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Hydroboost + Power Steering Fluid Cooler

hydroboost power steering fluid cooler

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#1 OFFLINE   thesameguy

 
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Posted 06 July 2015 - 03:41 PM

Howdy folks -

 

I am new to the forum but have been referring to it (via Google searches) for many years. I finally ended up with a scenario I just couldn't find an answer to!

 

The vehicle in question isn't exactly a Chevy Truck, it's a 1993 Fleetwood motorhome built on a Chevy P30 chassis. The components in question are pretty much identical to what you'd find on an early GMT400 - a TBI 454 with hydroboost.

 

The power steering pump on these things provides steering boost and brake boost like a normal fullsize, but also does one other thing: Powers a hydraulic system called "autopark." The 4L80E on the motorhome does not have parking pawls in the transmission because idiot owners were relying on the transmission to hold 16,000lbs and shearing them off - so they just removed them. Instead, there is a gigantic drum brake on the driveshaft with huge springs that lock it up. When the engine is running and the transmission in D or R, the power steering pump actuated a big hydraulic cylinder that releases the drum. What that means is that the power steering system is pretty much overworked all the time.

 

Last summer I thought I was a real smartypants and installed a B&M heat exchanger in the return line from the pump to the remote reservoir like you would any other car. What I did not realize that under normal operation there is almost no fluid circulating out to the remote reservoir, it's all happening in the "internal" pump reservoir... so my heat exchanger is about useless. The only time it does anything is when put the thing in park and all the fluid displaced from the autopark actuator flushes back into the reservoir... and then it's really effective!

 

I am going to be replacing the power steering pump in the next week or two as it's groaning like crazy, and while it's apart I'd like to re-engineer my cooler situation. I think I need a cooler on the high pressure side - I don't know any other way of getting fluid circulating through it. B&M says they do not endorse their coolers on the high pressure side, and I can't risk a cooler failure that costs me steering AND brakes AND would lock up the driveshaft (or burn up the autopark drum). I'm thinking about using a normal tube & fin transmission cooler as it should be mechanically solid - but maybe someone else has another idea and that's why I'm here. :)

 

Related, does anybody happen to know offhand:

 

1. The P/S pump has six ports on it. I assume two are the to/from reservoir, two are to/from hydroboost+autopark, and two are to/from steering. Given the choice between a cooler in the hydroboost or a cooler in the steering system, which will net the biggest result?

2. Anyone happen to know what the fittings are on the back of this pump? It should be the same as any GMT400 with hydroboost. I'm just trying to figure out the safest/most reliable way of integrating a cooler. Here's a pic of the installed one:

 

 

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#2 OFFLINE   Hedge

 
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Posted 06 July 2015 - 05:24 PM

That is a wild setup you have there and I am very curious to hear what some of the gurus can recommend on this.

 

On the GMT400's w/hyroboost, the cooler is plumbed between the steering gear and the power steering pump.  This could be for a myriad of reasons (pressure, flow, etc etc) so it's hard for me to comment as to what would be a "better" option...between steering or hydroboost.  However, in general I tend to stay w/GM designs whenever possible.

 

I'm not sure if this will help, but here is a link to a hydro setup w/part #'s:

http://www.gmc4x4.co.../?hl=hydroboost



#3 OFFLINE   thesameguy

 
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Posted 06 July 2015 - 05:48 PM

That is *very* helpful. Looking at that cooler:

 

IMG_8105_zps445d2738.jpg

 

I 100% agree - if between the gear and pump is where GM placed the cooler, that's the best place to start. Thanks! Do you happen to know which end of the hose goes where? Does the metal flared end go into the pump or attach to the steering gear? It looks like maybe the cooler goes onto the return side of the gear? 

 

Part of my original motivation for placing the cooler where I did was access - it was very easy to get to the reservoir lines. However, now I've made access to the pump so now is the time to do this. I'll take another look at the hose arrangement this evening and see what I can see.

 

Edit: Another consideration about this system is that it "tends" to trap air. I put tends in quotes because there are relatively few motorhomes on the road and the "official" bleeding process is not widely known. It seems that if trapped air was legitimately a problem, like it is with brakes, etc., that RV shops would know that power steering system work requires a bleeding. But they don't. As it's a recirculating system I imagine air *can* get trapped, but it just doesn't seem reasonable it would stick around very long. The bleeding process is *painful* and troublesome and often entails multiple assemblies & disassemblies, and honestly I feel like it's time or luck rather than science. That said, I'm thinking that installation of a cooler would possibly allow me to create an easy to access high point in the system that would allow for quicker & more effective bleeding.


Edited by thesameguy, 06 July 2015 - 05:53 PM.


#4 OFFLINE   Hedge

 
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Posted 06 July 2015 - 07:09 PM

The flared end connects to the steering gear, the other side goes to the pump and use a clamp to tighten it down.

 

Air in PS systems w/hydro is more work...I can't even imagine in your case.  But I would bet if you jack the front end up and simply turn the wheel back and forth for a really long time it would bleed the air out.  The only difference is that once you get the air out of the steering gear and tubing, you would have to pump the brakes for the hydro and then shift the trans for the brake there as well.

 

To help jump start the cooler, you could fill it with fluid, plug the ends, then quickly remove each plug one at a time and insert into the PS pump and steering gear.

 

Even though my system originally called for convention power steering fluid, I went w/Amsoil synthetic.  Even after wheeling in 100F, the fluid didn't burn...great stuff.



#5 OFFLINE   thesameguy

 
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Posted 06 July 2015 - 10:38 PM

That arrangement is what I would expect, so that makes sense. Thanks much for the tip on Amsoil - I used to love Valvoline's Synpower fluid for its heat resistance, but they stopped making it. I don't have confidence in the parts store fluid I'm using, so when I do this work I'll have a gallon of Amsoil on standby.  ;)

 

I am regretting selling my '84 Suburban right now because it would have been nice to reference its hydroboost system right now...

 

 

Looks like the pump has four connections on it - fluid fill (external reservoir), pressure to hydroboost, return from hydroboost, and return from power steering (via some other motorhome things). Does that sound right?

 

Here is my hydroboost pump:

 

southwind_hydroboost.jpg

 

You can see the inlet from the pump, the return to the pump, and the pressure off to the steering. That's where things get interesting:

 

southwind_autoparkthingy.jpg

 

In here you can see the steering gear and the autopark valve. The circuit is pump -> hydroboost -> steering gear -> autopark valve -> return to pump. The autopark valve has its own interaction with an actuator (think clutch master/slave) and it's own return to the external reservoir, but that's not all that important.

 

Based on all this, it seems like I need to relocate my cooler to pump -> hydroboost -> steering gear -> autopark valve -> COOLER -> return to pump. I can maybe create a loop of hose going up with a 3-way T (maybe a valve?) in it to give a place to bleed air, a point higher than everthing else.

 

If someone could confirm that my hydroboost is normal that would be helpful - specifically: That it sits between the pump and steering gear, and has its own return to the pump.

 

Good fun!



#6 OFFLINE   thesameguy

 
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Posted 09 July 2015 - 12:16 PM

I got my new pump in and my cooler relocated - 

 

southwind_pscoolernew.jpg

 

I did not have time to dot Ts and cross Is before it got dark, so I will finish up tonight. Hopefully this solves my groan and eases the wear on the pump a little. I found some other crazy design details while I'll post later on.

 

The pump I got is a Cardone reman with an integrated Magnifine filter. In retrospect, I think this was a bad choice as it means using the pump itself to collect power steering system debris. What I am thinking about doing is grabbing one of the lines going into the cooler and installing an external filter - I have the space. Anyone running a power steering filter? Recommendations?







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