Front Brakes Don't Work - Need Help!

[Dens240]

This is the tail end of a 4 year restoration. Nearly everything else is finished. It's ready to go...I just need to be able to stop once it goes. So, this isn't a random issue that cropped up. There is something not right with the brake reassembly.

I should have a new hose today then will get it on the car in the next day or so.

[Captain Obvious]

Cool. Hope it's as simple as a collapsed hose.

And if it is... I'd replace all four of them, not just the one corner.

[SteveJ]

12 hours ago, Captain Obvious said:

Yeah, I'd really take a real good look at that flexible hose. I don't remember if I've ever seen it specifically on a Z, but I've seen several cars where those flexible lines had closed down inside and restricted flow.

I had a slave cylinder hose get blocked up, but that was from years of brake fluid sitting in it.

[Dens240]

Latest...I changed the flexible hose - no change.

Disconnected all lines between the warning switch and the left caliper and confirmed I can blow through them without any issue

Removed the caliper and set it up to try to blow through from the inlet to the bleeder valve. It was difficult so I set up a vacuum on the bleeder to see if I could do better. Nothing. So, I put on a different caliper (yes - I have quite a number of parts on the bench as I'm trying to chase down this issue. I mounted the different caliper, hooked it up, and...no improvement.

I'm about out of ideas on this. I've changed everything between the MC and the caliper including a replacement pressure switch that I got from @zKars.

Again...I get good brake engagement at the right caliper but not the left. This has be sufficiently perplexed that I may look for an actual professional to diagnose the issue!

[Patcon]

If the lines from the switch to the caliper are good on both sides, then move upstream. I would suspect the switch next

[SteveJ]

If it gets to working on the switch, this thread may help: 

 

 

[Zed Head]

58 minutes ago, Dens240 said:

Removed the caliper and set it up to try to blow through from the inlet to the bleeder valve. It was difficult so I set up a vacuum on the bleeder to see if I could do better. Nothing.

You didn't describe the same action on the right side.  Since you have a symmetric system you're in a good place to compare one side to the other.  Might be that the piston will retract in to the bore far enough to block passage from the inlet to the bleed screw.

With two sides that should be equal you can compare identical actions until you find the one that's different.

[Dens240]

The right side is now working. I had a small leak at the inlet to the pressure warning switch for the front brakes. Once I replaced that inlet line and no longer had the leak, the right brake started working fine (after bleeding). I still don't get the same performance on the left.

Are you saying that it's possible for one or both pistons in the caliper to be retract too far and block the fluid path? This doesn't seem possible and would be a pretty poor design. But...I could put air pressure on the caliper inlet and see if I can get the pistons to move some, then try the whole thing again. 

[Zed Head]

I'm just saying try the same things on both sides.  You have one side that works and one side that doesn't.  See if you can blow air through the inlet to the bleed screw on the right like you tried to do on the left.

And yes, I am saying that the piston might be able to press far enough in to block the holes.  The calipers are designed for a known thickness of pad and rotor.  So, whatever works on the right, match it exactly on the left.  And, vice-versa.

Edited November 16, 2021 by Zed Head

[Zed Head]

I'm not saying that blocking the holes is your problem.  I'm just focused on your testing methods.  You haven't isolated the source of the problem to a smaller area.  Everything after, and including, the switch is still in play.

[Captain Obvious]

On 11/15/2021 at 8:36 PM, Dens240 said:

Disconnected all lines between the warning switch and the left caliper and confirmed I can blow through them without any issue

When you ran that test, where did you break into the line out at the wheel? Did the section of lines you were able to blow through include the small "S" bent hardline on the back of the caliper? Or did you split it where the flexible line meets the "S" bend metal line?

Kinda running out of ideas here...   

[Dens240]

I removed the bent s line as well - disconnected at the caliper. I’m going to take a couple days off from putting hands on the hardware and possibly start over from the MC in a few days and work my way back out to the wheel…unless I get a good suggestion from someone.