Rear drum brakes work...sometimes

I have an 05 Z-71 with 89,000 miles and rear drum brakes and it feels like the rear brakes don't work all the time. I have checked the rears for adjustment and found it to be good. When I drive and start to apply the brakes sometimes I get a lot of pedal travel. Other times I get a good firm pedal and it feels like the back brakes are working. My CEL and ABS lights aren't on and the truck passed inspection a few weeks back with no problem. If I remember right isn't there a proportioning valve on these trucks to sense load shift or weight in the box? I am not sure if it is related to the weather warming up or just a part(s) intermittently not working properly?. Any thoughts? Thanks in advance.

I have an 05 Z-71 with 89,000 miles and rear drum brakes and it feels like the rear brakes don't work all the time. I have checked the rears for adjustment and found it to be good. When I drive and start to apply the brakes sometimes I get a lot of pedal travel. Other times I get a good firm pedal and it feels like the back brakes are working. My CEL and ABS lights aren't on and the truck passed inspection a few weeks back with no problem. If I remember right isn't there a proportioning valve on these trucks to sense load shift or weight in the box? I am not sure if it is related to the weather warming up or just a part(s) intermittently not working properly?. Any thoughts? Thanks in advance.


I would bleed the complete system start at r/r , lft/r , r/ft , lft /ft......first check for leaks ..these vehicles have very bad brake lines ...this should be a recall...the most common leak area is the frame rail fuel tank area ,,,this is where the line is hidden very hard to see...

this happened to me .....

Thanks J Cat for the tip. I will look this weekend. Will a spot show up in the driveway under the truck? I park in the same position and no oil spot. I also checked the reservoir and it was at the max line.

Thanks J Cat for the tip. I will look this weekend. Will a spot show up in the driveway under the truck? I park in the same position and no oil spot. I also checked the reservoir and it was at the max line.

IT MIGHT ! on my vehicle the brake fluid got on the fuel tank strap ...though it was a fuel leak ....then I remembered how when first starting out in the morning the pedal would go down lower than normal ...

the lines on these vehicles are very poor quality and will not stand up to the rust belt that you and I must operate ...GM should have not used this poor metal ....many have had these failures yet no recall ...

when a vehicle is designed these lines must be routed to ensure visibility so that when the vehicle is inspected this is corrected ....

If you have a badly rusted line and that abs starts pulsing because your hitting the brakes harder than normal to avoid an accident those rusted lines will blow ...

Well I got a chance to look under the truck and didn't find any signs of a leaking brake line. The brakes seem to be working normally now other than having warped front rotors. Anything else I should look at or test?