Adjustable Modulator

[Its Just Me]

This should be a simple question for those in the know. I have a TH400 trans with an adjustable type vacuum modulator. I think is shifts too soon (into second under 10 mph). Can anyone tell me which way to turn the adjustment to get the trans to shift at a higher speed? Clockwise or counterclockwise assuming facing the transmission/modulator with the screwdriver in hand.

And how sensitive are they, should I make 1/8th turn adjustments or 1/2?

Thanks

Scott

[cny first gen 71]

My brother has one on his ferd if I remember correctly they are pretty sensitave but not sure which to turn it I would try 1/4 turn clockwise see what that does, may be a hit or miss thing.

[wallaby]

My big block so effortlessly pulls the car around, it has high vacuum unless my foot has the secondaries open. I tried adjusting the modulator to delay the 1-2 shift, but it really only changed the 2-3 shift point...I was a little disappointed.

Keep in mind that the modulator adjustment will do nothing for full-throttle shift points. Most adjustable modulators list a 2-3 mph adjustment range.

I'm trying to remember, but I think I went like a full turn clockwise.

[Mike 57]

The modulator will only affect the shift point a few miles per hour. It will make the shift a little bit harsher. The governor controls the speed the the trans shifts at.

[Mike Brichta]

My TH400 trans shifts too late. The trans was recently rebuilt by a local trans shop and has a shift kit installed. I tried adjusting the modulator but it made no difference. I'm not surprised from what I have read about them.

 

My questions are:

 

- If the governor controls at what speed the trans shifts, what do I do to adjust the governor? Can it be adjusted?

 

- Are TH350 and TH400 governors the same?

 

- Anything else I can adjust in addition to the governor?

 

Thanks!!

Mike

[bobsmc]

if it is shifting late i would check the vacuum source at the modulator.

no or low vacuum will cause late shifts

 

[bobsmc]

does it hace a big cam in the motor?

 

the only way to adjust the govenor that i know of is by changing the wieghts.not recommended.

[footballubet]

I would talk to the shop that rebuilt the transmission and installed the shift kit. They know what modifications they made when installing the kit and may know away to change the shift points. If there is any kind of warranty on the rebuild and you start messing with it they will probably void the warranty.

[stangeba]

What has changed?

You mention a shift kit.

Why was it in need of rebuilding?

Was it OK prior to them rebuilding it or is this a "rebuilt" trans from an unknown donor vehicle?

Rear axle ratio?

At what RPM is it shifting 1-2?

How far down are you pressing on the gas?

Is the kick-down system working and adjusted correctly?

[Mike Brichta]

Wow. Lots of questions. Here are some answers.

 

- Brand new vacuum hose directly from manifold to new modulator

- Engine is a ZZ454, 3.31 posi rear

- Trans guy is no longer available - he got a better job somewhere else

- I drove the car with trans for about 3 weeks before taking the entire car apart for restoration - rebuilt trans just because that seemed like the time to get it done - put in a Transgo shift kit

 

Here is what it is doing:

- When pulling out from a stop nice and easy the trans shifts fine but shifts later then expected (not sure of the RPM)

- When cruising at steady speed and then hitting the pedal to make it downshift, unless I come off of the pedal it will not shift back into 3rd gear

 

I have not checked the fluid level when warm yet. I will do this next before touching anything else.

 

Does that help any?

 

Thanks!!

Mike

[bobsmc]

CHECK YOUR VACUUM WITH A GAUGE AT IDLE AT THE MODULATOR

[wallaby]

Are you working with a TH400 or TH350?

 

It sounds as if your kickdown is not adjusted right. If it thinks you are really into the throttle, it will behave as you describe. Do you have engine braking when you decel, or does it feel as if it's in neutral when you let off the gas?

[Mike Brichta]

What should the vacuum be at idle at the modulator?

 

I have a TH400. When I let off the throttle it just shifts into 3rd and I'm good to go. Do you think the solenoid could be bad and holding on too long?

[Mike 57]

run a steel line from the intake to the modulator. I bet the hose is collapsing.

[stangeba]

Steel vacuum lines to the trans, always have a point higher than the carb (looks like a reverse drain trap or upside down U) to (I believe) protect the diaphragm from being exposed to gasoline if the carb floods. Just something that I thought I would share...

Bruce