92ragtop

I flush the brake fluid on my 1992 every 3 years. Did it again this weekend, and now my brakes don't really work at all. Never had a problem before this.

• I used DOT 4 like always
• There is no air in the lines, based on what I saw coming out of the bleeders.
• I used the correct bleeding sequence per the FSM, using the "press and release" method.
• Pedal goes to the floor, but if I pump it 4 times, it feels good and does not continue slowly go to the floor
• The "Brake" warning light on the dash does not illuminate like I expect it should (It does come on for a moment in the Run position, so the bulb is good)
• I did not bleed the Modulator valve in the rear compartment, since neither the MC or the reservoir was removed.

The only thing I thought was odd during the procedure is that the fluid flow from the front bleeders was not as fast as I would have thought.
Given this info, I am suspecting that the MC has failed, but this seems way to coincidental.
So to you brake experts.... do you think that my suspicion about the MC is correct? Is there a sure way to confirm this? And, if I do need a MC, RockAuto has Raybestos (Professional Grade), Dorman and Cardone. Are any or all of these made in China?

Kevova

ABS codes? The "Brake" light has become a low fluid level light over the years. If the master cylinder is full the light's off. I would try bleeding master cylinder to see how the fluid flows. If its strong Master cylinder is probably ok. I would continue down the line. Anything is possible on a 20+ year old car. Make sure the rear caliper pistons (parking brake actuators) not retracted, and will firmly apply pads to rotors.

If after rebleeding the entire system I would go with the master cylinder mostly because cost and availability compared to ABS valve block

c4cruiser

By any chance, did you let the MC reservoir run dry or down to where the holes for the fluid lines were exposed? That could have caused air to get into the MC which may require doing a bench bleed, then re-bleeding the lines.

Fluid type (DOT 4 or DOT3) is not really an issue.

The "Modulator" is actually the ABS system. Unless you have access to a GM Tech 2 Scan Tool and the appropriate brake module for the Tech 2, the ABS system can't really be bled. The tool operates the ABS pump and fluid is pumped out through a port on the side of the pump. This can be a messy job....

If the pedal can be pumped a few times and then the pedal stays firm, I would do a bench bleed and than re-bleed the lines. If it turns out that you decide to replace the MC, stay away from either the Dorman or Cardone pieces. The Raybestos Professional Grade MC is much better than either one. An AC Delco Professional MC will work great too. Most all reman components are now done in China or assembled in the US from Chinese-made parts.

92ragtop

Thanks. Regarding fluid level, I first sucked the old fluid out of the MC, then filled it with fresh fluid. Once I started the bleed procedure, the level was kept topped right up. I'll have to try the bench bleed idea.

jsmn4vu

If it gets to the point you're thinking about a bench bleed, you might want to consider reverse bleeding instead:

ghoastrider1

usually, if a MC is going bad, the pedal will slowly sink towards the floor, even after pump up .Make sure your pads are good and not worn down. I noticed you said you emptied the MC then refilled it. That may be the problem as air MAY have been introduced to the system. Try another bleed.

Mikeceli

It is not unusual for a MC to fail after bleeding. Bad MC's can exhibit slow leak down, or severe pedal drop.

pcolt94

The only weird stuff if can think of besides of what's already been said is this.

Make sure the proportional valve is where it should be and has not moved. You can view it from the electrical connector on the passenger side of the master.

Due to all the dirt and grime that was removed from the fluid flush, the seals in the old master are not sealing properly now.

92ragtop

Thanks. I found an old post from years go that stated...."the prop valve in the master has been triggered & is off center. If there is a brake warning switch in the master remove it & look in the bore. The prop valve [I]piston has a groove machined into it, the groove should be centered in the bore[/I]." Would pressing the pedal to the floor during the bleeding process possibly cause this? My brake warning switch does not come on when the pedal goes to the floor.

Also, if I undo the hard lines from the MC and use a bench bleeding hose kit, can I bench bleed the MC while it is still attached in the car?...essentially using the brake pedal/pushrod instead of a tool or dowel?

Ripe93

For the last 10 years, I only use my Motive Products Power Bleeder. You'll need the p/n 0108 for late model GM's ~$60 on Amazon. One man bleeder that is stupid simple to use. Better than the Phoenix turkey baster. Product endorsement aside, you may have to build a bit of pressure in the system. I have done a 2000 s-10 and my 93 40th and both went to the floor on first press after the bleed but both came up hard after the third press. Scared the Trump out of me at first. But a great pedal when I am done.

9T3VETTE

Not sure about the prop. valve question, but yes you can bleed the master with a bench bleeding kit on the car.

Ripe93

Sorry 9T3, but you can NOT bench bleed the MC while it's still on the car. First of all, they'd call it 'on-the-car' bleed if that was the case. ;^) And the reason you do it on the bench in a vise is to push the piston farther than it would naturally go with the brake pedal to get the air trapped in the tip of the cylinder.

92ragtop

I'm on Rockauto and found two Raybestos Professional Grade MC model numbers. Unfortunately both claim to fit 1992-1996, and we know that 92/93 is different. RA does not offer mechanical or application advice, so can anyone tell me which of the following would be correct for a 1992?

#MC391429 with 12mm (1/2") switch length

#MC390255 {E150608, MC390073} with 3/8" switch length

9T3VETTE

Sorry ripe, you are completely misinformed. Is it better to be done on a bench? Probably. But the master can also be effectively bled when it's installed.

To the op...big box auto part stores sell cheap universal master bleeding kits which work well. Try one of those and bleed the master ON the car using the brake pedal.

Cruisinfanatic

done all the time

92ragtop

Sometimes when you are very sure of something, it pays to go back and triple-check anyway. I re-bled the brakes today and found that there was a very large air bubble in one of the front calipers. How it got there, I have no idea because the reservoir was kept topped up. Lesson learned. I just glad it was any easy fix and not a MC.

ghoastrider1

congrats, I know your feeling pretty good right now.. as you should. now its time for you to buy around for all the folks that helped.

9T3VETTE

Glad you got it figured out

pcolt94

Good job……it's done.

Didn’t have to go into left field today. It's one of my rules also, always go back to where you were if something unexpected comes up.

Just wondering what method of bleeding did you initially used?

92ragtop

I have a Mighty-vac, but find that when using it to bleed brakes it seems to draw a bit of air from around the thread of the bleeder screw, making it hard to tell if any bubbles are coming from the brake system itself. In this case, I used the press & release method.

I'm a happy camper today....it's a beautiful sunny day and I just took the car out for it's first drive of the year. Reminded me why I love this car.