Question about 1997 Chevrolet Blazer

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Trying to bleed brakes on 1997 blazer. Have fluid on front circuit in and out of HCU. Fluid going into HCU for rear wheels but nothing coming out. Scan tool needed for bleeding procedure?

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  • Chevrolet Master
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No nothing electric or fancy tie the load sensor valve up then try

Posted on Nov 14, 2010

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I have an 01 GMC Jimmy 4.3L 4WD & we are trying to bleed the brakes but the scanner says my vehicle is going 3MPH so we manually bleed the brakes but the pedals still easily is pushed to the floor.


Bad master cylinder . What are you using a scan tool for ? No need Unless your Installing a new Electro-Hydraulic Control Unit (EHCU) or new Brake Pressure Modulator Valve (BPMV).
Hydraulic Brake System Bleeding (Manual)
Caution: Refer to Brake Fluid Irritant Caution in the Preface section.
Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in the Preface section.
Place a clean shop cloth beneath the brake master cylinder to prevent brake fluid spills.
With the ignition OFF and the brakes cool, apply the brakes 3-5 times, or until the brake pedal effort increases significantly, in order to deplete the brake booster power reserve.
If you have performed a brake master cylinder bench bleeding on this vehicle, or if you disconnected the brake pipes from the master cylinder, you must perform the following steps:
3.1. Ensure that the brake master cylinder reservoir is full to the maximum-fill level. If necessary add GM approved brake fluid from a clean, sealed brake fluid container. Refer to Fluid and Lubricant Recommendations.
If removal of the reservoir cap and diaphragm is necessary, clean the outside of the reservoir on and around the cap prior to removal.
3.2. With the rear brake pipe installed securely to the master cylinder, loosen and separate the front brake pipe from the front port of the brake master cylinder.
3.3. Allow a small amount of brake fluid to gravity bleed from the open port of the master cylinder.
3.4. Reconnect the brake pipe to the master cylinder port and tighten securely.
3.5. Have an assistant slowly depress the brake pedal fully and maintain steady pressure on the pedal.
3.6. Loosen the same brake pipe to purge air from the open port of the master cylinder.
3.7. Tighten the brake pipe, then have the assistant slowly release the brake pedal.
3.8. Wait 15 seconds, then repeat steps 3.3-3.7 until all air is purged from the same port of the master cylinder.
3.9. With the front brake pipe installed securely to the master cylinder, after all air has been purged from the front port of the master cylinder, loosen and separate the rear brake pipe from the master cylinder, then repeat steps 3.3-3.8.
3.10. After completing the final master cylinder port bleeding procedure, ensure that both of the brake pipe-to-master cylinder fittings are properly tightened.
Fill the brake master cylinder reservoir with GM approved brake fluid from a clean, sealed brake fluid container. Ensure that the brake master cylinder reservoir remains at least half-full during this bleeding procedure. Add fluid as needed to maintain the proper level.
Clean the outside of the reservoir on and around the reservoir cap prior to removing the cap and diaphragm.
Install a proper box-end wrench onto the RIGHT REAR wheel hydraulic circuit bleeder valve.
Install a transparent hose over the end of the bleeder valve.
Submerge the open end of the transparent hose into a transparent container partially filled with GM approved brake fluid from a clean, sealed brake fluid container.
Have an assistant slowly depress the brake pedal fully and maintain steady pressure on the pedal.
Loosen the bleeder valve to purge air from the wheel hydraulic circuit.
Tighten the bleeder valve, then have the assistant slowly release the brake pedal.
Wait 15 seconds, then repeat steps 8-10 until all air is purged from the same wheel hydraulic circuit.
With the right rear wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged from the right rear hydraulic circuit install a proper box-end wrench onto the LEFT REAR wheel hydraulic circuit bleeder valve.
Install a transparent hose over the end of the bleeder valve, then repeat steps 7-11.
With the left rear wheel hydraulic circuit bleeder valve tightened securely, after all air purged from the left rear hydraulic circuit, install a proper box-end wrench onto the RIGHT FRONT wheel hydraulic circuit bleeder valve.
Install a transparent hose over the end of the bleeder valve, then repeat steps 7-11.
With the right front wheel hydraulic circuit bleeder valve tightened securely, after all air has been purged from the right front hydraulic circuit, install a proper box-end wrench onto the LEFT FRONT wheel hydraulic circuit bleeder valve.
Install a transparent hose over the end of the bleeder valve, then repeat steps 7-11.
After completing the final wheel hydraulic circuit bleeding procedure, ensure that each of the 4 wheel hydraulic circuit bleeder valves are properly tightened.
Fill the brake master cylinder reservoir to the maximum-fill level with GM approved brake fluid from a clean, sealed brake fluid container.
Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
If the brake pedal feels spongy, repeat the bleeding procedure again. If the brake pedal still feels spongy after repeating the bleeding procedure, perform the following steps:
21.1. Inspect the brake system for external leaks. Refer to Brake System External Leak Inspection.
21.2. Pressure bleed the hydraulic brake system in order to purge any air that may still be trapped in the system.
Turn the ignition key ON, with the engine OFF. Check to see if the brake system warning lamp remains illuminated.
Important: If the brake system warning lamp remains illuminated, DO NOT allow the vehicle to be driven until it is diagnosed and repaired.
If the brake system warning lamp remains illuminated, refer to Symptoms - Hydraulic Brakes

Feb 26, 2017 | GMC Cars & Trucks

2 Answers

Replaced some brake line, rear pads and one rear wheel cylinder. Now no pressure and nothing happening when trying to bleed.


Does the car have ABS ? And does it have an equalizer block for the 4 wheels ?
It sounds like the ABS has been affected, or there is an equalizer block that is stuck on the front wheels only.
Can you open the bleeder or the rear line on the master cyl and get fluid to come out by depressing the pedal ?

Jul 07, 2013 | 1997 Mercury Tracer

1 Answer

I replaced my front brake router and brake pads today. when i bleed the front left brake, a line which im assuming is a brake line near the rear left tire burst and is leaking brake fluid. when u tried...


First, there is NO Pumping of the brake pedal
involved in bleeding brakes

I think your smart enough to know you
need to replace both rear brake hoses,
before you proceed with the bleeding

Mar 22, 2011 | 1997 Chevrolet Cavalier

1 Answer

2005 jeep grand cheroke limited with A hemi, been to the dealer more times then I can count, and still to this day the same problem. The service elect brake system light illuminates intermit and so for...


The braking force of the rear wheels is controlled by electronic brake distribution (EBD). The EBD functions like a rear proportioning valve. The EBD system uses the ABS system to control the slip of the rear wheels in partial braking range. The braking force of the rear wheels is controlled electronically by using the inlet and outlet valves located in the HCU. The HCU is a Hydraulic control unit. The HCU consists of a valve body, pump motor, and wire harness.

Did they check for DTC (diagnostic trouble codes) in the system? if so, what were they?

Accumulators in the valve body store extra fluid released to the system for ABS mode operation. The pump is used to clear the accumulator of brake fluid and is operated by a DC type motor. The motor is controlled by the ABM.
The valves modulate brake pressure during antilock braking and are controlled by the ABM.
The HCU provides four channel pressure control individually to all the front and rear brakes. Each of the four channels control the rear & front wheel brakes individually.
During antilock braking, the solenoid valves are opened and closed as needed. The valves are not static. They are cycled rapidly and continuously to modulate pressure and control wheel slip and deceleration.
During normal braking, the HCU solenoid valves and pump are not activated. The master cylinder and power booster operate the same as a vehicle without an ABS brake system.
During antilock braking, solenoid valve pressure modulation occurs in three stages, pressure increase, pressure hold, and pressure decrease. The valves are all contained in the valve body portion of the HCU.


PRESSURE DECREASE The outlet valve is opened and the inlet valve is closed during the pressure decrease cycle.
A pressure decrease cycle is initiated when speed sensor signals indicate high wheel slip at one or more wheels. At this point, the ABM closes the inlet then opens the outlet valve, which also opens the return circuit to the accumulators. Fluid pressure is allowed to bleed off (decrease) as needed to prevent wheel lock.
Once the period of high wheel slip has ended, the ABM closes the outlet valve and begins a pressure increase or hold cycle as needed.


PRESSURE HOLD Both solenoid valves are closed in the pressure hold cycle. Fluid apply pressure in the control channel is maintained at a constant rate. The ABM maintains the hold cycle until sensor inputs indicate a pressure change is necessary.


PRESSURE INCREASE The inlet valve is open and the outlet valve is closed during the pressure increase cycle. The pressure increase cycle is used to counteract unequal wheel speeds. This cycle controls re-application of fluid apply pressure due to changing road surfaces or wheel speed.

Nov 09, 2010 | 2005 Jeep Grand Cherokee

2 Answers

I replaced the brake master cylinder on my 91 Lincoln Mark 7 with a non high pressure master cylinder and the rear brakes do not hold. Do I need to change the cal. on the rear also?


ANTI-LOCK BRAKE SYSTEM (and HCU-Hydraulic Control Unit)
General Information The 4-Wheel Anti-lock Brake System (ABS) is an electronically operated, all wheel brake control system. Major components include the power brake booster, master cylinder, the wheel speed sensors, and the Hydraulic Control Unit (HCU) which contains the control module, a relay, and the pressure control valves. The system is designed to ****** wheel lockup during periods of high wheel slip when braking. Retarding wheel lockup is accomplished by modulating fluid pressure to the wheel brake units. When the control module detects a variation in voltage across the wheel speed sensors, the ABS is activated. The control module opens and closes various valves located inside the HCU. These valves, called dump and isolation valves, modulate the hydraulic pressure to the wheels by applying and venting the pressure to the brake fluid circuits. Some models are equipped with a Traction Assist (TA) system. The TA system senses wheel spin upon acceleration, turns on the Hydraulic Control Unit (HCU) pump and applies fluid pressure to the appropriate rear wheel. Two additional isolation valves in the HCU will also close to permit fluid to flow only to the rear wheels. The TA system monitors TA usage to avoid overheating the rear brakes. If the system does sense brake overheating, the ABS module will inhibit TA operation until the rear brakes are permitted to cool down.
---
SYSTEM COMPONENTS The anti-lock brake system consists of the following components:
  • Vacuum booster and master cylinder assembly
  • Hydraulic Control Unit (HCU)
  • ABS module
  • Wheel sensors
  • Pedal travel switch
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On 1992-1994 and 1995-00 a scanner is used to perform the brake bleed. But on yours, I think it's different according to the manual.
---
What do you mean change the cal. on the rear also? Do you mean Caliper?

Jul 26, 2010 | 1991 Lincoln Mark VII

4 Answers

How do i bleed the brake system


First, before you do the bleeding, did you "open" any of the lines? Was there a caliper replaced?

If no line was opened, you do not need to bleed the brakes.

If so, please let me know and I will post the bleed procedures for you.

Why are you thinking about bleeding the brakes? Spongy brake pedal?

Oct 08, 2009 | 1995 Chrysler Town & Country

1 Answer

Very little (almost nonexistent) rear brakes. Cannot stop rear wheels even with wheels off the ground. Replaced MC, wheel cyl.,Rubber hose, booster, proportioning valve, bypassed rear ABS, shoes, drums,...


What happens when you try to bleed the rear brakes? If nothing comes out, trace each line back toward the proportioning valve--something would be blocking flow of fluid. Disconnect each line at the forward end and see if fluid comes out of the valve openings. You will need a scan tool to complete the bleeding process with ABS. Suggest buying a Chilton's manual for this truck because of the complexity of the ABS system.

Sep 30, 2009 | 1997 Dodge Dakota

1 Answer

How to bleed brakes to a 2006 honda


start by bleeding the fluid from the drivers front wheel first,till the fluid comes out. then the passenger front wheel then the rear right wheel then the rear left wheel, repeat again make sure to keep the aster cylinder full of fluid so it doesnt run dry. bleed till u get a steady stream of fluid from each of the wheels when bleeding them in the sequence ive stated.

Apr 03, 2009 | 2006 Honda Accord

2 Answers

I need to know how to bleed the brakes on a 1999 chevy blazer


Start from right rear, then, left rear, right front, left front. Fill master cylinder. Have helper sit in car, have helper hold brake pedal down. open bleed screw. fluid and air comes out. close screw. release brake pedal. Continue until no air comes out. Move to next wheel. Keep an eye on master cylinder fluid level after each wheel.

Mar 27, 2009 | 1999 Chevrolet Blazer

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