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Vacuum modulator


Skullzaflare
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So I have my diesel in a auto now.

As of right now I have to manually shift it or it shifts to soon (vacuum pump is on modulator)

Unhooked it shifts way to late.

Aside from effecting shift points,does it effect gear shift pressure? Sometimes 2nd has a soft shift like it's low on fluid.

 

Is there any way to adjust the modulator? Going auto because I didn't want to shift lol. I would bleed off the vacuum source but it is T'd off my brake booster

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What about an adjustable regulator inline from the vacum pump? Im talking blind right now, not even sure if what im saying is relevant to the shifting rpm. Is it vacum that makes the transmission shift too early or too late?
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What about an adjustable regulator inline from the vacum pump? Im talking blind right now, not even sure if what im saying is relevant to the shifting rpm. Is it vacum that makes the transmission shift too early or too late?

If the vacuum source fluctuated that would work, but it pulls a steady 15-17 psi vacuum no matter rpm.

Yes, at full vacuum I'm in 3rd at 20mph, and OD tries to kick in at 25, lockup doesn't occur until above 45mph.

If i remove the line, it shifts at 3300-3400. That's to high, and if the hose is off, manually shifting won't go in next gear until that rpm.

If i could find a way to make it shift at 2200-2500 I would be happy. And if I need more rpm I can shift manually.

 

Though right now, passing gear will not exceed 3100rpm before shifting, so i think the vacuum modulator effects passing gear too

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The modulator is plumbed to the intake on the turbo gas cars. It is supposed to see boost and vacuum off boost. Try it that way. I assume there is no throttle plate? So it will sometimes see boost when it it would not in a gas car, but I think plumbed to the intake manifold is where it should be.

 

If I recall, there Is also an electric kick down switch on the gas pedal

Edited by StarquestRescue
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The modulator is plumbed to the intake on the turbo gas cars. It is supposed to see boost and vacuum off boost. Try it that way. I assume there is no throttle plate? So it will sometimes see boost when it it would not in a gas car, but I think plumbed to the intake manifold is where it should be.

 

If I recall, there Is also an electric kick down switch on the gas pedal

Diesel is boost or no boost, no vacuum in intake, even if it did have a throttle body, still now vacuum

yes there is a kick down, which i mentioned before lol

 

Ok i found a adjustment screw IN the vacuum nipple of the vacuum modulator. i have adjusted it, it now shifts at ~2500-2700, and 2nd gear hits alot harder, no more soft shift!

i manually shifted and took off, 2nd gear FEELS alot better too

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I did not think this trans would shift right in this application. I also did not think you would want to here that and would want to try it any way.

 

Maybe an rpm switch and a air solenoid?

 

Internally there is a part called a governor that may effect the shift rpm if modified.

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I did not think this trans would shift right in this application. I also did not think you would want to here that and would want to try it any way.

 

Maybe an rpm switch and a air solenoid?

 

Internally there is a part called a governor that may effect the shift rpm if modified.

It's shifting where I want it to now though lol

Still cruising 85mph at 2900rpm too, instead of 70

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I did not think this trans would shift right in this application. I also did not think you would want to here that and would want to try it any way.

 

Maybe an rpm switch and a air solenoid?

 

Internally there is a part called a governor that may effect the shift rpm if modified.

 

The governor controls Max RPM shift points. The modulator controls cruising/engine load based shift points. Boost disables the modulator making the governor take over. Since his trans is from a gas motor the governor is set for too high of a RPM. Since he has a diesel with steady vacuum from the pump the modulator can't function the way it's supposed to. Turning the modulator adjustment screw to make it act the way he needs it too is his only option other than finding a diesel governor.

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The governor controls Max RPM shift points. The modulator controls cruising/engine load based shift points. Boost disables the modulator making the governor take over. Since his trans is from a gas motor the governor is set for too high of a RPM. Since he has a diesel with steady vacuum from the pump the modulator can't function the way it's supposed to. Turning the modulator adjustment screw to make it act the way he needs it too is his only option other than finding a diesel governor.

dont think ill find one either lol

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dont think ill find one either lol

 

I don't think you would either. But if you had a FSM for the diesel trans you could get some specs for the springs and replace replace yours for whatever you could find similar to the diesel specs. But it may be tough to find the right springs and there's no guarantee it will work the way you want it to. The modulator adjustment may be a patch but it's the best option you have.

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You're always going to have some clutch material in the fluid. Putting a shift kit in gives you longer clutch life and snappier shifts. The factory setup is designed to give smooth shifts. To do that there is some overlap during gear changes. That is achieved by slipping the clutches during gear changes. A good shift kit will make it bang into the next gear without slipping.
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