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Canadian Poncho Homepage -> Canadian Poncho -> 58-64 Full Size Power Train Tech Forum -> Powerglide help needed - problem solved!
Post Info TOPIC: Powerglide help needed - problem solved!
Urban_suburban


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Powerglide help needed - problem solved!
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I have a powerglide in my 64 chev. It was rebulilt and I have had an issu that I am stuck on.  The trans shifts up nice and crisp but downshifts harsh.  We installed a small vacuum resivoir as the car has low manifold vacuum at idle.  When costing to a shop it downshifts harsh. If I manually shift it it's perfect.  Any thoughts where I should start to figure this out. Linkage too tight? vacuum still? Getting hard to find powerglide experts and don't want to be sending it just anywhere with the interior colour to have it all greased up. 

Thanks 



-- Edited by Urban_suburban on Tuesday 30th of May 2017 11:53:06 AM

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beaumontguru


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RE: Powerglide help needed
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Its a bad modulator valve(the round thing on the back of the trans,  or it is not getting constant vacuum.   Make sure there are no leaks in the vac line.  Also be sure that the vac line from the modulator is conected to a constant vac source at hte engine, go right off the manifold if you can, rather than the carb,  it is possible that the carb vac line is "ported" vac and not constant.

If it only downshifts harsh, the modulator is to blame



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Beaumontguru

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Urban_suburban


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It is off the manifold. I will check the vacuum lines. I know the car produces poor vacuum at idle. I just picked up a tool to measure exactly what it's getting. I will price out a new modulator valve too.

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timbuk


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1. put in first gear.2 floor car till valves float.3 shift into gear 2. 4.cruise:)

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Urban_suburban


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Powerglide help needed - problem solved!
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So turned out it was a super easy fix. It's was simply an obstruction in the steel vacuum tube. The car was not getting any vacuum to the modulator. Can't hardly feel the car shift. It's truly amazing how smooth it drives now

Thanks for the help. Got me on the right track

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rabbit64cs


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wealth of knowledge here !! 

 

thanks for sharing the solution ,, sometimes simple trouble shooting is the last thing we check !!



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beaumontguru


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Cool,  glad to help,  i knew right away that the modulator vac was to blame.



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Urban_suburban


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It was so silly. I have a took to create and test vacuum and did it at the top and bottom and all the lines held vacuum. But when checking to see if I had healthy vacuum at other locations that's when things were off. I had 15 hg off the intake and got a point under the car where it was 0. Found some dirt a crusty buildup of under coating in the steel vacuum line and cleared it out and re tested. Now had 14 hg under the car. Hooked it up and tried to test the car on the hoist. Couldn't tell if it was shifting or not so had to put it down and go for a road test. As something as I remember for my childhood.

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