I am working on my son's 94 Del Sol SI. The brake pedal hasn't had good pressure for quite a while so we changed the master cylinder, but it didn't get better. We bench bled the master cylinder and bled the brakes (ran 2 12oz cans of brake fluid through the system and everything is clear). The strange thing is that there is good pressure on the passenger rear and driver front wheel (same circuit) but very little pressure on the driver rear and passenger front side. Tried using a vacuum brake bleeder, and got fluid through it, but the pedal still goes to the floor.

Other weird thing is when bleeding the driver front, the pedal seems to build pressure, but doesn't stay.

Could this be the proportioning valve? I wouldn't see how since the front and rear seem to have the same low pressure on that side.

Maybe new master cylinder is bad? Any way to check that before I ask for a refund/replacement?

Thanks for any help!

Scott

 

Sounds like a proportioning valve is blocked or clogged when you take the calipers off of that wheel does the piston go back in easy or is it stuck?

If its hard going in it might be a froze caliper and that might have created a leak somewhere but there is possible air trapped in that line somewhere.

When you bleed that wheel does the fluid come out nice and steady or just drip out?

 

Thanks for the reply. On both the driver rear and pass front, the fluid sort of drips out, like there is little or no pressure. Made me wonder about a blocked prop valve, but wouldn't the pedal have pressure if the line was blocked?

Haven't tried moving the caliper piston... Maybe we will look at that as well.

 

x's 2

 

Yes, the bleeding process was:

1 passenger rear : Good pressure, fluid was dark, but pushed through until it was almost clear.
2) driver front : Fairly good pressure, clear fluid
3) drive rear : As soon as the bleeder screw is opened the pedal went to the floor and never really got better. Used a vacum pump and after a lot of work, finally got 3-4 oz of fluid until it was fairly clear.
4) pass front : same story as driver rear.

Have worked with both of these now trying to bleed, went through 2X 12oz cans of fluid, but the pedal still goes back to the floor.

I think that I'll start the whole sequence from the start to see what we get.

Thanks.

 

did you ever come to a conclusion on the issue, this is the identical issue I'm having but on my 95 S model, did it end up being the proportioning valve or just air in your line?