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Username Post: TH400 Vacuum Modulator Selection        (Topic#189656)
55 BelAir Wagon 
Member
Posts: 190
55 BelAir Wagon
Loc: Michigan
Reg: 10-04-04
05-15-08 07:38 PM - Post#1433912    

Can anyone enlighten me on choosing a vacuum modulator for my TH400 in my '62 454 Impala? The part stores offer a 'Green', 'Blue', or 'Red' stripe version, but they don't tell you what the difference between them is. I'm just getting my car ready to drive for the first time and have decided to change the modulator because it is caked with oil and crap and I figure it might not function properly. The trans supposedly has a shift kit in it, but I don't know what brand or spec. The engine is fairly stock except for a Holley 750 double pumper and a set of hooker headers (the big tube ones that go around the frame with the back pipe). Any info would be greatly appreciated! Regards, John
Current Vehicles:
55 BelAir 4-Door Wagon (Project)
59 Corvette (Driver)


 
MikeB 
Senior Member
Posts: 9486
MikeB
Loc: Plano, TX
Reg: 08-28-03
05-16-08 10:21 AM - Post#1434339    
    In response to 55 BelAir Wagon

Not sure what the stripes mean, but I've always bought adjustable modulators to tune part-throttle shift points.

Here's an adjustable red stripe modulator from a good vendor:

http://www.bulkpart.com/Merchant2/merchant.mvc?Scr...




1982 C-10 SWB pickup -- Unmolested, original paint, 250 six, 3-speed (soon to be 350 Vortec & TH350)

Sold my 55 sedan in June 2014, having owned it 11 years.


 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15641

Loc: Colorado Springs, CO
Reg: 08-08-04
05-16-08 12:31 PM - Post#1434447    
    In response to MikeB

Get an adjustable modulator. They aren't very expensive.

http://www.jegs.com/p/TCI/762212/10002/-1 /10727

 
55 BelAir Wagon 
Member
Posts: 190
55 BelAir Wagon
Loc: Michigan
Reg: 10-04-04
05-17-08 11:21 AM - Post#1435049    
    In response to Vaughn

Thanks guys! I ordered an adjustable modulator yesterday. Now I just need to get all my house chores done so I can get out to the garage!
Current Vehicles:
55 BelAir 4-Door Wagon (Project)
59 Corvette (Driver)


 
frikenwoodro 
Contributor
Posts: 491
frikenwoodro
Age: 25
Loc: ABQ
Reg: 11-14-07
05-18-08 07:23 PM - Post#1435949    
    In response to 55 BelAir Wagon

what exactly is an"adjustable modulator"? does it control when the trans shifts?
Just an old Truck





 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15641

Loc: Colorado Springs, CO
Reg: 08-08-04
05-19-08 09:07 AM - Post#1436262    
    In response to frikenwoodro

A vacuum modulator adjusts the speed of the upshift of the trans, based on the amount of vacuum in the intake manifold. If intake vacuum is high (in other words at nearly closed throttle), the upshift happens early, because there is little to no load on the engine.

If the vacuum is low, like at wide open throttle - the upshift is delayed because the engine is operating under heavy load.

The adjustable part of the modulator is a screw tied to a spring - screwing/unscrewing the adjustment screw in combination with the vacuum signal changes the point at which the trans upshifts.

 
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