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Discussion Starter · #1 ·
Okay, let me be perfectly clear here, we're talking about a stock powerglide behind a stock engine, not a "built 'glide" in a dragster....

My question is, let's say a person had a Chevelle equipped with a powerglide, and wanted to partake in a situation that would require rapid acceleration from a stand-still... :) Just imagine with me here a second...

What's the deal with the down-shift mechanism. When you floor the acclerator pedal, a rod swings down and hits the shift linkage (we're talking about a column shift car here) and apparently it forces the powerglide into low???????

I'm confused as the original owners manual says not to drive above 40 mph with the powerglide transmission in low....but if you floor it for passing or rapid acceleration aren't you shifting it into low anyway???


The bottom line is, if you go back to my original scenario, wouldn't it make more sense just to shift it into low before taking off? Or do you have to keep it in Drive to start out with if there is some sort of magic that goes on inside the tranny (vacuum controls?)....

:confused:
 

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Years ago my 69 Camaro came with a PG behind a 255 HP 350. I added headers, Z28 intake with 600 Holley and had a lot of fun thinking it was fast. With the original 2.56 gears, it would downshift at 60+ mph. Low on a glide is like 2nd on a turbo. Car would take off in either low or drive.

My next mods were adding 3.55 geared 12 bolt and Vega torque converter - remember these?? Worked great for a little while, I was young (stupid) and didn't add a transmission cooler - it cooked after a few months but was a way more fun than stock. Would really roast the old F60x14 bias tires!!

I still have that car now but it has a 427 with a 4 speed. Purchased the 427 in 1978 for a sum of $300 - was a complete 435 hp tri-power engine from 68 Vette. Still in use today only with single 950 HP carb, Ultradyne hydraulic cam and MSD distributer. Kind of old school but it works.

Wish I still had the old PG - would likely be a good combo with today's new drag radial tires. Even more, wish I had all the A/C parts I took out to save weight and threw in the dumpster.
 

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Passing is regulated by TV linkage, vacuum at modulator and vehicle speed from govenor. No magic, no black box, just good engineering. I had a 194 cu. in. 6cyl convertor and a Trans go shift kit when I first ran a PG. My 67 Camaro ran F/OA with a 350, 295HP. The Stocker cam it had won't work with the stock convertor and the 6 cyl was marginal. The bottom end was tortise like, but after 300 feet it really pulled. It went 13.50's at 105 MPH. Lots of guys lifted early and I blew past them like a rocket. The next year I got a manual VB and a "real" A-1 4500 convertor, then the Camaro worked really well. We wired the TV pulled right to the Passing gear detent to boost line pressure. It hand shifted well around the pits and at speed.

The 40MPH in Low is to keep the customer from over reving the engine. Most street "stock" PG equipt Chevys would go about 60 MPH at WOT in Low.

Steve O.
 

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Really a 4 speed was THE way to go "back in the day". ;)
 

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The same holds true today.:D
 

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Okay, let me be perfectly clear here, we're talking about a stock powerglide behind a stock engine, not a "built 'glide" in a dragster....

My question is, let's say a person had a Chevelle equipped with a powerglide, and wanted to partake in a situation that would require rapid acceleration from a stand-still... :) Just imagine with me here a second...

What's the deal with the down-shift mechanism. When you floor the acclerator pedal, a rod swings down and hits the shift linkage (we're talking about a column shift car here) and apparently it forces the powerglide into low???????

I'm confused as the original owners manual says not to drive above 40 mph with the powerglide transmission in low....but if you floor it for passing or rapid acceleration aren't you shifting it into low anyway???


The bottom line is, if you go back to my original scenario, wouldn't it make more sense just to shift it into low before taking off? Or do you have to keep it in Drive to start out with if there is some sort of magic that goes on inside the tranny (vacuum controls?)....

:confused:
The Power Glide has two forward speeds. Low and High (direct drive). In Drive you start in Low and it automatically shifts into High. The speed it shifts at varies by how far down you push the accelerator and that's the extra linkage you refer too. It's called the Kickdown linkage and it controls the TV or throttle valve and is internal, it doesn't actually move the shift linkage. Most stock Power Glides shift at a much lower RPM than one would want for maximum acceleration. So you are right if desiring maximum acceleration one would normally start in low, not to take off any faster but to hold low gear longer as it would not shift until you moved your shifter into drive. Automatic downshifting (kickdown) from high to low by flooring the acelerator normally only engages at a modest speed so it would not be un common to floor the accelerator at say 45 mph and the transmission not downshift. The driver could manually move the gear lever to low while still floored, this would engage low and he could hold it there until the engine reached the desired rpm then manually shift into Drive. There is also a vacuum control (modulator) but that is mainly to cushion the one big shift. In my younger days I discovered some cars could reach up to 105 mph indicated in low with high gears. A 67 Camaro with a 295 H.P. 350 and Power Glide was one. In all out desperate circumstances where loosing was not an option brave people were known to hold the accelerator to the floor in neutral until the engine reached maximum rpm then pull the shift lever into low!!! Neutral Start. Zora Duntov once was quoted as stating you could do this 50 times with a Power Glide before breaking the transmission. This was just after he made a high 10 second run in a stock 69 Corvette with a Turbo 400 and slicks. The magazine testers were not able to match his claimed 10 second run with said Corvette before he drove and he told them your not doing it right. He pulled to the starting line and floored it as the lights came down, selected low and lurched off to the claimed high 10. He said a Turbo 400 can do this even more times than a Power Glide but I don't know of anyone that has ever attempted such a thing. Not to mention it would be strictly prohibited during any sanctioned or sober event. What model Chevelle engine are you dealing with??

Thanks
Randy
 

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Discussion Starter · #9 ·
Randy-


Great post, this was the kind of info I was looking for...

But I'm still unclear on some things....okay, based on what I've read, there's no real advantage to putting the transmission in LOW before flooring it off the line? Remember, this is a stock powerglide. I've got a 307 with 3.08 rear end (non-posi). I certainly won't be doing any street racing but was just curious on what I could do without trashing the original #'s matching drivetrain.

On the downshift linkage, so it doesn't knock the shift mechanism control? I could swear mine hits the connector where the shift linkage connects to...
 

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Randy-


Great post, this was the kind of info I was looking for...

But I'm still unclear on some things....okay, based on what I've read, there's no real advantage to putting the transmission in LOW before flooring it off the line? Remember, this is a stock powerglide. I've got a 307 with 3.08 rear end (non-posi). I certainly won't be doing any street racing but was just curious on what I could do without trashing the original #'s matching drivetrain.

On the downshift linkage, so it doesn't knock the shift mechanism control? I could swear mine hits the connector where the shift linkage connects to...
Correct, no difference in selecting manual low for off the line accelaration. It will just stay in low as long as you desire rather than up shifting automatically. If you look closely you should see the kickdown linkage is independant of the shift linkage. Your shifter is linked to the arm on the transmission and as you move it you will feel the "detents" P R N D L. that are provided by the "rooster tail" inside the transmission. The kick down is another linkage that connects the transmission to the carb to sense the throttle position. It moves smoothly without any detents. If you examine the linkage as the carb opens you can watch it's action and it looks like it is acting on the shift arm but it's actually moving a sleeve that the selector shaft runs through. This way two things can happen at the same time through one hole in the transmission. Tell us about your car and your goals. I happen to like 307's and P.G.'s but they aren't exactly the best combination for blazing off the line acceleration. A high stall torque convertor will help along with rear gears and not be seen but cruising speed and mpg will suffer. A long time ago I built a 66 Bel Air 4 dr sedan with a 283, P.G. and 5:13 rear gears with intentions of NHRA class racing but just street raced it instead. It was bone stock looking and was fun for short bursts of acceleration.

Thanks
Randy
 
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