Teal daily driven farm truck.

[GrimsterGMC]

No

Idk, I’m going to have to bleed them again. I think the travel is worse than it was before.

That nasty fluid might be a sign, that was the end of the second quart going through the system.

Something I noticed while bleeding, the first few inches (close to 5”) of travel won’t move any fluid. The fluid going to the fronts will move before the rears (I’m assuming that’s normal).

I have a NOS Raybestos master cylinder that I bought at the same time as the brake hoses. I guess I could put that on.

The truck stops fine, I don’t feel like they’re going to give out, but the amount of pedal travel is not confidence inspiring.

Actually, thinking out loud, that nasty brake fluid is probably a clear indicator that they aren’t bled enough. I bet if I keep going until there’s clean fluid at all 4 corners the brakes would improve. 2 quarts is a lot of fluid but maybe the ABS module just holds a bunch of it. Maybe cycling the ABS twice per bleed would help.

I know it’s advised against, but maybe the pressure bleeder would help. It will at least hold 2 gallons of fluid that I don’t have to constantly top off.

All that black in the fluid used to be rubber seals in a previous life, definitely bleed until clear but consider that the master cylinder may be on it's last legs as well.

 

[Road Trip]

All that black in the fluid used to be rubber seals in a previous life, definitely bleed until clear but consider that the master cylinder may be on it's last legs as well.

I agree with GrimsterGMC's diagnosis. Given this, there's a real good chance that the seals in the master cylinder
are on their last legs, and the poor pedal feel is due to internal leaking between the 2 circuits in the master.

Based on my own GMT400 ('99 C2500 w/JD7) it *is* possible to have a firm pedal with normal travel.
(And with factory RWAL ABS still installed & working according to the last snowstorm earlier this year.)

****

One more thought. Some of the fluid discoloration could also be from the rubber brake lines breaking down internally.
If the ones you have were installed on the assembly line they are probably ready for retirement. Most would
recommend a stock replacement, but for me on a couple of vehicles with a so-so brake pedal after all was said
& done new braided stainless hoses were recommended for improved pedal feel.

And in both cases they were right! Not only did the pedal firm right up, but the improved 'communication' between
foot and braking system was an unexpected bonus. If this chore truck ends up being the last truck to waltz me out
into the night, I may upgrade to the braided lines just to make every time I use the brakes just that much better.

EDIT: Just went back and saw the new braided stainless. If you have that everywhere then the old master cylinder
is the best bet. (Assuming a really good bleed with no air hiding anywhere.)

All depends upon your priorities. But depending upon which flavor brakes your truck was built with, they
don't have to be bad. A firm, confidence-inspiring brake pedal really improves the day-to-day driving
experience.

Best of luck getting your brakes back to new/better than new behavior.

FWIW --

 

[Road Trip]

As you can see by the date on the box, I’ve had these Russel brake lines for a little while. The rear hose got replaced when I swapped the rear axle in 2018…

...and there's the last piece of the puzzle for yours truly. My bad for not reading for comprehension. With all new braided stainless, everything fully adjusted,
and a fresh, correct master I would expect a really good pedal?

I'm looking forward to what you figure out. This is a head scratcher.

 

[Orpedcrow]

@GrimsterGMC @Road Trip
Excellent points on the master. I was only thinking of a singular failure of the master cylinder continuing to bleed off and not building any pressure.

I bet if I take it apart I’ll find soggy rubbers and pitted cylinders. The truck did sit for a few years so the damage is probably in the first few inches of travel. Makes total sense when you think about it.

I tend to drive pretty conservative so the extensive, full travel bleeding most likely pushed the rubbers to their final end.

 

[Road Trip]

I tend to drive pretty conservative so the extensive, full travel bleeding most likely pushed the rubbers to their final end.

I'm old enough that we used to rebuild Master Cylinders as the default, and only swapped them out when the original
unit was beyond repair.

Anyway, I just wanted to share that your last sentence is spot on. Back in the day we would have a vehicle with a
firm pedal, but noisy wear squealers brought the customer in. We would do a careful brake job on all 4 corners, bleed the brakes,
and no matter how much fluid was used after the last air bubbles appeared we'd still end up with a mooshy pedal? And
when you removed & disassembled the master you would see that the bore looked perfect where all the normal driving
pedal travel occurred, but in the untraveled area the bore would be a rough, rusty horror show. It was easy to see
how the rusted walls would shred the rubber seals (once pushed into this area) with a cheese-grater like efficiency, almost instantly.

Essentially the old master cylinder seals were fine right up to the point where we were giving the brake pedal full strokes
during the bleeding process. Some master cylinder bores would hone back to new, and with a rebuild kit it would be
bench bled, reinstalled, brakes rebled, and sure enough a firm pedal would magically reappear.

On the other hand, some of the really rusty/pitted ones were just too far gone and would require a new replacement.
Since the rebuild kits were affordable and I was a $4/hr labor cost (45+ years ago :0) ...a new MC back then usually meant
much extra sadness for the customer when it came time to pay the bill. (I do remember the boss would keep the damaged master
for the customer to see that we weren't artificially inflating the bill and also tell them that renewing the blake fluid according
to the PM schedule in the owner's manual would help prevent this from happening down the road.)

I *do* remember that the owner's rule was that no vehicle left the shop with anything but a firm pedal. This was one
of the better life lessons I learned from the time I spent apprenticing at a 1 1/2 man shop back in the day. :0)

****

The fact that the master cylinder sees a much longer pedal travel than normal during classic bleeding procedures is a
good thing to keep in mind. Once you see your first master cylinder bore after it has been in service for awhile with
unchanged brake fluid is a genuine eye opener. Makes perfect sense.

 

[95OBSMan]

I tend to drive pretty conservative so the extensive, full travel bleeding most likely pushed the rubbers to their final end.

This is so close to my problem it isn't even funny!!!!

My truck had sat for 8yrs prior to me buying it, 95 SCSB, but had been driven 2 or 3 times, short trips, in that 8yr time period, it was a 2 and a half hour trip home on the highway, brakes where for all practical purposes non-functioning, so new rotors, re-pack wheel bearings, new front loaded brake calipers, new front rubber lines, complete rear brake job with correct parts, used my power vacuum bleeder on all 4 corners, correct "ABS" bleed procedure and out for test drive and the pedal went to the floor, "WTF" I thought, did everything right and by the book!!!

Back in the garage and scratch my head and go thru the whole system again, this time a double ABS bleed and this time a whole lot of nasty green fluid about a quart came out and, a replacement step bore MC with correct bench bleed for it, was needed, install MC and do a vacuum bleed on all 4 corners again until new fluid was at bleeders.

Well this is the best brakes I have ever had on any vehicle bar none, yes there is the ever so slightly pedal drop due to the "no drag/low drag calipers design for the truck, but the brakes are better than when the truck rolled off the line IMHO!!

I can't remember when GM did away with the low drag setup, for now they're doing great with about 1200 miles on them system, not if, but when that Kelsey Hayes ABS goes out on me, I guess it'll be the NBS upgrade everybody raves about..

the bore looked perfect where all the normal driving
pedal travel occurred, but in the untraveled area the bore would be a rough, rusty horror show

So I tore apart my MC and yes it was OEM to the truck, and as stated ^^^^ mine was heavily pitted with some sort of weird corrosion on it, and some rust as well, which baffled me do to the fact the truck spent its whole life in the dry as hell southwest desert area, but brake fluid is hygroscopic, and it amazed me that in a so called sealed hydraulic system that moisture had found its way in, but its also amazing that the system was at that time almost 30yrs old and still trying to hold its own on all OEM parts pertaining to the braking system!
A lot of us here have seen your wrench skills and I have no doubt that you will get them dialed in!!!

 

[Orpedcrow]

I’ve been provided a shop assistant. She’s eager to work, but completely useless.

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[Orpedcrow]

So far so good. Really firm pedal during bleeding. I made up a contraption for the pressure bleeder. If it looks stupid but it works, it isnt stupid.

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[fancyTBI]

I had a similar idea. I ended up not doing it due to being frustrated lol.

 

[Orpedcrow]

She even needs help pushing the pedal. Sheesh. Kids these days are so soft.

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