Hydraulic Brake Problems -- New to Me

lobo · 10-25-2009, 10:51 AM

I have a 94 Suburban K1500 (4wd) that hasn't had a brake flush since it was new. I put some speed bleeders in and flushed out the old fluid at the rear brakes (drums), but now I have real problems. (The breaks actually worked great before I did this.)

Here are some things I have observed:
1) The pedal is mushy and goes all the way to the floor.
2) The brake warning light is on.
3) While I was bleeding the brakes, fluid in the rear half of the reservoir would shoot up into the air. This was happening when I ***depressed*** the pedal. I'm not sure if that's supposed to happen.
4) I re-bled the rear brakes to make sure there were no bubbles in the line, and they looked alright.
5) Some braking is working, but it seems a lot softer. (I can't stop suddenly, anymore.)

By the way, the ABS warning light has been on for about 5 years with no additional problems. (I decided not to repair that, because I understand that the brakes revert to normal, non-ABS operation. It has performed very well since then in that way.)

So I'm not sure if I need is a new master cylinder or it could be something else. Does anyone have any suggestions about what might be the problem?

Case 7230 · 10-25-2009, 01:04 PM

You still have air in the system, probably in the RWAL unit.
The red light is probably from the pressure differential valve. If you open a front bleed screw and press the pedal down slowly the light should go out and then close the bleed screw.
By flushing the rears only you will still have old fluid in the front system.
Fluid gushing out of the resevoir is not unusual, just place the cap on loosely.
You are correct about the abs light, it is telling you that the computer has detected a fault and has disabled the RWAL system so you have ordinary brakes.

lobo · 10-25-2009, 05:59 PM

Since the master cylinder was so grimy looking, and I suspected it may have a gasket leak, I replaced it ($55 from Pep Boys). It really turned out to be less mysterious than I have always thought. Aside from the time to bench bleed the new unit, it only took about 15 or twenty minutes to remove the old unit and install the new one.

Now I have a clean reservoir and clean fluid.

I re-bled the back brakes and found more bubbles. Some were probably from the new master cylinder, but I also got very clean fluid coming out the bleeder valves.

Then I did the fronts. Once the bleeding was done, the pedal was solid. I started the engine and it's still firm like it should be. And the brake warning light is out.

Like I said, a lot of the mystery about my brakes has been eliminated. However, I wouldn't have started this project without speed bleeders. They really do make this an easy job.

Jim

--- This project involved brake bleeding and replacing the master cylinder ---

BernieB · 10-25-2009, 10:11 PM

I've never tried Pep Boys parts, so I don't know what their quality is like, but I could tell you some horror stories about their repair and maintenance services.

10-25-2009, 10:51 AM	#1
lobo Junior Member Join Date: Oct 2009 Posts: 2	Hydraulic Brake Problems -- New to Me I have a 94 Suburban K1500 (4wd) that hasn't had a brake flush since it was new. I put some speed bleeders in and flushed out the old fluid at the rear brakes (drums), but now I have real problems. (The breaks actually worked great before I did this.) Here are some things I have observed: 1) The pedal is mushy and goes all the way to the floor. 2) The brake warning light is on. 3) While I was bleeding the brakes, fluid in the rear half of the reservoir would shoot up into the air. This was happening when I *depressed* the pedal. I'm not sure if that's supposed to happen. 4) I re-bled the rear brakes to make sure there were no bubbles in the line, and they looked alright. 5) Some braking is working, but it seems a lot softer. (I can't stop suddenly, anymore.) By the way, the ABS warning light has been on for about 5 years with no additional problems. (I decided not to repair that, because I understand that the brakes revert to normal, non-ABS operation. It has performed very well since then in that way.) So I'm not sure if I need is a new master cylinder or it could be something else. Does anyone have any suggestions about what might be the problem? Last edited by lobo; 10-25-2009 at 11:21 AM. Reason: Edited #3. The fluid shoots up when I step on the pedal.

10-25-2009, 05:59 PM	#3
lobo Junior Member Join Date: Oct 2009 Posts: 2	Thanks, I got it working Since the master cylinder was so grimy looking, and I suspected it may have a gasket leak, I replaced it ($55 from Pep Boys). It really turned out to be less mysterious than I have always thought. Aside from the time to bench bleed the new unit, it only took about 15 or twenty minutes to remove the old unit and install the new one. Now I have a clean reservoir and clean fluid. I re-bled the back brakes and found more bubbles. Some were probably from the new master cylinder, but I also got very clean fluid coming out the bleeder valves. Then I did the fronts. Once the bleeding was done, the pedal was solid. I started the engine and it's still firm like it should be. And the brake warning light is out. Like I said, a lot of the mystery about my brakes has been eliminated. However, I wouldn't have started this project without speed bleeders. They really do make this an easy job. Jim --- This project involved brake bleeding and replacing the master cylinder ---

10-25-2009, 10:11 PM	#4
BernieB Senior Member Join Date: Jul 2009 Location: Fredericksburg, VA Posts: 1,910	I've never tried Pep Boys parts, so I don't know what their quality is like, but I could tell you some horror stories about their repair and maintenance services. __________________ If the guys who design 'em had to take one home, use it every day for 2 years, and do all the maint and repairs themselves, cars would have a button on the dash to change the oil, filters & plugs.

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10-25-2009, 01:04 PM	#2
Case 7230 Senior Member Join Date: Dec 2007 Posts: 547	You still have air in the system, probably in the RWAL unit. The red light is probably from the pressure differential valve. If you open a front bleed screw and press the pedal down slowly the light should go out and then close the bleed screw. By flushing the rears only you will still have old fluid in the front system. Fluid gushing out of the resevoir is not unusual, just place the cap on loosely. You are correct about the abs light, it is telling you that the computer has detected a fault and has disabled the RWAL system so you have ordinary brakes.