1961 Chevy C20 Apache with a 1967 drive train!

[61Chevy454]

Hey guys, I'm a Ford man but yesterday, I drove 3 hours and paid $3000 for a 1961 Chevy C20 Apache 4x4 long bed stepside with a 454 and a TH400. When I test drove the thing, it ran good, pretty much what you'd expect from an old truck. The motor has an Edelbrock performer intake, headers, a Mallory ignition box, and an Edelbrock carb.

About 37 miles from home, the thing wouldn't shift into second... It would go up to around 2000 RPM and then act like you put it in neutral. If you mash the thing, it will kick down into first and go. Sometimes, the RPM it goes into neutral at changes. After it does that, it will not down shift until you let it go really low and give it some gas. It has fluid in it. Occasionally, it will shift into second but not very often. It won't shift into third either, except once when I had it up to 60. I had to limp the thing 30 mph all the way back to Missoula... Took me 6 hours and I got home a 3:30AM last night. It did not magically heal itself over night, sadly, except when it was cold, it did go into second.

Any ideas?

[Bigdav160]

Cool truck but 454/TH400 drivetrain might have been from a 1977 but not a 1967.

For not shifting and acting like it was going to neutral I would check the governor. Especially the gear part.

[61Chevy454]

Originally Posted by Bigdav160

Cool truck but 454/TH400 drivetrain might have been from a 1977 but not a 1967.

For not shifting and acting like it was going to neutral I would check the governor. Especially the gear part.

Sorry about the wrong post. Admin, please move it if needed. I'm just hoping the tranny isn't dead. I really don't want to do my first tranny rebuild in my apartment kitchen, haha.

[Steeveedee]

Sounds like the vacuum modulator or the line to it. Pull the modulator vacuum hose up on the manifold and see if there is ATF in it. Since it is a 4X4, it might be easier to just pull the line at the trans. The vacuum modulator is on the passenger's side of the trans. If you get fluid out of it, it's bad. It might be bad anyway, but fluid in the vacuum line is a certainty that it is toast. And they can go bad, just like that, too.

[Coley]

Also check to make sure the vacuum line is intact that goes from the intake manifold down to the (modulator?) on the transmission.
If that is off, missing or broken you will get a lot of weird shifting results.

Coley

[MARKDTN]

Originally Posted by Steeveedee

Sounds like the vacuum modulator or the line to it. Pull the modulator vacuum hose up on the manifold and see if there is ATF in it. Since it is a 4X4, it might be easier to just pull the line at the trans. The vacuum modulator is on the passenger's side of the trans. If you get fluid out of it, it's bad. It might be bad anyway, but fluid in the vacuum line is a certainty that it is toast. And they can go bad, just like that, too.

X2 on the modulator

[61Chevy454]

Originally Posted by Coley

Also check to make sure the vacuum line is intact that goes from the intake manifold down to the (modulator?) on the transmission.
If that is off, missing or broken you will get a lot of weird shifting results.

Coley

As far as I can tell, there isn't a single vacuum line on the manifold going to anything... I do see a strangely twisted metal line on the back... Hmmm...

[61Chevy454]

Originally Posted by 61Chevy454

As far as I can tell, there isn't a single vacuum line on the manifold going to anything... I do see a strangely twisted metal line on the back... Hmmm...

It shifts OK when it's cold. The hotter it gets, the harder it is to get it into 2nd. I'm gonna change the fluid and filter today.

[Coley]

I'm pretty sure you need a vacuum line running down to the a modulator which would be located on the passenger side (forward) on the transmission. It is round looking diaphragm device with a vacuum port on it.
I'm not sure what port it connects to up on the engine but usually, on the stock intake there is a vacuum port (spiggot) on the manifold...or maybe on the carb?...that the rubber vacuum line runs down from to the transmission (modulator) port.
Visually Check to see if you have the modulator diaphragm unit on the trans...it would be sticking out towards the side of the truck (at right angles to the driveline)....is there anything on its vacuum port/spiggot? ...any quick pics of the passenger side of the trans available?...and maybe of the back of the intake?
Regardless, maybe some of the other guys more familiar with the TH400 can weigh in here as well.
(note: I also recommend 'googling' GM TH400 transmission modulator vacuum...this will help with some of the understanding)
Keep us posted.
Coley

[hugger6933]

That line needs to be manifold vacuum [under the throttle blades] that is why there is normally a fitting in the intake for it. Make sure the line isn't bent anywhere where air can flow all the way through and also make sure the rubber hoses on the ends aren't sucking shut when the truck is running.Those rubber hoses collapse all the time once they get a little age and cause all sorts of problems.

[61Chevy454]

Originally Posted by hugger6933

That line needs to be manifold vacuum [under the throttle blades] that is why there is normally a fitting in the intake for it. Make sure the line isn't bent anywhere where air can flow all the way through and also make sure the rubber hoses on the ends aren't sucking shut when the truck is running.Those rubber hoses collapse all the time once they get a little age and cause all sorts of problems.

I'm an idiot. The tranny is a 700R4.

[57taskforce]

Check to make sure you tv cable up at the carburetor is hooked up. Do a little research as the tv cable set up is crucial to the longevity of a 700r. If it's not going into second my gut says it's rebuild time but I've been wrong many more times than once in my life.