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Discussion Starter #1 (Edited by Moderator)
I have a 2006 LBZ. My brakes have gotten pretty spongy over time, so I pop the hood to find a signs of a leak around the master cylinder and hydro booster. Both the master cylinder and the hydrobooster's exterior have a fair amount of grease/grime built up on them.

When I checked the levels of the power steering fluid - it's right on the money. However, the brake fluid reservoir on the master cylinder was 1 inch/1.5 inches below the "MAX" fill line.

My hydro booster performs properly when doing a function test. All that to say, I believe my master cylinder was the source of the leak and not the hydrobooster, but the grime on the hydrobooster's body (especially on the accumulator) has me second guessing myself. I don't think a leaking master cylinder could have gotten all this mess on the hydrobooster/accumulator. Maybe it could.

Should I just replace the master cylinder and see if things get better. Should I be worried about the build up on the hydro booster? Thoughts?
(Attached picture is hydro booster after removing the old master cylinder. you can really see the amount of grime on the accumulator after I wiped a little spot off.)

Thank you for your time and your expertise!
 

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A couple of cans of brake cleaner spray and a new MC will make your day a little brighter. If nothing else, NOT having a leaky MC will allow you to find any other leaks in the area more easily.
 

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I have a 2006 LBZ. My brakes have gotten pretty spongy over time, so I pop the hood to find a signs of a leak around the master cylinder and hydro booster. Both the master cylinder and the hydrobooster's exterior have a fair amount of grease/grime built up on them.

When I checked the levels of the power steering fluid - it's right on the money. However, the brake fluid reservoir on the master cylinder was 1 inch/1.5 inches below the "MAX" fill line.

My hydro booster performs properly when doing a function test. All that to say, I believe my master cylinder was the source of the leak and not the hydrobooster, but the grime on the hydrobooster's body (especially on the accumulator) has me second guessing myself. I don't think a leaking master cylinder could have gotten all this mess on the hydrobooster/accumulator. Maybe it could.

Should I just replace the master cylinder and see if things get better. Should I be worried about the build up on the hydro booster? Thoughts?
(Attached picture is hydro booster after removing the old master cylinder. you can really see the amount of grime on the accumulator after I wiped a little spot off.)

Thank you for your time and your expertise!
From your pic, the wet high psi line and the low psi return line both have o-rings that could be bad. Especially the low psi side. The weep hole where the booster and the mc bolt up together would be the area to check for booster leaks. If it feels oily = PS (booster) and if it feels drying = brake fluid (ms).

My 06 LBZ with less than 80,000 miles, it was the booster. Pretty common. I also fight with those PS lines seeping ever since.

Another way besides feeling the slipperiness or dryness of the leaking fluid is if it's eating any paint = brake fluid.
 

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Discussion Starter #4
Thank you for the reply! That makes a lot of sense. I'll check that area closely when I get home this evening.
 

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Discussion Starter #5
From your pic, the wet high psi line and the low psi return line both have o-rings that could be bad. Especially the low psi side. The weep hole where the booster and the mc bolt up together would be the area to check for booster leaks. If it feels oily = PS (booster) and if it feels drying = brake fluid (ms).

My 06 LBZ with less than 80,000 miles, it was the booster. Pretty common. I also fight with those PS lines seeping ever since.

Another way besides feeling the slipperiness or dryness of the leaking fluid is if it's eating any paint = brake fluid.
I'm looking back at my picture...and your comment is spot on - that low pressure side connection is nasty. While the high pressure side is pretty clean (I didn't wipe it off). Would it make sense for me to replace that low pressure line? I say replace the line because I'm pretty sure the o-rings for those lines are specialized and I've only ever seen them when they come with a new PS line. Thoughts?
 

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Thank you for the reply! That makes a lot of sense. I'll check that area closely when I get home this evening.
My guess from how much build up there is up high on the booster is it is the booster leaking up high like one of those o-rings. BUT, that doesn't mean the booster isn't leaking at the weep hole. Mine was when I went in to change the leaking lines.

Some have optioned to rebuild and some have had issues with rebuilding / buying reman. So I bought new. I purchased the booster for the 2011 Duramax. It was cheaper and supposedly 'improved'. I had to Dremel out the push rod hole very slightly. There are several posts here and competing sites about replacing and rebuilding our boosters.
 

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I'm looking back at my picture...and your comment is spot on - that low pressure side connection is nasty. While the high pressure side is pretty clean (I didn't wipe it off). Would it make sense for me to replace that low pressure line? I say replace the line because I'm pretty sure the o-rings for those lines are specialized and I've only ever seen them when they come with a new PS line. Thoughts?
lol - I was writing at the same time....

The o-ring is special. Viton and a particular size. I'll be back into mine this week and will look up the o-ring size. I ordered extras.

I'm also replacing my lines with smaller lines if I can - 11/32 instead of 3/8. I swear these return lines won't stop seeping so I'm trying all I can, making it a TIGHT fit. See:
https://www.dieselplace.com/forum/76-speciality-forums/80-suspension-steering-2001-2010/897457-another-lucky-failure-ps-return-hose-came-off-3.html#post9878766

All of the hoses are pretty cheap. And after you replace the o-ring you could still discover the hoses and the booster are leaking too. Anything I do, if I were you with old hoses, I'd replace the hoses regardless. And if they're off, pull that nipple on the booster and replace the o-ring too. It's the booster and MC you'll have to find out about as you go, imho.
 

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* Return line nipple at booster o-ring = 902 Viton (V90902)
* All high PSI lines o-ring = 903 Viton (V90903)

I have my doubts about these sizes because mine always seem to seep within a year. But that's the 411 I found when searching and so that's what I bought. If somebody finds something different, PLEASE post it.
 

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Discussion Starter #9
Thank you for looking! I might buy a few of those o-rings and give that a shot. To be honest, I'm not driving my truck a ton - so even if that gives me a year of no leaks until I have to change them out again - I'd call that a win...considering you can get a pack of 20+ orings for $2
 

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Thank you for looking! I might buy a few of those o-rings and give that a shot. To be honest, I'm not driving my truck a ton - so even if that gives me a year of no leaks until I have to change them out again - I'd call that a win...considering you can get a pack of 20+ orings for $2
Too windy to mess with it today. Maybe tomorrow, but I figured you were waiting for the info. You're welcome. :thumb:

Yea, that's what I did. I heard the dealer only costs $9 per o-ring :eek: .

I used larger non-viton o-rings in the past and got about the same time out of them. They were pretty deformed when they came out. PS fluid attacked them.

Oddly, I don't believe any of the o-rings at the pump or gearbox ever seeped. Just at the booster. Then again, those are harder to see, so maybe.
 

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Discussion Starter #11
Curious - any idea why it's an -903 oring from PS pump to HB.....and -902 from HB to gear box? Would figure those 2 orings on top of the hydrobooster would be the same? Aren't those lines the same size?
 

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Curious - any idea why it's an -903 oring from PS pump to HB.....and -902 from HB to gear box? Would figure those 2 orings on top of the hydrobooster would be the same? Aren't those lines the same size?
The fitting is different. There are actually 3 o-rings on the booster for hoses / lines. Let me clarify. All the high psi lines take the 903 and only the nipple for the low psi return hose from the booster takes the 902, iirc. In your pic, that's the 180 curved hose right on top of the booster closest to the mc. Once you remove the hose clamp and hose the nipple can be backed out. And that's the o-ring that most likely leaks if its anything like mine. And it won't take a 903 because it's a smaller diameter than the metal portion of all the other lines. The 903 o-ring inner diameter is too big for that nipple.

Edit: A pics worth a 1000 words (my old booster):
 

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High pressure lines
Amazon PS pump to booster $16 AC Delco 36-358980
Ebay Boost to steering gear $20 AC Delco 36-365453 (Amazon $29)

If replacing both lines, be certain to properly bleed the system.
 

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Discussion Starter #16
I know everyone has been hanging on a thread regarding my truck.

Quick update - Hydrobooster was just leaking like crazy, even with new orings. Decided to do a full replacement of the hydrobooster and mastercylinder (was leaking a bit as well). Everything has been replaced...now I just have to flush the power steering fluid and bleed the brakes. Any reason why I should do one before the other? Does it matter?

Thanks again for all the guidance on this project.
 

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I know everyone has been hanging on a thread regarding my truck.

Quick update - Hydrobooster was just leaking like crazy, even with new orings. Decided to do a full replacement of the hydrobooster and mastercylinder (was leaking a bit as well). Everything has been replaced...now I just have to flush the power steering fluid and bleed the brakes. Any reason why I should do one before the other? Does it matter?

Thanks again for all the guidance on this project.
Ya got me there, but..... If I had to guess... since you need the brakes for the PS bleed, but not the PS for the brake bleed, I'd do brakes first - with engine off so as not to pump air thru the PS system.
 

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Discussion Starter #18
Hi all - After replacing the hydrobooster I'm still getting a good bit of "hissing" from behind the dash when I'm turning at low speeds (parking lot type speeds) and applyin the break - worse when I'm doing both at the same time. Could this be air in the lines still? I don't drive this truck too often, so maybe have only driven it 100 miles since the replacement work. Fluids are all fine, no visible leaks. any recommendations to make the hiss go away?

Thanks!
 
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