20-degree calliper angle/squealing brakes

[K-Jetronic]

Hi there,

...doing some maintenance on my car this week (the rainseason has started here in Holland it seems) and thought about looking into the squealing I have coming from my brakes. Did the normal routine on the brakes but keep reading here about a 20-degree angle of the calliper/piston?I have done a search but I am not sure I understand. Can one of you explain to me what I have to do to check/correct this? And is this difficult or can it be done on the car? Thanks in advance!!

Gerko
1978sc

[Superman]

I'm sure there is an explanation, like in Bentley for example. I used a piece of a cereal box, cut at 20 degrees, as a guide. You'll have to unbolt your calipers. Or, well, I guess you might be able to do this just by removing the pads.

[Rot 911]

Here is an excellent tech article:
And an excerpt: 911 Caliper Rebuild

Reassemble the caliper. Begin by lightly coating the caliper bore, piston, and rubber piston seal with silicone assembly lube (such as Sil-Glide, available from NAPA auto parts stores). Don’t coat the dust seal. If you can’t get silicone lube, coat the parts with clean brake fluid. (Figure 13)

Insert the piston seal into the groove in the caliper bore, and insert the piston. It should slide in a short distance without too much effort. Don’t force the piston, and be careful not to get it cocked in the bore. Orient the piston at a 20-degree angle from the top of the brake pad slot in the caliper. This angle is important to keep the brakes from squealing. Use a template, which you can make from thin sheet metal or even cardboard. The template is just a triangle about 4 ½ inches long with a 20-degree hypotenuse. (Figure 14 and in the drawing below)

After you are sure the piston is going in straight, and is at the correct angle, push it the rest of the way in with a piece of wood. If you get the angle wrong, blow the piston back out, and start again. Check the angle of the piston at least twice before going further. It is frustrating to get a caliper mounted on the car, and then see that the angle of one of the pistons is wrong. Here is the factory manual diagram of how to check the piston angle.



After making sure the piston angle is correct, install the rubber dust boot and retaining ring. The front caliper pistons should be pushed all the way in before installing the dust boots. On the rear calipers, leave the pistons sticking out about ¼ inch to make installing the dust boots easier (the boot fits like a turtleneck sweater on the rear pistons). The dust boots should be clean and dry on the outside after you finish installation. Repeat the installation process for the second piston.

Remount the calipers on the car. Check the piston angle one more time. (Figure 15) Torque the caliper mounting bolts to 70 ft/lbs.

[AirCooledExcellence]

Hi Gerko,

Are you sure they aren't just gummed up with brake dust?

After I did a track day in my car the pads/rotors were lined with dust causing the brakes to squeal terribly. Took the pads out scrubbed them down with wire wool, followed by a good squirt of brake cleaner all over the pads/rotors/calipers. Squealing has gone!

If that doesn't work, take a look at this diagram:



I would say this is something you can check with the brakes still on the car.

Good luck!

Cheers,

Tim.

[AirCooledExcellence]

dammit Kurt, your too quick for me!

[Neilk]

Check out this thread to make your own 20 degree angle tool.

[Jesset100]

Note the direction that the rotors turn also. Don't ask!

[juanbenae]

aircooledexcellence you new avatar is making me dizzy.

[Parkin Hunter]

An easy way to do it is to us an adjustable carpenter's bevel. You can set the bevel on the basis of the existing set in your calipers. You will be putting the handle of the bevel across the caliper oppening.