I have run out of ideas on how to get the brakes in my 2001 Chevy Blazer working

I got the vehicle from a friend, knowing that it had a ruptured brake line in the rear. It was otherwise in good shape, and he knew of no other brake problems.

I installed all new brake lines (a kit from Inline Tube) and hoses as a first step. After sorting out a few leaks, I still could not get anything but very spongy brakes.

It looked like I had a leak from the rear of the master cylinder, so I replaced it with a new AC Delco "Professional". I tried bench bleeding the new master cylinder, but with limited success -- the shaft was very difficult to push. Once installed, I did several bleeds to make sure of things in terms of making certain the master cylinder was properly bled, but still no improvement.

As a next step, I bought an Autel scanning tool to do the automated ABS bleed procedure. After I fiddled with it for awhile, I got to work -- I could feel it working via the brake pedal and also I could hear it cycling the ABS internals. After doing multiple brake bleeds and automated ABS bleeds, there was still no pressure to speak of -- it was firm when the vehicle was not running, but immediately got spongy and basically went to the floor with the engine running.

I then noticed some weeping from one of the rear caliper bleeder screws, so I went ahead and replaced both rear calipers.

Today I tried bleeding the brakes with the vehicle running, which didn't seem to make any difference. All in, I have probably run 6 quarts of brake fluid through this thing, with no improvement. I continue to get a hard pedal when the vehicle is off, and it pretty much goes to the floor immediately upon starting the engine.

The only things I haven't replaced are the front calipers (which seem fine), the ABS modulator (worked fine until the brake line blew, as far as I know) and the power brake booster/check valve, etc.

In other threads I have looked at, the answer seems to be "air trapped in the lines" and to keep bleeding the thing. I have not worked on brakes that much, but when I have, it never took this much to bleed them. I am thinking maybe it could be something wrong with the new master cylinder, or maybe in the non-hydraulic part of the brake system. like the booster or the ABS unit. That said, I am reluctant to just throw more new parts at the problem when everything previously was working OK, and it seems like the problem could, in fact, be a simple one.

I am out of bright ideas. Your comments and suggestions are welcomed.

 

Have you bled the brakes on all four wheels?

 

Yes, I have bled all four brake calipers, using a sequence of passenger rear, driver rear, passenger front, then driver front.

Another thing I wanted to aske is about something I found online titled “Bleeding a Delphi DBC-7 ABS Unit” which looks to be the one I have in the Blazer. This indicates you need a pressure bleeder (at 35 psi) and a scanner tool that bleeds the ABS first, then also cycles on to clear out the ABS module after bleeding each brake caliper. All this sounds like a procedure that probably needs to be done by a dealer at some considerable expense.

However, I could run through the automated ABS procedure after bleeding each line. I could do it while running the engine, too. Anyone think that might work?

At this point I am willing to stand on my head with my left hand pointed to the North, chanting "GM is good, GM is good" if I thought it would get me through this mess

 

I am not usually into lo tech hacks (solutions) but since your struggling:

I have never tried this myself nor do I know what ABS systems this would work on but I read on multiple forums about the gravel road trick. Bleed the brakes the best you can first then take the vehicle onto a gravel road and do several aggressive panic stops. Then back to the shop to bleed some more. May require rinse and repeat. I have seen several posters saying this worked but I cannot verify this. The theory is that the rapid random ABS engagement performs a similar function to bleeding with a high end scanner.


George

 

Thanks for the gravel road trick suggestion. I, too, have found this mentioned in several forums. I may try it because we have a lot of snowy icy roads where I am, and it shouldn't be hard to get the ABS to activate. Problem is, it feels like I have almost no brakes to begin with, so it will be a bit risky for me to try.

I also figured out I have the Kelsey Hayes 4WAL ABS unit, not the Delphi one I mentioned. I have found the ABS bleed procedure. It is fairly complicated and requires building a few simple tools. If anyone happens to have experience with bleeding this unit, I'd sure appreciate any advice you have to offer. The You Tube video on it seems pretty good.

This whole thing is crazy complicated for something so simple in principle. At least I think I have narrowed it down to air trapped in the ABS.

 

If you get this to work, be sure to give us an update and perhaps your own write-up on it so other may learn.

I sure hope it works for you!! Good Luck!

 

I use a capable scanner to activate the brake bleeding program in the vehicles PCM.
You select one free car maker with this device. Obviously I chose GM.

 

I ended up getting another master cylinder. This, along with doing multiple brake bleeds interspersed with running the Blazer on an icy road and activating the ABS multiple times, seems to have resolved the problem. I am getting a firm pedal and, other than the red brake light in the dash refusing to go off, I think this may be fixed. The Autel scanner I bought to do automated ABS bleeds seemed to be working, although it didn't seem to make a difference--it was running the car on an icy road and activating the ABS dozens of times that seemed to make the difference.

Thanks for the replies and suggestion.

 

Glad the "gravel road trick" worked, or I guess in your case "the ice road trucker trick"

George