Brake caliper issues

[Phil73]

For a long time not my TR6 has had 2 issues that I recently found to be related. One was a problem where under heavy braking the car would pull noticeably to the right. The second is a clatter on rough roads somewhere up in the front-end. About a month ago I discovered that the outboard brake pad on the left (driver's) side of the car was pretty much just clattering around in the caliper. I pushed both pistons all the way back into the caliper and pumped the brakes to find that both pistons move but the outboard piston simply didn't come out far enough to put the pad in strong contact with the rotor.

It had been over 15 years since I rebuilt the calipers so I decided now was as good of a time as any. I pulled both calipers, disassembled them, cleaned them, painted them and reassembled with new seals and brand new pistons all around. Bled the system and took the car for a spin yesterday.

No difference what so ever. If anything the pulling to the right is worse, the pad is still loose in the caliper and now the brake pedal is kind of soft.

The flexible rubber lines are new last spring and now both calipers are freshly rebuilt. Not sure what to try next.

Ideas?

 

[DrEntropy]

How did the left outer piston look when you had it out? Is there a possibility the pad in question is hanging up on some part of the caliper?

Very odd, indeed, that you don't have equal pressure on both sides of that caliper. With the caliper unbolted and a STOUT C-clamp holding the inboard pot fully back can you have an assistant s l o w l y depress the pedal to observe whether the outside pot travels out all the way (stopping the pressure before it completely comes out of the bore, of course)?

 

[Phil73]

Actually, all 4 pistons looked decent but not perfect. They all had some pitting around the top edges so I replaced them anyway.

This issue really boggles my brain. I even replaced the retaining pins out of fear that one of them was letting the pad hang up.

I'll get an assistant out there today to help me diagnose the problem and see where that leads.

 

[Phil73]

OK, put the car up and tried a number of tests, unfortunately nothing that leads to an answer.

I took out the pads and had an assistant slowly depress the brake pedal. Both pistons move out of the cylinder at an even pace. Definitely not a stuck piston.

When my assistant let up on the pedal the outer piston withdrew very slightly, the inner one didn't. That's interesting.

With the pads back in place my assistant hit the brakes and I watched the action on the driver's front brake. Both pads came in strong contact with the rotor. Couldn't tell how much pressure but both are very definitely moving.

That makes me think there's a pressure differential somewhere else. Since the rubber hoses are new I wonder about the brake lines themselves. I could pull all the lines on the front, inspect and clean them and then reassemble. Not what I'd call a good time but I'm out of ideas.

 

[DrEntropy]

Rather than remove them completely, disconnect each end and flush with denatured alcohol and compressed air?

...and I'd not rule out a flex-line issue just because its "new" either. Tho if you saw one puck retreat slightly that'd be a long shot.

 

[tdskip]

Weird - if you've ruled out the calipers it has to be the lines, no?