65Delta88

I have a stock TH-400 in my '65 Delta 88 w/ a 425, I was reading about a way to adjust the modulator and I was wondering how to go about it? Is there a screw inside where the vaccum hose goes? or is there another screw on the outside of the modulator?


Thanks

Bluevista

I'm no tranny expert but the big original one I have on my '71 Vista with a Turbo 400 has an adjusting screw on the end and the hose connects on the side. The smaller new replacement type with the vac fitting coming straight out the end I have on another car has a little screw inside the vacuum fitting to adjust it. I seem to remember that there was an instruction sheet in the box that showed how to adjust it with a small flat bladed screwdriver.

Allan

J-(Chicago)

Stock factory modulators are pre-set and most are sealed. If you do have an adjustable one however,
turning the adjusting screw (found in the vacuum nipple) counterclockwise, you will lower the spring pre-load. This will cause earlier shifts. By turning the adjusting screw clockwise and raising the spring pre-load, the shift points will go up. The range of adjustability is only a few mph either way.

Olds64

Learn something new everyday!

d2_willys

I have not worked on TH400 VM's, but Furd VM's have the adjustment, and it does control the shift points, but also increases pressure for firmer shifts too. I would think this may apply to TH400'S

65Delta88

Thanks for clearing that up, I'll have to go and investigate this today and see what I can come up with.

RoaringRelic

The Vacuum Modulator controls the modulator valve which raises or lowers modulator pressure. The Modulator pressure will then effect both the line pressure and the governor shift point.

65Delta88

How do I go about pulling the old one out? is it just pressed in? I have my new one and from the looks of it, I think it is just pressed in with an o-ring.


Any info??

Oldsguy

I think there is a clamp similar to the way the distributor is secured, one bolt holds the clamp down tight on the modulator valve.

look here