Hydroboost - Hard Pedal

[Scottgenex]

I searched and browsed for a bit, but didn't find anything exactly like my issue.

So. Here's the deal. My 496 swapped '76 K20 has a hydroboost swap from a diesel (just for helpful info) must be getting an air lock, or something like that. I'm not a hydroboost specialist, but understand the workings. A few weeks ago I drove the truck it's furthest distance since the swap and restore. On my return trip (100 miles freeway) the power steering pump was whining when I exited. Brakes had some kickback, steering was lackluster, so I figured it'd aerated while cruising home in rush hour.

Confirmed when there was a lot of fluid spilling out the PS filler neck. The junkyard booster never had much gusto when I put it on, I assumed it was going bad for a while. And now it had fluid coming out of the flange between the master and itself. Ordered a reman and swapped it on. Brakes felt wayyy better. Thought my issue was gone.

Today I cruised the highway for about 30 miles and when I got off it had a repeat issue, this time the brake pedal wouldn't go down more than an inch. I babied it to my buddies trying not to rear end anyone. Checked everything out and saw no leaks. Let it sit for a bit and drove to the gas station, issue mostly gone.

On my return trip I took back roads in case it was RPMs whipping the fluid. Guessing not cause after 20ish minutes of driving it happened. No PS whine. Steering feels just fine. When I press the brakes I have nothing. Just solid pedal. If I steer to a lock it will suddenly sink and skid to a stop like it should. Assuming the turning pushed air out...

I assume the reman hydro is bad cause steering remains fine during the issue.

Can a power steering pump fail internally and cause aeration? All hoses are new. O-Rings are new. The power steering pump is original to the engine. No clue how old it is. I see no leaks. I rechecked tightness of fittings and clamps. All seems to check out. So somewhere air is getting in and locking my unit up?

Again, I'm a newbie with hydo systems. This is all just assumptions I'm making. Looking for suggestions.

Thanks!

 

[edgephoto]

You do have it plumbed correctly?

If the fluid is aerating it may actually be overheating. Do you have a p/s cooler?

 

[Scottgenex]

You do have it plumbed correctly?

If the fluid is aerating it may actually be overheating. Do you have a p/s cooler?

Plumbed the way I thought was best with a cooler in place.

I have the return line from the booster going through the cooler and back in the PS pump res. Then the return off the steering box to the second port on the PS resovoir. As shown in the attached diagram.

 

[AuroraGirl]

Plumbed the way I thought was best with a cooler in place.

I have the return line from the booster going through the cooler and back in the PS pump res. Then the return off the steering box to the second port on the PS resovoir. As shown in the attached diagram.

the highest velocity fluid return should be the lower port im pretty sure

Not sure that matters for this moment with your issue just thought to mention. if you could remove your pump and then pull out the control valve (bottom picture) and show us what it looks like, note any debris that comes too)The cutaway photo is to show you what it looks like in the pump. the valve operates in the bore it comes out of, and if the edges of the valve, or the walls of the bore, are bad, youll quickly overheat and overpressure and overcirculate fluid. Youd probably feel it in the steering wheel, but not necessarily either. The example I show came from a worn tired pump, only worked if I gave it throttle. Id like to see your valve condition.
Also pictures of your setup would help

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[AuroraGirl]

Do you have this issue:

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[Scottgenex]

I don't seem to have the "self apply" thing happening. But it's good to know that's a thing happens on that gen of engine.

I can definitely throw a new PS pump at it. In my quest of building this thing everything else is new. So no worries there. At least it could knock out a variable before I warranty out the new hydroboost.

I snapped a couple photos. Nothing fancy. I can grab some others if I'm not showing what you're looking for.

 

[HotWheelsBurban]

Do you have this issue:

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Interesting to know GM actually had a tech bulletin about this! My '97 C3500 had this happen after I had the hydro boost unit replaced. The replacement unit went bad and the installer didn't do the job correctly either...so this happened. Another shop got it fixed but it was a very interesting couple of months; had just bought the truck and then was afraid I would have to sell it....

 

[AuroraGirl]

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Third photo is yours, i just did this to compare myself.

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last two photos are from my 2005, just because it has a cooler plumbed in

 

[Scottgenex]

On the '05, does the booster low pressure line go into the PS reservoir, or the cooler? I have mine running out to the cooler and the steering box one goes right into the rear/lower return port on the PS res as can be seen in my photo. I'm wondering if I switch my lines around if I might see something different. Hard to find diagrams and photos online of exactly what I'm needing.

Just spit balling random thoughts. I figured it didn't matter as it's all one big loop. However, I'm wondering if the ports do matter in which return they want to see. Possibly to help dissipate any turbulence/small air bubbles the system generated by giving the fluid some pool time in the reservoir. Probably over thinking it. Just hard to figure out when the steering works just fine and it's only the brake side acting up after extended driving. Just trying to fully understand before I start slamming new parts at it.

I can always check my DMAX as well. It's an '08. Guessing similar setup as the gasser 2500HDs had.

 

[AuroraGirl]

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[edgephoto]

These are from the repair manual for 1987. Maybe these

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will help.

 

[AuroraGirl]

These are from the repair manual for 1987. Maybe these

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will help.

I only sent 2005 ones because it has a cooler in the circuit, and his hydrboost appears to match more the 2005 than the original hydroboost setup in these trucks

 

[MrMarty51]

A guy over in these parts had a SB GM pickup that had been converted from diesel to gas.
For some reason he thought the master cylinder had gone bad.
He got a replacement MC and stuck it on the hydro boost.
Then his problems multiplied.
After richard cranium with it for several months he asks me to fix it, told me everything He had done.
Told him his MC is for a vacuum boost unit.
He di cks with it for a while longer then finally takes the MC off and back to the PH with it. Another MC dont fix it, another month and he comes back, did you get a MC for a hydro boost system, gives me the old dumb look, removes the MC and hauls it back to the PH, I knew he was headed that direction, called the PH and explained the shitssuation. Parts manager gives him a MC for the hydro boost system, end of problems.

 

[AuroraGirl]

A guy over in these parts had a SB GM pickup that had been converted from diesel to gas.
For some reason he thought the master cylinder had gone bad.
He got a replacement MC and stuck it on the hydro boost.
Then his problems multiplied.
After richard cranium with it for several months he asks me to fix it, told me everything He had done.
Told him his MC is for a vacuum boost unit.
He di cks with it for a while longer then finally takes the MC off and back to the PH with it. Another MC dont fix it, another month and he comes back, did you get a MC for a hydro boost system, gives me the old dumb look, removes the MC and hauls it back to the PH, I knew he was headed that direction, called the PH and explained the shitssuation. Parts manager gives him a MC for the hydro boost system, end of problems.

they are different?
I guess im not sure how but im willing to let you educate me

Bore size??

 

[AuroraGirl]

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The front and rear reservoir are swapped size wise, but if they are plumbed right its not a big deal.
The reservoir is bigger than the one on my dads truck

So I suppose bore maybe..?>

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