Will adjustable vacuum modulator work with installed shift kit Turbo 350?

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azmusclecar

G-Body Guru
Feb 13, 2018
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I installed a Transgo shift kit in my 1979 Hurst Olds with the Turbo 350. This shift kit hits hard.......and I was wondering if the modulator can soften the rpms where the shift kit hits? I did adjust the screw out for less vacuum to lower shift points. and I replaced the rubber vacuum lines at the engine and the hose going to the modulator. My question is, IS there enough adjustment in the modulator to override that hard high rpm shift?

If this is the original modulator, could it just be bad? I'm not sure how to test it or shoudl I just replace for $15-$20 and call it a day.

I hate to uninstall the TRansgo kit. I just want to tweak the rpm range a bit. Any suggestion? Thanks, AZ.
 
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techg8

Master Mechanic
Feb 29, 2012
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If it was a bad modulator it would be sucking trans fluid into the vacuum line. OR shifting hard and late all the time thinking it was at wOT all the time.

The modulator can have some effect on shift firmness and timing because it is modulating pressures in the trans according to engine load, seen as vacuum. I look on it as a fine tuning tool. It will change all your shifts at once to some degree. It can help hold shifts off longer or bring them on sooner.

WOT shifting is best modified at the governor by changing the weights. heavier weight = earlier shift. this effects all shifts at once.

If the transgo kit had you remove an accumulator spring, however, this would have a lot more effect on the shift hardness, and could not be countered effectively by adjusting a modulator. This would effect only the specific shift circuit modified.

So I guess the answer is try it and see.
 
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azmusclecar

G-Body Guru
Feb 13, 2018
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If it was a bad modulator it would be sucking trans fluid into the vacuum line. OR shifting hard and late all the time thinking it was at wOT all the time.

The modulator can have some effect on shift firmness and timing because it is modulating pressures in the trans according to engine load, seen as vacuum. I look on it as a fine tuning tool. It will change all your shifts at once to some degree. It can help hold shifts off longer or bring them on sooner.

WOT shifting is best modified at the governor by changing the weights. heavier weight = earlier shift. this effects all shifts at once.

If the transgo kit had you remove an accumulator spring, however, this would have a lot more effect on the shift hardness, and could not be countered effectively by adjusting a modulator. This would effect only the specific shift circuit modified.

So I guess the answer is try it and see.

I'll give it a try. I didn't want to go adjusting the modulator and then finding out the TRANSGO shift kit will sort of override the changes I make
with the adjustment screw. That's why I wondered if my modulator changes would even make a difference on the shift points.

Great info you offered. Thank you kindly.(y)
 
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Oct 14, 2008
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Melville,Saskatchewan
The modulator should help part throttle shifts somewhat. I have mine set to the firmest without a shift kit and it is a bit annoying around town.
 

azmusclecar

G-Body Guru
Feb 13, 2018
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Just an update on my nearly 3 week old thread, I've adjusted the vacuum modulator turning it OUT and shifts points have dropped and
shift firmness is now much more tolerable. I'm just about out of threads I think inside the vacuum modulator.

Now if the transmission would ONLY STOP LEAKING...............leaks toward the front and now I am thinking it must be somewhere
around the torque converter................oh well...................one step forward.......two steps back.
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
Probably the seal behind the torque converter, the O ring rarely leaks. I have had leakage issues even after replacing seals. I have had good luck with tractor hydraulic fluid stopping leaks with just enough ATF to colour it.
 

azmusclecar

G-Body Guru
Feb 13, 2018
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Probably the seal behind the torque converter, the O ring rarely leaks. I have had leakage issues even after replacing seals. I have had good luck with tractor hydraulic fluid stopping leaks with just enough ATF to colour it.

My curiosity is peaked......and where would I get this tractor hydraulic fluid? Like Tractor Supply.......is there a weight I should use?

I have nothing to lose by trying it............right?
 
Oct 14, 2008
8,806
7,746
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Melville,Saskatchewan
I know many use the John Deere Hyguard with good results. Yes your local John Deere dealer or farm supply will have it or similar. I use the 10w30 dinosaur or 5W30 synthetic blend in our Coop brand. I was sick of it seeping one place or another. Worked good on my TH350. My 2004R has Dexron 3 and it seeps a least a couple of places. I am changing the selector shaft seal and slowly adding tractor fluid.
 

azmusclecar

G-Body Guru
Feb 13, 2018
601
306
63
I know many use the John Deere Hyguard with good results. Yes your local John Deere dealer or farm supply will have it or similar. I use the 10w30 dinosaur or 5W30 synthetic blend in our Coop brand. I was sick of it seeping one place or another. Worked good on my TH350. My 2004R has Dexron 3 and it seeps a least a couple of places. I am changing the selector shaft seal and slowly adding tractor fluid.

I hear ya'.......preach it brother............I replaced the speedometer seal (both) and a new pan gasket and a new tail shaft seal and the Dex III just seems to find somewhere else to run to.

Thanks for the info, I'll go to Tractor Supply and see what I can find...........If I use John Deere fluid do I need to paint my car green and yellow:puke: and resemble a Green Bay Packer fanatic?:unsure: Nothing against Green Bay mind you...........(y)(y):cool:
 

azmusclecar

G-Body Guru
Feb 13, 2018
601
306
63
For Father's Day I treated myself to a gallon of John Deere HY-Gard transmission and hydraulic fluid.
Just added the gallon today and went for a test drive. And I tweaked the vacuum modulator just a tad
and shift points are now lower and I think I may need to go a turn or two back in on the adjustment screw
for the modulator.

I'll keep tabs on any leaks..........fresh cardboard under the transmission now. I enjoyed the short ride in the H/O.
Nice way to spend Father's Day with my toy.
 
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