TH350 tranny modulator adjustment...anybody know how?

[JK]

I installed my switch-pitch tranny last weekend and just got to drive it this weekend. I noticed it has a problem shifting into third. First-second was kinda higher than I liked, but, I managed to get it down to a reasonable rpm. I can get it to shift into third if I manual shift it. Is the trans not shifting into 3rd because I don't have the mod adjusted right? How do I tell if I have a bad modulator? I do have straight manifold vaccum going to the mod. What else am I missing?

[hiboy32]

I would kinda like some help also, similar symtoms. help, please!!!

later, jeff

[CptKaos]

if you back out of the throttle real quick when you feel it should shift to 3rd will it make the shift, if it does you may have a vacuum problem. if you have an adjustable modulator turn the screw in to delay the shift and out to make it sooner, 1/4 turn at a time. how many RPM's does it shift at?

Larry

[HotRodHon]

Originally Posted by CptKaos

if you back out of the throttle real quick when you feel it should shift to 3rd will it make the shift, if it does you may have a vacuum problem. if you have an adjustable modulator turn the screw in to delay the shift and out to make it sooner, 1/4 turn at a time. how many RPM's does it shift at?

Larry

Could also be your kick down cable is adjusted too tight. It thinks your trying to pass so it wont go into 3rd.
Disconnect it as an experiment and see what happens. If things change, you've found your problem. If they don't, you've elimonated a possibility.

Craig

[JK]

Cpt, I've got it shifting 1-2 at about 1800rpms. second just winds up and never shifts, not even when I jump out of the throttle. I've been driving it like a manual valve body all day today.

[Gator]

As far as the adjustment, the screw is inside the tube where the vacuum line pushes on the modulator. Like CPT said, turn it in for a quicker shift. There's really not a bunch of adjustment there though. Check and make sure the vac line's not rotten or collapsing, that it's connected to the right fitting on the engine, etc. Any idea how much vacuum you're pulling?

[JK]

1) There is no cable on this tranny it's a '66 buick S/P.
2) the adjustment screw is sticking out the side of the modulator with the vac. line going into the top of the mod.

[crash 51]

i dont know. tell the family i said hello!

[squirrel]

sounds like it might be a really old original equipment modulator! try getting a new small replacement type modulator, that might fix the problem, or maybe the tranny has internal problems.

[junk runner jr]

Bringing this one back up rather than starting a new one. We are having a similar problem. except ours is shifting way to early. Its in high gear long before it should. Am I to understand that turning it counter cloock wise should correct this.

[JK]

I just dropprd a new, smaller unit in it. It does have some adjustment as far as shift points. I think out is later. If all else fails, take it out and play with it.

[enjenjo]

If it's the original trans, and it has switch pitch, it's not a T350 . It would be a T400, or a ST300. ST 300 only has two speeds. T400 has an electric kickdown

[Normal Norman]

JK, On the newer stuff you have a TV cable that affects the shift points along with the modulater. On yours you should have a kick down rod that attaches at the carb and transmission. It works with the accelerator linkage as a cable would. Is that assy. there? Normally you turn in the modulator screw to delay the shift,out to get it to come in earlier. I like the idea of a faulty vaccum line to the modulator though,sounds like a possibility. N.N.

[Haunted Ken]

ST300's are junk, I can't give them away..... it's likely that either the pump is bad or the modulator is bad..... there is hardly any adjustments to be had through dicking with the modulator, ecspecially if it is all original.... they are finicky about internal pressure......

if you want, I have two ST300's that worked fine when I pulled them...... free for the taking..... just pick them up, and give me some space..... I hate throwing out stuff that works fine, even though I will never use it.....

The good news is, is that a BOP TH350 will bolt right in, in place of the ST300.... you just have to put in a kick down cable..... Tranny mount and all lines up...... just make sure it's a short shaft th350......

As far as adjustments, in my experience I have discovered that with these, when the Swith is out of Pitch, I swap em out for the 350, I have had luck getting ahold of them for cheap..... they are out there.... alot of people have the BOP TH350s and don't know there is a difference between the bellhousing patterns.... if you play your cards right, you can usually get them for pretty cheap.....

edit: ST300s are okay for lower-powered engines.... anything north of 300 ft/lbs of torque and they instantly transform into boat anchors....... I would install one in a low-speed tail-dragging cruiser, but not in a stop-light burn-out, street/weekend-strip car.......

[squirrel]

st300 converter is a plus in a sp400

[JK]

JR jr., in all honesty. I'd drop in a new modulator. Mine was like $9 or something. It shifts so smooth now I have to really listen to it to hear it shift. That would be a good starting point.

[tfeverfred]

I know this is an old thread, but I just want to know... Do I turn the modulator screw "in" for a later shift or "out" for it to shift a little sooner?

I just installed a freshly rebuilt TH350. It shifts to 3rd, but a little later than I like.

Thanks for the help.

Okay.... I turned it out about one revolution and no real change. I'm going to recheck vacuum.

[tfeverfred]

Bttt

[tfeverfred]

No opinions/advise at all?

[squirrel]

when you turn the screw in, you increase the spring pressure that the vacuum has to overcome, so it should make it shift later/harder.

Try it...if that doesn't work turn it the other way