W123 Brake issue

[Diescipel]

I did a search but nothing was specific enough.

78 240D

I have never had to diagnose brake problems--mostly just replace pads, bleed and flush etc. so I need some help so I don't run down the wrong path and spend $$$ unnecessarily.

The passenger front caliper on the 240D seized so I replaced it with a rebuilt caliper along with new pads in both calipers, rotors turned, flushed and bled system yada yada. Immediately I noticed the pedal feel was not as crisp as before. After driving it for a while (ie when the car warms up a little), the pedal will now go to the floor with little brake power.

I figured it was the booster loosing vacuum so I checked that. As far as I can tell there's no problem with the vacuum up to the booster, so I figured the booster was shot. Sound correct? is there a rebuilt kit or are there rebuilt boosters out there?

I seem to remember, though, that if your booster goes (ie vac leak) you should retain the same pedal travel but it will be much harder to push.

your thoughts appreciated.

B

[dieseldiehard]

I believe you have some air in the lines. What method did you use for bleeding the system? Start with the wheel farthest from the master cylinder, use a power bleed and it should feel the same after bleeding

[Motorhead]

More than likely you need a master cylinder. When a brake system is working normally, the master cylinder pistons and cups only travel a short distance in the bore. When you bleed the system, you work the master cylinder the full length of its bore. Any rust or build up in the master cyl bore now gets a shot at tearing up the piston rubber cups and causing the master cyl to fail.

[jwhughes3]

I agree is sounds like it hasn't been bled completely - but I do not agree with replacing one caliper at a time - I would replace the Master Cylinder and other caliper too and re-bleed with fresh fluid.

John

It does not sound like a bad booster. I would bleed the system again too make sure you have all the air out of the system. It's possible you have a problem with the master cylinder, but that would be quite a coincidence.

BTW, you really shouldn't turn W123 rotors, you should replace them in pairs.

[Diescipel]

I've bled the system twice to try to eliminate air as the problem. Yes, started with furthest caliper. No, don't have a power bleeder so I did the old pump and hold.

On the second bleed absolutely nothing but clean brake fluid came through.

Replacing both calipers seems excessive, as does replacing the master before I have a solid diagnosis. I'd rather not spend all the $$$ for a process of elimination as a substitute for a focused diagnosis.

If there were still air in the lines I believe it would feel spongy. Instead, as I said, once the car warms up/I drive it a ways the pedal goes through almost the whole length of its travel before I get any actual braking, and then it is difficult to brake. It reminds me a bit of what happens when I don't adjust rear drums on my landcruiser properly.

I'm wondering also if I got a bum caliper or something else happened when the old one seized.

Thanks,
B

Dumb question, are you sure you refilled the master cylinder tank enough to get fluid in both chambers? It needs to have fluid in both halves of the tank.