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Topic Review (Newest First)
12-23-2012 07:31 AM
ducrider123 I had the same problem multiple times. This is what i did.

I checked out the tag on the trans to see what it originally came from. IE bigger car usually ment lower rear gears, and earlier shifts for comfort.

Then made sure i had a new red line (adjustable) vacuum modulator. I drove my car and checked the vacuum while the car was at cruising speed. I set my modulator to start pulling in at this measurement. that way when the car is under light throttle it shifts smooth and a lil early but then under heavy throttle it's a lot more firm and a little later.

Normally running anything over 3.42 you have to do governor work. Buy a governor recalibration kit. and start playing with springs and weights. I use a scale and weigh all the weights and compare them to the ones that are original. I also make a graph to record my findings on each combination. also you can remove weight off the outer weight which will help raise your shift points under light loads. inner weight under heavy loads, and the springs separate the shifts.

I went from a 55g outer weight to a 44g. 14g inner weight to a 9g. and 2 step heavier spring. on a 67 firebird 400 th400 3.42 rears. heavy load 1-2 shift 5500, 2-3 shift 5200 rpm.

Also a thing to note is instead of picking 5500 rpm to shift at, you should choose a shift point that correlates with your engine peak torque and hp rpms.
12-21-2012 08:17 AM
MARTINSR Are we talking normal shifting or full throttle shifting?

12-21-2012 07:35 AM
496CHEVY3100 You can drill and tap a port at rear for vacumn connection ,be shure you have Heavy grease on drill bit to catch alumimum shavings ,i would also remove carb and duct tape on inside where you will be drilling. or you can buy an aluminum spacer plate to go under carb with vucumn port already in it ,I have one but do not know how to put pictures on this sight ,if you cant find one i will posy picture in my picture albumn Also do you have the elactric kick down connected if not it will shift to early part throttle or WOT
12-13-2012 11:59 PM
cobalt327 Yeah, w/those 3.90 gears it's gonna shift through the gears quick under light throttle/light load conditions. It's normal for it to do that. Holding the gears manually is about the only way around it.
12-13-2012 11:23 PM
sscanrun 468 bbc ,th400 trans, cam has a 640 lift and rpm range 2500-6500 , single plane intake ,2600-2800 stall , gear 3:90
12-13-2012 06:22 PM
cobalt327 "Same thing" = shifting too quick?

What is the rear gear ratio? If you're talking about part throttle, low throttle shifts, they do tend to be very quick if there's no load on the engine. The best way around this is to shift it manually. It will always shift through the gears quick if left in Drive, under low load, light throttle settings.
12-13-2012 02:45 PM
sscanrun Cobalt327- I hook it up and does the same thing
12-12-2012 07:38 PM
sscanrun I'm using the one on the metering block
12-12-2012 07:37 PM
sscanrun Cobalt327- thanks ima try that tomorrow
12-12-2012 06:23 PM
Originally Posted by sscanrun View Post
I'm using the one on the metering block
That is the wrong place to get vacuum for the modulator. Use a full time port from the baseplate.
12-12-2012 04:37 PM
Originally Posted by sscanrun View Post
I have to drill a hole on the single plane intake. That means I have to remove it?
Not necessarily. "Manifold" vacuum only means a full-time vacuum source that is there even at idle. "Ported" vacuum is NOT there at idle, and that's the main difference between the two (there are subtle differences besides that, but they do not apply here).

So you can use a carb port that has manifold vacuum just as easily as using a vacuum port that's in the intake manifold itself, if you follow me.

If you have a Holley, the metering block has a ported vacuum port- do not use that. You can use a port that's located on the baseplate, but still double check to see that it has full vacuum at idle.

An Edelbrock carb has a manifold vacuum port on the front, driver side.
12-12-2012 04:03 PM
sscanrun Its a single plane not the dual plane
12-12-2012 07:52 AM
Originally Posted by sscanrun View Post
I have to drill a hole on the single plane intake. That means I have to remove it?
Really? There are NO provisions on that intake?
There is usually one on the rear face of the manifold, below the carb mounting flange. If not, that's where I would CAREFULLY drill and tap a 1/8" NPT hole for a small vacuum hose-barb.

You may be able to do this by simply removing the carb and taping off the intake runners to prevent any material getting away on you. Drill and tap the hole, and then vacuum up the debris.

Use extreme care when tightening any pipe thread fittings on an aluminum intake, as the the thread is tapered and can crack the intake if over-tightened.
12-11-2012 11:35 PM
stea I was lucky, got it first try. Used stock springs and IIRC I went 4 grams total lighter on the weights. The original weights that were on the governor were a lot lighter than i expected.
12-11-2012 11:09 PM
632Mantis Yup, you need the governor recalibration kit. Easy to do, but you basically have to guess the springs and weights, then test drive it.
Took me 4 tries to nail mine down.
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