Carlarena1

I've Seen vacuum modulators advertised with multiple different colored stripes. Red, black, green, blue, even double red, red and black. What do they all mean? I cant seem to find anything comparing them, There has to be a difference, or why would they color code them? Anyway if anyone knows, id appreciate a lesson in modulators. Thanks guys!

Olds64

The colored stripe indicates how much vacuum is needed to activate the modulator.

oddball

Yup. I've never seen a table or guide to the colors. TH350 "performance" modulators are usually one red stripe, and they usually have an adjustment screw so the band doesn't really matter. I assume there's non-adjustable ones with different color stripes and that's important.
Generally just get an adjustable one and start fiddling with it until you get shifts where you like them. It's a quick and easy process (accessible by just taking off the vacuum hose) and the changes are obvious and significant.

oldcutlass

The changes are not that significant, maybe a 3-5 mph difference. Be careful, some modulators have no stop and you can easily screw it in too far to the point where it screws through the adjustment plate and renders the modulator useless..

matt69olds

Supposedly, the red stripe is gasoline engines, the black strip is for the diesel engines with vacuum pumps. I don’t know how true that is.

About the best you can hope for is 2-4mph adjustment either way on shift points. it’s more of a fine tuning adjustment. If you need more than that, it’s time to start playing with the governor. Keep in mind, the modulator has ZERO influence on full throttle shift points. At WOT, the modulator see zero vacuum.

Carlarena1

Ok, sounds good guys. My current modulator is a single red stripe and is adjustable. What sparked my question is that there are so many different modulators available. I guess if its not much of a difference ill just stick with what i have. I was more curious if there was an option that would put me closer to the factory shifts my car was designed to have. If so, then i would go that route. Seems the consensus would be to leave well enough alone though lol. Thanks guys!!

matt69olds

You can change part throttle shift points 2-4 mph either way with the modulator. Anything more requires modifications to the governor. And you will never get the WOT shifts where you want them if the kickdown cable (th350) or kickdown solenoid (TH400) is functional. The trans will tend to short shift at wot without it.