brake caliper rebuild

[bigbore2]

84-1100         Got one of the pistons out with compressed air but how do I get the other one out?
Will I need to separate caliper into halfs for some reason?

[Mike 86 in San Dimas]

According to Clymers repair you do separate the caliper halves. Discard o rings, replace with new later. pad the piston with wood block or rags, blocking expose fluid holes. Use compressed air through hose joint and blow out the piston.

Mike

[SlowOldGuy]

Remove the seals from the half that the piston is out of.
Re-install the piston and use a tie-wrap to hold it in place.
Use air pressure to blow the other piston out.

If you split the caliper, be aware that Yamaha does NOT sell the o-ring.  Either reuse it or find a replacement.

DavidR.

[bigbore2]

OK, got the other piston out. Thanx fellas. I went thru the rebuild kit I bought from yamaha and your right, no seals for the halfs. Hopefully Randy has them.

[bigbore2]

Did not see them in Randy's parts.  Where do I get some seals? I do not want to take the chance of putting this back together only to get leakage later.  Do it once, do it right.

[racerrad8]

Did not see them in Randy's parts.  Where do I get some seals? I do not want to take the chance of putting this back together only to get leakage later.  Do it once, do it right.

No, I don't have them as they are serviced by Yamaha or an aftermarket source. I have recommended to several they take the body to a local NAPA auto parts store and get new Viton o-rings. They need to seal against the parallel surface of the caliper and not be too thick.

I also told them to leave a little room on the O.D. to allow for compression of the o-ring when the caliper halves are bolted together. One of these days I will pull a caliper apart a spec out the o-ring and put them on my site.

Randy - RPM

[bigbore2]

I have a good gasket/seal store here I can go to find anything I need.  And they don't have a minimum.  The brake caliper is built by Sumitomo- any chance on finding it with them?

[SlowOldGuy]

Also be aware Sumitomo switched from a round cross section o-ring to a square section o-ring at some point.  All the 2-piston calipers I've seen were round o-ring, but I know I've seen a square section o-ring in the later model calipers.

DavidR.

[bigbore2]

These in my 84 are square cross section. Looks like a piece of a small hose cut thin to fit in caliper cutout.  Local gasket/seal outlet said nothing available in that shape so I guess o-ring is the only way to go. An o-ring should work if sized correctly?
I measured the original seal and came up with OD .55,  ID. 32, width of .09 . I have a couple  -202 size o-rings to see if they will fit well enough. The 202 rings have enough room to expand on the OD, as they are visibly short on the OD.

Also the gasket store guy said Viton would be a poor choice of material because brake fluid would cause swelling of Viton and breakdown the Viton. He recommended EDPM for use with brake fluid. Randy, not trying to challenge your suggestion of Viton as i am like Schultze on Hogan's Heroes. "I know nothing" on this subject, just stating what I have been told. I have a couple of Viton rings from him and will put in brake fluid to see what happens to them.

I would think with all the caliper rebuilds members have done someone would chime in as to how they have done theirs.

[SlowOldGuy]

Every time I rebuilt a caliper by pulling them apart, I was careful with the o-rings and successfully reused them.  The monobloc (blue/gold dots) don't require this o-ring.  Think about changing to these calipers, it's a side benefit of upgrading the front wheel to a 17 inch. 

Highly recommended great mod for the early models!

DavidR.