Underdriving Power Steering pump... ??

Katmandu · Mar 29, 2004

Has anyone underdriven the P/S pump to INCREASE steering input ??

HISSIN50 · Mar 29, 2004

i think the problem would be that the pressure seems to be marginal as it is. i would worry about not having enough pressure for the rack.
just my thoughts, good luck.

393Bird · Mar 29, 2004

March sells one:

Michael Yount · Mar 29, 2004

Katmandu - what do you mean by "INCREASE steering input"?

Katmandu · Mar 29, 2004

Michael Yount said:
Katmandu - what do you mean by "INCREASE steering input"?

Actually, I would like to convert to Manual Steering. I personally like the "feel" of Manual Steering-Vs-Power Steering.

I trying to find out if Underdriving the Power Steering Pump would give me more of that Manual Steering "feel"withOUT going thru the hassels and costs of converting to Manual Steering.

Katmandu · Mar 29, 2004

393Bird said:
March sells one:

Hmm! Haven't seen that yet.

How does it affect the Power Steering "Feel" does it give it less assisted (require more physical input) ??

393Bird · Mar 29, 2004

I havent fired it up yet, so dont know how it will be. I am about 1 week away from starting it.

Michael Yount · Mar 29, 2004

Katmandu - that's what I thought you meant. I don't think it will work that way. Anyone who puts on 'underdrives' is underdriving the power steering pump. That's what the smaller pulley on the crank does. In my experience, it doesn't change the feel at all - it just made my pump 'groan' more during low speed (parking lot) manuvers. Feel was unchanged. Besides, that pump sees quite a range of speed (engine rpm varies about 10X - 600 rpm to 6000 rpm) -- so the pumps speed changes accordingly. Even if you under-drove just the pump, as soon as you step on the gas (most around town driving is in the 1500-3000 range) your speed is right back up higher levels.

Feel is a function of the type rack, the way it's mounted, the way the steering assist is provided and the suspension geometry (tire/wheel selection makes a big difference too). Altering the speed/pressure on the pump won't change feel - under some circumstances it might make it harder to turn the wheel, but don't mistake more effort for better feel. If you like the feel of a manual rack, that's likely what it's gonna take to achieve that feel on the Stang. Or, you can buy one of many newer cars where they've gone to great lengths to build variable-speed assisted steering that has feel close to a manual once rolling, but provides assist to make the wheel easy to turn during parking lot manuvers.

BarnStang · Mar 29, 2004

THere is an answer for this. My friend Allen and I obsessed with putting the 93 power steering pump on the 68 project. Here are the numbers:
The min and max values for a '93 P/S pump:

1050 PSI
1320 PSI

Can't find the numbers on the 68 pump in my email but they are less. Something like 870-1075 or something like that.

Inside the 93 pump is a pressure relief valve that controls the pressure. otherwise you would blow all the seals in the rack under high RPM.

We obtained an assortment of springs and a power steering pump tester and got the 93 pump down to the 68 spec by installing a lighter spring.

Underdriving the pump will work at idle, but once you come off idle, the pump will come up to the limit of the reliev valve-or at some point off idle depending on how slow you are turning the pump.

For what you want to achieve, save up and get the manual rack. It will be easier.

Hope that helps.

Katmandu · Mar 29, 2004

Very, Very Helpful info guys!

Much appreciated!

Looks like I'll save my $$ for a Manual Rack.

Michael Yount · Mar 29, 2004

Be careful what you wish for - the heavier vert with big tires on the front is not going to be much fun to turn at lower speeds with a manual rack. Then again, looking at your sig, it's turning it at higher speeds that you're probably trying to make more fun!

HISSIN50 · Mar 29, 2004

i agree with what Michael says. im old school and dont particularily like power steering, but i have read horror stories from folks whom have gone with manual racks. really a personal thing. i might try disconnecting the PS pump (shorter belt) and running with no PS for a bit on the stock rack. while the stock rack wont feel/act just the same as a rack intended to be manual, it would give a good idea - before you spend some more money. just my thoughts. good luck.

Mavrick · Mar 29, 2004

HISSIN50 said:
i agree with what Michael says. im old school and dont particularily like power steering, but i have read horror stories from folks whom have gone with manual racks. really a personal thing. i might try disconnecting the PS pump (shorter belt) and running with no PS for a bit on the stock rack. while the stock rack wont feel/act just the same as a rack intended to be manual, it would give a good idea - before you spend some more money. just my thoughts. good luck.

Will that work if you drain all the fluid?

Michael Yount · Mar 29, 2004

I would not try running the power rack without the pump hooked up. It's designed to be operated full of fluid in power mode - I believe the effort required to turn it without the pump running is much higher than a properly selected manual rack would be.

Katmandu · Apr 1, 2004

Michael Yount said:
I would not try running the power rack without the pump hooked up. It's designed to be operated full of fluid in power mode - I believe the effort required to turn it without the pump running is much higher than a properly selected manual rack would be.

Well....I inadvertently got to drive my car withOUT Power Steering last night.

I had just swapped in Underdrive Pulleys (crank and waterpump), and my belt was too loose (Tensioner at Full travel). Needless to say, it was NOT near as bad as I was thinking it was gonna be to turn (even at low speeds).

I'm going out now to buy a Short Belt (70.5") to by-pass the Smog Pump along with by-passing the Power Steering pump.

See pic below....

Mavrick · Apr 1, 2004

Michael Yount said:
I would not try running the power rack without the pump hooked up. It's designed to be operated full of fluid in power mode - I believe the effort required to turn it without the pump running is much higher than a properly selected manual rack would be.

Ya, because every time you turn the wheel, you are compressing fluid in the rack through the strength of your arms, rather than the pump doing it for you.

Thats why i was curious as to how it would act with no fluid.

Katmandu · Apr 1, 2004

Mavrick said:
Ya, because every time you turn the wheel, you are compressing fluid in the rack through the strength of your arms, rather than the pump doing it for you.

Thats why i was curious as to how it would act with no fluid.

GOOD workout!

Isn't nearly as bad as I thought.

Guess it depends upon how strong your arms are too.

I just got back from the parts store with a 705KD belt (70.5"). I'll go install it now and report back later.

Katmandu · Apr 1, 2004

Well, the belt ended up being a 68.5"s after w/Underdrive pulleys, Smog Pump Delete and P/S Delete.

Part #685K6 Dayco

The results are no-the-less astonding!

BIG TIME SOTP improvement! Feels like I've unleashed another 20HP (at least!!).

Yea, the P/S take work, but the "Feel" is just the way a "Muscle Car" should feel IMHO!! The steering is now VERY predicable and firm.

I think I'll now proclaim that P/S is for Sissies!!

sleeper89 · Apr 1, 2004

good, now go get a manual rack and save some weight too

-steve

Katmandu · Apr 1, 2004

sleeper89 said:
good, now go get a manual rack and save some weight too

-steve

No doubt!

I need a new shifter first though.

Underdriving Power Steering pump... ??

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