The 510 Realm

Beyond frustrated at this point so any help would be greatly appreciated. Pulled into Dean Sherman's garage this morning to start working on some long overdue projects. One of the first things we started to take care of was upgrading my front brake pads from some cheap Centric pads to Porterfield RS4 pads along with installing speedbleeders all the way around. Back story is about 8 months ago I rebuilt my rear drums, installed a new 7/8 master and put 280zx front struts and brakes on the car. The 280zx brake setup was used but had fairly new slotted and cross drilled rotors (0.75 inches thick). I remember at that time having to struggle to put the caliper with pads onto the rotor. It was like the thickness of the pads made it very challenging to get the assembly onto the rotor. Dean and I struggled back then and finally got them on and everything worked fine for the past 8 months.

This time, we had the exact same problem! PITA to get the caliber assembly with pads (yes we pushed the piston back all the way) onto the rotor. Finally resorted to grinding down part of the bump on the back side of the pad that goes against the piston. That and a soft mallet got them on and once on they turned freely. So we go to bleed the brakes and once that happens the front brakes lock up and the rotors are very hard to turn by hand. Here is what we have tried and the results:
1. Removed speedbleeders and put stock ones on back on and no change.
2. By slightly unbolting the caliper and using the screwdriver to move it around the rotor frees up and stays that way until I push on the brakes and then they bind up again.
3. Back brakes are fine and not binding.

My main questions are why, in the first place, has it been so hard for us to even get the new pads onto the rotor in the first place?! Every other car you push the piston back, swap the pads in and the caliper easily slides back into place. Wondering if this has to do with the master cylinder? It was cheap through Rock Auto but still.....it was working fine when I pulled in the garage this morning. What are we missing? Anything else to try?

Thank so much in advance!

Pads material thicker than stock or the backing plate metal thicker, making it overall thicker.

Piston not clean or has anti rattle dressing on it.

After market rotor is slightly offset?

Clevis/push rod from pedal to master... Make sure there is some free play.

JordanTr wrote:Clevis/push rod from pedal to master... Make sure there is some free play.

This is exactly what I was thinking. If the piston rod does not return far enough to uncover the compensation port on the MC, then hydraulically the front brakes can not release. As Jordon mentions, make sure the rod running to the brake pedal comes back far enough.

Byron

Master cylinder push rod to long. I replaced my original ZX MC with a Troy Ermish 7/8 MC set up for 4-wheel disks and had to make a new shorter push rod. I doubt two set of pads were to thick especially the RS4's.

Yeah, but OP didn't change the push rod length during the pad service. Has worked for 8 months, and rear brakes don't lock. The push rod is the go-to solution for similar issues, but perhaps not this one. Definitely something to check, but...

OP, are pads difficult to install on both sides? Easier to think something got bent if only one side is an issue. Assuming both sides, perhaps the fancy discs have too much runout? At this point with the parts and car having gone through so many POs, there's no telling what combination of bits and bobs you are dealing with now. Perhaps a past caliper rebuild used the wrong seals and won't allow the piston to go all the way in the body?

None of which really addresses your lockup issue.

I'll check the push rod length but looked at it last night and I had free play and the front brakes were still binding. As was mentioned I didn't mess with it during the pad swap out so doubt that could be it.

Everything is equal on both sides. Tried another one of Dean's 280zx calibers and was having a similar issue of fitment. Rotors recently turned and within factory specs. After I left, Dean put in some old 1/2 worn pads and after having to pump 4 or 5 times to get pressure back the brakes work and also release when letting off the brakes. Have no idea why the Porterfields would cause this issue and many guys use them on the 280ZX calibers. Going to try to remove all the anti-squeal shims and see if that give us enough clearance.

Removing the shims might get you just enough. Good luck. Curious to see what the outcome is.

Just an FYI, I swapped in Porterfield pads along with new slotted rotors on ZX struts with no problems.

With the pads installed and too tight to turn by hand, loosen the bleeder. If fluid squirts out and the caliper releases then yes pressure is trapped and master is not returning probably due to a too long pushrod adjustment.

What was the 7/8 master out of??? Any chance the front disc and rear drum residual valve were swapped during a rebuild?

Mike brings up a good point relative to the F/R ports on the BMC. Another check is to see if there's any corrosion on the caliper slides or where the pads mount.

So...figured out the problem and it is a little embarrassing to post but that's how you learn. Dean snapped off the brake pad wear sensors with the understanding that I would be checking the brake wear as part of the regular maintenance schedule. Unfortunately, we didn't notice that part of the tab was left on the back of the pad causing the pads not to seat evenly. Lesson learned and the brakes are all good now.