Do you need a vacuum mod to increase line pressure?
Thread Starter
Launching!
Joined: May 2003
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From: Canadian West Coast
Do you need a vacuum mod to increase line pressure? My head is spinning from all the tranny research I've been doing lately...
I'm looking to get a 'modified' trans-go shift kit, mainly to increase line pressure and minimize slippage. I believe I have some wear in the bore currently, causing the line pressure to be too low. I notice there are a couple of types of kits. Some have a vacuum accumulator, some don't (I think). Do all the kits come with a vacuum modulator? Does it just increase the line pressure faster?
I want to keep most of the slippage you get stock at part throttle, which I understand you can do, but improve it at WOT to increase durability.
I'm looking to get a 'modified' trans-go shift kit, mainly to increase line pressure and minimize slippage. I believe I have some wear in the bore currently, causing the line pressure to be too low. I notice there are a couple of types of kits. Some have a vacuum accumulator, some don't (I think). Do all the kits come with a vacuum modulator? Does it just increase the line pressure faster?
I want to keep most of the slippage you get stock at part throttle, which I understand you can do, but improve it at WOT to increase durability.
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The vacuum modulator will raise WOT pressure in 1st & 2nd some, but quite abit in 3rd gear. I use the modulator on the majority of my builds, along with the "modified" Trans-Go Performance Shift kit.
Last edited by Pro Built Automatics; Jul 3, 2005 at 04:21 AM.
Thing with a vacuum modulator is, you no longer have
to stand for the lame line pressure vs load profile that
GM programmed into the PCM. Like 0% commanded
line at 80MPH cruise, that's dumb. But haven't seen a
tool yet that offers up this mapping to be edited, the
most fundamental thing. So you have to jack around
the force motor layer instead of the commanded pressure
for load profile. A well engineered vac mod setup will
have a more sensible profile to it (one would hope,
anyway). Plus it's quicker to respond and not subject
to all kind of secondary PCM meddling neither.
But the modulator does not alter main line, just the
derived, applied pressure profile. Which may be all
you need, especially if your main slip problems are at
part throttle and not WOT.
to stand for the lame line pressure vs load profile that
GM programmed into the PCM. Like 0% commanded
line at 80MPH cruise, that's dumb. But haven't seen a
tool yet that offers up this mapping to be edited, the
most fundamental thing. So you have to jack around
the force motor layer instead of the commanded pressure
for load profile. A well engineered vac mod setup will
have a more sensible profile to it (one would hope,
anyway). Plus it's quicker to respond and not subject
to all kind of secondary PCM meddling neither.
But the modulator does not alter main line, just the
derived, applied pressure profile. Which may be all
you need, especially if your main slip problems are at
part throttle and not WOT.
Thread Starter
Launching!
Joined: May 2003
Posts: 290
Likes: 0
From: Canadian West Coast
Yes, from I have see, the pcm control for line pressure is not beneficial for a stalled car. Thats a strong reason for the vac modulator.
I may have to call a shop to discuss what I really need.
I'm looking for a good strong street set up, not a strip only set up. Part of me does like the wimpy soft shifts of stock. SO I am trying to avoid getting TOO hard core in the tranny's feel. If you know what I mean.
I may have to call a shop to discuss what I really need.
I'm looking for a good strong street set up, not a strip only set up. Part of me does like the wimpy soft shifts of stock. SO I am trying to avoid getting TOO hard core in the tranny's feel. If you know what I mean.
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With my modified Performance Shift kits & and/or the vacuum modulator, I setup all of my kits or transmissions with smooth part throttle 1-2 shifts. There is "no reason" to have a harsh 1-2 part throttle shift.
Originally Posted by Pro Built Automatics
With my modified Performance Shift kits & and/or the vacuum modulator, I setup all of my kits or transmissions with smooth part throttle 1-2 shifts. There is "no reason" to have a harsh 1-2 part throttle shift.
Thread Starter
Launching!
Joined: May 2003
Posts: 290
Likes: 0
From: Canadian West Coast
Originally Posted by Ragtop 99
Its amazing how many people (wrongfully) assume that a harsh banging shift is somehow better than a properly set-up less harsh shift.
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Originally Posted by SmokingWS6
I increased my stock max line pressure from 90 to 95% with HP Tuners and there was a noticeable difference.
max line value. On some vehicles the 100% column is
populated with a "blow-off" value of 1245 (?) and if
you run the commanded line up past 95%, you will
start getting less pressure (much less), rather than
more. You probably want to just fix that column.
hey "Do you need a vacume mod to increase line pressure?" This I belive is the original question....simple answer No. There are several ways to raise base line pressure, however; IMO vacume modulation not only raises it but delivers a more reliable method of line control....Haveing optimal line pressure does you NO good if you can't deliver it at the proper time....increase throttle... increase line...decrease throttle ...decrease line. Simple really....then you put a computer on it......ummmmmm Hope this helps ...Dave
Originally Posted by jimmyblue
Beware of the force motor table if you increase the
max line value. On some vehicles the 100% column is
populated with a "blow-off" value of 1245 (?) and if
you run the commanded line up past 95%, you will
start getting less pressure (much less), rather than
more. You probably want to just fix that column.
max line value. On some vehicles the 100% column is
populated with a "blow-off" value of 1245 (?) and if
you run the commanded line up past 95%, you will
start getting less pressure (much less), rather than
more. You probably want to just fix that column.
I got a question about the Vacuum mod. Who makes a good kit, where is it avalible and WIll it work properly in a FI car? (Hope this is not too off topic). Thnaks, Ark
Last edited by Arkangel77; Jun 16, 2005 at 08:34 AM.
