1999 tahoe brake issue

[mkingan]

i cannot get the spongy feel out of my brakes. 1999 tahoe z71. No open lines. All i did was brakes rotor swap. Bled then multiple times still really soft, no leaks anywhere. now i did read have to wait 10-15 secs on pump/release to let master cylinder come back but i have gotten no air. pedal seems to travel too far. now after bleeding then starting truck it travel further to floor, bad master cylinder? No ABS lights on. I'm stumped, any help/suggestions would be great. thanks

 

[96-2D-Hoe]

You may have done what I did, possibly more than once when changing my MC 3x, if when bleeding you push the pedal too far to the floor you will screw up the MC seals and it will need to be replaced. Is why they say to put a block under the pedal when bleeding.

If the brake pedal continues to move down after pumping up the pedal and holding it firmly while the engine is running your master cylinder is bad. If you change that you will need a scan tool to do the ABS bleed procedure or you will still have spongy brakes. If you've never done the ABS bleed it probably needs doing anyway as the fluid in the ABS system will be nasty. You can get some crap out the ABS by setting it off by braking ******* gravel etc and then bleeding. But that is a band aid fix as it won't completely get all the air out but will improve the pedal some.

Otherwise you could try taking off the rear wheels and adjusting them up fully to see if that helps. Or just a full bleed starting at the back might help too if the fluid is old and nasty.

 

[TahoeVet86]

I know this is an older thread but just ran into this exact issue after installing an upgrade brake kit up front from Powerstop (Z36) with new rotors, calipers and pads. Also replaced my MC with an AC Delco Pro OE one as well as braided steel lines up front. We bled everything we can think of but still soft pedal. We only bled the ABS at the plunger valve but not what’s described above. What is the “scan tool” mentioned above?

 

[east302]

We only bled the ABS at the plunger valve but not what’s described above. What is the “scan tool” mentioned above?

There is an automated ABS bleed procedure that requires a scanner to activate. A GM Tech2 will do it and probably some Snap-on scanners.

Here’s a thread with confirmed scanner models:

Confirmed brake bleeding scan tools

Aluminum RWAL ... "1) No Special bleeding procedure is required for this ABS system. Factory recommends bleeding r-rear first, then l-rear, r-front & l-front." Can I get a second point of verification on this?

www.gmt400.com

 

[Eman85]

Let's just do something really simple. Buy 2 plugs for the master cylinder, remove the lines and put the plus in. If the pedal is hard the MC is bled and good, if it's spongy the problem is in the MC.
I have bled these brakes every possible way and never had a problem getting a pedal. Rarely ever used a scan tool for bleeding. I can't tell how many brake jobs I've done on these vehicles and I worked for the dealers when they were brand new.
It's basic hydraulics, isolate the problem.