Hey guys, I'm looking for some diagnostic advice for my '66 coupe. It's a basic 327-300 with a 2 speed power glide trani. When first started and driven, it takes about 10 min's of just babying it until it will shift from 1st to 2nd. Once it shifts, it will then shift perfectly every time while l drive it that day.....unless it sits for awhile. Letting it warm up does not help. It doesn't pull (try to shift), it will just finally smoothly shift into 2nd...I don't think it's the modulator or vacuum. Any advice/ suggestions would be greatly appreciated.
Meanwhile...Wrap your *** in fiberglass
Buy a 'Vette

 

Check for fluid in vacuum line- bad Modulator valve. Replace vacuum hose! Easy first try. Lots of threads!

 

Say HI!!!
It appears this is your first post and thus new to the forum. You will be hounded until you post pictures of your ride. We love Eye Candy.

As far as your problem, I would have guessed the modulator as itsforfun has suggested. The only other thing I can think of that may be related would be the fluid viscosity which would thin out as it gets warm. Have you changed the fluid and filter recently? There are professionals on here that will eventually chime in and are old enough to remember the power glide. I owned quite a few, but that was many years ago.

Ron

 

Not the modulator valve but the vac modulator itself possibly. First, make sure you are getting good vac at the modulator. Engine idling, pull hose off mod, idle should speed up, put finger over end of hose and you should feel vacuum. Should be about 14-16 inches I believe if you have gauge on it. Be careful under car with it running. Make sure vac hoses on engine are all good, any vac leak up top can cause a loss down at trans.

Shut it down, leave hose off for 15 minutes and see if fluid drips out mod or hose, if it does it's bad internally. Usually if the diaphram is good in modulator will work. But lots of times vacuum from engine is low from carbon in vac line. If you change modulator don't loose the 1 inch pin in end of modulator, if it has a spring on it you can reuse it or discard it. We always tossed the spring but has to have the pin. Don't forget gasket on new mod. Years ago there was a 6 cyl and 8 cyl modulator, I used to stock both but don't know if there is one size fits all now or not.

Check passing gear linkage on left side of case to make sure it isn't sticking down in detent mode, causes late delayed shifts. Should have a spring on it to pull it back up.

Other possibility is sticking or problem with the govenor on output shaft/flange inside extension housing. A pin slides thru the govenor body and held at each end by two little e-clips. Govenor valve sticking is rare unless trans has a lot of gunk and trash inside.

Very little trouble with PG valve bodys with stuck valves unless trans is full of trash from more serious problems. Last resort is direct clutch drum problem with hard, torn or worn out lip seals on piston and the clutch pack itself worn out.

Also, if you have the vac mod off the trans to replace it get a pocket magnet and see if the actual modulator valve itself in the case is free. Just touch valve with magnet and slide it in and out, it should move easily. if it's stuck pull it out and find out why. If valve has burrs on it you will have to clean it up with some fine sandpaper but I don't like doing that unless you are forced to because transmission valves have self cleaning edges on valve lands and if you get to aggressive sanding you destroy those edges so go easy with the sanding.