My power glide slips between 1st and 2nd. You have to lift your foot off the gas and then put it back on to shift. My parents are the original owner of the car and my Dad says it's been doing it as long as he can remember. When he had it looked at many years ago he says the mechanics would say drive it until it breaks if it doesn't bother you much and then we'll replace it.
A guy at work says that the Vacuum Modulator may just need adjusting. Is this true? And how is that done if that is the case?

If its original modulator, it may have a crack in the diaphram and need replacing. OE modulators are not adjustable.
Check the rubber interconnect hoses for cracking and replace them if you think they are questionable.

The modulator can be changed without dropping the pan, if you are steady.

Thanks Everett
It is original. Is this something that someone with limited skills (me) can accomplish in the garage? Any other tips you can provide would be helpful. I have an old Chiltons and didn't see anything in there about how to go about replacing the modulator. Thanks again

Oh man... Its broke beyond repair. Just have to upgrade I guess :D

Everyone here says to replace it with a TH-350 and you won't be sorry. If you want to retain it's originality... keep your old parts if you ever want to go back.

First, get a new modulator.
Get a wrench to fit the hex portion.
Jack up the car level with stands.
Disconnect the hose from the mod.
Use wrench to loosen the mod from the case.
Use hand to finish unscrewing the mod from the case. Pull straight out when unscrewed.
Transfer the short rod from the old one to the new one.
Use new gasket and insert new mod into case.
Screw mod into case.
Tighten with wrench.
Hook up hose, might replace hose if original.
Done.

Early cast iron case glides donot have a modulator. The later Alumiunm cases do, they can be tested with a vacumn brake bleeder. The second gear shift is a band that tightens down on to the drum, if my memory is right.

Well, I found the modulator. It's kind of hidden behind a cross member. I think I'll go after it Sunday. It looks and feels like metal hose going into the modulator. I thought it was supposed to be rubber to the mod? Does this just pull off? I ask because I don't want to force it and mess something else up causing me different problems.:confused:

There are rubber hoses on each end of the hard line.
And yes, the rubber connection hose does slip off. After being on for 40 years, it may take alittle force or s lit with a razor knife to split it and roll it off.

Early cast iron case glides donot have a modulator...

"Iron" PowerGlides ended in 1962 (except for a few truck applications).
So his original, and all Camaro's that used them, would be equiped with an Aluminum one.

The bands operate the Low and Reverse planitary set - the clutch pack locks to effect 1:1, or 'High' gear in a PowerGlide ...

And yes, I agree with others that the Modulator/Vac. Lines are most likely the cause of the hanging-upshift ...
But, I'd also check the throttle linkage to be sure it is hooked-up and adjusted correctly while you at it.
And I've seen a hanging Governor cause them not to upshift properly ...

OK
I put on the new modulator and now it won't shift at all. Went back and looked up the modulator (part # 1-4699) the guy at NAPA gave me and now find out that it is adjustable.

My question is...How do you adjust it?:sad: HELP Please

Vacuum line is hooked and no leaks.
Generally, they are pretty much adjusted for stock set-up. A 3/32 inch Allen wrench through the hose nipple to adjust. I would do one complete turn in either direction to see results.

There may have been a little rod, called plunger and a spring, came out with the old one or the rod may have stayed with the valve body and may be off center. Transfer this plunger and spring to the new one, a dab of petro jelly would hold it in place, then install. If plunger is out of place, it may be holding the valve in max position not allowing upshift. Then governor takes over for upshift as in WOT mode.

A little hollow rod I found on the driveway?? Does it go into the end that screws into the transmission? Is it just the hollow rod or did I loose something else?
Everett you are the man

Maybe a 1/2 inch long at most, 3/16 inch diameter. Plunger would fit into the new modulator hole, then assembly screws into the case.
Maybe a spring fitting over the plunger?

That's the rod I found on the driveway. I found no spring though??? The rod fits pretty good into the modulator hole on the end that screws into the case. Don't know if a spring would fit over it.
Are you sure there is supposed to be a spring?? If so it must have ended up in the grass to the side of the driveway. Then I am sunk!

Try it without the spring.

When I did mine, I didn't notice a spring either, but Motors Manual, 1974, shows a spring. This is why I suggested the spring.

OK. Thanks Everett. Just so I understand and then I will leave you alone.... The rod goes into the the hole in the threaded end that screws into the case, right??? I assume there is something in the case it contacts to hold it in place? You have been a huge help. I'll let you know then how it goes after work tomorrow

OK. The rod goes into the the hole in the threaded end that screws into the case, right???Yes. I assume there is something in the case it contacts to hold it in place?Shift valve on the valve body. You may want to smear some petro jelly on the plunger/rod to hold it in place. Thanks Everett, You have been a huge help. I'll let you know then how it goes after work tomorrowYou're welcome, let us know the outcome.

I would have to agree with the ones that say to replace it. I have a Powerglide and it does the same as yours. I had a shift kit put in it and it came with an adjustable modulator. It didn't help. What I did was disconnect the vacuum hose running to it and that helped A LOT. It gave it a very sharp low-high shift. Try disconnecting the vacuum hose and try it.

Mine does not have a spring.

Well I'm glad I apparently didn't loose the spring and found the plunger on the driveway.
You disconnected the vacuum hose to the Modulator?

Yes. Make sure you plug the port at the carb.

Well I put the plunger back in and now it shifts again, but it is slipping just like it was before with the old modulator. Oh Well. Thanks all for your comments.

When I take the modulator off should I be getting ATF coming out of that hole?? It looks like there is another valve in there.

Should not be any fluid as the mod would be above the oil level. Yes, there is an upshift valve, or an oil pressure regulator, to control the next upshift dependent upon the load, vacuum, or lack of vacuum, throttle is open, until the kickdown valve comes into play at WOT, then the governor takes over since there is no vacuum to control upshifting.

Whew!

Pull the dipstick and wipe the stick on a white rag. If oil is black and smells burnt, then trans needs an overhaul.

I checked the ATF fluid 2 days ago and it was clean. No odd color or burnt smell to it.
My next guess is that I have a bad upshift/throttle valve as I am getting ATF passing through it to the MOD port. Seems logical as my problem is in the upshift. Then again...what's logical???;) At least for now it's back to the way it has been for oh the last 20 years and I can shift it with my foot.

Does is slip the same if you manually shift from low to high?

I haven't tried that. Why??

And I haven't tried your vacuum hose trick yet. I thought the transmission needed the vacuum to work at all.:confused: What did you plug the carb port with?