Way OT - Chevy Avalanche Brakes

I hate to post such a stupid question, but I'm trying not to waste money.
(it's not my money to waste)
2002 Chevy Avalanche, 1/2 ton 4x4 dual piston calipers on all wheels.
Brakes have always been "squishy" but now the pads wore out.

BIL put all new pads and rotors on it.
Same day while testing the brakes, truck had not left the shop,
rusted out brake line to the right front wheel ruptured.
Replaced the line.

Now trying to bleed the brakes since the line was opened.
Got good pedal pressure engine off, solid fluid at the bleeders.
All four wheels.

With the truck running he's got air back in the lines.
LOTS of it. Right rear will sometimes bleed clear and the next
time blow mostly air. Not two or three tries, 40 or so!
Same symptoms keep repeating.

Go back to engine off, bleeds clear, good pedal.
Start the engine, pump the brakes, air in the lines again.

No fluid leaks anywhere.
Opinions? Bad master cylinder?

Probably will need to be bled at a dealership or shop with a $$$$ enough scan tool to put the ABS unit in "bleed" mode.

Or maybe patience and persistence will pay off and he will eventually get at the air out by repeated bleeding.

If the right front brake line ruptured then the left it probably not long for this world. When the line ruptured and the driver released the pedal he might have sucked some air into the system. Ditto what Bob said.

My .02 worth.

Some GM's require that you not pump the pedal to bleed the brakes. Try pushing down once and holding it while they open the bleeder. wait 15 seconds and repeat several times. Pumping the fluid may aerate the fluid. Do this on every wheel brake where the bleeder was opened.

I'm not super familiar with the 2002 model, but I'll assume it has the frame mounted ABS unit?

if so, there is a "special" bleeding procedure to bleed the brakes on gm trucks with it. I can't remember it off the top of my head, but there is no pump, hold, open to release air, repeat. with that abs unit you have to do everything very slow, and I mean like wait 30 seconds between cracking bleeders open.

bleeding the brakes the "normal" way usually messes with the abs, which is why you cant get brakes.

other option is take it to a dealer or someone you know with a tech II, you can use it to bleed the abs unit, however it uses A LOT of fluid to do this

Good old chebby brakes :evil: if there is such a thang...
They will test your religion and have beat up on the best...
I don't know of a simple answer its a process of elimination...

My first thoughts are lots of folks can hang a pad but few do it correctly... DIY will push the contaminated fluid back into the system this may cause all kinds of issues.. They don't service the related brake components... Even when you do ensure none of the contamination went back into the system and catch it just pushing the caliper piston in will trap contamination and can cause the caliper piston to stick this insures a comeback...

For now I would skip the DIY issue and look at what issue was induced by a broken brake line... Its rare to have a bad master but it does get the blame often for low pedal issues on a chebby... If you go there make sure you get the correct one they all look alike but work different BTDT....

The combination valve in the ABS may be sticking are shutting fluid flow off to a wheel/axle mainly because there is air in the system some were... The ABS has a accumulator in it if it gets air bound even under normal braking no ABS the fluid pushes again the air bound accumulator = low/no are a extreamly soft pedal.

I could go do some ABS activated brake stops to force the air out of the Accumulator and repeat the song and dance routine till ell froze over and sometimes get lucky and get the air out...

My scanner sometimes will not activate the ABS are do a ABS bleed. On a 4wd I lift it put it in 4wd trans in gear with a little throttle and stand on the brake peddle (ride the ABS long and hard) to force ABS activation to clear out the air...

It a P.I.T.A. and I can tell you the dealer don't want it either...

You will read about the booster being a issue because it can overpower the master I have not had that issue other than they are strong to strong....

I would either block off the brake lines are remove them at the master and block to eliminate the master as a issue I bet its not... Another issue is the master is a quick take up master its a different animal all together...

If any of the fluid was black like burnt motor oil it needs all the hoses and calipers and a good flush... You can flush it only but you will never get the contamination out of the calipers...

Have fun looks like a hard days work to me...

'Back in the day', when I was mekkanikin' - bleeding the brakes meant 2 guys, 1 at the bleeder, 1 at the pedal. NO PUMPING the pedal. Down on the pedal, open bleeder - close bleeder - up on the pedal - repeat etc. Start at the farthest corner (left or right rear). Haven't had to deal with ABS, so can't help in that area. HTH

Thank you all for the help! I think I got it tonight.
I put my vacuum pump on each bleeder valve, one at a time,
attached through a bleeder cup and applied about 10 inches of
vacuum and let it bleed out air and fluid slowly.

Then I drove it and nailed the brakes hard to actuate the ABS.
Lather, rinse, repeat. A real PITA, but, the pedal is better than
it has ever been. No fade at all and not "squishy" like it was.

Sister and BIL didn't like my recommendation of jacking up the
radiator cap and driving a new truck under it, although that isn't
going to be too far away. Only one brake line rusted out, but the
others can't be far behind.

Hobo, the fluid is darker than new, but not oil black by any means.
Still NOT a good sign, things aren't looking good.
I appreciate the tip on the ABS workings also. I'm sure it helped.
Now if I can just convince them to buy something else. :roll:

The last 2 are 3 day affair I had with one of those in the end they had put the wrong master on it... I called the previous mechanic that had worked on it and he had the box the replacement came in. It was a customer supplied part neither the customer are parts store would admit to it but the parts store did eat it... I got a quick education on quick take up masters...

Some of the late 90's are not free bleeders (KELSEY-HAYES 4WAL ABS and a few Bendex systems), now that my friend is a tuff'N to get the air out of...

When they get high mileage most everything is suspect...

Foreign manufactures have always recommended brake fluid flushes domestic is catching on... I flush every 30K are anytime I preform brake work...



http://www.brakeandfrontend.com/troubleshooting-abs-modulator-mechanical-problems/

http://www.aa1car.com/library/bfluid.htm

http://www.aa1car.com/library/abs_bleeding.htm

B'N a one man show I have invested big bucks in brake bleeding equipment and it pays well

Thanks again Hobo. Took me a while to read through that info,
but I did. I always like to learn something new!

I didn't end up buying or replacing the master cylinder.
Gut told me it wasn't the problem, along with the responses here.
Turned out to be a good call because that wasn't it.
Shoot, it was good enough to blow that line out!

That right front line is one bear of a line to replace though.
Glad it's done. Next, rear lights on a '92 Dakota with rust induced
bad grounds. Gotta love Calcium Chloride on the dirt roads here.
They spray it on to keep the dust down.

That's tomorrow night, another sister.
Pretty sure I got this one, but if not I'll holler!

(quoted from post at 09:44:23 09/23/15)
I could go do some ABS activated brake stops to force the air out of the Accumulator and repeat the song and dance routine till ell froze over and sometimes get lucky and get the air out...

Click to expand...

does it work?
waiting patiently for the snow here...couple weeks probably
95 Chevy truck....had a new master cylinder and some lines installed before I got it. air in the ABS, no bleeders.
don't know anybody with the clips or scan tool.
gonna give the snowy road hammer the brakes abs thing a try, then rebleed, repeat.
eh, they still work better than my old cars manual drums on all 4.
I'm old, so pumping the brakes is second nature.

(quoted from post at 22:18:42 09/24/15)

(quoted from post at 09:44:23 09/23/15)
I could go do some ABS activated brake stops to force the air out of the Accumulator and repeat the song and dance routine till ell froze over and sometimes get lucky and get the air out...

Click to expand...

does it work?
waiting patiently for the snow here...couple weeks probably
95 Chevy truck....had a new master cylinder and some lines installed before I got it. air in the ABS, no bleeders.
don't know anybody with the clips or scan tool.
gonna give the snowy road hammer the brakes abs thing a try, then rebleed, repeat.
eh, they still work better than my old cars manual drums on all 4.
I'm old, so pumping the brakes is second nature.

Click to expand...

NNP, on this 2002 I posted about, pumping didn't help the pedal
height at all. It was just low all the time. Did not fade if held though.
Hammering the brakes at 25-30 MPH on a dirt road made the
ABS activate. Much better than snow or ice IMHO.
That worked in my case. Can't vouch for any others.

(quoted from post at 23:33:02 09/24/15)

(quoted from post at 22:18:42 09/24/15)

(quoted from post at 09:44:23 09/23/15)
I could go do some ABS activated brake stops to force the air out of the Accumulator and repeat the song and dance routine till ell froze over and sometimes get lucky and get the air out...

Click to expand...

does it work?
waiting patiently for the snow here...couple weeks probably
95 Chevy truck....had a new master cylinder and some lines installed before I got it. air in the ABS, no bleeders.
don't know anybody with the clips or scan tool.
gonna give the snowy road hammer the brakes abs thing a try, then rebleed, repeat.
eh, they still work better than my old cars manual drums on all 4.
I'm old, so pumping the brakes is second nature.

Click to expand...

NNP, on this 2002 I posted about, pumping didn't help the pedal
height at all. It was just low all the time. Did not fade if held though.
Hammering the brakes at 25-30 MPH on a dirt road made the
ABS activate. Much better than snow or ice IMHO.
That worked in my case. Can't vouch for any others.

Click to expand...

thanks Royce....got a dirt road just around the corner, I'll give it a go. Pretty much the same here. bled them so many times, I should have stock in the fluid company. First push, they work, but the pedal goes too low, light comes on.
pump it once, it still is too low, but high enough the light stays off. brakes work fine either way.