Adjusting the power steering pump for lower pressure, has anyone done it?

[destrux]

I'm looking for a way to increase the steering effort a bit without swapping to PPS (if that's even possible). Preferably without spending hundreds of dollars.

On my eclipse years ago I bought a modified bypass valve for the power steering pump (for $40) that lowered the pump pressure to increase the steering effort without increasing it so much that it makes low speed driving unsafe (like it does when removing the pump/doing a power steering bypass). Does anyone make that for this car, or has anyone modified theirs to do that?

I was looking at some 4x4 sites where people shimmed the pump bypass to achieve higher pressures and more assist for offroading, but adding shims to preload a spring is easy... taking preload off of a spring to do the opposite thing isn't. I was thinking of possibly drilling the spring pocket deeper, and then shimming it back if I go too far. I have a spare 7M pump I'm going to tear apart to experiment with.

Any thoughts?

 

[destrux]

After reading the description of thow the flow control and bypass valve works (looked up the patent for it), it seems lowering the pressure can't be done the way the offroad guys are raising the pressure. They are pretty much shimming the safety bypass valve so it doesn't open till a higher pressure. This valve only really opens when you overload the steering system, like when hitting the steering stops, or putting massive offroad tires on and turning them on top of rocks with the brakes on. So lowering the opening pressure of it would probably end up with a scary and unexpected loss of steering assist while doing a sharp low speed turn, or when quickly swerving on the highway. Not good. It also wouldn't achieve the result of lowering the system pressure during normal driving. So the bypass valve will be left alone.

The flow control spring may be what I need to experiment with, but it's more difficult to "adjust" because of it's design. I may be able to do something as simple as put a thin copper washer under the high pressure outlet port to move it out and lower the preload on the flow valve spring. It will change the relationship of the spools and the ports in the valve when at rest though, which may cause problems. If only a tiny change in spring preload is needed to lower pressure, it may be achievable without messing up the spool/port relationship too much.

It may be that port sizes in the pump need to be altered, but first I will try the spring.

 

[ifyouaint1sturlast]

Not the answer to your question, but related.. I was wondering if you knew if the 7M pressure is higher than 2JZ? Since doing my 2JZ swap I've noticed that it's not as assisted as the 7M was. I have to put forth a lot more effort to steer the car.

 

[ifyouaint1sturlast]

After reading the description of thow the flow control and bypass valve works (looked up the patent for it), it seems lowering the pressure can't be done the way the offroad guys are raising the pressure. They are pretty much shimming the safety bypass valve so it doesn't open till a higher pressure. This valve only really opens when you overload the steering system, like when hitting the steering stops, or putting massive offroad tires on and turning them on top of rocks with the brakes on. So lowering the opening pressure of it would probably end up with a scary and unexpected loss of steering assist while doing a sharp low speed turn, or when quickly swerving on the highway. Not good. It also wouldn't achieve the result of lowering the system pressure during normal driving. So the bypass valve will be left alone.

The flow control spring may be what I need to experiment with, but it's more difficult to "adjust" because of it's design. I may be able to do something as simple as put a thin copper washer under the high pressure outlet port to move it out and lower the preload on the flow valve spring. It will change the relationship of the spools and the ports in the valve when at rest though, which may cause problems. If only a tiny change in spring preload is needed to lower pressure, it may be achievable without messing up the spool/port relationship too much.

It may be that port sizes in the pump need to be altered, but first I will try the spring.

Something simpler: Change pulley size?

 

[destrux]

Not sure, but I do know the assist is light as a feather with my 1JZ pump, which is the same pump body as the 2JZ pump from what I've found. I can't imagine the 7M pump being even lighter than this already is. Maybe your pump is worn or something?

I thought of pulley sizes... but the flow control valve works on outlet pressure, so if the pump is pumping less the valve will just adjust output to be the the same volume/pressure that it was before.

The way I see it, there's only two possible ways to do it.

1. Modify the flow control valve so the output pressure is lower. The advantage to this is you're removing some parasitic drag from the pump, because it isn't using as much power to develop lower pressures. So you gain a few HP (bonus!). It also costs next to nothing (all you may need is a few dollars worth of small parts like shims or springs). Disadvantage is it's hard to adjust the results, and figuring out how to do it in the first place is an obstacle.
2. Bleed off fluid from the high pressure line after the pump and return the fluid to the return line before the power steering cooler. You can't use a pressure regulator in the high pressure line because any restriction in the line would cause the pump to respond with higher pressure (it thinks you're turning). Advantage here is you're not modding your pump and you can use this (http://www.heidts.com/_uploaded_files/in-053.pdf) and have it easily adjustable if you want more or less assist. Disadvantage is you have more complexity and stuff to break and take up space, and you're wasting power pumping and heating up the fluid that you're bypassing. Plus it costs about $100.

 

[NashMan]

the only way to make it harder to turn is to change the torsion bar

now the question is what one will fit into a supra rack and work with the spool valve

it would be easyer to run pps unit and then make your own controller

 

[destrux]

Ok, so I found something interesting.

Toyota sells different springs and flow valve pistons for their power steering pumps, and each one allows for a different steering feel. I found this out looking up flow control springs and pistons in the toyota parts system. There are quite a few different ones that all fit the same style pump.

The piston design dictates the assist "curve", or how quickly the pump provides assist when you turn the wheel. I guess in trucks and luxury cars you don't want the thing being all twitchy, but you still want high assist for that luxury feel. In sports cars I'd believe it would be designed for moderate response and moderate assist. The spring rate designates the actual pressure the pump runs at. The heavier/longer the spring the higher the pressure.

My pump is from a Soarer 2.5GT, and has a letter C stamped on the valve piston. The spring inside is 1 11/32" free height with a 12.875 Lb-in rate (determined with a valve spring tester).

I'm curious what piston "letters" and spring rates were used in other cars, specifically the JZA80 and the JZA70. I'm not sure what other cars used this pump, but the best shot for the lowest assist piston/spring possible would be from the lightest or sportiest cars, so maybe a celica or a corolla?

Guess I'll be making a junkyard trip soon.

Another option for high quality springs that might be the right size and come in different rates.... 1/10 scale RC car suspension springs.



Oh and the 87' 7MGTE pump I have here is similar inside design wise.... but nothing fits between the two, they are different.

 

[destrux]

You're right about the torsion bar. That is a much better way to do this. A stiffer torsion bar would improve steering feel (especially on-center feel) and reduce the amount of fluid allowed through the spool valve, which would reduce assist. That would be the best way to do it. Finding a rack with an interchangeable spool valve (that also has a larger torsion bar) is going to be tough though.

Lowering the pump pressure like I was originally planning would work to lower overall effort, it would make the car less twitchy at high speeds when you're trying to turn a little (and the car responds by trying to turn ALOT). It wouldn't do much for on-center feel though, which needs the most improvement out of any aspect of the steering system.

If it comes down to it... taking the power steering pump completely off, purging and venting the rack, and welding the spool valve solid would sure improve the steering feel ALOT.... but then I'd curse myself every time I parallel park (and I have to do this daily). It's very temping though. If anyone doesn't know what I mean about welding the spool valve; here's a nice explaination: http://www.motoiq.com/magazine_arti...sa-part-5--de-powering-the-steering-rack.aspx

 

[IJ.]

Do you have room for a bigger pully?

 

[IBoughtASupra]

Ian, wouldn't you want a smaller pulley for more revolutions to make the steering wheel easier to turn or is it less revolutions that make the steering easier to turn?

 

[mecevans]

Bigger PS pulley= lower pressure.

 

[Crypton2006]

Simply changing pulley size will do nothing. The regulator will simply increase pressure to compensate for lower rpm. It would be a larger pully on the pump or smaller on the crank.

Sent from my SCH-M828C using Tapatalk

 

[NashMan]

You're right about the torsion bar. That is a much better way to do this. A stiffer torsion bar would improve steering feel (especially on-center feel) and reduce the amount of fluid allowed through the spool valve, which would reduce assist. That would be the best way to do it. Finding a rack with an interchangeable spool valve (that also has a larger torsion bar) is going to be tough though.

Lowering the pump pressure like I was originally planning would work to lower overall effort, it would make the car less twitchy at high speeds when you're trying to turn a little (and the car responds by trying to turn ALOT). It wouldn't do much for on-center feel though, which needs the most improvement out of any aspect of the steering system.

If it comes down to it... taking the power steering pump completely off, purging and venting the rack, and welding the spool valve solid would sure improve the steering feel ALOT.... but then I'd curse myself every time I parallel park (and I have to do this daily). It's very temping though. If anyone doesn't know what I mean about welding the spool valve; here's a nice explaination: http://www.motoiq.com/magazine_arti...sa-part-5--de-powering-the-steering-rack.aspx

there is one issue with lowering persure it's called power streeing pump groan from lack of persure

the pps alter the flow control valves movement

technically the best option you have is to swap the rack then remove the pps unit and then use a fule regulator to control steering effort or some type of by pass ween valve

so i suggest 3 things

1 pps unit
2 change out the flow control valve and bar
3 just replace the torstion bar
4 school bus steering wheel

ps toyota made 3 racks for the supra (86 to 87 soft) (harder 88 only) (then 89 92)

so if i am right the torsion bar is the same from 88 to 92 and 89 plus they just added the new bleed section pps conrtoler


good luck

 

[IJ.]

Simply changing pulley size will do nothing. The regulator will simply increase pressure to compensate for lower rpm. It would be a larger pully on the pump or smaller on the crank.

Sent from my SCH-M828C using Tapatalk

I played around with a bunch of different size pullies, it made a difference...

Think about it at low engine speeds the pump isn't anywhere near the Pressure bypass.

 

[destrux]

The bypass valve is separate from the flow control valve though IJ, the bypass valve is always closed (unless you hit the stops) but the flow valve is constantly operating whenever you're above idle. A larger or smaller pulley really shouldn't have any effect unless you go beyond the design limit of the flow valve, which would require a very large pulley. A larger pump pulley would free up some power though, that fluid that's being recirculated inside the pump is sucking up some power.

I wish I would have found this video earlier today, I spent an hour reading and re-reading a poorly translated patent to figure it out.

[video=youtube;xeWmNpZ5sD0]http://www.youtube.com/watch?v=xeWmNpZ5sD0&feature=related[/video]

The first part is the flow valve, they cover the bypass valve near the end. There's also a video on the rack and pinion which is pretty good.


Anyway, I did manage to lower my steering pressure by about 93psi. :naughty: It was pretty easy. I took the flow valve spring out and ground 1/32" off each end, being careful to only remove material from the dead coils so that I wouldn't raise the spring rate. Also was sure to keep the spring cool so it wouldn't be ruined. Right now the flow rate didn't drop enough that the rack is "studdering", but if it did, some machining could be done on the exit port to raise the flow rate at the lower pressure to keep the rack fed.

It feels about the same as the steering effort in my mazdaspeed3, which was my goal. The on-center feeling still sucks, but that's the torsion bar in the rack. You can actually see the bar if you look at the end of the steering shaft going into the rack, so some junkyard digging might net some swappable parts.

I do have an 87' rack, so possibly the 88+ racks might have a stronger bar that might fit, or I could swap to an 88+ rack if I find one for the right price. I'm hoping to find something from a more common car though, since I haven't seen a MKIII supra in a junkyard around here for a while.

For now though, I'm happy that it doesn't steer like a 65' Continental anymore.

 

[mecevans]

Care to take pictures and write up a procedure? Thinking of doing this myself. I have to much on-center assistance.

 

[destrux]

I'll do a write up on the torsion bar once I figure that out, since that's responsible for 99% of the on center feel. The spring mod I just did only makes the steering feel "heavier" when you're sawing through turns. Gives the car a "substantial" feeling, sort of.


For the spring mod, all you do is take the high pressure banjo bolt out where the hose connects to the pump, then use a 24mm wrench (27mm on a 7M) to remove the flow control valve. The first part is the part that unscrews, but you need to use a magnet to pull the piston and spring out from deeper inside the hole in the pump. Don't worry, there aren't any small parts to get lost. Once you have the spring out, you just carefully file the ends so it's shorter. You don't want to remove any full coils, just file some off the ends. The max you can remove is 1/32" on each end, and that's what I did. Clean it all up so there's no burrs or dirt, dip it in PS fluid or ATF and re-assemble it. The spring goes in first, then the piston, then you screw the top back on, that's it.

There will probably be less of an effect on a 7M pump since the spring is so much lighter, removing 2/32" of preload will only have half the effect it did on the 1JZ pump.

 

[IJ.]

Nice job figuring that out Dest, I just ran a lot of castor in mine and it was near enough, when I went PPS I used the MoTeC to control the rack so could tune it for any feel I wanted.

 

[NashMan]

I'll do a write up on the torsion bar once I figure that out, since that's responsible for 99% of the on center feel. The spring mod I just did only makes the steering feel "heavier" when you're sawing through turns. Gives the car a "substantial" feeling, sort of.


For the spring mod, all you do is take the high pressure banjo bolt out where the hose connects to the pump, then use a 24mm wrench (27mm on a 7M) to remove the flow control valve. The first part is the part that unscrews, but you need to use a magnet to pull the piston and spring out from deeper inside the hole in the pump. Don't worry, there aren't any small parts to get lost. Once you have the spring out, you just carefully file the ends so it's shorter. You don't want to remove any full coils, just file some off the ends. The max you can remove is 1/32" on each end, and that's what I did. Clean it all up so there's no burrs or dirt, dip it in PS fluid or ATF and re-assemble it. The spring goes in first, then the piston, then you screw the top back on, that's it.

There will probably be less of an effect on a 7M pump since the spring is so much lighter, removing 2/32" of preload will only have half the effect it did on the 1JZ pump.

you can thank me later but grab a torsion bar form Cecilia gts/gt or it will fit since the car was so light not sure of the gt but I did know the gts had longer streeing arms


good luck



your going to laugh at this but a guy I know put a spring in the rack on the power piston to stiffen it up

not sure how that would work but go for it lol might be springy hahaha


you can buy rebuilt pps at jay marks toyota because they have company that rebuild racks for them so might be able to get parts form them who know but good luck


if you open up the rack there alot of mods you can do wail in there too

 

[Typhoon]

You need to modify the pressure relief valve on the rack. All you are doing by dumping pressure at the pump is making the pump lag behind the rack's needs. I've been there and done it with various steering boxes on older vehicles. Lowering pump output pressure causes all sorts of fun side effects, like varying assistance under high turn rates and load etc as the pump fails to maintain line pressure to the steering box as large amounts of fluid move.
The non PPS racks have a much nicer feel than the PPS racks, my 90 turbo had the much lighter steering you guys are complaining about, but my 86 non turbo is VERY nice in every respect. I am even running the same tyres, so it's a pretty fair comparison.
As IJ said, lots of caster helps, as does a little more toe than most performance wheel alignments put in too.