Ready to give up- front brakes won't bleed, pedal goes to floor

AZDrifter

AZDrifter

True Classic
Hi, sorry I haven't been on the forums in a long time. I am trying to prepare my 1980 X for sale, and I started having a brake problem. Based on research, I figured it was the master cylinder giving up. I tried replacing it, but couldn't get the front brakes to bleed either with forced air into the reservoir cap, suction at the nipple, or pushing the pedal.

I called Matt at M-B and he said try removing the plunger from the cylinder. Sure enough, the fluid started to flow. I got the car back together and went for a test drive. The pedal was still soft. I tried bleeding again and got some air out of the back lines. Went to try the fronts, and again they won't move fluid at all. Any ideas?

I'm ready to throw in the towel. Three months with the car on blocks and no better off than when I started. I'm in Arizona if anyone wants a car with a strong motor and race suspension. The body has lots of dents but otherwise the car is fine.
 
AZDrifter said:
Hi, sorry I haven't been on the forums in a long time. I am trying to prepare my 1980 X for sale, and I started having a brake problem. Based on research, I figured it was the master cylinder giving up. I tried replacing it, but couldn't get the front brakes to bleed either with forced air into the reservoir cap, suction at the nipple, or pushing the pedal.

I called Matt at M-B and he said try removing the plunger from the cylinder. Sure enough, the fluid started to flow. I got the car back together and went for a test drive. The pedal was still soft. I tried bleeding again and got some air out of the back lines. Went to try the fronts, and again they won't move fluid at all. Any ideas?

I'm ready to throw in the towel. Three months with the car on blocks and no better off than when I started. I'm in Arizona if anyone wants a car with a strong motor and race suspension. The body has lots of dents but otherwise the car is fine.
Click to expand...

Check that the flexible lines from the reservoir to the master cylinder aren't kinked anywhere.
 
Sounds like it might be the classic "internally collapsed rubber hoses". If you crack the junction between the hard line and the rubber hose, do you get flow?

Pete
 
AZDrifter said:
Hi, sorry I haven't been on the forums in a long time. I am trying to prepare my 1980 X for sale, and I started having a brake problem. Based on research, I figured it was the master cylinder giving up. I tried replacing it, but couldn't get the front brakes to bleed either with forced air into the reservoir cap, suction at the nipple, or pushing the pedal.

I called Matt at M-B and he said try removing the plunger from the cylinder. Sure enough, the fluid started to flow. I got the car back together and went for a test drive. The pedal was still soft. I tried bleeding again and got some air out of the back lines. Went to try the fronts, and again they won't move fluid at all. Any ideas?

I'm ready to throw in the towel. Three months with the car on blocks and no better off than when I started. I'm in Arizona if anyone wants a car with a strong motor and race suspension. The body has lots of dents but otherwise the car is fine.
Click to expand...

So Matt suggests pulling the plunger on the MC. This suggests it is riding forward and closing off the inlet of fluid into the MC. Is the pedal mechanism driving the plunger slightly forward? The opening inside the MC for fluid to go into the pumping chamber is very small. The sealing cups close off the opening as the piston moves forward when you press on the pedal.

I would look carefully at the length of the plunger, the static “up” position of the pedal (is the brake light switch preventing the full return of the pedal to ‘up’?), the static position of the MC (was it installed slightly moved back?) causing it to be back against the plunger? Believe it or not a 16th of an inch could close off the opening into the MC chamber preventing the ingress of additional fluid.
 
It could be something to do with the plunger. I just replaced all the soft lines. I will check for a kink though. Thanks.
 
Well I removed the brake sensor to allow the plunger to fully release, and still no dice. Maybe a hose got kinked above the pedals or something
 
I had ran into this problem many years ago when I actually worked on fiats commercially. the master cylinder did not return. therefor i could not "pump up" the system. feel the pedal and make sure you are making contact with the plunger, by hand you can feel if the pedal is actually moving the plunger inside the master. you can feel if the rod is hitting the internal plunger of if it just feels like nothing is happening. it is a light feeling but you will understand when you try.
 
Another odd thought, we've heard of new replacement masters being bad from the beginning. But the previous suggestions seem more likely.
 
If you disconnect the rubber hose from a front caliper and push the brake pedal, do you get fluid coming out the hose?
I would start working backwards from the front calipers to see what's happening.
 
I escalated to having a friend pump the pedal for me while vacuum bleeding; I have a pressure bleeder I didn't need to use in this case.
Following Hussein's suggestion, I had my reservoir up on the windshield wiper for the process. And I had to repeat one wheel because I let the reservoir run dry.
Keep at it, mine took longer than I expected.
 
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