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Username Post: powerglide vacuum modulator        (Topic#101834)
flazz 
Member
Posts: 24

Loc: Gainesville, FL
Reg: 01-05-05
05-24-05 04:47 AM - Post#703402    

my powerglide seems to shift into second very early. i was told that my vacuum modulator is worn out. i cant seem to find one of these parts anywhere for the powerglide.

i found a few for TH350,and TH400, i did find powerglide plugs for them tho.


are there different names for these parts?
what exactly does it do?
is this really my problem?
64 hardtop - in progress


 
Robert_May 
Old as Dirt Member
Posts: 6939

Loc: San Marcos, CA USA
Reg: 01-03-02
Re: powerglide vacuum modulator
05-24-05 06:26 AM - Post#703403    
    In response to flazz

Does the tranny shift at higher rpms when the vacuum is lower like it doesn with the foot further down on the throttle?
If so, the modulator is working.
The tranny should be shifting at low rpms when the acceleration is light. Typically about 15mph with a 3.55 rear end ant typical tires. You should be able to get up past 45mph with a full power acceleration in low gear, depending upon the power of the engine.
For a new modulator, you mich try the better auto parts places like NAPA and CarQuest.
Robert May Fat? Eat less and you will get thinner!


 
flazz 
Member
Posts: 24

Loc: Gainesville, FL
Reg: 01-05-05
Re: powerglide vacuum modulator
05-24-05 07:03 AM - Post#703404    
    In response to Robert_May

it shifts somehwere between 15 and 20 no matter how hard i accelerate.
64 hardtop - in progress


 
flazz 
Member
Posts: 24

Loc: Gainesville, FL
Reg: 01-05-05
Re: powerglide vacuum modulator
05-24-05 09:03 AM - Post#703405    
    In response to Robert_May

Quote:


For a new modulator, you mich try the better auto parts places like NAPA and CarQuest.




napa doesnt carry it, carquest has to order it. Are there alternative suppliers? if i have to order it i'd like to order more than one little thing.

are the TH350 and TH400 vacuum modulators compatible with the my PG?
64 hardtop - in progress


 
Robert_May 
Old as Dirt Member
Posts: 6939

Loc: San Marcos, CA USA
Reg: 01-03-02
Re: powerglide vacuum modulator
05-25-05 10:26 AM - Post#703406    
    In response to flazz

Ordering the part doesn't cost you any money other than having to go back there again. All of the auto parts stores have daily deliveries between stores and the local wharehouse. Distant wharehouse deliveries are usually 2nd day.
Kind of supprised that NAPA doesn't have it as the part should be in their database as they have parts back that far.
Ordering from someplace like Summit, etc. which mail it to you will cost more due to the shipping charges.
Robert May Fat? Eat less and you will get thinner!


 
2x4 
Senior Member
Posts: 653

Age: 42
Loc: s/w michigan
Reg: 11-11-01
Re: powerglide vacuum modulator
05-25-05 11:16 AM - Post#703407    
    In response to flazz

http://www.bulkpart.com/Merchant2/mercha...rglidemodulator

Theres one
According to them, a TH350 & PG take different ones, so I dont think I'd go swapping a TH350/400 one in there.

A little tip here-the majority of modulators are adjustable. Take it out, clean it up & look inside the port where the vac line goes. If its adjustable youll see a slot for a small screwdriver in it. Generally you will only be able to adjust shift points about 3-4mph higher or lower, so its not really a worthwile change.

While its out, yank out your vac tester & test it. I'm guessing its not bad, they dont really just kind of go bad, its either fine or its trash. Also if it were bad, you would be sucking tranny fluid into the engine through the vac hose & it would be smoking so bad youd have other questions Theres a spool valve behind the modulator in the tranny case. GENTLY pull that out & clean all the varnish off it & the bore in the tranny case. Its very possible the spool valve is sticking in the bore.

All a modulator really is a rubber diaphram, spring & a housing, not really much in there to fail other than the diaphram leaking/blowing out. Check out the spool valve behind it!
1985 Monte SS


 
Anonymous 

Re: powerglide vacuum modulator
05-25-05 02:15 PM - Post#703408    
    In response to flazz

I have to think your T.V. linkage is either adjusted wrong or maybe not even there.
T.V. means throttle valve.This linkage increases control pressure as you open the throttle.It allows control pressure to overide govenor pressure and raise the shift point and firmness.
Some times the socket for the bottom rod gets worn out and the rod falls off.Sometimes a "hack" removes the linkage not knowing what it does.Is your linkage installed?a rod should run from the bottom of the carb to a bell crank by the rear of the intake,then another rod runs down to a lever by where the shift linkage connects.
If your linkage is all there and connected,have someone hold the throttle open and adjust the rod by the carb till it is pulled tight.(done with the engine not running)

 
Robert_May 
Old as Dirt Member
Posts: 6939

Loc: San Marcos, CA USA
Reg: 01-03-02
Re: powerglide vacuum modulator
05-26-05 09:50 AM - Post#703409    
    In response to

Ah, Micheal, there is no Trhottle Valve rod on the aluminum Powerglide tranny!
There is a modulator just like the TH350 and TH499.
I suspect that the modulator is frozen in the high vacuum position. You might want to pull it and see if it is still working in and out when you put a vacuum on it.
Robert May Fat? Eat less and you will get thinner!


 
Crosley 
Senior Member
Posts: 238
Crosley
Loc: Gilbert , AZ
Reg: 05-01-01
Re: powerglide vacuum modulator
05-26-05 05:24 PM - Post#703410    
    In response to Robert_May


ah... yes there is ( should be) a throttle link from the carb to the tranny on a glide. This controls/changes shift points

the vacuum modulator on a glide does NOT control shift points as a t-350 & t-400. It regulates the internal pressure only


Quote:

Ah, Micheal, there is no Trhottle Valve rod on the aluminum Powerglide tranny!
There is a modulator just like the TH350 and TH499.
I suspect that the modulator is frozen in the high vacuum position. You might want to pull it and see if it is still working in and out when you put a vacuum on it.


Tony.........


Farts are natures method of crowd control


 
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