Help with missing part for a Powerglide
Thread Starter
Racer
Joined: Oct 2013
Posts: 251
Likes: 24
Help with missing part for a Powerglide
Today I removed the vacuum modulator from our '64 aluminum Powerglide. According to the FSM there is suppose to be a plunger that fits between the modulator and the valve. Ours doesn't have this part. I went to NAPA and they told me that the part is no longer available and I should try to find one at a transmission shop. I went to 3 shops that repair old transmissions, and none of them had one.
One shop told me that the part looks like a roll pin. The illustrations I've seen look similar to a roll pin, but they look more like a tube.
The other 2 shops told me the pin is solid. One shop said it's 1.450" +/- 0.060" but the illustration he used didn't look like a factory modulator. That seems too long. When scaling a picture of the modulator and the plunger side by side, the plunger looks closer to 1.250".
Does anyone have a spare plunger, or does anyone have an accurate length so I can make a plunger?
One shop told me that the part looks like a roll pin. The illustrations I've seen look similar to a roll pin, but they look more like a tube.
The other 2 shops told me the pin is solid. One shop said it's 1.450" +/- 0.060" but the illustration he used didn't look like a factory modulator. That seems too long. When scaling a picture of the modulator and the plunger side by side, the plunger looks closer to 1.250".
Does anyone have a spare plunger, or does anyone have an accurate length so I can make a plunger?
Drifting
Joined: Sep 2004
Posts: 1,470
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I just called my friend that I sold 3 Alum PG Cases to. He said one still had the Mod screwed in it. He measured the "pin" and it measured 1 inch long. It's nothing more than a hollow roll pin. Has to fit into the open end of the modulator and contact the valve in the case. Don't remember if the valve is hollow or a flat end, shouldn't matter as the valve contacts it.
But anyway he said it is 1 inch long.
With modulator "pins" you usually want them to just contact the modulator valve in the case and inside the modulator itself with very little to no pre-loading of the valve. Easy to check with a push in type modulator but harder with a screw in modulator because you have to allow for the threads on the modulator.
But anyway he said it is 1 inch long.
With modulator "pins" you usually want them to just contact the modulator valve in the case and inside the modulator itself with very little to no pre-loading of the valve. Easy to check with a push in type modulator but harder with a screw in modulator because you have to allow for the threads on the modulator.
Last edited by J.Moore; Oct 25, 2017 at 05:55 PM.
Le Mans Master
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Drifting
Joined: Sep 2004
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Good to hear and glad it solved the shift problem. That was, is a common problem with modulator pins, guys remove the modulator and the pin falls out usually in the drain pan and is forever lost. Without that pin the modulator is sort of "dead" even with engine vacuum pulling the valve that 1 inch gap with no pin kills any pressure increase. Fords with the C4 and C6 were worse as they had various length pins for all the different modulators used thru the years. I used to keep a bin box full of assorted length pins.
Too long of a pin and shifts are late and firm, too short a pin and shifts are early, soft and usually flare-ups. No good.
Melting Slicks
Joined: Jan 2007
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From: Pasco Florida
I think there's also supposed to be a short damping spring that rests on the outer diameter of the valve. Most are missing though. The unit will work without it.
Last edited by Critter1; Oct 26, 2017 at 09:43 PM.
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Drifting
Joined: Nov 2007
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From: Hightstown NJ
All Toledo and Cleveland Powerglides stamped 911 (Sept 11th '62) and later used the plunger pin. The spring around the end of the valve was used in production but not really required for service. The pin was p/n 3830311 to go with a 3830276 modulator
All the '62 Powerglides and very early '63s had a valve that had an extension on it which did the same thing as the plunger pin (and used no spring) They used a 3789122 modulator.
Verne
All the '62 Powerglides and very early '63s had a valve that had an extension on it which did the same thing as the plunger pin (and used no spring) They used a 3789122 modulator.
Verne
Melting Slicks
Joined: Jan 2007
Posts: 2,842
Likes: 622
From: Pasco Florida
All Toledo and Cleveland Powerglides stamped 911 (Sept 11th '62) and later used the plunger pin. The spring around the end of the valve was used in production but not really required for service. The pin was p/n 3830311 to go with a 3830276 modulator
All the '62 Powerglides and very early '63s had a valve that had an extension on it which did the same thing as the plunger pin (and used no spring) They used a 3789122 modulator.
Verne
All the '62 Powerglides and very early '63s had a valve that had an extension on it which did the same thing as the plunger pin (and used no spring) They used a 3789122 modulator.
Verne
Did you know the original PG modulators were adjustable? During a change, the old and new modulators were to be placed back to back with a rod about two inches long inserted in both units. On the pin, a line should be marked in the center of the rod. As both modulators are pressed together against the rod and spring tension, note the movement of the line on the center of the rod. To be correct, the center mark should not move more to one or the other modulators. To adjust, insert a small flat blade screwdriver into the vacuum end and turn the small screw.
I don't think aftermarket modulators had this adjustment.
Melting Slicks
Joined: Jan 2007
Posts: 2,842
Likes: 622
From: Pasco Florida
All Toledo and Cleveland Powerglides stamped 911 (Sept 11th '62) and later used the plunger pin. The spring around the end of the valve was used in production but not really required for service. The pin was p/n 3830311 to go with a 3830276 modulator
All the '62 Powerglides and very early '63s had a valve that had an extension on it which did the same thing as the plunger pin (and used no spring) They used a 3789122 modulator.
Verne
All the '62 Powerglides and very early '63s had a valve that had an extension on it which did the same thing as the plunger pin (and used no spring) They used a 3789122 modulator.
Verne
Drifting
Joined: Nov 2007
Posts: 1,711
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From: Hightstown NJ
Thanks Verne.
Did you know the original PG modulators were adjustable? During a change, the old and new modulators were to be placed back to back with a rod about two inches long inserted in both units. On the pin, a line should be marked in the center of the rod. As both modulators are pressed together against the rod and spring tension, note the movement of the line on the center of the rod. To be correct, the center mark should not move more to one or the other modulators. To adjust, insert a small flat blade screwdriver into the vacuum end and turn the small screw.
I don't think aftermarket modulators had this adjustment.
Did you know the original PG modulators were adjustable? During a change, the old and new modulators were to be placed back to back with a rod about two inches long inserted in both units. On the pin, a line should be marked in the center of the rod. As both modulators are pressed together against the rod and spring tension, note the movement of the line on the center of the rod. To be correct, the center mark should not move more to one or the other modulators. To adjust, insert a small flat blade screwdriver into the vacuum end and turn the small screw.
I don't think aftermarket modulators had this adjustment.
Thanks
Verne
Drifting
Joined: Sep 2004
Posts: 1,470
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And also, the 6 cyl and 8 cyl modulators for Alum PG were different too.
Yep, remember seeing that cap on the band adjustment screw, and the spring on the valve, most times that spring was pitched in order to make the 1-2 shift a little firmer.
Band adjustment- loosen nut, tighten screw 70 inch pounds and back off 3.5 turns. Seemed a little loose and we usually did 2.5 turns, could never tell a difference in function.
For drag racing Powerglides I set them at 3.5 turns and never had a band failure even using transbrakes with between 600 and 1000 1/4 mile and 1/8 mile runs.
Yep, remember seeing that cap on the band adjustment screw, and the spring on the valve, most times that spring was pitched in order to make the 1-2 shift a little firmer.
Band adjustment- loosen nut, tighten screw 70 inch pounds and back off 3.5 turns. Seemed a little loose and we usually did 2.5 turns, could never tell a difference in function.
For drag racing Powerglides I set them at 3.5 turns and never had a band failure even using transbrakes with between 600 and 1000 1/4 mile and 1/8 mile runs.
Melting Slicks
Joined: Jan 2007
Posts: 2,842
Likes: 622
From: Pasco Florida
And also, the 6 cyl and 8 cyl modulators for Alum PG were different too.
Yep, remember seeing that cap on the band adjustment screw, and the spring on the valve, most times that spring was pitched in order to make the 1-2 shift a little firmer.
Band adjustment- loosen nut, tighten screw 70 inch pounds and back off 3.5 turns. Seemed a little loose and we usually did 2.5 turns, could never tell a difference in function.
For drag racing Powerglides I set them at 3.5 turns and never had a band failure even using transbrakes with between 600 and 1000 1/4 mile and 1/8 mile runs.
Yep, remember seeing that cap on the band adjustment screw, and the spring on the valve, most times that spring was pitched in order to make the 1-2 shift a little firmer.
Band adjustment- loosen nut, tighten screw 70 inch pounds and back off 3.5 turns. Seemed a little loose and we usually did 2.5 turns, could never tell a difference in function.
For drag racing Powerglides I set them at 3.5 turns and never had a band failure even using transbrakes with between 600 and 1000 1/4 mile and 1/8 mile runs.
Weren't the early 6 cyl PG's air cooled and had great big holes on the case area around the converter?
Le Mans Master
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And also, the 6 cyl and 8 cyl modulators for Alum PG were different too.
Yep, remember seeing that cap on the band adjustment screw, and the spring on the valve, most times that spring was pitched in order to make the 1-2 shift a little firmer.
Band adjustment- loosen nut, tighten screw 70 inch pounds and back off 3.5 turns. Seemed a little loose and we usually did 2.5 turns, could never tell a difference in function.
For drag racing Powerglides I set them at 3.5 turns and never had a band failure even using transbrakes with between 600 and 1000 1/4 mile and 1/8 mile runs.
Yep, remember seeing that cap on the band adjustment screw, and the spring on the valve, most times that spring was pitched in order to make the 1-2 shift a little firmer.
Band adjustment- loosen nut, tighten screw 70 inch pounds and back off 3.5 turns. Seemed a little loose and we usually did 2.5 turns, could never tell a difference in function.
For drag racing Powerglides I set them at 3.5 turns and never had a band failure even using transbrakes with between 600 and 1000 1/4 mile and 1/8 mile runs.
Set my aluminum glide band (63 Impala) 2.5 turns and it shifts like a Turbo 350, it does go into gear quick from park, and I thought maybe I was to aggressive, but that was 16 years ago and 21,000 miles. No change no muss, no fuss. Prob the best automatic ever devised (from a longevity standpoint, not performance).
Dan
Drifting
Joined: Sep 2004
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Some of the V8's may have been air cooled too, don't remember for sure.
Last edited by J.Moore; Oct 27, 2017 at 07:41 PM.
Melting Slicks
Joined: Jan 2007
Posts: 2,842
Likes: 622
From: Pasco Florida
I found a picture of an air cooled 6 cyl unit.
Last edited by Critter1; Oct 27, 2017 at 09:48 PM.