Soft brake pedal

Tiny
EZ_DUZZIT_ALL
  • MEMBER
  • 1998 CHEVROLET SILVERADO
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
K1500 Z71. Owned for six years. Brake pedal has always been soft. When stopping I always pump once half way and then step on pedal to brake. If I push hard I can make ABS go off. Decided to bleed brakes and broke off bleeder screw on caliper so replaced both front calipers and pads. Rear pads were fine. Bled system. Brake fluid was dark so bled until fresh fluid came through bleeders beginning with passenger rear, driver rear, passenger front, ending at driver front. Rear brakes and wheel cylinders inspected for leaks. All good. Brakes were still soft. With vehicle not running pedal is firm. Start vehicle and they go to the floor. Unplugged brake lines from master cylinder and installed plugs. Stepped on brake pedal with moderate pressure and hard as a rock. No movement other than pedal free play. Reinstalled lines and bled system. Still soft pedal. Checked rear drum adjustment and they were needing spread out quite a bit. So I adjusted them to two clicks in from not being able to turn drums by hand. Still soft peddle. So I broke the rules and got rubber fuel line and three clamps and clamped the rubber brake lines at each caliper and at the splitter for the shared rear line. Started vehicle and pedal is hard as a rock. Released rear clamp and pedal went to floor. Put rear clamp back on. Nice and firm again. Took off front driver clamp and went to floor. Put it back on and firm again. Same with passenger clamp. What am I missing?
Friday, November 2nd, 2018 AT 8:57 AM

2 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,176 POSTS
Hi and thanks for using 2CarPros. Com.

Take a look through this link to see if there is anything that is helpful.

Please run down this guide and report back.

It could be something as simple as a rubber hose expanding or air in the ABS.

Follow these directions for bleeding the system / ABS. See if it helps or makes a difference. It will require a live data scan tool.

___________________________

ABS BLEED PROCEDURE
Important:
- Use the two-person bleed procedure under the following conditions:
Installing a new Electro-Hydraulic Control Unit (ECU) or new Brake Pressure Modulator Valve (BPMV).
Air is trapped in the valve body.
- Do not drive the vehicle until the brake pedal feels firm.
- Do not reuse brake fluid that is used during bleeding.
- Use the vacuum, the pressure and the gravity bleeding procedures only for base brake bleeding.

TWO PERSON PROCEDURE
1. Raise the vehicle in order to access the system bleed screws.
2. Bleed the system at the right rear wheel first.
3. Install a clear hose on the bleed screw.
4. Immerse the opposite end of the hose into a container partially filled with clean DOT 3 brake fluid.
5. Open the bleed screw 1/2 to one full turn.
6. Slowly depress the brake pedal. While the pedal is depressed to its full extent, tighten the bleed screw.
7. Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.
8. Repeat the previous steps for the remaining wheels. The brake fluid which is present at each bleed screw should be clean and free of air.
9. This procedure may use more than a pint of fluid per wheel. Check the master cylinder fluid level every four to six strokes of the brake pedal in order to avoid running the system dry.
10. Press the brake pedal firmly and run the Scan Tool Automatic Bleed Procedure. Release the brake pedal between each test.
11. Bleed all four wheels again using Steps 3-9. This will remove the remaining air from the brake system.
12. Evaluate the feel of the brake pedal before attempting to drive the vehicle.
13. Bleed the system as many times as necessary in order to obtain the appropriate feel of the pedal.

Let me know if this helps.

Take care,
Joe
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Monday, February 22nd, 2021 AT 5:30 PM
Tiny
EZ_DUZZIT_ALL
  • MEMBER
  • 1 POST
Thank you Joe. I did everything in your reply except the ABS scan tool. I am looking into getting a OTC 3808 or 3809 scanner. I did get it to improve. I discovered that when I pushed on pedal while rubber lines clamped it was hard as a rock. But then I did it again and applied more pressure with my foot after about ten seconds of very hard pushing, it started to creep to the floor. At least I think that was problem. Regardless, they are better than they were. Thanks!
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Monday, February 22nd, 2021 AT 5:30 PM

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