Brake HELP !!!!

[wasted wages]

Changed the rear shoes and wheel cylinders on my 97 Yukon 2-3 weeks ago,

I'm sure I got air in the lines,,,buttoned up everything,,bled the lines by
gravity and the old "you push the pedal and I'll bleed 'em" method.

But I was never really satisfied with the results,,after about 2 weeks of driving ( my wife drives it as her D.D. ) I noticed the front wheels brake dusted really bad. I jumped in hit the pedal and it almost travels full stroke before it starts to firm up. So I think,,,master cylinder,,,bled and installed a new master cylinder,,pull and inspect rear shoes and check shoe to drum clearance,,
run 3 quarts of brake fluid thru the lines bleeding the brakes AGAIN,,,I get bubbles out of the left rear wheel when I bleed it but I can't tell if it's from the threads of the bleeder screw or the line.I'm on my 4th quart of fluid,,,

My shop that repairs our service trucks told me I screwed up when I changed the wheel cylinders and let to much air get into the antilock system,,,

The pedal travels almost full stroke and now lights the 'Brake" light on the dash comes on,,,the front pads are in good shape as well as the rotors,,none of the drums or rotors are damaged or have ever been cut.truck has about 80k on it. I raised the rear axle on jack stands and put the truck in gear ,,hit the brakes and the rear tires never slow down,,the emergency brake is good and tight and will stop the wheels in a few clicks,,

What the hell am I missing here ?????

 

[diesel4me]

NEW master??--or "Rebuilt"??

Is it a NEW master cylinder,or a cheapie rebuilt??..was it bench bled before you installed it??( I ass-ume it was,you sound like you know what your doing!)..I know bleeding the anti-lock brakes can suck on later cars and trucks..I get called to my friends shop a lot when he's alone,needing someone to pump the pedal!...we found some bleed better with the engine running--others with the engine off..and some take forever to bleed,and we still dont like the pedal "feel"...

If the rear brakes arent getting any fluid to them(what it sounds like),it could be a defective master cylinder..you could loosen the line to the rear brakes at the master and press the pdal to see if its pumping any fluid,but hold the pedal to the floor until you tighten the line again with something,so air wont be pulled back into the master cylinder...There is usually another bleeder screw in the antilock brake unit itself too,dont overlook bledding that after bleeding the master cylinder,then go on to the other wheels..

We had a few later GM trucks and cars we sent to another shop that had a power bleeder,rather than listen to the customer complain about a mushy pedal or excessive travel in the pedal..sometimes you HAVE to say UNCLE!--and let someone else fix it !!..

 

[wasted wages]

There is usually another bleeder screw in the antilock brake unit itself too,dont overlook bledding that after bleeding the master cylinder,then go on to the other wheels..

I just got off the phone with the shop and he said the same thing,,,I did not know there was a bleeder in the ABS unit,,he said there are some chambers in the unit that could have filled with air when I let the lines bleed when I had the wheel cylinders off,,lesson learned,,I should have plugged the lines

I will try to bleed the ABS unit tonight and see what happens,,
It was a NEW master cylinder and I did bench bleed it.

 

[diesel4me]

Another tip I forgot...

We usually hold the brake pedal to the floor while we open a bleeder,or remove any lines or hoses--if you hold the pedal down with a stick or something against the seat while the system is open,it prevents air from getting back to the ABS or master cylinder..saves a lot of time when things are buttoned back up--.
Usually 4 -6 pumps of the pedal and its all bled out doing it that way..we pumped 2 qts thru one truck we let drain all the barake fluid out sitting overnight on the lift--that was one of the trucks we had to send out to be pressure bled--we gave up after a half hour--fearing we'd wear out the master cylinder! ...

 

[YZEATER]

just a quick guess. were the adjusters on th bottom of the backing plate moving freely? maybe they need to be adjusted up to take up some extra slack?