Fixitman's car.

4 hours ago, Matthew Abate said:

First, I can’t get the system completely empty of air. Every time I think I’m good, I come back the next morning and the pedal is soft (I usually do this at night so I don’t drive immediately after I finish). There are no leaks. I’ve been over the entire under side of the car and it’s completely dry, plus no drops on the ground and the reservoir levels are constant. I

4 hours ago, Matthew Abate said:

The second problem is that if I pump the brakes to get pedal pressure up, the brakes are still ineffective.

If the system ended up with some sort of vacuum (pressure differential) it might slowly suck in air through the tiniest of "leaks" that might not be large enough to show a fluid leak from internal pressure over the very short time you tested the brakes after bleeding.

You might check that the cap on your reservoir is properly vented. If the reservoir wasn't vented a vacuum might be created as things cooled down overnight.

It's a stretch.

And/or, another leak area is behind the caliper piston dust seals, at the piston seal itself.

When I bled them, I did it with the caps off, so I don’t think I have a problem with vacuum.

I just wiped around the calipers with a blue paper towel and I’m not seeing any residue. It’s pretty pristine.

This is why I’m so stumped. Other than maybe having a huge bubble that just won’t come out no matter how often I bleed it, I can’t think of how air is getting in without the reservoir levels going down or evidence of a leak somewhere.

It has to be air, though, right? Why else would the pedal get stiff and then soften after a minute?

This is a stretch mind you, Which way is the arrow pointing on the booster check valve. I believe it needs to be pointed to the intake manifold. I had a similar problem in the past. I realize it’s a Strech.

2 hours ago, Yarb said:

This is a stretch mind you, Which way is the arrow pointing on the booster check valve. I believe it needs to be pointed to the intake manifold. I had a similar problem in the past. I realize it’s a Strech.

No totally. That’s why I posted. I can’t think of anything I missed and that’s the kind of stuff people forget.

The arrow is pointed away from the booster and toward the manifold.

That’s the correct positioning.

Did you replace any of the steel brake lines on the car during the build. The reason I ask is I had a similar problem, Hooked it up to a vacuum bleeder machine and we found a couple at “T” locations at the front and rear that appeared to be tight.

The entire system was either brand new or rebuilt. One thing I was thinking is the junction above the differential might have a bubble that won’t come down. That’s the only real high spot I can think of, though.

6 hours ago, Matthew Abate said:

When I bled them, I did it with the caps off, so I don’t think I have a problem with vacuum.

I wasn't talking about leaking during the bleeding but at night as thngs cool down after working on them and driving. As the fluid and air above the fluid cools a vacuum might be created. Air will pass through a tiny gap much easier than brake fluid.

I've never heard of it happening. Just coming up with ways to pull in air overnight.

11 hours ago, Matthew Abate said:

Every time I bled it I got some air,

Which end gets the air? Might be a clue. And is it both sides of one end, front or back, or just one corner?

7 hours ago, Zed Head said:

Which end gets the air? Might be a clue. And is it both sides of one end, front or back, or just one corner?

Tough to remember because I've done it so many times now, but i think the last bleed i got some air at all of the calipers except the front left. But it wasn’t a huge amount. Every time it seemed like things were good to go, then the next morning it was back to where it was.

I think you MUST have a leak somewhere.. as without that there can not come any air in a system that has a hard pedal after bleed.. Did you test it at the end by staying on the brake hard and feld no lowering of the pedal? If there is the smallest leak it should go down very slow..

Also i trust you started the bleeding with the rear left then the rear right and final the front brakes (does not matter witch first) Use a liter, say a pint of brakeoil and pump it through the lines so your sure there is only oil in the lines (1 pint for the whole car offcourse.)

Do you use the brake pedal or do you use a vacuumpump at the claws to get the air out and oil in?

At NO point of filling was the brake master cylinder empty i trust.

2 hours ago, Matthew Abate said:

but i think the last bleed i got some air at all of the calipers except the front left. But it wasn’t a huge amount

And is the front left the caliper that is fed by the line on the front of the mastercylinder?

That would suggest that there is a fault in the mastercylinder .. maybe a rubber cup was installed in the wrong direction in the cylinder near the rear and other (R) front lines on the cylinder? (But on the other hand.. would it work well if that was the case also only a small amount of time?)