 someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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10-29-18 10:15 AM - Post#2749877
Truck in question is a Louisiana/Texas truck, there is zero and I mean ZERO indication of rust on the brake lines. I mean they are so clean they still almost look new. I know a lot of people have suffered greatly on the material quality of these lines, but down here, they just don't rust/corrode.
I'm losing brake fluid and can't find a leak anywhere. Lines are clean as mentioned, abs module, flex hoses, calipers, backing plates (hybrid 9.5" 14 bolt with drums), master cylinder and reservoir, even the booster below the master is clean and dry. Everything dry, dry, dry.
The truck stops fine and has firm pedal (as long as I top of the fluid every month or so) and I don't have any real indication of weird feeling from the pedal that would make me suspect the booster...
So where's the fluid going? For it to get sucked into the booster, that would have to mean the booster has a leak in the diaphragm AND the rear seal on the master is leaking too, right? I would almost expect to see at least minimal evidence of seepage down the booster under the master.
When I say I'm losing fluid, I don't mean the usual gradual amount from pad/shoe wear. It gets down low enough that the "service brake system" warning message kicks in as the sensor in the reservoir is tripped.
Ideas?
Thanks,
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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454cid
Valued Contributor
Posts: 3232
Age: 50
Loc: West Michigan
Reg: 02-18-12
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10-29-18 11:07 AM - Post#2749883
In response to someotherguy
I had brake fluid leaking to the inside, under the carpet from a clutch master cylinder. Is there any way for that to happen with a brake master cylinder with the booster in between it and the firewall?
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someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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10-29-18 11:35 AM - Post#2749886
In response to 454cid
Nope...booster in between pretty much makes that an impossibility.
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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junkman104
Frequent Contributor
Posts: 1561
Age: 64
Loc: Murphy N.C.
Reg: 01-25-14
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10-29-18 05:48 PM - Post#2749935
In response to someotherguy
Look at the lines around the plastic looms near the front cab mount again. My 04 started leaking there first. The rest of the lines looked nice.
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junkman104
Frequent Contributor
Posts: 1561
Age: 64
Loc: Murphy N.C.
Reg: 01-25-14
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12-18-18 06:33 PM - Post#2754966
In response to junkman104
Ever find out why?
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 rockfangd
"10th Year" Gold Supporting Member
Posts: 3273
Age: 37
Loc: Utica ny
Reg: 04-13-10
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12-18-18 07:50 PM - Post#2754975
In response to junkman104
Check the hoses very good where the hose is crimped by the steel. I cant tell you how many I have had leak on GMS, Not just brake lines, but transmission, AC, and PS cooler lines as well.
Not sure why GM had issues with these.
Especially the front wheels as they are the ones that get flexed the most by turning and bumps.
Not often You have a question. MAkes me feel better lol
| Old School GM fan FOREVER |
Edited by rockfangd on 12-18-18 07:50 PM. Reason for edit: No reason given.
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someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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12-18-18 10:46 PM - Post#2754986
In response to rockfangd
Work has kept me way too busy to look closer - all my peeks at it so far have turned up not even so much as a damp spot much less any sign of a real leak...and about once a week or so it sits in the garage, never a hint of a drop on the floor. 
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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rockfangd
"10th Year" Gold Supporting Member
Posts: 3273
Age: 37
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Reg: 04-13-10
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12-19-18 09:43 PM - Post#2755072
In response to someotherguy
you sound just like me.
Not enough time to really look but just to peek.
Something as stupid as a lightbulb van be weeks.
Sounds simple but not without time
| Old School GM fan FOREVER |
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someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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09-17-23 08:55 AM - Post#2862610
In response to rockfangd
Here's raising an old thread from the dead!
Not on the original truck I was asking about, which is my black 2006 SS, but my wife's truck, the silver 2006 SS. It's been doing the same thing for the past few years - slow depletion of the brake fluid (quicker than the normal drop due to shoe/pad wear) where I'm topping it up every now and then, no signs of leaks ANYWHERE, and I mean none..
Until today. Was chasing possible suspects for a front brake lockup issue (that isn't hoses, believe me; I just replaced all 3 as they were originals) and thought, let me pop the master cylinder loose from the booster.
It's leaking out of the rear seal into the booster. Pretty sure that has either ruined the booster, or the booster went bad and is sucking on the master cylinder. Never saw even the slightest dampness between the two pieces, as there's a seal on the m/c where it goes into the booster. However, once separated, it's clear to see the m/c is leaking at the rear, and the inside of the booster is wet with brake fluid.
Like most of us, I hate seeing posts where there never seems to be a resolution.. now I've figured out the mystery as to where the brake fluid is going. Pretty sure I'll find the same when I check the black truck.
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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wagonman100
Site Ambassador
Posts: 15795
Loc: Baltimore, MD
Reg: 11-27-04
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09-19-23 07:40 PM - Post#2862694
In response to someotherguy
Thanks for posting the cause. I don’t know how I never saw the original post, but that is what my suggestion would have been.
Jay
Friends don’t let friends drive Fords.
1999 Silverado Z71 4X4 extra-cab short bed
1983 Malibu Fauxmad - tubbed
1978 El Camino Kustomized
1972 Monte Carlo
1957 210 handyman wagon
1957 Nomad sport wagon
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someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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09-20-23 08:52 PM - Post#2862704
In response to wagonman100
I'm posting this around the web a little bit because I did a lot of searching and kept finding posts where people would ask about the issue and try some things but never, ever post a resolution.
As I mentioned earlier, the reason I ended up going into my wife's truck to see what the problem was, is that she called me because the brakes were acting up. She wasn't far from the house so I went over and checked it myself, brakes were locked up, hard pedal, it would move but you had to really gas it. Left it where it was and took her home (she had groceries that needed stashing) and called a coworker to tow it to the house. I figured when he arrived I'd pick it up to try to determine if it was front, rear, or both locked - but it rolled freely.
After I got it home, some test-driving until it misbehaved showed that the front brakes were locking up. Familiar with flex hoses issues and considering the truck is at 133K miles, I figured no harm in shotgunning the flex hoses, so I did all three. No improvement. Fluid looked horrible so I basted it out of the reservoir and replaced with fresh fluid. No improvement (didn't really expect it, just knew it needed some level of attention.)
I loosened the master cylinder from the booster and pulled them apart, and there was a big sucking sound as stored vacuum depleted. Stuck my finger in there and noticed the inside of the booster was wet with brake fluid. Not good.
Parts came in today, GM Genuine master cylinder and booster. Not risking any reman stuff. Part #'s were 19418518 on the booster, which is a different design than what was on the truck. Application notes indicate if you have the reservoir held on with roll pins, you need a different master cylinder with the tab style attachment on the reservoir. I used part # 19432749. This truck being a 2006 Silverado SS, it's RWD and disc front/drum rear.
Test drive feels pretty good; pedal a tiny bit soft so I know I need to bleed the thing some more. My scan tool won't bleed the ABS module. Drove it around for about 15-20 minutes and did plenty of braking, no issues detected. Gave it back to my wife and we'll see how it does.
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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09-28-23 03:14 PM - Post#2862933
In response to wagonman100
Thanks for posting the cause. I don’t know how I never saw the original post, but that is what my suggestion would have been.
I wonder what the actual cause was, though. The booster is definitely suspect when it's full of brake fluid, but my truck (subject of the original post - losing brake fluid) isn't locking up the front brakes, not yet anyway.
One thing I noticed when cleaning up after working on my wife's truck is I went to drain the old master cylinder and used my screwdriver to pump the remaining fluid into the drain pan, and there was a bit of rough/random resistance from the m/c. I mean it's obvious it's leaking due to failed seals, but I also imagine it's possible a failed seal was causing the piston to drag or hang intermittently.
When I went to order parts I found the only GM booster available that fits the truck is a different design, and requires a different design master cylinder. Chicken/egg scenario I have to wonder was the booster design flawed, or the m/c design? I'm leaning more towards m/c, but in the end it doesn't matter, as both parts need to be replaced after this type of failure.
So far, so good; she's been driving the truck all week now with no braking issues. Before the repair, I could get it to lock up within about 10-15 minutes of test-driving.
All in, about $500. GM hoses (all 3) $126, GM booster and master cylinder $326, couple bottles of brake fluid $26 and tax.. and I know I've got all brand-new quality parts in there instead of whatever marked-up reman junk someone else may have chosen.
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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Keith Seymore
Contributor
Posts: 781
Loc: Southeast Michigan
Reg: 09-17-08
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09-29-23 07:45 AM - Post#2862945
In response to someotherguy
Thanks for the follow up, Richard.
K
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someotherguy
Senior Moderator
Posts: 29722
Loc: Texas
Reg: 08-01-03
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09-29-23 11:07 AM - Post#2862952
In response to someotherguy
What kills me is I knew way back in 2018 what the likely cause was, but just didn't suspect it because there was zero visible evidence of a leak. What I didn't know was due to the design of the master cylinder having such an extended mounting flange into the booster, with an o-ring seal, that it would be very unlikely I would ever see evidence of a leak without disassembly.
So where's the fluid going? For it to get sucked into the booster, that would have to mean the booster has a leak in the diaphragm AND the rear seal on the master is leaking too, right? I would almost expect to see at least minimal evidence of seepage down the booster under the master.
Not often You have a question. MAkes me feel better lol
I think I just now caught this comment, maybe missed it all those years ago for a variety of reasons. Saw it today and it cracked me up. I definitely don't know everything, probably not even a small fraction of everything  but I get by with an early foundation of a great mentor, years of hands-on experience, and continuing support and experience from others through the forums!! I try to search the hell outta stuff before I ask. When I come up empty I'm usually surprised someone hasn't been there before, or I'm just not finding it, ya know?
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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