Brakes are Hard

"Andy Sheehan, StreetsideStig" (AndySheehan-StreetsideStig)
05/12/2015 at 13:13 • Filed to: None

Well, they’re not really. Or they shouldn’t be, especially on something as simple as my ‘87 CRX. I recently replaced the master cylinder, the booster, and the pads up front. I did a master cylinder on my Tercel and it went smoothly. I even bought a little vise for bench bleeding.

But I had never done a booster and didn’t know they were adjustable. I drove home the night I replaced it and the brakes were smoking by the time I got there. The calipers were compressed just slightly the whole time and I didn’t realize it.

So I went back and adjusted the booster, and the rubbing was a bit better, but it’s still there. What am I missing? Maybe I didn’t bleed the system well enough? Could air in the lines cause this? Do I just need to drain some out of the lines? Did I put my the booster’s vacuum hose back on backwards?

Anybody run into this? Thanks!

DISCUSSION (12)

RamblinRover Luxury-Yacht > Andy Sheehan, StreetsideStig
05/12/2015 at 13:20

Rubbing when the vacuum line is on the booster only, or rubbing at all times (booster depresses master cylinder regardless)? Air in the lines can cause things to expand to odd positions if put under compression and released, but that’s not the first thing I’d think of. When you wonder about the direction of the vacuum hose, is that because it has a check valve? That would be easy to notice if wrong because you wouldn’t have assist. I think.

Mattbob > Andy Sheehan, StreetsideStig
05/12/2015 at 13:22

the interface between the output rod of the booster and the master cylinder is important. if the output rod is too long, it will always push on the master cylinder. There should be a tiny bit of gap between the output rod of the booster and the MC piston. When vacuum is applied from the engine, it will shift the rod out just a bit usually and take up some of this gap. Maybe put some ink on the output rod and put the MC on. If the ink transfers, it means that the output rod could be a bit too long. Where is the adjustment on the booster?

I’ll go ask a vacuum booster engineer. Because I work with a few.

Andy Sheehan, StreetsideStig > RamblinRover Luxury-Yacht
05/12/2015 at 13:27

Yeah, there’s a check valve. I didn’t think that would be the problem, because I definitely feel some assist.

I should have done some more testing, but I’ll disconnect the booster and see if it’s still happening. Perhaps the pedal isn’t pushing on the booster, but the booster is still pushing on the cylinder?

Or maybe I fouled the caliper piston seals because they were so far out with the old brake pads, and now they’re stuck?

Andy Sheehan, StreetsideStig > Mattbob
05/12/2015 at 13:31

Nice! I adjusted the input rod until there was a little play in the brake pedal so I knew it wasn’t always being compressed. I didn’t know the output rod could be adjusted, too. I’ll pull off the master cylinder and give it a try. Thanks!!!

Mattbob > Andy Sheehan, StreetsideStig
05/12/2015 at 13:34

just asked my source, It sounds like the output rod is too long. See if you can adjust it in a bit. A output rod that is too short will make the pedal a bit sloppy, ie, some dead travel before you get braking. A long one will get what you are experiencing.

Hopefully yours is adjustable.

Sethersm > Andy Sheehan, StreetsideStig
05/12/2015 at 13:39

Did the new booster come with any instructions? I seem to recall the one I replaced (may have even been on a CRX!) came with instructions about how to go about setting the rod length. If I remember correctly, I had to measure pedal free travel with the engine off and after having bled any remaining vacuum by pumping the pedal a few times.

If it didn’t come with any instructions, or you tossed them and they’re long gone, go back to the parts store and ask if you can peek in the box of another one for just a bit. Take a cell phone pic of the relevant parts of the instructions so you can reference them when doing the actual work.

Andy Sheehan, StreetsideStig > Mattbob
05/12/2015 at 13:42

Awesome! Thanks! And thank your coworker. I’ll take a look, probably tomorrow night, and let you know what I find out. Even if I can’t adjust it, I can probably space out the cylinder from the booster and make a gasket to fill the gap.

Andy Sheehan, StreetsideStig > Sethersm
05/12/2015 at 13:49

It came with a few instructions, but I don’t remember anything about rod adjustment. Of course, as a true member of the Idiots Guild, I promptly threw them away.

RustedSprinter > Andy Sheehan, StreetsideStig
05/12/2015 at 17:38

More pictures of the CRX?

Andy Sheehan, StreetsideStig > RustedSprinter
05/12/2015 at 21:07

I’m afraid it’s not very photogenic right now. Some of the plastic body panels were broken when I got it...and they’re still broken. But I’m going to get some of the mechanical issues fixed before I fix the aesthetic stuff.

Mattbob > Andy Sheehan, StreetsideStig
05/14/2015 at 13:16

hey, did you ever get it figured out?

Andy Sheehan, StreetsideStig > Mattbob
05/14/2015 at 13:37

I haven’t had a chance to look at it. It will probably be tomorrow night, when I, ironically, help a friend change his pads and rotors.