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04 Sonoma slow to stop

04 GMC is slow to stop like weak brakes …is it the brake booster or calipers or something else ? Thanks

Bob , since you are on the web asking a forum for Brake advice I assume you do not know how to repair a brake system . Therefore you only have one option . Have this thing towed to a brake shop before you have a wreck and injure yourself or someone else.


If you have a good firm pedal (i.e. it isn’t sinking to the floor when you press on it), and the stopping performance is always poor, common causes

  • pads are worn out
  • rotor is worn out
  • caliper problem
  • only one half of the brake system (e.g. rear brakes only) is working
  • contaminated surfaces on the pads and rotor
  • faulty power booster

This is something a good shop can usually figure out quickly.

soft pedal?

rock hard pedal?

Its parked in the garage…not driving it Volvo 70

It’s my project. I like to work on it and ask dumb ques and after awhile it all comes together…thx

I’m thi kin the proportioning valve…cuz not gettin fluid to the back brakes…was that on your list?

I’m thinking you need a special tool/scanner to bleed them because of the ABS unit.

Soft but pumps up to rock hard then goes to floor after you start it…

Yea me too. Ebay or Amazon abt 200$ with autobleed…

Obvious question, but does the master cylinder have fluid? Is the brake system (hard lines etc) leaking fluid anywhere?

sounds like the brake booster is working, for what it’s worth

But it definitely appears you have a problem with the hydraulic part of your brakes . . . air in the system, bad master cylinder, something like that

So please answer this next question . . .

When you’re sitting at a stop light in “D” and your foot on the brake pedal, does it slowly sink to the floor?

Havnt driven this trk in 2 years however dont recall that happening…a little history…my son in law bled the brakes said were spongy…then now fluid is not present to rear…so I’m thinkin its prop valve…may try to bypass it on rear only…also why couldnt I unscrew that little reset switch at the end of the valve pull it out and stick something like a pick in there and push it back to it’s normal position?

Gonna bypass prop valve on tear brake line and jump from m cyl to rear line with tubing …maybe can get some fluid in rear lines.

If you bypass the prop valve permanently, the rear brakes will lock long before the fronts and cause you to spin. Don’t do that permanenly.

Have you checked to see if you have fluid at the combo valve? Then the ABS unit? Have you cracked the brake hose connection at the caliper? Keep in mind, bleed screws can easily corrode up the holes solid. Try removing the entire bleed screw and see if fluid comes out. If it does, the screw itself is clogged.

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Agree that bleeder valves could be, and most likely are, corroded / plugged. I’ve never had issues with the proportioning valve or the ABS unit (regarding bleeding) on this year model truck cause me issues, despite supposedly needing a scan tool to bleed. Usually, it’s something simple.

Yep it’s at both lines from master cylinder…it flows well from the prop valve(front brakes only).Just a very small drop or 2 from prop valve rear brake.

Both front calip bleed ok…

I separated the single line going to back rear at a little block by the differential and it was bone dry.

Could I put an inline valve on the back brake line…like the original prop for front and an inline valve for back…I dont know if it would be a metering valve or what its called.