vacuum mod or not?
We set the transmission, min. and max pressure. Just like the pre Elvis transmissions...we set ours to do no more than 230 max pressure at zero vacuum, Install any cam you want zero speaks for it’s self (230 psi line = 0 psi vacuum). Stock does No more than 180 (I’ve seen a couple @190) No matter how you tune it… that’s all the force motor can produce ....Unless you go into the transmission and jack up the pressure set screw…then that’s a whole other subject!!
Does it hit hard at 230 psi pressure? Yes!! Are you at this pressure constantly??? No!!! Remember it is not high pressure you have to worry about its low pressure....low pressure kills transmissions. High pressure has its own set of rules (which in this Trans really limit it) Can you have hard garage shifts with high pressure??? Yes!!
Generally speaking my guys would rather hard garage shifts than soft hi rev shifts ... wouldn't you rather have high pressure shifts?? (Even post Elvis tuners tune for higher pressure). Our typical Low pressure is 90 psi at 14 inches of vacuum. My customers complain at 110 psi which is my preference, but hey who wants to argue?? I’ll compromise. It’s a win, win my line of thinking is 110 is closer to 230 than 90 is so it’s got to build faster …seems logical… suffice it to say 90 psi works well. John you can chime in any time you want, yours is 110 does it have a bad garage shift to it??(Sorry I missed you the other day)
So let’s review…Zero inches of vacuum equals 230 psi MAX line pressure. 14 inches. Of vacuum equals 90 psi MIN line pressure. So there’s your max and min, go install your cams…have fun, I can’t spell vacuum so if I’ve misspelled it forgive me I’m in a hurry. Hope this helps…. Dave
Does it hit hard at 230 psi pressure? Yes!! Are you at this pressure constantly??? No!!! Remember it is not high pressure you have to worry about its low pressure....low pressure kills transmissions. High pressure has its own set of rules (which in this Trans really limit it) Can you have hard garage shifts with high pressure??? Yes!!
Generally speaking my guys would rather hard garage shifts than soft hi rev shifts ... wouldn't you rather have high pressure shifts?? (Even post Elvis tuners tune for higher pressure). Our typical Low pressure is 90 psi at 14 inches of vacuum. My customers complain at 110 psi which is my preference, but hey who wants to argue?? I’ll compromise. It’s a win, win my line of thinking is 110 is closer to 230 than 90 is so it’s got to build faster …seems logical… suffice it to say 90 psi works well. John you can chime in any time you want, yours is 110 does it have a bad garage shift to it??(Sorry I missed you the other day)
So let’s review…Zero inches of vacuum equals 230 psi MAX line pressure. 14 inches. Of vacuum equals 90 psi MIN line pressure. So there’s your max and min, go install your cams…have fun, I can’t spell vacuum so if I’ve misspelled it forgive me I’m in a hurry. Hope this helps…. Dave
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Even Ed Wright at fastchip.com uses the vacuum modulator on his performance setups, as he states that the vacuum modulator is more reliable than the electronics, and he is one of the best in the business when it comes to electronic computers (chips). Even with a "big" camshaft, you will not get more line pressure. When you reach WOT, the vacuum should drop to near zero, which ='s max. line pressure. A side note, if your throttle body is to small, and you are running a "big" camshaft, you will start to create vacuum at high rpm's, which will drop the max. line pressure, and will soften the WOT shifts. To fix this you will need a larger (higher cfm rating) throttle body to keep from creating vacuum at WOT. I have seen this a few times and this is how it was solved.
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From: Philly
lol you can tell the website was acting up 
thanks Rock-On and PBA. you've really helped me understand vacuum modulation. you can be as sure as the sky is blue that my next tranny (if my stocker ever goes...and i hope it doesn't) will have the vacuum mod.
thanks Rock-On and PBA. you've really helped me understand vacuum modulation. you can be as sure as the sky is blue that my next tranny (if my stocker ever goes...and i hope it doesn't) will have the vacuum mod.
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From: The beautiful Kingdom of Bahrain
Originally Posted by ohohsilverado
talked to the tranny guy again today after doing some more investigation on the vacuum mod. He says that he has had problems when he used to do them years ago with the hoses leaking, trannies acting up after people change to a bigger cam, something about it leaking in the case, etc. After reading some of the threads im not so sure about the mod because i have read of several people with problems with leaking hoses, the wrong kind of hoses being used by the installer, and higher line pressure due to bigger cams. I've got to have a daily driven vehicle that i can beat the mess out of without having to deal with/worry about a vacuum leak. Is it possible for me to program the computer in a way that will help the tranny last longer or does everyone believe that the vacuum mod is still the way to go. thanks,
Bryan
Bryan
With the stock cam, and a vacuum modulated tranny, my air conditioner pumps out nothing but hot air at idle. Get driving and the air turns cold (like intended). Is this due to the VM tranny, or is there a leak?
I now have a little 214* cam and I still have the hot air @ idle.
As for shifting... It is great, especially @ WOT... I love the tire bark on the 1-2.
I now have a little 214* cam and I still have the hot air @ idle.
As for shifting... It is great, especially @ WOT... I love the tire bark on the 1-2.
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"With the stock cam, and a vacuum modulated tranny, my air conditioner pumps out nothing but hot air at idle. Get driving and the air turns cold (like intended). Is this due to the VM tranny, or is there a leak? " There is a leak. It should be simple, just look at the line going to the power brakes, and recheck them, for a loose fit.
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From: Richmond, Texas
Thanks everyone, this has been one of the most helpful threads i've read, mainly cuz it pertains to me, but now i understand better how it works. btw, one tranny installer also told me i had no need for a tranny cooler cuz the only time i would build heat would be while im stalling the converter and the heat would go away once i was in motion. but, if im in day to day traffic then isnt it going to be stalling at every light, therefore creating lots of heat, which means i need a cooler.....just curious
thanks,
bryan
thanks,
bryan
i've heard heat is caused from the converter "slipping" or stalling, which its safe to bet you'll need a cooler because my impression is the converter is always slipping to some extent until lock-up...
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From: belton, tx
vac tranny question In a forced ind set-up, would there be a disadvantage for vac control? Theres no or very little vac under boost right? If i've got it hammered will it still shift hard? Excuse if this is a dumb question.
boost is the opposite of vacuum unless i'm stupid, so instead of going from a negative pressure to 0 at WOT, you would be going from a negative pressure to a positive pressure.
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Originally Posted by stssilverado
In a forced ind set-up, would there be a disadvantage for vac control? Theres no or very little vac under boost right? If i've got it hammered will it still shift hard? Excuse if this is a dumb question.
Last edited by xxxhp; Aug 9, 2006 at 02:59 AM.
With a boosted application there is a check valve in the vacuum line. The vacuum modulator sees vacuum to 0 pressure and no boost.
Pre-vacuum modulated tranny I saw two occasions of complete slip on the 1-2 shift. Both times were when I had issues with my new header install and a plug wire getting onto the header and burning. Didn't know what was going on until developed a dead miss. The second time I had a slip I went straight to the plug wire. It had burnt enough to arc to the header but not missing yet. I feel that the spark voltage (noise) getting to the engine upset the ECM line pressure control.
Pre-vacuum modulated tranny I saw two occasions of complete slip on the 1-2 shift. Both times were when I had issues with my new header install and a plug wire getting onto the header and burning. Didn't know what was going on until developed a dead miss. The second time I had a slip I went straight to the plug wire. It had burnt enough to arc to the header but not missing yet. I feel that the spark voltage (noise) getting to the engine upset the ECM line pressure control.
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From: Tyler, TX.
Not to start up an old thread but where can i get these vaccum mod. at? I called trans go and asked them about a 46-mod (part number) And he pretty much told me that i was an idiot because i wanted to do that. Was this the wrong part number or whats going on? 
Why would trans go not recomend their own product?
Why would trans go not recomend their own product? 
Originally Posted by ohohsilverado
Ok, i've been looking at getting a rock-on 4l60 with vaccum mod but my local builder says thats the worst thing i could do. i've talked with the local builder about a dozen times and told him what guys on here tell me and he still swears that its a really bad idea. He builds street and full out race trannies and he's been in business for 25 years. this tranny will go in my daily driven regcab silverado 5.3 bolton. Please give me your opinions. tranny is going fast. thanks
Bryan
Bryan