Topic: 1973 cb750 front caliper question

[galaxian]

 I took apart the caliper as part of the brake rebuild and noticed that the piston will not move easily. It was not leaking before was just sticking and not retracting. SHould the piston move somewhat freely or not so easily?

[rob]

Yeah, the piston should move easily, the piston most likely has corrosion on it.  Take the whole caliper apart, and clean it with the finest grade steel wool you can find.  Make sure to clean out the cylinder that the piston sits in, and to clean out the notch where the O-ring sits.  After that your brakes should be much better.  I think there is some more detailed info in the FAQ section under brakes on this forum.  Keep in mind that if the piston has too much corrosion, you may need a new one.

Also, this page has some info http://oldmanhonda.com/MC/Rbrakes.html

Rob

[Paul]

The pistons although should move freely. it is difficult to pull them out "freely" if they are all the way in without using a SMALL shot of air into the fluid inlet port. obviously as the pads wear the piston protrudes more. It is this section usually in as far as the seal that corrodes and in under the seal (white powder from the alluminium). If the piston is pushed in in this state chances are the seal is gone and makes it even harder to get out. If theres rust on the protruding part of the barrell and it needs to go back in with new pads.....bin it and also get a new seal anyway.

[Jonesy]

For cleaning out the piston bore and seal groove, a Dremel tool with a tiny wire wheel also works nicely.

[TwoTired]

Point of information.
Using steel abrasives against aluminum, leaves behind small bits of steel embedded in the aluminum.  When these two metals are bridged with water a small battery is created.  The result is galvanic corrosion.  Since brake fluid is hygroscopic (absorbs water), all the ingredients for corrosive degradation are present.

It is therefore recomended that abrasive cleaning of aluminum surfaces such as the caliper body, be done with non-steel abrasives, such as Silica based or Aluminum oxide papers, Scotchbrite pads, etc.

FYI

[galaxian]

Excellent info but...
How do I get the piston out now? I tried compressed air with not luck. My other choice is to assemble the master cyl and lines with the caliper and push it out with the fluid doing the work. I dont want to do this but will at this point. Also I cannot seem to find where to purchase the seal itself for the caliper. Can you point a noob in the right direction?

[Bob Wessner]

You should be able to get the seal through a Honda dealer, that's where I got mine. Another alternative to pumping the piston out via the brake system, or compressed air is to tighten the bleed screw on the caliper and lightly screw a small grease gun into the brake line hole and pump. It worked for me. I had no compressor and the rest of the break system was shot so that route was out also. You end up having to clean some grease out of the bore side of the caliper, but that's no big deal.

[galaxian]

Bob, that sounds like a great idea. Will try this tonight.
Many thanks for evryones help!!

[rob]

TwoTired, that is a great bit of advice, that never occured to me. 

Rob