Caliper Rebuild advice - 20 degree clarification

[thulsadoom]

Ok - first off, I have never rebuilt a caliper nor seen one in real-life up close. However, I am reasonably mechanical and I have taken it upon myself to (possibly) rebuild a pair.

Having read all the articles I could find, one thing still confusing is the 20 degree issue mentioned the tech article.

Originally I did not know about the notches in the piston face. I think I figured it out from these notches that I noticed in a pair of beautifully clear calipers (still for sale on the boards right now), but I am going to post pictures any how.



Here is my original confusion


Any caliper rebuild advice appreciated.

[Wil Ferch]

Simplest answer...based on the pic above...is that the "long edge" of the tool rests against the surface shown under the word "degree"

- Wil

[thulsadoom]

Pistons are hollow cylinders that push on the pads, they have a cut out or notch, about 120 degrees ish (thats a guess) [in arc length], which does NOT contact the pad. These stop squeal and aid cooling (another guess). The pistons are inserted into the caliper as mirror images, the notch kind of faces up, towards the direction of on coming rotor rotation. The notch edge towards the hub is sort of central in the caliper, the notch edge towards the inside of the wheel is therefore more rotated up towards the top of the caliper- just a little- 20 degrees ish. The template just sets the piston in this position.

[It seem the alignment of the notch is arbitrary and controlled only by the person who sets the pistons in the caliper.. which is probably why the tech article says template is *about* 4 1/2 inches long. Exactitude is not 100% necessary? I imagine if the notch is not aligned, perhaps air will not circulate properly and cause squealing]

[Bill Verburg]

Just keep in mind that the reason for the notch and 20&deg orientation is to get the edge of the notch perpendicular to the rotation of the rotor, it allows an escape path for the hot gases that build there and tend to lift the pad from the rotor, the escape path is radial toward the axle and away from it

[thulsadoom]

Its all becoming clear to me now...

[Hendog]

Yes, this little detail had me scratching my head when I rebuilt my calipers as well, but once you get it, it's like a light goes on BTW I admire your annotaded diagrams

[Dixie]

You're over analyzing.... Just make a simple 20 degree wedge that looks like a slice of pizza. You can make it using cardboard and a grade-school protractor. Make it big enough so you can slide it around some.

Two key points to keep in mind:
1) The "mouth" on the piston faces into the turning rotor.
2) I doubt being too exact is really important. After one track-weekend the pistons in my calipers had rotated every which way.

[Zeke]

Just to clarify Bill's post (and others), the 20 degrees puts the leading edge of the pad perpendicular to the rotor at that point. The piston itself is over-rotated as it would appear in the diagram. There should be a silhouette of the pad in the caliper to show this.

[der Mond]

Would installing new pads with dry backing plates against the pistons help prevent piston rotation? I'm trying to decide if I'm supposed to put my new pads in with Lubriplate smeared on the back, or dry.

[der Mond]

By the way, it's simpler than you think to use a home-made "guage". Here's one I made with mailing envelope paper, and if the piston is right, there's only one way the wedge will fit. The length or width of any "handle" is irrelevant.

[thulsadoom]

That's flippin beautiful. No more need be said.