Quick TH350 Modulator Question

[YourBuddy'sTruck]

Hey there...
Old threads already have me diagnosed and ready to fix it, but....
What does the color coding around the Vacuum Modulator mean?
I see others with a Red ring.
The one I found in town has a Purple ring.
Just curious as I'm hauling a heavy load once a week with my C20.
Thanks for any answers.

[18Z]

Good Question, I would like to know the answer myself.

[swamp rat]

It has to do with the sensitivity of the unit, I'd have to Google it for more info. Something like this"TH350 modulator color code sensitivity"


You do know its adjustable with a small screwdriver right?

[hugger6933]

This is [or was] an adjustable type modulator valve that had a screw inside to adjust . i don't know if those are still around I just assume they are. I have not bought a modulator valve in many years.

[YourBuddy'sTruck]

The one I put in is adjustable.
I installed it and it is just fine.
I've hauled some heavy loads since then too, and no trouble.
Guess I'm just curous about the colour ring thing?
Makes sense that they'd be bench tested for a value and coded for that?

[Gromit]

This site shows the specs on the purple stripe modulator:

http://www.rostratransmission.com/tr...on-listing.php

Looks like it is adjustable to actuate at a vacuum range of 12 to 14 (the site says that is in pounds - which I take to mean psi) anyway, that one has an effective diaphragm area of 1.9 square inches.

That is compared to the red stripe version with an adjustable range of 12.5 to 18 and effective diaphragm area of 1.7 square inches.

There are a lot of considerations for optimal modulator selection - A/C or not, six cylinder or V-8, vehicle weight, 4x4 or 2WD, cam profile, whether you a towing something heavy, altitude of your location are a few..but I don't know enough to know if the purple stripe is optimal or not, but hopefully that info helps.

[Mrturner1]

Originally Posted by hugger6933

This is [or was] an adjustable type modulator valve that had a screw inside to adjust . i don't know if those are still around I just assume they are. I have not bought a modulator valve in many years.

Mine has a red ring and is also adjustable but it's a th400. I thought the 400's were red and 350's were purple

[YourBuddy'sTruck]

Thanks, Gromit!
That's super helpfull!
Mystery solved!