brake issues

[RLC2020]

Hi all,

Issue is when at a stoplight for an extended period of time, the pedal will slowly inch down while holding it and the brake light will come on if stopped long enough. Once I let off the brakes they are fine again. The brakes all seem to work great and the truck stops just fine even towing my 5,000lb boat. I had to do a panic stop the other day and I was actually impressed with how quick it stopped. Any suggestions? This is my daily so I don't want to tear it all apart without having replacement parts ahead of time if possible.

Brake fluid level in the master cylinder is full, clean and has not moved. I don't see any wet spots on the back of the drums either so I don't think I have a leak anywhere.

 

[Curt]

Stock brakes?If so,most likely your combination valve on the back of the forward most cross member.

So people have said you can slam on the brakes and reset it.Can’t vouch for that.

I would look for leaks,check master cylinder level,then bleed brakes.If it persists,change the combo valve.If that doesn’t work,probably start getting into the brakes themselves.

If it is a stock setup,if you go after a combo valve,make sure it’s disk/drum and not disk/disk

 

[idahovette]

Usually when the pedal goes slowly to the floor under pressure, the master cylinder is bypassing inside?? I'd think the master needs replaced

 

[Craig 85]

I would say master cylinder. I had this happen to me 40 years ago right after I started driving. I was sitting at a red light and the brake pedal started inching towards the floor. I lost enough pressure that the car started rolling into the intersection. I was able to pump the pedal, but lost pressure again and had to apply the parking brake to keep it stopped till the light changed.

 

[fast68chevy]

def something going on with the M/C if fluid is no disappearing. pistons seals in the M/C are toast. is the booster end of the M/C wet with fluid?

 

[GXPWeasel]

Yep, master cylinder. My other guess would have been leaking into the booster, if you didn't see any leaks on the ground, but fluid level was low. This has happened to me before as well.

 

[idahovette]

AND DON"T get a reman or rebuilt, just buy a NEW one!!!!

 

[highdesertrange]

yep master cylinder is bypassing internally. highdesertranger

 

[RLC2020]

So it seems that Master Cylinder is the place to start. I'll order one of those. Where are you all getting your parts? I'm sure there is a preferred vendor most of you use. I want to make sure I get OEM for something like this for sure.

I'm going to refresh everything in there while I'm at it. New pads/shoes, calipers, wheel cylinders, new fluid, etc. Any other suggestions? I haven't done drums in many many years. Can I reuse the springs and hardware, or should I order a new kit for that as well? Thank you for all the responses.

 

[Goldie Driver]

So it seems that Master Cylinder is the place to start. I'll order one of those. Where are you all getting your parts? I'm sure there is a preferred vendor most of you use. I want to make sure I get OEM for something like this for sure.

I'm going to refresh everything in there while I'm at it. New pads/shoes, calipers, wheel cylinders, new fluid, etc. Any other suggestions? I haven't done drums in many many years. Can I reuse the springs and hardware, or should I order a new kit for that as well? Thank you for all the responses.

I agree with new on the brake stuff all the way.

I just went with the Advance Auto stuff, though - if there is an Xcel auto parts around you might find AC Delco, but my 35 dollar ish one works fine.

The drum hardware kits are pretty cheap, and the springs do lose tension with heat and time, so those , and wheel cylinders, would be a good call.

You can change wheel cylinders with the removal of 1 brake spring and the shoes still on, BTW.

At least on my half ton.

 

[RLC2020]

^ I'm going to do O'reily since they can get the parts next day. I was on a few websites but they were all 1 week plus and I need to tow this weekend with it. Any idea on bore size for the master cylinder? Looks like there are 2 that say they will fit my truck. 1.19" and 1.25"

my vin#1G8GC26J4DF155651 if that helps.

I couldn't find the brake code on the tag under the hood.

Since I'm diesel I guess I have the hydroboost set up. Anything I need to know with that? I've never replaced a master cylinder, but I'm going to learn as I go.

 

[Blue Ox]

Any idea on bore size for the master cylinder? Looks like there are 2 that say they will fit my truck. 1.19" and 1.25"

my vin#1G8GC26J4DF155651 if that helps.

You can probably sort that out with drum size. C6P heavy duty would be 13" drums and the larger master. Standard would be 11" drums and a 30mm master.

 

[Goldie Driver]

^ I'm going to do O'reily since they can get the parts next day. I was on a few websites but they were all 1 week plus and I need to tow this weekend with it. Any idea on bore size for the master cylinder? Looks like there are 2 that say they will fit my truck. 1.19" and 1.25"

my vin#1G8GC26J4DF155651 if that helps.

I couldn't find the brake code on the tag under the hood.

Since I'm diesel I guess I have the hydroboost set up. Anything I need to know with that? I've never replaced a master cylinder, but I'm going to learn as I go.

Pretty straightforward - you will need flare wrenches for the lines to the MC , and to bench bleed it before installation. I *think* the new MC's come with instructions on how to do it, and eons ago they came with plastic thread in fittings and rubber hoses to flop back into the MC.

I still have my old ones as my new ones did not come with - cheap ass Chinese bastages ...

And, yes, good luck finding US made parts. I was shocked that my BW ignition module was made in the US, but no telling how long it sat on the local Advance Auto's shelf.

Don't know where it was made, but they stocked the floor switch for the dimmer, too ,which was good since my OE died - at night.

 

[75gmck25]

Since it’s a C20, do you have a 14 bolt FF rear axle?

If so, the rear drums are a much bigger job. With a FF axle you have to remove the axles before you remove the drums. Not really that hard, but a lot more involved than just slipping the rear drum off like you do on a light duty axle.

Bruce