as I can see it doesn't have any metallic material in it. Kind of at a loss right now. Any help would be appreciated. Thanks in advance.

[EARNHARDT#3]

Rip that trans back out and have it rebuilt. Not all that expensive.

[mcgoo26]

Originally Posted by EARNHARDT#3

Rip that trans back out and have it rebuilt. Not all that expensive.

Thanks. Working my way to that point. Want to exhaust every option first Everything worked fine (to a degree) before the torque converter swap. Thanks again. Rough estimate on how much a rebuild at a shop would run? I like your name btw.

[daily_danger]

The lunges and stops as if in park sounds weird. Its possible, but unlikely the linkage in the pan is not working properly. Sounds like a candidate for a rebuild to me though. either piston seals or fluid crossing path because of valve body sealing issues.

If you need internal linkage reference photos, I may still have mine. I just rebuilt my 350

[mcgoo26]

Thanks. If you have the photos that will be useful. Just odd it started doing this. I thought about rebuilding it myself, but figured I'd work from least time involved and cost effective to more involved to more expensive. Thanks again.

[70']

I would guess you could get a rebuilt trans swapped for 500 bucks or so if you do the R&R. If the shop does it turn key, a grand or so.

[swamp rat]

You adjusted the modulator a second time 1 full turn then the problem started, adjust it back to where it was before you do anything else.

[daily_danger]

I'm sorry I don't have my reference photos any more. I'm always tight for space on my phone. I looked at the ones in Ron Sessions' book, but being black and white, they wouldn't do you much good. I couldn't find a joint I trusted to rebuild my tranny for less than $1000 down my way, your results may very. I popped my auto trans cherry and rebuilt it myself. Wasn't bad, put me back less than a grand including new tools and a new converter. If you're thinking of tackling it, I would recommend Ron's book. It helped me a ton.

[franken]

There are also C20, C30, K10/20, GMC models like 1500/2500/3500, etc.
Why limit yourself to C10?
I was thinking a modulator or shifter in the wrong position problem. If the truck is in a lower gear, it won't come out till ~2x normal speed. Could be that drive is in the spot of neutral on the indicator.