GM Powerglide Question

[4by4bygod]

Hi All!

Anybody have one of these trannys? I'm looking to find out what MPH is normal for the thing to shift out of first, at both part throttle cruising, and flooring the SOB.

My dad is having difficulty with the one in his 66 chevelle. the thing shifts at 20 -25 mph regardless of how hard he mashes the gas. It will work fine if shifted manually. The car isn't driven very much.

Any guesses as to what could be wrong, if anything?

Thanks!

Tom

 

[bablazer73]

My god!! a Powerglide???
Last time I had one, I shifted it at 6,800 rpm!! It's been so long since I've even seen one!! But I think they still used a centrifical speed governor. The springs for them are cheap. you can access that from the side of the tranny. As to what it SHOULD shift at, i have no idea.

 

[4X4HIGH]

Check the vacuum hose to the modulator valve or maybe even replace the modulator valve.

 

[HarryH3]

The one in my old '70 Nova would upshift at 60-65 MPH if I was holding the pedal to the floor.

 

[4X4HIGH]

Unless someone installed a powerglide in a 70 nova it wasn't a powerglide. GM stopped using them about 1967 or 1968. It would have been a TH350

 

[bablazer73]

beg to differ a bit, but My all stock 70 nova, with a BIG 235ci 6cyl had a glide.

 

[diesel4me]

I had quite a few "Powerslides"

The powerglide was a good tranny,they even used it with air shift on dragsters,and many dirt track cars still run them--All the stock ones I had would shift at 15-20 mph in drive at light throttle,and if you floor it they wont upshift until 55-60 mph depending on the rear end gear ratio..Yours probably needs a new vacuum modulator,or the vacuum line or hose to it might be disconnected or leaking,the govenor is adjustable by changing springs,but unless the springs or weights screwed up its probably ok--a new modulator and fluid and filter change may cure your problem...if not,you'll have to take it in for a pressure check and see if its within specs...I'm not sure if the pwerglide had a throttle pressure hookup linkage to the gas pedal linkage,I'm thinking they did--if thats out of whack it will affect the shift points too...

GM used the Powerglide tranny until 1973 in passenger cars and light trucks(as far as I know never in a 4x4,only 2wd)--I wish they had used them in 4x4's,I bet they would oulast the TH350 trannys...the Powerglide had the lowest first gear ratio of any automatic GM ever made,except perhaps the 700R4...I had several of them and I beat the crap out of them,none ever failed!--one 68 nova I sold to a friend for a winterbeater used to shift it into reverse at 40-50 mph and smoke the skins off it--he did it many many times and it only broke the tranny mount,the tranny never had any issues at all,despite all the abuse!...

 

[4by4bygod]

The powerglide was a good tranny,they even used it with air shift on dragsters,and many dirt track cars still run them--All the stock ones I had would shift at 15-20 mph in drive at light throttle,and if you floor it they wont upshift until 55-60 mph depending on the rear end gear ratio..Yours probably needs a new vacuum modulator,or the vacuum line or hose to it might be disconnected or leaking,the govenor is adjustable by changing springs,but unless the springs or weights screwed up its probably ok--a new modulator and fluid and filter change may cure your problem...if not,you'll have to take it in for a pressure check and see if its within specs...I'm not sure if the pwerglide had a throttle pressure hookup linkage to the gas pedal linkage,I'm thinking they did--if thats out of whack it will affect the shift points too...

I appreciate all the replies folks... The vacuum modulator was the first thing we changed, haven't done the fluid / filter change yet, but we will. Is it common for the governor to crap out from just sitting? the tranny only has 60k miles on it.

It does have a throttle pressure linkage..I always called it the kickdown linkage.. are we talking the same thing? it's a rod that comes from a lever on the tranny and connects to the carb just below where the throttle linkage attaches. My dad changed from a 2 barrel carb to an edelbrock 4 barrel. Right now, the rod only gets pulled forward at WOT. could that be the source of the problem?

Tom

 

[diesel4me]

yup!

Yes,if that throttle linkage thing is out of adjustment,it will alter the shift points of the tranny--I think it also "tells" the tranny what internal pressure to run at,so I wouldnt drive it too far out of adjustment or you might fry the clutches in it by driving it with the pressure too low...Sorry,I dont have a book with the adjustment procedure handy,if you need me too look it up I can and post back later(but I have no way to post any photos)-
-Its probably that linkage thats causing your problem,when you put the 4bbl carb on it probably changed the position of the rod enough to throw it out of whack..I'd adjust the linkage before going any further right now--no sense in putting in a new filter and fluid in a tranny that might be toast...The Powerglides used a fine brass screen as a filter,most of mine I just took the filter out and washed it in a bucket of gas and put it back in ,using a new gasket on the pan if you had too..

 

[4by4bygod]

.Sorry,I dont have a book with the adjustment procedure handy,if you need me too look it up I can and post back later(but I have no way to post any photos)-

If you can do that, I'd appreciate it.

Thanks, Tom

 

[HarryH3]

Unless someone installed a powerglide in a 70 nova it wasn't a powerglide. GM stopped using them about 1967 or 1968. It would have been a TH350

You've been misinformed. I had not one, but two different 1970 Nova's that came with Powerglides. Both were bone stock.

 

[diesel4me]

I'll try to find the adjustment procedure...

Sorry I havent had time too look for the adjustment procedure for the powerglide--it snowed 14 inches here last night,and I have been plowing all day!..I'll try to post it here later tonite if I can..

 

[BlueBlazer]

My 68 Firebird with a powerglide from the factory had no linkage going to the trans, only a TH400 style kickdown switch that was mounted on the carb.

 

[gravdigr]

Unless someone installed a powerglide in a 70 nova it wasn't a powerglide. GM stopped using them about 1967 or 1968. It would have been a TH350

Incorrect. My 70 chevelle came stock with a powerglide. TH350 has 1, 2, and D. Powerglide has L and D. Easy to check in the shift indicator panel.

My powerglide was set to shift to drive at about 30mph part throttle. At full throttle I could run it to 70mph before shifting. I had a guy in a cute little sports car (a honda something) pull up beside me at a stoplight to the interstate onramp. We floored it and he shifted from 1st to 2nd to 3rd while I was still in low smoking his ricer.

Drag racers love the powerglide.

 

[4X4HIGH]

I may be incorrect about the year that GM stopped using the powerglide but ALL the books i have at my shop say that powerglide was used in GM cars up until 1968. I also called the dealer and ask a buddy of mine who just retired from a GM dealership and he also said 1968.

 

[HarryH3]

From page 197 of the "Chilton's Repair and Tune-up Guide for Chevy II & Nova-1982-1977":

"There are two basic automatic transmissions. The first is the two-speed Powerglide which was available until mid-1973. The second type is the three-speed Turbo Hydra-Matic which is available in three load capacites, Turbo Hydra-Matic 250, 350, and 400"

 

[4X4HIGH]

I will have to take another look at my book tomorrow then. My chiltons and motors book both said 1968 was the last powerglide, but once again that doesn't mean the book is correct either. I have found many mistakes in both chiltons and motors books in the past but more so with the chiltons.

 

[4by4bygod]

Sorry I havent had time too look for the adjustment procedure for the powerglide--it snowed 14 inches here last night,and I have been plowing all day!..I'll try to post it here later tonite if I can..

I found the adjustment procedure, so you don't have to worry about it. I appreciate the offer and all of the responses from everybody.

Tom

 

[diesel4me]

Sorry I didnt get back to you...

It seems my 68-75 GM book is missing--I think I let someone borrow it,and I havent got it back!- -my Chilton's book is useless,it doesnt say how to adjust it...sorry I didnt get back to you sooner,its been kinda crazy here this week!--hope the adjustment cures your shifting problems...