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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: achevy1978 on December 20, 2013, 07:35:43 pm

Title: modulator valve
Post by: achevy1978 on December 20, 2013, 07:35:43 pm

i was told that a 454 takes a different modulator for a th400...a gm part supposedly made by holly
anyone have any info ??
thanks

Title: modulator valve
Post by: achevy1978 on December 22, 2013, 04:15:46 pm

 does anyone know what the modulator valve is for a th400 with a 454.
 been told the adjustable ones that come with the kits really isnt the rite one,
its either a white or orange one..

thanks

Title: Re: modulator valve
Post by: Engineer on December 22, 2013, 05:41:12 pm

Unless you buy the exact modulator for your application by the book, getting the one that works right for you may be difficult. Many factors affect the modulator's specs. Things like vehicle weight, rear axle ratio, engine tune, cam specs, etc. etc......

I recommend using the adjustable one. If the tranny shift points are too high back out the screw one turn at a time until it suits you. If the shift points are too low do the opposite.

Title: Re: modulator valve
Post by: roger97338 on December 23, 2013, 11:15:29 pm

I looked at B&M's website, and they sold one vacuum modulator for the Turbo 400 transmission. It was adjustable.

You could maybe call a couple transmission shops, especially shops that specialize in racing or towing transmissions. Guys that work on transmissions all day for a living probably could give you the best answer to your question.

Title: Re: modulator valve
Post by: VileZambonie on December 24, 2013, 01:59:20 pm

Unless it's bone stock and you are going for an all original restoration follow Engineer's advice. All you need is a pocket screwdriver to fine tune it.

Title: Re: modulator valve
Post by: mcintyrederek on December 30, 2013, 08:59:12 pm

Just a quick tip, when replacing the modulator with the adjustable one, make sure the vacuum hose is not floppy and soft.  There is usually a steel or aluminum tube coming from the engine intake down to the modulator, but sometimes there is a short piece of flexible tubing that connects it at the end.  I had one on my '86 C10 that sucked itself shut when the vacuum was up, causing it to think there was no vacuum.