Hydro boost failure

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farmermedic

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I have what seems to be a mystery to all of the mechanics in my area. I have a 1984 k20 with 6.2L diesel. The original hydroboost had a leak into the cab. Replaced with rebuilt unit. Brakes functioned fine for approximately 1000 miles. While the pickup was siting (not running) the accumulator exploded almost puncturing the hood. Second replacement was installed with new hoses from the power steering pump and return lines installed. Approximately 1000 miles again, accumulator explodes for a second time. Has anyone had this problem before or know of a fix?
 

SirRobyn0

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No I have not. It shouldn't be a much of a mystery those systems are not very complicated. If I was looking at it in the shop there's only about 2 possibilities I can think off. Excessive power steering pressure, which you'd think would be causing other parts to fail, or a faulty hydroboost unit. If I was a betting man I'd bet on the hydroboost unit. It's not unheard of for reman units to have a bad batch and I bet both of those units are the same brand out of the same batch. And I'd bet they are reman units. If you have the equipment and ability to test the pressure of the P/S system it would be worthwhile to do so, otherwise get a new hydroboost unit, and get a different brand. ACDelco if they still make them.
 

Turbo4whl

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The OP has not returned since he posted the question. Rob, I have to agree on both points. Pressure may be too high, the OP did state the original had a leaking seal and he also replaced the hoses.

After shut down the only thing that could change is underhood heat, so full accumulator the oil expands with heat off the engine, no moving air to cool, and pops the accumulator. This still should not happen, maybe wrong or bad service part, the accumulator shell?

I'm also thinking the accumulator system should have some sort of pressure relief also. Could just apply the brakes after shut down and bleed some oil that way.
 

SirRobyn0

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The OP has not returned since he posted the question. Rob, I have to agree on both points. Pressure may be too high, the OP did state the original had a leaking seal and he also replaced the hoses.

After shut down the only thing that could change is underhood heat, so full accumulator the oil expands with heat off the engine, no moving air to cool, and pops the accumulator. This still should not happen, maybe wrong or bad service part, the accumulator shell?

I'm also thinking the accumulator system should have some sort of pressure relief also. Could just apply the brakes after shut down and bleed some oil that way.
Thanks Wayne I did notice that he hadn't returned. He may well be gone but maybe someone else will see this thread and learn something. The truth is though I was in the unanswered threads department, and while diesel is definitely not my specialty I've worked on enough hydroboost systems in vans to know them pretty well and his question got my wheels turning.
 

SquareRoot

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How is it possible a hydroboost can leak into the cab? This whole post sounds fishy.
 

Turbo4whl

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How is it possible a hydroboost can leak into the cab? This whole post sounds fishy.
The rod that is pushed by the brake pedal through the firewall moves the hydraulic valve in the the booster. Yes, there is a seal, yes it can leak there.
 

Blue Ox

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FWIW, we had two hydroboosts fail when the truck was new. Turned out that despite GM's recommendation to use Dexron, you needed Power Steering Fluid. Changed to PS fluid and the failures stopped. Did the O.P. change the fluid when he changed the booster? Maybe a problem was installed.
 

SquareRoot

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Ok, I get it now. Just had to get a better mental picture. I was thinking the bracket between the firewall and booster had a space between them so if it leaked from the seal it would be inside the engine compartment.
 

Turbo4whl

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Ok, I get it now. Just had to get a better mental picture. I was thinking the bracket between the firewall and booster had a space between them so if it leaked from the seal it would be inside the engine compartment.

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Borrowed picture. Nose of the booster right into the cab.
 

Snoots

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I've been told (but cannot verify) that tranny (ATF) foams and that PS Fluid will not and that's why some people have problems with hydroboost because they use ATF in their PS.
 

SquareRoot

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Borrowed picture. Nose of the booster right into the cab.
Thank you sir. I stand corrected. Embarrassing given the fact that I converted mine to Hydro like 2 years ago.
 

Blue Ox

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I've been told (but cannot verify) that tranny (ATF) foams and that PS Fluid will not and that's why some people have problems with hydroboost because they use ATF in their PS.

We never had an accumulator go boom, but I believe the seal failures were a chemical compatibility problem. Maybe too much detergent in the ATF? :shrug: We switched to PS fluid and the truck still has the same hydroboost in it from the mid '80s.
 
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