Only two brakes work!
 

First off this is my first post. I just found this forum and it is full of great information.

My problem...

1992 Bonneville SE with the upgraded 16" wheels and sportier suspension.

Brake pedal sinks to the floor where I have some braking if pushed hard on the pedal.
Jacked up the vehicle and had someone apply the brakes.
Right front has brakes meaning I can't turn the tire with the brakes applied.
Left front has no brakes meaning it turns freely.
Right rear has no brakes.
Left rear has brakes.

So what the heck is going wrong?

How's the fluid level in the master cylinder?
Has the car been in storage?

Fluid level is fine. Car is driven daily.

Symptoms came on suddenly.

I'm reading about the hydraulics being a dual system. Is this front and back or is it RF LR and LF RR

As far as I know all GM cars with dual system is front/back. I'd start by bleeding the brakes at all four wheels.

Bleed the brakes a TON. Keep the MC full during the procedure. Start at the right rear, then left rear, then right front, then left front. Repeat several times.

OK...

I'm thinking about replacing the master cylinder. I hope it's not something to do with the hydraulic unit seeing as it is $550+

I disconnected the negative battery terminal. Had a helper press the brake and then I opened up the left front bleeder screw. The right front has no braking pressure. Fluid came out very very slowly. We did this several times with no change. And I am still not getting any braking. The caliper piston doesn't squeeze seeing as there is no fluid pressure.

How do I bleed if there is no pressure? Shouldn't the fluid come streaming out?

Any more thoughts?

Yes, keep bleeding, you're not there yet.

If you can't get the lines bled, as above, replace the master cylinder, ensuring that you bench bleed it first.

I have no pressure in the two lines to bleed.

I open the screw and nothing comes out.

How can I bleed without pressure?

I've never seen a master cylinder so toasted it wouldn't pump fluid through an open line, so I believe you either have a petcock open or a broken brake line somewhere.

Ensure the master cylinder is full of fluid, pump the brakes for a minute or so, and then look under the car to see where the fluid you're pumping is going to.

An assistant will help this process a lot.

Agreed.

Look for any leaking fluid on the back tires from the wheel cylinders as well as all other areas of the car and if bleeding fails, it's probably a master clyinder.

Well I got it working.

I was only able to bleed the two wheels that had braking power. The other two I would open the bleeder screw and nothing would come out. No pressure at all.

So I decided to try the master cylinder. I bought a remanufactured one at checkerauto for $47 Cardone. Bench bled it and was able to bleed all the wheels.

Now the brakes work better than ever.

I don't understand exactly why I only had braking power at the RF and LR wheels.

Anyway I hope my problem may help someone else with the same symptoms.

Because that's how it's designed, so if one section of the MC fails, you have brakes on both ends of the car.

Glad to hear it.

I thought that it was a diagonal system; however, the dealership and everyone else I asked told me it was a front rear split system.

Oh well...

I'm just glad it is working again.

They are wrong, and it is a Diagonal system... The left front and right rear are one part and the right front and left rear are on the other part of the system... Chances are that both parts or Halves of the system most likely not fail at the same time leaving you with half the braking system which is a lot better than no brakes at all... ;)

Glad you got it fixed 8)

__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote