1999 poor braking

[Burban22]

The brake pedal feel in gmt400 half ton aka non hydro boost brakes sucks. On my 97 k1500 I installed power stop drilled and slotted front rotors and adjusted the rear brake shoes so they are dragging a bit when turning the drum. This significantly improved braking performance, pedal feel still spongy but better with rear brakes adjusted. More importantly i have confidence stopping the truck and pressing the pedal past halfway now the truck will actually stop quickly.

 

[Burban22]

Still using original master cylinder. Bled brakes then bled the abs by putting truck on jack stands. Put in 4wd high accelerate to 30 - 40 mph slam on brakes and the abs will go crazy which cycles the abs without having a special gm tech 2 scanner.

If you don’t have 4wd then you can bled abs on a loose dirt road or icy parking lot

 

[exp500]

Cycling the key on/off while pressing pedal works to cycle ABS once.

 

[RubyRedLTZ]

Original type obs master was installed at the shop. Took truck home. It’s worse now. I think it’s a bad mc. Pedal goes to the floor. Bringing it back. This really sucks. I just want to drive it.

 

[east302]

Kind of surprised that they sent it out the door like that.

 

[Hoesgottaeat2]

Kind of surprised that they sent it out the door like that.

X2

 

[Eman85]

Easy check for a bad MC is buy 2 plugs that fit the MC ports. Install the plugs and step on the pedal. If the pedal is hard as a rock and doesn't sink MC is good. if it's soft it might not have been bled properly, most common problem. If the pedal sinks while pressure on it the MC is NG. Or you can keep changing parts and guessing. You usually won't find anyone to do actual diagnostics, it doesn't pay but replacing parts does. Diagnostics is a labor of love no one wants to pay for labor which is why a do it yourselfer can do better than a shop if they apply themselves. instead of paying labor rates you buy tools.

 

[Hoesgottaeat2]

Easy check for a bad MC is buy 2 plugs that fit the MC ports. Install the plugs and step on the pedal. If the pedal is hard as a rock and doesn't sink MC is good. if it's soft it might not have been bled properly, most common problem. If the pedal sinks while pressure on it the MC is NG. Or you can keep changing parts and guessing. You usually won't find anyone to do actual diagnostics, it doesn't pay but replacing parts does. Diagnostics is a labor of love no one wants to pay for labor which is why a do it yourselfer can do better than a shop if they apply themselves. instead of paying labor rates you buy tools.

Really like the way you think here @Eman85

 

[RubyRedLTZ]

The MC was changed to the one with the smaller bore. 1-1/8” that I think is correct for the JB5 brakes. Pedal travel is better. Still doesn’t stop very well. The shop suggests trying a new booster. Not sure if I want to pay for another “long shot” and hope it works. FWIW Shop owner has been flexible and cooperative on cost. I’ve been dealing with him for over 10 years. But this would likely be another $350

 

[Eman85]

Basic hydraulic theory, smaller bore MC more pressure, less volume, longer pedal travel.