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Can I disable the line pressure boost in Reverse (and how)
UPDATE: See post #24 below for success and details.
My Camaro has an LS3 with an extreme camshaft (19 degrees overlap) which produces very little power at idle; heck barely will idle below 1000 RPM.
My 4L65E trans mods have increased line pressure across the board with the Sonnax boost valve.
Despite many tuning changes over the years, the engine will stall many times when I put it in Reverse from idle; going into Forward is fine.
Therefore, I would like to try disabling the line pressure boost in Reverse because I'm confident this is putting additional load on the engine, via the trans pump, and stalling the engine.
Ideally I would like to do this without removing the trans. I have looked at the hydraulic diagrams, but its now clear how to do this and still make Reverse work.
Thanks for any ideas.
Last edited by mrvedit; Nov 16, 2025 at 06:00 PM.
Reason: Add Update
My Camaro has an LS3 with an extreme camshaft (19 degrees overlap) which produces very little power at idle; heck barely will idle below 1000 RPM.
My 4L65E trans mods have increased line pressure across the board with the Sonnax boost valve.
Despite many tuning changes over the years, the engine will stall many times when I put it in Reverse from idle; going into Forward is fine.
Therefore, I would like to try disabling the line pressure boost in Reverse because I'm confident this is putting additional load on the engine, via the trans pump, and stalling the engine.
Ideally I would like to do this without removing the trans. I have looked at the hydraulic diagrams, but its now clear how to do this and still make Reverse work.
Thanks for any ideas.
Funny thing - I thinking about it 3 days ago and I think I have a solution
You need to remove pump and remove from it boost valve
After that you need to delete plug that goes thru boost valve area and with suitable tool bump it above boost valve bore to block incoming reverse oil
With chisel or so damage metal to prevent that cap from falling back
The boost valve can be removed without pulling the trans. You will have to drop the pan to get at it.
There will be a tiny feed hold in the boost valve that feeds the large (reverse) land of the valve.
Plug the feed hole and then grind a small "flat" on the reverse land of the valve to exhaust any oil that may leak past the small land due to bore clearance.
Won't be too difficult
As for the plug in the sleeve. Few ways to do it.
Easiest will be just to drill the hole to 1/16, don't go ALL the way through.
Insert a short chunk of aluminum TIG fill rod.
Peen the tig rod to close the hole.
You could also just TIG the hole shut
You could drill to a nominal size and drive in a small steel ball with the proper press fit
Thanks guys! @MaroonMonsterLS1 I assume you are implying that either the boost valve modification OR plugging before "237" (as mentioned by @V8fan ) should do the trick, and that I don't need both. With the trans in the car and working well, I prefer not to remove it. I will study the hydraulics again after my upcoming trip and make the mod.
@V8fan - Interesting that you were thinking of this a few days ago. Why?
Thanks guys! @MaroonMonsterLS1 I assume you are implying that either the boost valve modification OR plugging before "237" (as mentioned by @V8fan ) should do the trick, and that I don't need both. With the trans in the car and working well, I prefer not to remove it. I will study the hydraulics again after my upcoming trip and make the mod.
@V8fan - Interesting that you were thinking of this a few days ago. Why?
I wanna use reverse area to boost forward pressure
Boost valve actually hyd amplifier and the bigger its area -bigger force it apply to PR valve = in result line pressure bigger
So Im thinking about to use reverse in addition to existed
And for doing than I need to eliminate leaks from TQ sig to reverse and block reverse flow into boost valve
So I decided to block incoming passage to boost valve and block 237 bleeder because I dont wanna made custom boost valve and I dont wanna block reverse hole into boost sleeve cuz I can damage its shape and boost valve can stuck inside
So for me safest way is to block before boost and block area after boost where 237 and side plug located and drill hole inside boost valve itself (not sleeve) to connect both areas to once
My calculations says me that I can achieve 220-240 PSI with OEM and 270-290 with Sonnax boost valve
I wrote about that in tips and tricks tread
As mention Just plug the rev hole in the boost valve and grind a llittle flat on it to exhaust. I have noted with my own car I get a notable RPM drop when going to reverse but not a stall . It drops momentarily then the IAC compensates and back up. But plugging the feed in the valve should do the trick. Note may get a slight delay on reverse engagement. and HI long time since heard from you. Good to see ya here.
__________________ Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
Considering you can easily eclipse over 270psi without needing to use the reverse boost...I'm not sure why you feel you'd need to implement what you're thinking V8
mrvedit--blocking the boost valve is quite simple. Blocking it in the pump is not easy at all.
I would like to add...in the programming, on stock ECU you should be able to reduce the epc in reverse depending on which operating system you have...might be enough to fix your idle...might not be. But I'd sure try before I got my hands oily
This post brings back memories. I had a similar issue with reverse years ago with a cammed car, took me a while to find the file but this was the Orig vs mod EPC tables I edited. We went as far as hooking a trans pressure gauge up as well for logging the GM.DYNAIR, GM.TFMCUR, and GM.TRQTRANS parameters to see what cells were active in tune. If I remember right we were bouncing between cell 0, 6, 12. When increasing the EPC current we were able to drop line 5 or 10 psi at a steady idle. Now this is a global setting so it smoothed reverse and seemed to lighten the kick into drive as well. any throttle at all and logger was ramping past 24 cells so no fear of low pressure under load was evident. You can also simply test EPC current changes vs actual pressure in the DVT tab as well. We started there before flashing in any hard changes.
This was really only a solution to a car I had issues with long ago. Since then I spend more time in the actual idle tables, desired flow in Park/Nuetral vs in gear. Also look into the IAC actual steps. Make sure those are not unreasonably high or low at a steady idle. Much beyond the 60-120 range I would be looking at not just the tune but condition of throttle body, PCV system setup, and always the dreaded vaccum leaks.
Considering you can easily eclipse over 270psi without needing to use the reverse boost...I'm not sure why you feel you'd need to implement what you're thinking V8
But rising FWD pressure automatically will rise REV pressure
And I don't need it
But rising FWD pressure automatically will rise REV pressure
And I don't need it
Not sure you're making sense?
If you hijack the rev booster...and use it for EPC oil...you'll have higher FWD pressure as well?
And it'll be higher in reverse because EPC still active...I'm just not sure what you're trying to achieve
With stock booster orientation you can get more pressure than you really need so I have no logical explanation why you'd want to use the rev booster which has an even larger area and could force EVEN higher pressure?
If you hijack the rev booster...and use it for EPC oil...you'll have higher FWD pressure as well?
Yep
Originally Posted by MaroonMonsterLS1
With stock booster orientation you can get more pressure than you really need so I have no logical explanation why you'd want to use the rev booster which has an even larger area and could force EVEN higher pressure?
Have you ever ran any analysis on what happens to the 3/4 drum when you turn the apply force way up?
Have you ever put a dial indicator on the servo snap ring lugs of the case and seen how much they move when you crank up the apply force there?
Etc
Considering there are 4l60e's out there holding 700, 800, 900, +++ HP
And not Needing as much pressure you're applying
Again...I'm just not sure what you're trying to accomplish or if you fully understand the implications of what you're implying
Have you ever ran any analysis on what happens to the 3/4 drum when you turn the apply force way up?
Have you ever put a dial indicator on the servo snap ring lugs of the case and seen how much they move when you crank up the apply force there?
Etc
Considering there are 4l60e's out there holding 700, 800, 900, +++ HP
And not Needing as much pressure you're applying
Again...I'm just not sure what you're trying to accomplish or if you fully understand the implications of what you're implying
Yes I was just thinking yesterday about the apply backing plates , Even at 200psi they are known to dish Hence the SONNAX extra thick or the one I like with the enforcemet ring in bottom. It seems as line goes higher this would become more and more of an issue and a coned apply plate the more that happned you would get less and less apply area or at least very uneven defeating the purpose of the higher line.
__________________ Frank formerly of Performabuilt, Now just me, What can I build for you today? Call or message me. Click sig pic for my facebook
Have you ever ran any analysis on what happens to the 3/4 drum when you turn the apply force way up?
Have you ever put a dial indicator on the servo snap ring lugs of the case and seen how much they move when you crank up the apply force there?
I not tested lugs but later will
I have air compressor that can apply 300+
I only know that FWD piston apply force to FWD clutch x2 to force that 3-4 piston can reach because of difference in areas
And FWD friction disks looks not stressed at all every time I disassembled worn out tranny
Fine that we went a bit off-topic here. I guess the new topic is "screwing with boost pressure".
Finally got some time to work on this now. Examining a spare pump and boost valve while my trans pan drains.
Looking at Figures 28 and 48 in the Hydramatic 4L60E Technical Manual, and my spare inner and outer boost valve, it appears the tiny 0.5mm hole at the bottom of the outer boost valve is the torque signal and must not be changed.
There are two 2.0 mm holes in the middle of the outer boost valve which appear to be for the Reverse input. When you guys say to plug this "tiny hole", I assume you mean BOTH of the larger holes on the outer boost valve. ??
Also, yes I have tuned for the lowest possible line pressure at no throttle. I did this years ago with HP Tuners and with my current Holley Dominator. It helped, but not quite enough.
@RonSSNova Yes I still have my 419ci LS3. I have lived with this problem since day one and its now time to fix it. Lets talk soon; plan to road trip out to Oregon next year May.
Finally, I need ideas of how to plug the two holes; the wall is only 2mm thick. Set screws are too long; TIG might warp it; the inside is a precision fit and I could not "clean" it.
Last edited by mrvedit; Nov 11, 2025 at 08:11 PM.
Reason: Added last sentence of how to plug the holes.
Fine that we went a bit off-topic here. I guess the new topic is "screwing with boost pressure".
Finally got some time to work on this now. Examining a spare pump and boost valve while my trans pan drains.
Looking at Figures 28 and 48 in the Hydramatic 4L60E Technical Manual, and my spare inner and outer boost valve, it appears the tiny 0.5mm hole at the bottom of the outer boost valve is the torque signal and must not be changed.
There are two 2.0 mm holes in the middle of the outer boost valve which appear to be for the Reverse input. When you guys say to plug this "tiny hole", I assume you mean BOTH of the larger holes on the outer boost valve. ??
Finally, I need ideas of how to plug the two holes; the wall is only 2mm thick. Set screws are too long; TIG might warp it; the inside is a precision fit and I could not "clean" it.
Thats why I decided not to plug boost valve itself - too tiny walls and big chance to block shifter from moving or make sleeve not round -in result shifter also can't move freely
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Can I disable the line pressure boost in Reverse (and how) 
