Technical Hydroboost warning for builders

I added a hydroboost unit on my sons truck, I have used them before and love them, This time I didnt use power steering.
If you uses a hydroboost without power steering DO NOT plug the pressure hose side for the steering box! The hudroboost booster does not bypass. you can burn up a pump. We didnt but found this answer quickly. Research on the subject said to use the steering box side as an extra return. We did this and its working (yard driving) so far.
I was surprised that the fluid pressure from the booster to steering box is not very high.
If anyone here has done this please chime in.
if you plan to do an install like this you still need the PS pump with dual returns.

 

I found info on the web suggestion to just plug off the steering side, I had to dig deeper to find out this was incorrect.
this is why I posted

 

Thanks for the information. In my world of medium and heavy trucks, hydroboost is very common, but I’ve never seen a set up without power steering.


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same here, I have the set up on the bus and it works great (bus has PS) The truck steers great without the PS. I also wanted to see if it was possible, not every one likes PS.
I will install a PS box if I have to in order for the brakes to work properly if I have to. My questions would be does the PS box cause any back pressure needed for the booster? now Im curious at what pressure a GM PS system operates on, The pressure from the steering side of the booster seems low.
an Alan Grove PDF stated the gm pump delivered 1000-1200 psi. There is no way this pump is doing that from the booster to steering gear port

 

I’m not sure what the GM operating pressure would be. I’ve seen medium duty Internationals run at 1200 psi, but obviously will go higher if dead headed.


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hmmmm wonder why it seems low on the steering side?
the brakes seem like they have plenty of boost.

 

The pressure is low because you're using it as a return. If you plumbed it to the steering box, there would be a restriction and more pressure.

 

so the pump can see a need for pressure or it can increase if needed?
one online source suggested using a pressure regulator on the steering line but couldn't back that up with anything other than assumption

 

The pump just creates flow, the restriction through the steering box is what creates the pressure.


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found this on the web
"There are two distinct functions that the power steering pump is designed to perform. The first function is to deliver a constant flow rate to the power steering rack or box control valve. The flow rate will determine the sensitivity of the control valve when input is applied through the steering wheel. In conjunction with the control valve design, a given flow rate will result in a given steering feel and performance. Adjusting the flow rate is a fine tuning adjustment of the steering system and is not considered an all-inclusive adjustment.

The second function of the power steering pump is to provide enough pressure to assist the driver in overcoming steering load. The pump only builds pressure when it is required to by the steering rack or box control valve."

and this
http://prod.lv2014.gener8cms.net/in...st/1103-hydraulically-assisted-power-steering

I like learnin

 

Well being as how they are a positive displacement pump, as in they move, or flow, the same volume every revolution of the pump then it is the restriction to that flow that causes pressure. The directional control valve in the power steering gear is what determines the resistance to the flow.




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Have Hydra boost on two GM's and would like to take it off of one....

 

I like the set up we installed on my short bus. My only advise is buy a quality belt and change them regularly.

 

Funny you post this. I am building my shoebox with a 302, no power steering, with hydroboost and I had the same question. I was planning on running both return lines. One going through a cooler. I like the hydroboost set up since it does not take up a lot of space and I just happened to have one left over from a parts car. I just mounted it on the firewall a few days ago. Got a lot of work still ahead before I know how good it is. Let me know if you run into any other issues.

CN

 

I read some guys plumb both return lines into a single line. Some of them said this affected pedal feel?
Logic seems having 2 into one could increase line pressure on the returns

 

I'd have to go out and open the hood on ,my dualie to figure out the hose routing.
I can see not plugging the pressure hose to the steering box because you have then created a full time 100% pressure situation on that line. Worse case us that you have to put a restriction in the hose to put more pressure to the hydrovac If too much pressure is bypassing.

I'm not sure on teeing both return lines into the single return on the can. It may provide the restriction you need for the line that went to the steering gear but may cause more restriction for the return line for the hydrovac than you want. Then again it may have very limited effect.

SIDE NOTE!!! you don't have to change the whole pump, all you need is to change the can on he pump to a two return line can if you have a Saginaw pump.

 

going to look into that. Im going to work out the wiring issues and drive it a little. It seems to stop well but the pedal seems a little softer than my other ride with it. Going to re-bleed the brakes again then check. Everything is new on the system. On a side note, I used a master cylinder for an auto (single cyl Vs the tandem the manuals had) for the clutch master cly. Works great.

 

I like the note for the T on the return. seems logical
but that "high pressure" line to the steering gear was my only question on the set up originally. I have a barb adapter on that pressure line to test using it as a return. I expected to see a lot more pressure. It does flow a lot, but not much pressure. My concern was if the pressure from the steering gear port on the booster would be too much for a standard return line.
Most answers to this question when I researched it was people asking why run a hydroboost and not use a PS gear box? I guess some of us are just weird like that

 

Any updates on your project? I am soon to install the engine and transmission on mine. Still quite a ways from firing it up.

CN

 

Works great. Added a dual return pump and plumed the steering pressure side to the extra return.
A hot rod mag article on hydroboost brakes stated that the gm pumps may be the same physically but can have different pressure capabilities based on the vehicle installed.
My sons truck is a large truck so I ordered a dual return pump for a ton truck.
The hydroboost units themselves have few differences between them. Push rod style is one but most use the same overhaul kit.
The pressure charged reservoir ( safety incase a pump/belt failure) has a couple of different styles.
Most of those seem to be replaceable.
I found a bunch of trouble shooting info on the web.
Also, sometime around 1980, gm changed from flare to O-ring fittings. The flare is generally 79 down and seem to be harder to find.
The pressure fittings on the pumps are easy to swap. Lines were easy to find at the regular chain parts stores

 

As mgtstumpy shows in his post with the flow diagram that is how I have seen every one hooked up I have dealt with. There was a flow/pressure test tool we used with several adapters to find restrictions in the system. If there was a problem with the power steering box/rack and it caused a restriction we would sometimes see a "self application" of the brake pedal due to the buildup of pressure being more than the hydroboost returm line could flow. Symptom would be the brakes would start dragging as you drove, if you stopped and shut off the engine and pumped the pedal a few times it would bleed of the pressure and you could drive a few more miles. Normal pressure to the power steering box without moving the steering wheel would be 75 to 125 psi, if you held the steering against full lock it would spike over 900 psi. Dead heading the pump (closing the line with a valve on the tester) would spike to about 1400 psi, that was the pressure relief valve bypass point in the pump itself. This was all done on a Dodge with a Cummins diesel and is from the service manual. So as someone pointed out, lots of flow WITHOUT restriction = low pressure. Restrict flow = high pressure. Some cars even have a variable flow power steering pump that change flow with RPM, slow rpm (like parking) high flow high pressure, higher RPM low flow, less assist but not used with hydroboost.

 

I have. A friend of mine has an old bulletproof SWAT Chevy P30. It has Hydroboost brakes, and manual steering (which sucks).

 

This truck is amazingly easy to steer without PS.
The wife drove it last week and was surprised how well it steered.

 

To be fair, his steering gear box has a blown out sector shaft bushing, and a ton of play.

I gave him the part numbers for everything required to fix it, but nothing came of it.

 

When your power steering is in the neutral range, ( no hands on the wheel) the is very little pressure in the system. Just residual pressure from pushing fluid through lines and fittings. As you turn the wheel, pressure comes up according to the resistance of the wheels . The pressure will continue as long as the wheels are turning untill they hit the stop. Then the pressure goes to maximum and the bypass opens up limiting the pressure to the preset level. Usually between 1200 and 1800 psi.
I used to in stall winches powered by the power steering pump.Awsome winches , by the way.








Bones

 

A big difference in steering ratio and effort between manual steering and messed up power steering.

 

It's a messed up manual box.

 

Thanks

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I have a Hydraboost on the old Power Wagon ,and power steering returning in one line . This can get hairy it times . Some times you have no brakes after a hard turn in the lock position . Just a warning . I also have my winch powered by a belt driven PS pump . Its a good winch , but slow.