[Ivo]

Hello, there are different Vacum Modulators with red, two reds, red and black, black stripes. Can't find the exact description and where is the difference. I only found out that black / red is for low vacum engine. OK mostly all are adjustable and I know how to adjust.
What is the difference and which one is for which engine?
I am interested in which engine you drive which stripes.
Thanks Ivo

[1968GTO421]

Interesting question, Thanks for posting this.

[Karck]

Id like to know more about this also. I have 2 modulators that are adjsutable. One that came with the car and one from Standard. I tested both with vacuum gauge, other moves the plunger at 15 InHq and seems adjusting it really does not much, maybe 1-3 inhq difference. Other one acts the same but is stuck on 10inhq area... How should this adjustment work? Or is it the rate of the speed the plunger will bottom, that is hard to measure..

[Brewster]

Hmm, good one indeed.
Will be following the thread. Cheers

[Tim Corcoran]

Anyone? Buler?

[Half-Inch Stud]

...never paid much attention to the big FM Modulator cans. Well made but big and heavy. Tossed them faster than you could say stop no dont.

The adjust screw was welded on most that i tried to turn.

[68WarDog]

My 70 engine only make 9/10 " of vacuum, which led to some real late shift points that could not be adjusted out with a stock t400 vacuum modulator (modulator screw backed all the way out). I am now running the low vacuum t400 modulator ( red/black stripe) the screw set 1 1/4 turn from lightly seated.

[Schurkey]

Originally Posted by Half-Inch Stud

...never paid much attention to the big FM Modulator cans. Well made but big and heavy. Tossed them faster than you could say stop no dont.

Stop! No! Don't!

Well, at least if you're going up and down mountains/valleys a lot. The advantage of the bigass OEM modulators is that they're self-compensating for altitude variations. They're huge and heavy 'cause they've got an aneroid bellows inside.

Originally Posted by Half-Inch Stud

The adjust screw was welded on most that i tried to turn.

Yep. Pain in the ass. Sometime it's possible to break the weld and make them adjustable...sometimes not.

[stevep]

The red modulator covers the whole spectrum of gas engine cars. It has a wide range of coverage. We used to have a blue strip (high vacuum) and a purple stripe (low vacuum) and the red covered the range of both of them.
The black may be for diesels, which we used on low vacuum applications.
I'm not sure of the others.

[Cliff R]

They are tuning tools to provide the owner/driver with a range of adjustment for upshift points at light throttle, light load and in the "normal" driving range. They also help with the cut-in point when you apply heavy throttle but not enough to engage the detent on the TH400 or the kick down on the TH350.

All of these engines will make good to excellent vacuum at light load, even if you are heavily cammed and see "low" vacuum at idle speed, so you really don't pick the modulator based on those parameters.

Typically if your engine is cammed enough to kill off some power right off idle and lower RPM's a modulator with lighter spring tension will work better as throttle openings will be higher and vacuum lower in that range.

I've put vacuum gauges on these engines (manifold vacuum) and driven quite a few of these vehicles when custom tuning them, and it's remarkable how much vacuum they make in the "normal" driving range, and all of them peg the gauge on deceleration, then show really high readings just "tipping" back into the throttle to sustain vehicle speed. So most of the modulators currently being sold will work, but you may want to play around some to find one that works the best for your combination.

I'm using the black stripe in my TH400, just because that's what was sitting there when I assembled it. Never touched the adjustment on it, and it provides pretty "normal" upshifts at very light load, around 10 and 15mph, and with more spirited driving about 20 and 25mph, right about where they should be for my combination......Cliff

[dataway]

It will be a long time before I can see how the T400 acts on the road .. but I am using the original big can (68) ... doesn't leak vacuum and the plunger moves under vacuum .... is that about all you can do to test them prior to operation under driving conditions.

[Karck]

That is how i tested mine, but i dod notice that my old REd stripped one moves at different vacuum than new one from standard. So im not sure what to take of it. :/