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goodwrench9124
goodwrench9124, ASE Certified Technician
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My 1997 chevy 1 ton truck hydroboost has developed a ...

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My 1997 chevy 1 ton truck with hydroboost has developed a soft brake pedal and I can not stop quickly why? It has a new hydrboost, master cylinder, calapers and pads all around. Worked fine untill a week ago the pedal went half way to the floof with very little stopping power. Then pushed my foot to its original position of about a 1" from max up position and stopped well. When I finished my task (about 1 hour) it gave me a soft pedal and is continuing that after all this expense.
Submitted: 7 years ago.
Category: Chevy
Expert:  goodwrench9124 replied 7 years ago.
hello, i dont think you have a hydro boost concern, normally the hydro boost only aids in making it easier to push pedal. if the hydro booster was at fault in most cases you would have a hard pedal. souns like there is air in the brake system. can i ask is there a reason why all these parts where replaced??? for this concern or a another problem??
Customer: replied 7 years ago.
There is no air in the system they were bled properly and fully.
The parts were changed because when the inspection for frozen/broken/worn parts, was done. The brakes pads were worn at about 70% so they were changed and I did not like changing these parrts with out changing all parts related. this truck ia a dually with disc brakes front and rear, with abs. When this soft pedal happened, the fluid level was checked and it was at full level. and does not diminish.

Please advise,

Thank you
Expert:  goodwrench9124 replied 7 years ago.
ok, let me ask you this, did it feel like maybe abs was kicking in, did you hear any kind of noise when this occured???
Customer: replied 7 years ago.
I do not recall, the diesel engine is noisey and I may not have noticed.
I had a suspicision that the problem is in the ABS unit I asked the technician and he said no way.
It feels like the fluid is being recirculated to the reservoir.

Thank You

Plese advise
Expert:  goodwrench9124 replied 7 years ago.

it would look at the anto lock brakes real closely. the chevy trcks are very well know for low speed abs activation. which is usually a wheel speed sensor sending a irractic reading, causing the abs to activate when it shouldnt. and if the problems only occurs at times may very well be a abs problem. here is a service bulletin on this matter please read and see what you think

 

Subject:Antilock Brake (ABS) Activation at Low Speeds (Clean Wheel Speed Sensor Mounting Surface) #02-05-25-006B - (01/05/2006)

 

Models:1999-2000 Cadillac Escalade
1995-1999 Chevrolet Silverado (Old Style)
1995-2000 Chevrolet Suburban, Tahoe (Old Style)
1995-2003 Chevrolet Astro Van, Blazer, S10
1995-1999 GMC Sierra (Old Style)
1995-2000 GMC Yukon, Yukon XL (Old Style)
1995-2001 GMC Envoy, Jimmy
1995-2003 GMC Safari Van, Sonoma
1995-2001 Oldsmobile Bravada

 


This bulletin is being revised to update the correction and warranty information. Please discard Corporate Bulletin Number 02-05-25-006A (Section 05 -- Brakes).


Condition

Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause

The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction

Measure AC voltage and clean wheel speed sensor mounting surfaces.

  1. Raise the vehicle on a hoist.
  2. Disconnect both the front wheel speed sensor harness connectors.
  3. Place a DVM across the terminals of each sensor connector.
  4. Rotate the wheel with hand speed and measure the ACmV's. The reading should be at least 350 ACmV's.
  5. If the reading is between 200 and 350 ACmV's, remove the wheel, caliper and rotor in order to gain access to the speed sensor.
  6. Remove the wheel speed sensor and plug the hole to prevent debris from falling into the hub during service.
  7. Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, ScotchBriteTM, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
  8. Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
  9. Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (Canadian P/N 89022218).
  10. When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (Canadian P/N 993037).
  11. Install either the original sensor or a new one in the hub and secure the sensor. Ensure that the sensor is seated flush against the hub.
  12. Install the rotor, the caliper and the wheel.
  13. Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel by hand. The voltage should now read at least 350 ACmV's.

Parts Information

Part Number

Description

89022217

(Canadian P/N 89022218)

(Package of 2 cans)

Rust Penetrating Lubricant

(Each can will service 50+ vehicles)

01051344

(Canadian P/N 993037)

(Package of 12 tubs)

Wheel Bearing Lubrication - Tub

(Each tub will service 25+ vehicles

 

Customer: replied 7 years ago.
I have tried the brakes at different speeds from 50 mph to less than 5 mph and the brakes respond the same at any speed. That is why I did not suspect the sensors. Is the sensors active at any speed, or do the look at wheel speed to vehicle speed?
Is there any way the abs can be made inert to test if the problem is in the abs. There has been no abs light error displayed at any time.

Thank You

Please advise.
Customer: replied 7 years ago.
internet connection failed.
I am awaiting.

Thank You
Expert:  goodwrench9124 replied 7 years ago.
usually this abs concern happens at lower speeds. and yes you can turn off abs,but will have a abs light on at all times. i am doing some research on your concern. give me a little time
Expert:  goodwrench9124 replied 7 years ago.

Master Cylinder Diagnosis

These tests will not find all master cylinder malfunctions. If you cannot find the cause with these tests, refer to Hydraulic Brake Diagnostic System Check .

Visual Inspection
Check for a cracked casting or brake fluid leaks around the master cylinder. A leak will have at least one drop of fluid. A damp condition is normal.
Check the pedal linkage for binding and for incorrect pushrod length. If you do not find improper brake pedal travel or brake pedal binding disassemble the master cylinder. Refer to Master Cylinder Overhaul .
Check the master cylinder for swollen or elongated primary piston seals. If you find swollen seals, refer to Brake Fluid and Brake Fluid Handling .
Low Pressure Check

This procedure inspects for the following conditions:

Internal seal damage
Porosity
Component bore integrity
  1. With the ignition switch in the OFF position, pump the brake pedal in order to relieve the vacuum.
    - Pump the brake pedal 5 times for vacuum-assisted brakes.
    - Pump the brake pedal 25 times for hydraulic-assisted brakes.
  2. Apply the brake pedal slowly (approximately 3 mm 1/8 in per second). This generates pressure in the master cylinder.
  3. Gradually increase pedal force. Observe for gradually increasing brake pedal travel (Falling Away).
  4. If the brake pedal tends to Fall Away, perform the High Pressure Check.
  5. If the High Pressure Check does not locate a leak, then the master cylinder has an internal leak. Refer to Master Cylinder Overhaul .
High Pressure Check

This procedure tests for the following conditions:

Leaks at the following locations:
- Connections
- Hoses
- Casting
Gross internal leaks
  1. With the engine running, apply the brake pedal slowly (approximately 3 mm {1/8 in} per second). This generates pressure in the master cylinder.
  2. Gradually increase pedal force. Observe for gradually increasing brake pedal travel (Falling Away).
  3. Check for evidence of external fluid leaks. Examine the following items:
    - The ground
    - The pipe connections
    - The tires
  4. If you observe fluid around any component, that component has failed. Replace the component.
  5. If you find a leak at a connection, tighten the connection to specification. Refer to Fastener Tightening Specifications . Perform the High Pressure Check again.

Expert:  goodwrench9124 replied 7 years ago.

Brake Pedal Excessive Travel

Step

Action

Value(s)

Yes

No

DEFINITION: Excessive Brake Pedal Travel

1

Was the Hydraulic Brake Diagnostic System Check performed?

--

Go to Step 2

Go to Hydraulic Brake Diagnostic System Check

2

Inspect the disc brake pads and brake shoe linings for the following:

  • Excessive wear
  • Contaminated lining material
  • Uneven wear
  • Glazing
  • Abuse
  • Incorrect lining material

Refer to Brake Pad Inspection in Disc Brake or Brake Shoe Inspection in Drum Brakes.

Do any of the above conditions apply?

--

Go to Step 3

Go to Step 4

3

Replace the brake linings. Refer to Brake Pads Replacement in Disc Brakes or Brake Lining Replacement in Drum Brakes.

Is the repair complete?

--

Go to Step 22

--

4

Inspect the brake rotors for the following:

  • Hot spots
  • Scored rotor surface
  • Grooved rotor surface
  • Excessive lateral runout

Refer to Brake Rotor Lateral Runout Check in Disc Brakes

Do any of the above conditions apply?

--

Go to Step 5

Go to Step 6

5

Resurface the brake rotor. Refer to Brake Rotor Refinishing in Disc Brakes.

If refinishing the brake rotor results in a thickness that is less than the thinnest (Refinishing) thickness, replace the rotor. Refer to Brake Rotor Replacement in Disc Brakes.

Is the repair complete?

Go to Component Specifications in Disc Brakes

Go to Step 22

--

6

Inspect the drum brakes for improper adjustment. Refer to Drum Brake Adjustment in Drum Brakes.

Are the brakes improperly adjusted?

--

Go to Step 7

Go to Step 8

7

Adjust the drum brakes properly. Refer to Drum Brake Adjustment in Drum Brakes.

Is the repair complete?

--

Go to Step 22

--

8

Inspect the axle seals for leakage.

Is there any seal leakage?

--

Go to Step 9

Go to Step 10

9

Replace the axle oil seals.

Is the repair complete?

--

Go to Step 22

--

10

Inspect the brake assembly for missing or loose attachments. Refer to Brake Caliper Inspection in Disc Brakes or Brake Drum Inspection in Drum Brakes.

Are there any missing or loose attachments?

--

Go to Step 11

Go to Step 12

11

Replace or tighten the attachments as necessary.

Is the repair complete?

--

Go to Step 22

--

12

Inspect the wheel cylinders and calipers for leakage.

Are any of the components leaking?

--

Go to Step 13

Go to Step 14

13

Replace the leaking components. Refer to Brake Caliper Replacement in Disc Brakes or Wheel Cylinder Replacement in Drum Brakes.

Is the repair complete?

--

Go to Step 22

--

14

Inspect the hydraulic brake system for leaks. Refer to Brake Hose and Pipe Diagnosis .

Is there any sign of leakage?

--

Go to Step 15

Go to Step 16

15

Tighten the brake hose or pipe fittings. Refer to Fastener Tightening Specifications .

Is the repair complete?

--

Go to Step 22

--

16

Inspect the master cylinder for leakage. Refer to Master Cylinder Diagnosis .

Is the master cylinder leaking?

--

Go to Step 17

Go to Step 18

17

Overhaul the master cylinder. Refer to Master Cylinder Overhaul .

Is the repair complete?

--

Go to Step 22

--

18

Inspect the brake system for air. Refer to Hydraulic Brake System Bleeding .

Is there air in the system?

--

Go to Step 19

Go to Step 19

19

Bleed the brake system. Refer to Hydraulic Brake System Bleeding .

Is the repair complete?

--

Go to Step 22

--

20

Inspect the brake fluid for contamination. Refer to Brake Fluid and Brake Fluid Handling .

Is the brake fluid contaminated?

--

Go to Step 21

Go to Step 22

21

Flush the hydraulic brake system. Refer to Hydraulic Brake System Flushing .

Is the repair complete?

--

Go to Step 22

--

22

Verify the proper brake system operation.

Does the original condition still exist?

--

Go to Step 1

Go to Hydraulic Brake Diagnostic System Check


Expert:  goodwrench9124 replied 7 years ago.
you can pull the 60 maxi fuse in the underhood fuse block, this fuse will keep the abs pump from running and keep the abs from working.but will turn on abs light.
goodwrench9124, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3431
Experience: Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
goodwrench9124 and 5 other Chevy Specialists are ready to help you
Expert:  goodwrench9124 replied 7 years ago.

here is the functional test for hydro boost.

Hydraulic Booster Functional Test

System Tests

The hydraulic booster uses fluid pressure from the power steering system. A malfunctioning power steering system can affect the hydraulic booster. A malfunctioning booster can affect the steering system. Before beginning extensive testing, perform the following procedure.

  1. Check all power steering and brake pipe connections for leaks and restrictions.

    Notice: Power steering fluid and brake fluid cannot be mixed. If brake seals contact power steering fluid or steering seals contact brake fluid, seal damage will result.

  2. Ensure that the master cylinder is properly filled.

    Notice: Power steering fluid and brake fluid cannot be mixed. If brake seals contact power steering fluid or steering seals contact brake fluid, seal damage will result.

  3. Ensure that the power steering pump reservoir is properly filled. If the power steering fluid contains air, refer to Diagnosis of the Power Steering System in Power Steering System.
  4. Check the power steering pump belt for wear and improper tension. Refer to Diagnosis of the Drive Belt System in Engine Cooling.
  5. Check the power steering pump pressure. Refer to Power Steering System Test in Power Steering System.

Functional Test

  1. With the ignition OFF, apply and release the brake pedal several times. This will empty the accumulator.
  2. Apply and hold the brake pedal with 180 N (40 lb) of force.
  3. Start the engine.

The pedal should fall away, and then push back against your foot.

Expert:  goodwrench9124 replied 7 years ago.

review this information and runs some of the basic test to verify what is working like it is supposed too. then maybe pull abs fuse out and roadtest and see if problems reoccurs. anything you dont understand please ask me to explain

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