1998 Chevy Truck No front brakes

Tiny
FUN4VERN
  • MEMBER
  • 1998 CHEVROLET TRUCK
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 167,000 MILES
98 c1500 w/t 4.3L Auto
Truck was given to me and have been fixing little by little. Your site here has been loads of help but now have a problem that no one else has addressed so far as I see.
No brake pedal and the master cylinder looked like it had leaked some so replaced it. Bench bled and re bled all at all 4 wheels. But then I noticed that when the pedal was pumped brake fluid was coming back into the reservoir? I know that parts are bad off the shelf some time but before I go and remove the master cylinder and do a swap I was wondering if there might be something wrong with the ABS system or a check valve or something to let the fluid go back into the master cylinder resivoir, oh yes it is going into the chamber of the resivoir closest to the firewall. Any assist ya all can give will be greatly appreciated.
Thanks
Vern
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Monday, December 8th, 2008 AT 6:37 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Vern:
It sounds like a bad master cylender. When you say there are no front brakes, do they work at all? Are the calipers ok? Finally, do the rear brakes work properly?

Joe
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Tuesday, December 9th, 2008 AT 10:41 PM
Tiny
FUN4VERN
  • MEMBER
Thanks for the reply. Got a new master cylinder and yes have back brakes. The puzzle is when ya hit the brakes fluid returns to the back part of the resivoir of the master cylinder. Everything up front is good. This truck has the ABS system.
Thanks again
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Wednesday, December 10th, 2008 AT 9:13 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Vern:
My guess is that you got a bad master cylender. I can't think of anything that would send the fluid back into the resevoir.

I'll ask a couple of my buddies on this web site to take a look, but I'm not sure they will know what to say.

Let me know what they recommend.

Joe
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Wednesday, December 10th, 2008 AT 9:56 PM
Tiny
JNOVACK
  • EXPERT
Does this master cylender have the abs attached to it or is the abs on its own this is the most common used This will cause the issue you are having

EHCU Valve

See Figure 1

The EHCU valve is mounted near or under the master cylinder and combination valve. The valve is not serviceable and must be replaced if malfunctioning.


http://www.2carpros.com/forum/automotive_pictures/52960_0900c1528008f6dd_1.jpg


Fig. 1: Exploded view of the Electro-Hydraulic Control Unit (EHCU)
Front Wheel Speed Sensors

With one exception, on both 2WD and 4WD vehicles, the front wheel speed sensors are permanently mounted to the brake rotor splash shield. With the exception of the 1992-98 Suburban, if the sensor fails the rotor and splash shield must be removed. On 4WD vehicles, the hub and bearing assembly must also be removed for access.

The front wheel speed sensors on 1992-98 4WD Suburban vehicles are removable without disassembly of the hub or brakes.

Rear Wheel Speed Sensors

Except for 1992-93 Suburban, the rear wheel speed sensors are held by 2 bolts at each rear wheel. The brake drum and primary brake shoe must be removed for access.

The 1992-93 Suburban receives the rear wheel speed signal from the Vehicle Speed Sensor (VSS) buffer. The VSS is located at the left rear of the transmission. The buffer, a unit for interpreting the electrical signal from the sensor, is located behind the instrument cluster. The buffer, formerly known as the digital ratio adapter controller (DRAC), is matched to the final drive and tire size of each vehicle. If the final drive or tire size is changed, the buffer unit must be replaced to maintain accurate speedometer/odometer readings and proper ABS function.
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+2
Thursday, December 11th, 2008 AT 12:24 PM
Tiny
JNOVACK
  • EXPERT
Here i another system they used
C/K Series

MANUAL BRAKES

See Figure 2

Disconnect the brake lines at the valve. Plug or cap the lines and ports.
Unplug the switch wiring connector.
Remove the valve-to-bracket bolts.
To install:

Install the valve. Tighten the bolts to 20 ft. lbs. (27 Nm).
Bleed the system.


http://www.2carpros.com/forum/automotive_pictures/52960_0900c1528008f731_1.jpg


Fig. 2: Combination valve-C/K Series
POWER BRAKES

Disconnect the brake lines at the switch. Plug or cap the lines and ports.
Unplug the warning switch wiring connector.
Remove the anti-lock brake system control module from the bracket. See the procedure later in this section.
Remove the bolts attaching the ABS isolation/dump valve to the bracket. See the procedure later in this section.
Remove the nuts that attach the master cylinder and bracket to the booster.
Remove the bracket and combination valve assembly.
To install:

Position the bracket/valve assembly and install the master cylinder-to-booster nuts. Tighten the nuts to 20 ft. lbs. (27 Nm).
Install the ABS isolation/dump valve nuts. Tighten them to 21 ft. lbs. (24 Nm).
Install the ABS control module.
Connect the wiring.
Connect the hydraulic lines.
Bleed the system.
SWITCH CENTERING

Whenever work on the brake system is done it is possible that the brake warning light will come on and refuse to go off when the work is finished. In this event, the switch must be centered.

Raise and support the truck.
Attach a bleeder hose to the rear brake bleed screw and immerse the other end of the hose in a jar of clean brake fluid.
Be sure that the master cylinder is full.
When bleeding the brakes, the pin in the end of the metering portion of the combination valve must be held in the open position (with the tool described in the brake bleeding section installed under the pin mounting bolt). Be sure to tighten the bolt after removing the tool.
Turn the ignition key ON. Open the bleed screw while an assistant applies heavy pressure on the brake pedal. The warning lamp should light. Close the bleed screw before the helper releases the pedal.
To reset the switch, apply heavy pressure to the pedal. This will apply hydraulic pressure to the switch which will re-center it.
Repeat Step 5 for the front bleed screw.
Turn the ignition OFF and lower the truck.
If the warning lamp does not light during Step 5, the switch is defective and must be replaced.
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Thursday, December 11th, 2008 AT 12:59 PM

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