Drill stock PS pump orifice for more flow

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Dec 17, 2010
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Recently did a 6 inch lift and 38s for the fzj80 and its pretty hard to steer now lol. This is to be expected with large tires but im wondering if anyone has drilled out the restrictor in the stock PS pump to allow more flow to the box and hopefully easier / lighter steering.

I come from the toyota mini truck world and we used to do it to those pumps when we added hydro assist.

Has anyone done it on an 80, and if so, how do you do it (pump on or off truck), what size drill bit did you step up to, and was it easier to steer after?

Thanks!
 
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Yeah I drilled mine out to 13/64 based on what I read here and Pirate. Made a noticeable improvement in slow speed turning.

EDIT: I did this AFTER adding hydro assist. Not sure what effect it would have without a ram.
 
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Recently did a 6 inch lift and 38s for the fzj80 and its pretty hard to steer now lol. This is to be expected with large tires but im wondering if anyone has drilled out the restrictor in the stock PS pump to allow more flow to the box and hopefully easier / lighter steering.

I come from the toyota mini truck world and we used to do it to those pumps when we added hydro assist.

Has anyone done it on an 80, and if so, how do you do it (pump on or off truck), what size drill bit did you step up to, and was it easier to steer after?

Thanks!

You'd need to know the operating parameters of the stock box. Can it handle extra flow?
how much will the added flow decrease pressure? Pressure and volume of fluid moved are proportional.

when added an additional ram the flow is needed.
 
Joined
Dec 17, 2010
Messages
47
Yeah I drilled mine out to 13/64 based on what I read here and Pirate. Made a noticeable improvement in slow speed turning.

EDIT: I did this AFTER adding hydro assist. Not sure what effect it would have without a ram.
I feel like its worth a shot to try even without hydro assist. Im sure the box could benefit from a higher volume of fluid. I plan to add hydro assist down the road anyways, so if somehow it makes my steering worse without a ram, I can always add the ram and i'll end up in the same boat as you anyways.
You'd need to know the operating parameters of the stock box. Can it handle extra flow?
how much will the added flow decrease pressure? Pressure and volume of fluid moved are proportional.

when added an additional ram the flow is needed.
Its hard to find reliable information on what the stock box will flow. But it can be assumed it can handle quite a bit more, since lots of guys do LS swapped with aftermarket high volume PS pumps and the stock box holds up fine.

The stock PS pump has a pressure relief valve, so it would stand to reason that if you drill the orfice out, volume is increased, pressure is decreased, the pump would then build more pressure to compensate and flow more GPM while holding the factory pressure PSI.
 
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I feel like its worth a shot to try even without hydro assist. Im sure the box could benefit from a higher volume of fluid. I plan to add hydro assist down the road anyways, so if somehow it makes my steering worse without a ram, I can always add the ram and i'll end up in the same boat as you anyways.

Its hard to find reliable information on what the stock box will flow. But it can be assumed it can handle quite a bit more, since lots of guys do LS swapped with aftermarket high volume PS pumps and the stock box holds up fine.

The stock PS pump has a pressure relief valve, so it would stand to reason that if you drill the orfice out, volume is increased, pressure is decreased, the pump would then build more pressure to compensate and flow more GPM while holding the factory pressure PSI.

That only stands true if the OEM pump is capable of the additional pressure.
 
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For reference I drilled the restrictor ans shimmed the relief before going hydro assist, found zero difference with the factory box alone.

If you are going to go ram assist I would drill it, other wise no need in my opinion. L
 
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That long hose from the pump to the box is costing you pressure. There’s at least two foot of it. I think you may see a benefit from a much shorter one that’s routed the opposite way with less soft hose. Output from the pump and input on the box are inches from each other. Might be a noticeable difference. Might not be. But the father the fluid has to travel and the more turns it makes, the more you lose.
 
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I believe when we drill the restrictor out we are just shifting the point at which the valve will start bypassing flow internally, to a lower rpm? Because we now have more pressure working against the backside of the valve.

Not 100% on that, just trying to recall what I read years ago on pirate.

This sound correct?
 
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Joined
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That long hose from the pump to the box is costing you pressure. There’s at least two foot of it. I think you may see a benefit from a much shorter one that’s routed the opposite way with less soft hose. Output from the pump and input on the box are inches from each other. Might be a noticeable difference. Might not be. But the father the fluid has to travel and the more turns it makes, the more you lose.

I ditched the factory plumbing for about two feet of 3/8 hydraulic hose years ago, didn't notice any effects from it.
 

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