Near Zero Brake Pressure - HELP! [Archive]

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fantastixvoyage

11-21-2009, 22:42

Having a little hard time understanding how the brake system works on these 6.5s and with a potential buyer coming tomorrow afternoon I'm in a bit of a panic.

Driving the truck today all seemed fine for a good 20 miles or so. then I came up to a light and have almost no brake pressure whats so ever. I had to slam it to the floor and down shift to first just to stop it. It was getting dark so I couldn't investigate too far but here is what I did check:

- Brake and steering levels fine.
- Slight leak of steering fluid at hydroboost unit.
- No leaks at any of the wheel, or the distribution block under the hood.

I figured it would be related to the leak at the hydroboost unit but reading on here has me a bit confused. Appears a leak/hydroboost fail would NOT give me less pedal feel but actually a firmer feel. Is that correct??? My fail leaves the pedal as light as a feather with no real braking until its at the floor and even then is minimal at best.

Of course I can rebleed the system but that just seems odd as it was pretty instant failure from what I can tell. I'm up for all opinions, have a potential buyer coming out in less than 14 hours....what timing right??? Thanks!

DmaxMaverick

11-21-2009, 23:27

fantastixvoyage

11-22-2009, 13:14

Thanks for the input. I found a master cylinder locally for $50 for a reman, I know they are junk but I needed to get this together to show the truck.

Well swapped it out in well less than an hour, still not getting great brake pressure. Took a look at the rear and noticed the framerail was wet - hole in the main brake line. Damn. Sure enough wiping it with a rag opened up the hole and now it oozes out almost non stop.

Looking online where can a I buy the main steel brake line??? Google searches just take me to the individual flex hoses, I need the main steel custom bent line. Anyone know a source, part number, etc?

Worst part is I treated this truck to a new turbo last week and this is how it thanks me?! :mad::rolleyes:

JohnC

11-22-2009, 20:07

Buy a line at (insert nearest parts store here) and bend it by hand.

Subzilla

11-23-2009, 07:41

To bend it, use a combination of different items including a baseball bat, pipe and gentle patience. Quite simple to do if you take your time.

rustyk

11-23-2009, 20:39

Harbor Freight has tubing benders and flaring tools.

stingthieves

11-25-2009, 14:36

With no leaks (PS fluid at hydroboost doesn't count), it's simple. Either it has a LOT of air in the system, or the master cylinder is shot. If you bleed it and it doesn't improve, it's the master cylinder. Replace with new. Rebuilding is usually fruitless, and reman's are junk.

I had the same problem this past spring -- same diagnosis -- replaced the line and pressure bleed two gallons of fluid thru the lines -- I was sure I had all the air out.
No Brakes
Then I found a guy with the correct scanner and we bleed it in concert to the 4WAL ABS. I put on three master cylinders and bench bleed them before installing and bleed the system each time. I spoke with several GM guys that service dealers with problems -- The system is becoming too old - they vaguely recall drama and offered only general solutions.

Gallons of Brake Fluid later I still didn't have a good brake

I tore that $$$$$ 4WAL abs out and replaced it with the proportioning valve from a know good 1985 Dually --

Bleed it once - Problem solved

Recently I had a 96 K1500 smack the parking bumper in front of my store -- the guy said he just stopped at the corner but when he pulled into the lot the brakes failed -- Reservoir was full -- no liquor smell on his breath - not a leek to be found in the lines -- another 4WAL abs failure -- the 4WAL will fail to bypass and in an instant, you have NO BRAKES or the 60 amp fuse will not blow and you get an under hood fire.

I guess you can tell -- I am not a fan ;>)