Need brake help

[Cgantt21]

I have a 99 suburban and have a bad braking problem. I have searched and searched but found no answer. So first my pedal would go almost the the floor and would have little brakes. Replaced the rear shoes and a wheel cylinder and bleed them. Worked great for a week then slowly got worse and worse till my pedal went straight to the floor. One of the rear cylinder broke also I went ahead and replaced both of them. Worked great for about a week again then got worse and worse. Now I've got the same issue have to press the pedal almost all the way down to stop and I checked the fluid and the master cylinder is full. The fluid is a little dirty. I'm honestly lost on this and have no idea what it could be. Any help would be greatly appreciated

 

[magimerlin]

Did you adjust the rear drums out at all. Sounds like you might be over extending the cylinders. Adjust the adjuster so that you can just start to hear the shoes drag the drum.. crank the embrace a few times to re-enter it all and check to make sure they are still just bearly dragging (very light scraping nose).

As far as pedal keep going to the floor... sounds like the master cylinder might be papa's sing on the inside.. just a couple rubber cup seals and plungers in there. Seen it happen alot...

Make sure the fronts are working correctly aswell. If the calipers freeze they will are the rears do all the work aswell and to do that the master has to bypass to get the fluid to back there aswell..

sent from what use to be a great country...

 

[twomanymontes]

Did you adjust the rear drums out at all. Sounds like you might be over extending the cylinders. Adjust the adjuster so that you can just start to hear the shoes drag the drum.. crank the embrace a few times to re-enter it all and check to make sure they are still just bearly dragging (very light scraping nose).

As far as pedal keep going to the floor... sounds like the master cylinder might be papa's sing on the inside.. just a couple rubber cup seals and plungers in there. Seen it happen alot...

Make sure the fronts are working correctly aswell. If the calipers freeze they will are the rears do all the work aswell and to do that the master has to bypass to get the fluid to back there aswell..

sent from what use to be a great country...

What he said. Also, did you bleed the front brakes also? If you have ABS sometimes air can get trapped in the front lines as well.

 

[Ironhead]

Just to add a couple of things to the great suggestions above, I'd be sure to have the rear drums measured to make sure they are have not been turned past the maximum diameter specification. This could allow excessive rear wheel cylinder travel, and possible leakage. Checking thoroughly for leaks, not only at the rear wheels, but along the brake lines in the chassis would be smart.

If the fluid is dirty, it would just be good maintenance to flush the entire system. You have to activate the ABS to do this, either with a scan tool designed to do that, or by using the brakes on slippery surfaces to activate the ABS. Then remove the dirty fluid in the master cylinder, refill with clean, and bleed each wheel till the fluid runs clean.

 

[Cgantt21]

Thank you for all the replies. The drums are adjusted correctly and I believe I found the leak. At the bottom of the master cylinder resivour that leads to the rear, the seal is leaking. I'm going to do the gmt800 master cylinder swap and hopefully that should fix my problems