4L60E Vacuum Shift Modulator ...benefits ?
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4L60E Vacuum Shift Modulator ...benefits ? If the shift firmness would be controlled by engine vacuum instead of the PCM, what would be the advantage of that ?
Also for high HP applications which choice would be better for the 4l60E ? I mean for a head/cam or stroker engines, would it be better to install the vacuum modulator, or should I just program the PCM to set the shift firmness to be based only on TPS reading ?
Thanks
[ December 03, 2001: Message edited by: xxxhp ]</p>
Also for high HP applications which choice would be better for the 4l60E ? I mean for a head/cam or stroker engines, would it be better to install the vacuum modulator, or should I just program the PCM to set the shift firmness to be based only on TPS reading ?
Thanks
[ December 03, 2001: Message edited by: xxxhp ]</p>
Re: 4L60E Vacuum Shift Modulator ...benefits ? That's a really great question! Patrick definitely says it best, so here's a quote from one of his posts on LS1.com.
"Here's what's happening: With a heads/cam setup, the breathing potential of the LS1 often exceeds that of the Air Lid, MAF, or Throttle Body and a vacuum exists at WOT. If the MAP sensor sees atmospheric at WOT, it gives 100% line pressure. If the MAP sensor sees a vacuum at WOT, it will lower line pressure and this will lead to clutch slippage. A possible solution is to put on a conventional vacuum modulator on the tranny, but there still lies the problem of pulling a vacuum at WOT. A better solution would be for Ed Wright (or other reputable tuners) to have the tranny line pressure tied directly to TPS% only and delete the info coming from the MAP sensor. 100% TPS=100% line pressure."
You can view the full discussion at http://www.ls1.com/ls1forum/Forum11/HTML/004480.html
I don't know if a vacuum shift modulator would be better than setting your line pressure to vary with your TPS or not, but I bet Patrick can answer that, too. <img src="images/icons/smile.gif" border="0"> FWIW, I had my line pressure set to vary directly with my TPS when I had Ed Wright program my PCM.
"Here's what's happening: With a heads/cam setup, the breathing potential of the LS1 often exceeds that of the Air Lid, MAF, or Throttle Body and a vacuum exists at WOT. If the MAP sensor sees atmospheric at WOT, it gives 100% line pressure. If the MAP sensor sees a vacuum at WOT, it will lower line pressure and this will lead to clutch slippage. A possible solution is to put on a conventional vacuum modulator on the tranny, but there still lies the problem of pulling a vacuum at WOT. A better solution would be for Ed Wright (or other reputable tuners) to have the tranny line pressure tied directly to TPS% only and delete the info coming from the MAP sensor. 100% TPS=100% line pressure."
You can view the full discussion at http://www.ls1.com/ls1forum/Forum11/HTML/004480.html
I don't know if a vacuum shift modulator would be better than setting your line pressure to vary with your TPS or not, but I bet Patrick can answer that, too. <img src="images/icons/smile.gif" border="0"> FWIW, I had my line pressure set to vary directly with my TPS when I had Ed Wright program my PCM.
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From: Wichita, KS - 1400' above sea level ;-)
Re: 4L60E Vacuum Shift Modulator ...benefits ? ^ That's the basic impetus right there.
I know the solution to the possibility of pulling
an inch or two of vacuum at WOT, and that consequently not allowing full line pressure with the vacuum modulator:
It's supplied with an adjustable length pin that modulates the maximum pressure - so you would want to get one just a shade longer to allow for the fact that you aren't quite reaching 0 vacuum. Concurrently, you would want to make sure the pressure regulator in the pump is set to NOT OVEREXCEED the max desired pressure with the slightly longer pin when you first nail it and really ARE PULLING ~0" vacuum before you get up in revs and pull the slight vacuum. (shortening the pin length per a supplied chart reduces the pressure, mine is set to max and I have 3000 miles on it so far, but I completely rebuilt the transmission with every other hi-performance mod known to exist for the 4L60-E)
The vacuum modulator is only like $60, but I would describe it as a HARD-CORE mod not for the timid -
as you have to drill a pass-thru hole in the tranny case and clearance-grind the 1-2 accumulator housing.
Essentially then IMHO, the vacuum modulator is a bit of a cheap ghetto solution to the problem, and programming is a more robust way to do it.
Rob
1998 Purple T/A 2.73 A4
Free mods/lid/filter yadda yadda yadda, Pro Yank 3400 Extreme, !cats, !catback, Nittos
12.89 @ 105.1, 60' 1.85, Best MPH 106.8
[ December 03, 2001: Message edited by: Plum Crazy Rob ]</p>
I know the solution to the possibility of pulling
an inch or two of vacuum at WOT, and that consequently not allowing full line pressure with the vacuum modulator:
It's supplied with an adjustable length pin that modulates the maximum pressure - so you would want to get one just a shade longer to allow for the fact that you aren't quite reaching 0 vacuum. Concurrently, you would want to make sure the pressure regulator in the pump is set to NOT OVEREXCEED the max desired pressure with the slightly longer pin when you first nail it and really ARE PULLING ~0" vacuum before you get up in revs and pull the slight vacuum. (shortening the pin length per a supplied chart reduces the pressure, mine is set to max and I have 3000 miles on it so far, but I completely rebuilt the transmission with every other hi-performance mod known to exist for the 4L60-E)
The vacuum modulator is only like $60, but I would describe it as a HARD-CORE mod not for the timid -
as you have to drill a pass-thru hole in the tranny case and clearance-grind the 1-2 accumulator housing.
Essentially then IMHO, the vacuum modulator is a bit of a cheap ghetto solution to the problem, and programming is a more robust way to do it.
Rob
1998 Purple T/A 2.73 A4
Free mods/lid/filter yadda yadda yadda, Pro Yank 3400 Extreme, !cats, !catback, Nittos
12.89 @ 105.1, 60' 1.85, Best MPH 106.8
[ December 03, 2001: Message edited by: Plum Crazy Rob ]</p>
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From: Wichita, KS - 1400' above sea level ;-)
Re: 4L60E Vacuum Shift Modulator ...benefits ? *IF* you're getting programming for heads/cam, or
whatever, CERTAINLY do it that way/include it at that time.
*I* haven't got that far (YET! Wait for spring...) so this is maybe a temporary solution. Like most Transgo products, it does work very well when installed correctly. Hopefully I can really up the
power/torque on my setup (it will still be naturally aspirated and 346 CID FYI) and put the tranny to a good test.
The vacuum modulator and install certainly isn't anything that would faze somebody who has installed, say a shift kit for example. I just don't want anyone thinking its as simple as putting a lid on or whatever.
<img src="images/icons/smile.gif" border="0">
whatever, CERTAINLY do it that way/include it at that time.
*I* haven't got that far (YET! Wait for spring...) so this is maybe a temporary solution. Like most Transgo products, it does work very well when installed correctly. Hopefully I can really up the
power/torque on my setup (it will still be naturally aspirated and 346 CID FYI) and put the tranny to a good test.
The vacuum modulator and install certainly isn't anything that would faze somebody who has installed, say a shift kit for example. I just don't want anyone thinking its as simple as putting a lid on or whatever.
<img src="images/icons/smile.gif" border="0">
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That's a really great question! Patrick definitely says it best, so here's a quote from one of his posts on LS1.com.
"Here's what's happening: With a heads/cam setup, the breathing potential of the LS1 often exceeds that of the Air Lid, MAF, or Throttle Body and a vacuum exists at WOT. If the MAP sensor sees atmospheric at WOT, it gives 100% line pressure. If the MAP sensor sees a vacuum at WOT, it will lower line pressure and this will lead to clutch slippage. A possible solution is to put on a conventional vacuum modulator on the tranny, but there still lies the problem of pulling a vacuum at WOT. A better solution would be for Ed Wright (or other reputable tuners) to have the tranny line pressure tied directly to TPS% only and delete the info coming from the MAP sensor. 100% TPS=100% line pressure."
You can view the full discussion at http://www.ls1.com/ls1forum/Forum11/HTML/004480.html
I don't know if a vacuum shift modulator would be better than setting your line pressure to vary with your TPS or not, but I bet Patrick can answer that, too. <img src="images/icons/smile.gif" border="0"> FWIW, I had my line pressure set to vary directly with my TPS when I had Ed Wright program my PCM.
"Here's what's happening: With a heads/cam setup, the breathing potential of the LS1 often exceeds that of the Air Lid, MAF, or Throttle Body and a vacuum exists at WOT. If the MAP sensor sees atmospheric at WOT, it gives 100% line pressure. If the MAP sensor sees a vacuum at WOT, it will lower line pressure and this will lead to clutch slippage. A possible solution is to put on a conventional vacuum modulator on the tranny, but there still lies the problem of pulling a vacuum at WOT. A better solution would be for Ed Wright (or other reputable tuners) to have the tranny line pressure tied directly to TPS% only and delete the info coming from the MAP sensor. 100% TPS=100% line pressure."
You can view the full discussion at http://www.ls1.com/ls1forum/Forum11/HTML/004480.html
I don't know if a vacuum shift modulator would be better than setting your line pressure to vary with your TPS or not, but I bet Patrick can answer that, too. <img src="images/icons/smile.gif" border="0"> FWIW, I had my line pressure set to vary directly with my TPS when I had Ed Wright program my PCM.
First post!! Great info here, not sure I fully understand all of it...
Dont mean to thread jack, but I have been trying to find some info about my 2004 silverado/4l60e
About a month ago, I was merging onto the freeway, romped on it, it downshifted and revved right up, but i didnt accelerate. And had lately been a bit erratic with shifts (very hard 1-2 shift, difficulty shifting into 3rd). I feared my 4l60e was on its last legs (and still kinda do...)
I also had some check engine lights that led me to believe I had leaky intake manifold gaskets.
I just changed the IM gaskets on the weekend and have been driving it around... And it seems like the trans is now shifting better? Is there any logical explanation for this?
As he said " If the MAP sensor sees a vacuum at WOT, it will lower line pressure and this will lead to clutch slippage", I am not a mechanic but this gave me an "aha!!" Moment thinking maybe there was an explanation here!!
I am new to the GM game, this is my first gm, it has been plagued with issues and has been a money pit, but I want to like it!!
Thanks and happy wrenching
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I used the vacuum modulator in the early days and on pre-1999 vehicles. After 1999, I noticed the computers were doing a much better job, so the vacuum modulator was not needed anymore. Vehicles that came with the OBD1, was where they worked well.
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Thank you for the replies.
I am not interested in buying a vacuum modulator, I'm wondering if my leaky intake manifold gaskets could have been causing my transmission slippage issues.
Drove my truck over 600kms on the weekend without a single shifting issue- in fact with the cruise control on, it hardly even downshifted to climb hills (before it would downshift at the slightest change in grade)
It no longer just slips if I punch it from 60-80kmh, say when Im merging onto the freeway.
Thanks again!!
I am not interested in buying a vacuum modulator, I'm wondering if my leaky intake manifold gaskets could have been causing my transmission slippage issues.
Drove my truck over 600kms on the weekend without a single shifting issue- in fact with the cruise control on, it hardly even downshifted to climb hills (before it would downshift at the slightest change in grade)
It no longer just slips if I punch it from 60-80kmh, say when Im merging onto the freeway.
Thanks again!!
