Sticking Brake Calipers

[Jaymanbikes]

Not ignoring you Dave WM.  He only talked about replacing the MC so the assumption, maybe wrong, is that he didn't mess with the inside stuff.
Another reason that I might use a shim is that several people have had problems adjusting the adjustment on the booster rod.  It tends to get stuck.  Sometimes really bad.
Fender shims might be about perfect.  You could loosen the nuts, let the MC push out to where you can just feel it touching the booster rod, then slip the fender shims over the studs and clamp it back down.  You can get a whole box of various thicknesses at Harbor Freight, and thye're u-shaped so that you can slip them without complete disassembly.  A little bead of sealant across the top and sides to keep water out and you're done.
Big picture, if it works but you still don't like the shims you can take it apart and do it "right".  At least you'll know what the problem is.

Great idea, thanks for the suggestion!


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[Dave WM]

Sometimes I just read a part of the problem and get lost in the details, default mode to what I had problems with when exp the same symptoms, my bad. Agree with above analysis of a bad booster setup.

[Jaymanbikes]

Here's an update.  I went ahead and pulled the master, as mentioned, it is for a ZX and I compared the depth of the piston to the stock master.  According to my very rough caliper measurements, the stock master piston is substantially closer to the push rod than the ZX unit, I had thought it would be the other way around.  I then decided to reinstall the stock one.  The end result is the brakes work great!  I had originally purchased the new ZX master because it was recommended with the Toyota brakes, the stock one works just fine.  Thanks to all that chimed in on this!

[Patcon]

The stock master will work but the piston bore is smaller, so you will have more pedal travel to move enough fluid for the larger volume front calipers. The ZX has a bigger bore so pedal travel is less to supply sufficient fluid. I suspect you have an adjustment problem. I would try to get the ZX master in and working at some point...

[Jaymanbikes]

41 minutes ago, Patcon said:

The stock master will work but the piston bore is smaller, so you will have more pedal travel to move enough fluid for the larger volume front calipers. The ZX has a bigger bore so pedal travel is less to supply sufficient fluid. I suspect you have an adjustment problem. I would try to get the ZX master in and working at some point...

Visually they look almost identical.  I'm thinking there is something wrong possibly with the new ZX master, I'm going to return it and get another.  Someday when I don't have anything else to do I will try and reinstall.  I'm pretty happy with how the car is braking at this point. 

[Patcon]

Sometimes they have a bore size cast on the side. I believe the stock is 7/8" bore and the ZX is 15/16" bore. Doesn't seem like much but the cross section is 15% larger

[Patcon]

Glad you got it figured out...

[beermanpete]

One possible cause not already mentioned is a check valve in the master cylinder output port that is holding pressure in the line. Take the adapter fittings out of the ZX master (where the brake lines attach) and look for check valves.

[Jaymanbikes]

18 minutes ago, beermanpete said:

One possible cause not already mentioned is a check valve in the master cylinder output port that is holding pressure in the line. Take the adapter fittings out of the ZX master (where the brake lines attach) and look for check valves.

I got another master installed it, shimmed it out, still same issue as the first go round, system is holding pressure. Here is what I have under the adaptor in the ZX master. 

[Zed Head]

That's weird.  You're right, the ZX MC should need more push rod, not less.  So your problem is backward.  

You can test if the return port is blocked just by blowing back through the return line.  Kind of messy but might show something.  You can see how the seal closes off the reservoir return as soon as the piston moves.

 

[Zed Head]

Maybe your original MC is not the stock 77 MC.  Take a picture of the original M, that works, and post it.

[Jaymanbikes]

12 hours ago, Zed Head said:

Maybe your original MC is not the stock 77 MC.  Take a picture of the original M, that works, and post it.

Well, I reassembled it with the working master and didn't think to take a pic before I did so.  I have a car event to attend Saturday so wanted it up and going.  The one that I am referring to as stock was replaced by me when I got the car a year ago.  It does say 7/8 on the body.  I also replaced the booster at the time.  I didn't adjust the push rod at the time and I guess I just lucked out that it was in the correct position.