Hydroboost - Hard Pedal

[Scottgenex]

Update.

Not fixed.

Installed a hydroboost pedal, went on a Sunday cruise and it acted up.

So as a recap; I've replaced and/or rebuilt four master cylinders, four hydroboosts, three power steering pumps. Replaced and flushed lines, flushed the cooler. No leaks. No over pressure in the PS reservoir. Routing appears correct. Vetted against another truck. All works well until I drive for more than 30 mins. Wait an hour or so and it fixes itself.

When I steer close to lock I get braking power back. It's still crappy, and is an all or nothing situation, but at least it stops. I checked tempatures of the whole brake/steering system and they're all externally around 130-140°F. So I wouldn't think heat is an issue.

I've pulled the master off while the problem was occurring with engine running and it made no difference. Isolating it to the hydro system. I pulled the return line off and pressed the pedal and it spurted like I'd expect. Still had a bad pedal feel. Turned it off and cracked the pressure lines to see if there was an air lock. No dice. Fired it up and problem still there. Those were more of a "do this and see what happens" test.

Thinking out loud here. It's almost like a fluid "stack up" that won't let the pedal go in. Steering opens a path for the fluid to go Bing bang boom, room for the HB valve to move.

Any chance the steering gear box could be a source of an issue? Steering stays perfect when it happens. But that's the only thing I could think of next even though it's unlikely to be. Other than that I'm really out of ideas and a bit disheartened that nothing of the ordinary seems to correct it.

 

[AuroraGirl]

Update.

Not fixed.

Installed a hydroboost pedal, went on a Sunday cruise and it acted up.

So as a recap; I've replaced and/or rebuilt four master cylinders, four hydroboosts, three power steering pumps. Replaced and flushed lines, flushed the cooler. No leaks. No over pressure in the PS reservoir. Routing appears correct. Vetted against another truck. All works well until I drive for more than 30 mins. Wait an hour or so and it fixes itself.

When I steer close to lock I get braking power back. It's still crappy, and is an all or nothing situation, but at least it stops. I checked tempatures of the whole brake/steering system and they're all externally around 130-140°F. So I wouldn't think heat is an issue.

I've pulled the master off while the problem was occurring with engine running and it made no difference. Isolating it to the hydro system. I pulled the return line off and pressed the pedal and it spurted like I'd expect. Still had a bad pedal feel. Turned it off and cracked the pressure lines to see if there was an air lock. No dice. Fired it up and problem still there. Those were more of a "do this and see what happens" test.

Thinking out loud here. It's almost like a fluid "stack up" that won't let the pedal go in. Steering opens a path for the fluid to go Bing bang boom, room for the HB valve to move.

Any chance the steering gear box could be a source of an issue? Steering stays perfect when it happens. But that's the only thing I could think of next even though it's unlikely to be. Other than that I'm really out of ideas and a bit disheartened that nothing of the ordinary seems to correct it.

steering causing the brakes to work?
But no offense, you just made this post without a single picture. YOU need to show us.
You have a problem in the hose routing or you have a defective.. something. this is from a 2005 bulletin:

On vehicles with hydro-boost, customers may notice during full lock turns or near full lock turns that the brake pedal will move down or self apply. This can be caused by the internal dump valve of the hydro-boost not seating properly due to contamination in the steering system. The hydro-boost assembly is not tolerant to certain types of contaminates that may be present in the steering system.

 

[Scottgenex]

The brakes don't self apply in the sense of just turning. More so if I turn the wheel side to side, or almost full lock I can then press the brake pedal down to get them to work. They've never self applied. I tested that after seeing that bulletin a while back.

Either way, four bad dump valves in a row after multiple flushes would be awful luck. I can run a gallon more through it if you think it's that severe. But the fluid is clean and clear at the moment and only a few months old.

Something is defective and or wrong. After a multitude of parts swaps and rebuilds it has to be something that stays or comes from/with the truck. Bleeding procedure was followed each time after new parts install following the manual.

My next attempt will be to bypass the cooler for fun and make some heat shields. Neither of that is the likely cause, but hey, anything is worth trying and process of elimination is the game now. My last shot in the dark was the PS resovoir cap.

Below is the routing. Return from booster to upper PS port. Pressure from HB to PS box. PS box return to cooler. Cooler to lower PS pump port.

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This is the cooler to PS return. Fluid leak was from taking the hose off to see if it was clean and open. Not collapsed, etc.

 

[AuroraGirl]

The brakes don't self apply in the sense of just turning. More so if I turn the wheel side to side, or almost full lock I can then press the brake pedal down to get them to work. They've never self applied. I tested that after seeing that bulletin a while back.

Either way, four bad dump valves in a row after multiple flushes would be awful luck. I can run a gallon more through it if you think it's that severe. But the fluid is clean and clear at the moment and only a few months old.

Something is defective and or wrong. After a multitude of parts swaps and rebuilds it has to be something that stays or comes from/with the truck. Bleeding procedure was followed each time after new parts install following the manual.

My next attempt will be to bypass the cooler for fun and make some heat shields. Neither of that is the likely cause, but hey, anything is worth trying and process of elimination is the game now. My last shot in the dark was the PS resovoir cap.

Below is the routing. Return from booster to upper PS port. Pressure from HB to PS box. PS box return to cooler. Cooler to lower PS pump port.

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This is the cooler to PS return. Fluid leak was from taking the hose off to see if it was clean and open. Not collapsed, etc.

it sounds like the hydroboost unit is defective. did you modify your pump so you had more flow and pressure? If you dont modfiy the non hydroboost pumps you arent gonna have enough flow, this issue sounds like your filling the circuit with fluid and then braking its already present
factory pumps sometimes were also more capable mechanically but thats not always the case. a smaller pulley diameter, a drilled out orifice, and a higher pressure relief for the pump

Which your pump also needs to be checked for proper operation of the flow control valve. the bore needs to be nicely finished and not gouged so the valve will ride in it smoothly. You need to use PS fluid not ATF. what fluid? Pentosin, GM steering fluid , Valvoline conventional or synthetic ps fluid all will work great.

THe cap wouldnt be the issue. the caps job is to maintain a small pressure on the reservoir to reduce cavitation and the vent also has baffled passages to prevent dirt from finding its way in easily you can clean the vent with a air gun and some blasts in the stem and at the side of the stem and possibly at the top of the cap logo per

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Can you check these out for us and can you verify the things i mentioned

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[Scottgenex]

it sounds like the hydroboost unit is defective. did you modify your pump so you had more flow and pressure? If you dont modfiy the non hydroboost pumps you arent gonna have enough flow, this issue sounds like your filling the circuit with fluid and then braking its already present
factory pumps sometimes were also more capable mechanically but thats not always the case. a smaller pulley diameter, a drilled out orifice, and a higher pressure relief for the pump

Which your pump also needs to be checked for proper operation of the flow control valve. the bore needs to be nicely finished and not gouged so the valve will ride in it smoothly. You need to use PS fluid not ATF. what fluid? Pentosin, GM steering fluid , Valvoline conventional or synthetic ps fluid all will work great.

THe cap wouldnt be the issue. the caps job is to maintain a small pressure on the reservoir to reduce cavitation and the vent also has baffled passages to prevent dirt from finding its way in easily you can clean the vent with a air gun and some blasts in the stem and at the side of the stem and possibly at the top of the cap logo per

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Can you check these out for us and can you verify the things i mentioned

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Thanks for being helpful. Especially since you have vastly more knowledge of this subject than I. You had suggested that in an early post on this and I took the pump apart to check that and do a rebuild; didn't find anything abnormal with it at that time. I then changed the PS pump to a new, non-rebuilt one cause one of the return ports looked pinched. I was sure that was the cause. Didn't seem to change anything.

The pump I'm using is what would be factory for the 2005 8.1 Vortec. I hadn't seen anyone else that has done this swap worry about the pumps being newer on an "older style" hydroboost. Maybe I missed that somewhere. Would the pressures be that much different?

As for the cap, I did attempt to clean it out as you described. Still had the issue and got a new one just cause anything at this point could be an improvement.

I'm using Prestone power steering fluid, no ATF as I read somewhere that ATF could cause issues on these setups. I've flushed it maybe three times this year with a gallon or more each time. The fluid appears clear in the flush tube, and on a paper towel. When I put it in a jar it is darker, but still amber and smells normal. I assume it's just getting heated and turning dark? I'll attach some photos. I'm not sure if I should keep flushing or look for another issue. I'm more than willing to take apart the pump and booster again to check ports and whatnot.

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The only part that I can say I modified was the hydroboost to gear box pressure line. It was to get things running at the time (only had a 90 day warranty on the used engine). Instead of swapping to a new box I had a custom hose made at a hydraulic shop. I took in the line that came from the junkyard truck and asked for metric on one end and standard on the other.

Instead they suggested to cut the '85 K20 hardline, solder on a standard compression fitting at the hardline end and then made a standard to standard hydraulic hose. The ends of the rubber portion (18mm hose) are 5/8s...if memory serves me right. It was so I could pick up a hydraulic hose quicker if it were to blow. Or, so that's what the shop advised. Took their word on it.

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I'm not sure that would cause an issue. However, I've been proven wrong on things so you can speculate and advise me.

The cooler I'm using was a generic trans cooler from a parts store. Its on the front of the cooling stack. 3/8s transmission line. Assumed it's essentially the same as power steering line and it is on the low pressure side.

Anyways, that's the lowdown on my setup.

 

[AuroraGirl]

Thanks for being helpful. Especially since you have vastly more knowledge of this subject than I. You had suggested that in an early post on this and I took the pump apart to check that and do a rebuild; didn't find anything abnormal with it at that time. I then changed the PS pump to a new, non-rebuilt one cause one of the return ports looked pinched. I was sure that was the cause. Didn't seem to change anything.

The pump I'm using is what would be factory for the 2005 8.1 Vortec. I hadn't seen anyone else that has done this swap worry about the pumps being newer on an "older style" hydroboost. Maybe I missed that somewhere. Would the pressures be that much different?

As for the cap, I did attempt to clean it out as you described. Still had the issue and got a new one just cause anything at this point could be an improvement.

I'm using Prestone power steering fluid, no ATF as I read somewhere that ATF could cause issues on these setups. I've flushed it maybe three times this year with a gallon or more each time. The fluid appears clear in the flush tube, and on a paper towel. When I put it in a jar it is darker, but still amber and smells normal. I assume it's just getting heated and turning dark? I'll attach some photos. I'm not sure if I should keep flushing or look for another issue. I'm more than willing to take apart the pump and booster again to check ports and whatnot.

You must be registered for see images attach

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The only part that I can say I modified was the hydroboost to gear box pressure line. It was to get things running at the time (only had a 90 day warranty on the used engine). Instead of swapping to a new box I had a custom hose made at a hydraulic shop. I took in the line that came from the junkyard truck and asked for metric on one end and standard on the other.

Instead they suggested to cut the '85 K20 hardline, solder on a standard compression fitting at the hardline end and then made a standard to standard hydraulic hose. The ends of the rubber portion (18mm hose) are 5/8s...if memory serves me right. It was so I could pick up a hydraulic hose quicker if it were to blow. Or, so that's what the shop advised. Took their word on it.

You must be registered for see images attach

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I'm not sure that would cause an issue. However, I've been proven wrong on things so you can speculate and advise me.

The cooler I'm using was a generic trans cooler from a parts store. Its on the front of the cooling stack. 3/8s transmission line. Assumed it's essentially the same as power steering line and it is on the low pressure side.

Anyways, that's the lowdown on my setup.

the 8.1 had the capability of coming with vacuum brakes im pretty sure, its the only rngine that didnt need a SBA in addition to the 4.3 iirc. which means the pump needs to be orificed to the hydroboost standards

Also i forgot you were the 8.1 guy with the extended reservoir opening. is your hose in the center leaking around the clamps to the pump? that hose is NLA so if its swelling and leaking youre sucking air

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Look how little steering gears changed!
Also a 8.1 for a gmt900 would need more pressure and less flow then a gear box model!!!

(steering rack)

See my lines arent going to the same stuff, i bet you need to harmonize the loop with the gmt800
only one extra pipe in my loop here is for the one you have by your dipstick presumably (you need 2 returns)

 

[xm20k]

GM pumps run in the 750-1200psi range (rack vs steering box) possible you have one of the lower output pumps which could be your issue.

 

[Scottgenex]

the 8.1 had the capability of coming with vacuum brakes im pretty sure, its the only rngine that didnt need a SBA in addition to the 4.3 iirc. which means the pump needs to be orificed to the hydroboost standards

Also i forgot you were the 8.1 guy with the extended reservoir opening. is your hose in the center leaking around the clamps to the pump? that hose is NLA so if its swelling and leaking youre sucking air

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Look how little steering gears changed!
Also a 8.1 for a gmt900 would need more pressure and less flow then a gear box model!!!

(steering rack)

See my lines arent going to the same stuff, i bet you need to harmonize the loop with the gmt800
only one extra pipe in my loop here is for the one you have by your dipstick presumably (you need 2 returns)

Engine came from a truck with hydroboost. I assume the pump (and orafice) would have been correct. Anything could be possible though since it was at a salvage yard. In my quest to solve this I replaced it with a new one from the parts store. It had double return ports, I never gave any thought to it being oraficed wrong. I didn't dive too deep yet into web searches but I'm guessing I could open the pump up and check that?

The filler neck hose did have a small leak at the beginning of all this. I put a new clamp on the lower portion and it seemed to fix it. I can always fiddle with it some more and make sure its not skewampis. The resovoir holds pressure, when I pull the cap it vents. Assuming it doesn't have a leak. Worth double checking though. I'll loosen everything and re-seat just because.

Forgive me if interpet it wrong, by harmonize do you mean the hose routes? Or the metal lines? It currently has the booster return going in the top return, cooler runs to the lower. I think you'd mention needing the higher velocity on on the lower in a older post.

GM pumps run in the 750-1200psi range (rack vs steering box) possible you have one of the lower output pumps which could be your issue.

Didn't know they had different pressure ones. Each time I was getting parts I was following the engine (2005 Silverado 2500HD). Figured all the trucks with this big block were hydro units. Any way other than a pressure check to discern the two?

I'll clean up the mess I made today, bleed it a couple times for extra insurance. Check for any hidden leaks and give it a whirl tomorrow if possible. I flushed a little more than a gallon through today. If it does act up, armed with some new knowledge, I'll get to a parking lot and do some more thorough poking around so I won't endanger other motorist swerving around like a drunk.

 

[AuroraGirl]

Engine came from a truck with hydroboost. I assume the pump (and orafice) would have been correct. Anything could be possible though since it was at a salvage yard. In my quest to solve this I replaced it with a new one from the parts store. It had double return ports, I never gave any thought to it being oraficed wrong. I didn't dive too deep yet into web searches but I'm guessing I could open the pump up and check that?

The filler neck hose did have a small leak at the beginning of all this. I put a new clamp on the lower portion and it seemed to fix it. I can always fiddle with it some more and make sure its not skewampis. The resovoir holds pressure, when I pull the cap it vents. Assuming it doesn't have a leak. Worth double checking though. I'll loosen everything and re-seat just because.

Forgive me if interpet it wrong, by harmonize do you mean the hose routes? Or the metal lines? It currently has the booster return going in the top return, cooler runs to the lower. I think you'd mention needing the higher velocity on on the lower in a older post.

Didn't know they had different pressure ones. Each time I was getting parts I was following the engine (2005 Silverado 2500HD). Figured all the trucks with this big block were hydro units. Any way other than a pressure check to discern the two?

I'll clean up the mess I made today, bleed it a couple times for extra insurance. Check for any hidden leaks and give it a whirl tomorrow if possible. I flushed a little more than a gallon through today. If it does act up, armed with some new knowledge, I'll get to a parking lot and do some more thorough poking around so I won't endanger other motorist swerving around like a drunk.

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the 8.1 pump settings are different than the 6.0 for the HD, and possibly the diesels too. The pumps would be the same just not the reservoirs and the valve/orifice
Heres a below pic to see how the pumps hoses and the gear lines run around

 

[Scottgenex]

Sorry for the delay, life happened. Anyways, the saga may have come to an end.

After running tests in a parking lot when the brakes went goofy I kept leaning towards the hydro being internally bad. Got a good rebuild kit and went at it again. Then it began whistling after a short time of driving around when I expected the brakes to fail as they have. Being defeated I gathered all my vacuum swap supplies, but figured to give it one more warranty for old times sake since its free.

Swapped it out for another off the shelf unit and so far so good. I haven't run it long distance highway cruising to have 100% confidence, however, I can run errands all day for a couple hours with no issues. Couldn't do that before. Seems I just had bad luck and kept getting bad units time and time again. This one does seep, but not gonna mess with a win for now since it doesn't lock up.

I half expect them to fail at some point cruising around, and when they don't I get suspicious. Its a weird feeling having it back at full operation. Thanks all for the help. Ill update when I go for a long distance run whether its good or bad.