75 Grand Lemans auto only has first gear.

[Karnawgie]

I bought my project lemans awhile ago for 500$ and have gotten it running and worked on the brakes. After the first test drive, I've discovered I've only got first gear and it won't shift any further in drive.

I rolled down a hill after maxing out first pretty much and it not shifting, popped it into neutral, and put it back in drive and it drove into the driveway.

I'm not sure what transmission is in the car, but I've heard shifting is dependent on vacuum. It's a 350 w/ a Rochester 2 barrel.

I'm sure there's a few tell tale things I should check first and hopefully it's an easy fix. Can anyone tell me some of these things to check out/where? Any input would be appreciated, thank you.

 

[melsg5]

Is the vacuum line from engine connected to the transmission vacuum modulator?

 

[Karnawgie]

I do believe the vacuum line is connected to the modulator. The rubber hose from the modulator is connected to a hardline that runs on top of the frame up to the cannister. The cannister has three lines off of it.

1- A line that wraps back around and connects to an ac condenser line.
2- The line to the transmission.
3- A hose that leads nowhere.

Below are two pictures. One of the modulator and one of the cannister and its lines.


https://pontiacforum.com/pontiac/forums/pontiac-lemans-forum.22/

 

[melsg5]

That doesn't make sense. The canister is evaporative control for gas vapors. It needs to be connected to a vacuum source to work and can't imagine why the modulator is connected to it and it has nothing to do with AC. Turn on the engine, disconnect the vacuum line going to the modulator. Do you feel vacuum on the port that the modulator was connected to. If not, the transmission will not shift. Google 1975 charcoal canister vacuum lines. All Pontiacs will be the same setup, carb vacuum, gas tank, purge, and bowl vent. No modulator no AC.

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[92 Sunbird LE]

If connection to full vacuum doesn't help, ( pic shows a new modulator) could be a stuck governor.....

Doug in P.R.

 

[cammerjeff]

I agree with what Doug has said, but another possiblitly is a burnt trans, I had a TH400 do the same thing after it was run low on fluid and the clutch packs had welded themselves together not allowing it to shift gears.

I hope it is just a vacuum source issue or a bad Vacuum modulator, both easy and cheap fix's.

 

[Karnawgie]

It wasn't until this week I got back around to working on the Pontiac.

Among other things I followed the line from the transmission modulators vacuum port and I was completely wrong with my assessment of the vacuum cannister lines. They mostly lead to open ended hoses.

The line ran along the firewall and was connected to nothing near the carb. I roughly attached it to the first hose I saw with vacuum and the transmission works great!

Holding my finger over the line while running was my measure of if It was getting vacuum or not, thanks to melsg5.

I also appreciate all the other responses I've gotten. Your help has enabled an old parts car to be put back on the road for the first time in over 10 years and I'm having a blast driving it,

 

[cammerjeff]

Great news, thanks for the update!

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