Front Brake Pad Shims

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vwlover77
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Front Brake Pad Shims

Post by vwlover77 » Wed Oct 05, 2016 4:49 am

The front brake pads were starting to get thin so I replaced them with new Bosch QuietCast Premium pads ordered from Amazon (!).

https://www.boschautoparts.com/en/auto/ ... brake-pads

The pads came with a supposedly "high-tech" rubber-core shim glued on, but the shims do not have the anti-rotation tabs for the pistons stamped in them. So, I reassembled the brakes with the old shims with the tabs and the new pads with the integral shims.

Is having 2 shims per pad going to be a problem?

The brake pedal travel is a little longer right now, but I think this is due to the new pads seating in.
Don

---------------------------
78 Westy
71 Super Beetle Convertible Autostick

"When we let our compassion go, we let go of whatever claim we have to the divine." - Bruce Springsteen

71whitewesty
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Re: Front Brake Pad Shims

Post by 71whitewesty » Wed Oct 05, 2016 8:59 am

I don't have the answer but I just did the same thing last week. I'm curious what the experts say....

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asiab3
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Re: Front Brake Pad Shims

Post by asiab3 » Wed Oct 05, 2016 12:30 pm

From what I understand, there are two schools of thought on this:

1) When the pads have a slight "toe" to their landing on the rotor, noise/vibration is reduced.

2) Some pistons are not designed to rotate in the caliper. Seals harden and age with time, and certain makes/models don't age gracefully when the piston rotates. Stock ATE pistons have divots in them to index the shim and prevent rotation. Girling pistons allegedly don't have the indexing capabilities, but I've never had a set apart in my hands.

Both make sense to me, though I'm unsure on which reasoning the factory deemed more important. My old '76 howled under hard braking until I installed the shims. Let's try to get all four on our cars! :cheers:

Vanagons use the same shims, though I do not know if later models changed at all. Happy hunting!
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

71whitewesty
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Re: Front Brake Pad Shims

Post by 71whitewesty » Wed Oct 05, 2016 4:22 pm

It seems to me that by using the old indexed shims on top of the glued on shim the pads came with would just reduce the clearance a tiny bit. Didn't seem to matter on mine. They aren't dragging and make no squeals so far. I also put new rotors on at the same time. The new caliper pistons are indexed for the shim and so I decided to use the old shims on top.
I've only put 10 miles on it. I think I need to bleed it again.

kreemoweet
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Re: Front Brake Pad Shims

Post by kreemoweet » Wed Oct 05, 2016 7:52 pm

If you've ever tried to rotate an installed caliper piston, you will know that it takes a fair amount of force to do so. The dust boot and the
internal rubber seal are pretty darn tight on the piston. There is nothing acting on the piston in normal operation that would cause it to rotate.
There is no need for any device to prevent piston rotation. The ATE pistons are constructed such that they must be in a
certain position to act on the pads in the intended location, i.e., the trailing half. Therefore, the shims are designed so that the pistons
must be rotated into the correct angle to fit the nubs on the shim. The shims are more of an installation guide rather than something to prevent
piston rotation.

The Girling pistons are different, in that their contact face is flat. They are made to contact the pads on the trailing half by the simple
expedient of the shims having a big hole over the other side, so the pistons can not possibly contact that area. There is nothing whatever in
the Girling setup to prevent piston rotation.

Many have testified to running their ATE caliper brakes with no shims, with no apparent ill effect, or undue noise. That would be the expected
result, provided that the pistons were installed in the correct orientation. I'm not so sure that going shimless with the Girling calipers would
be equally satisfactory, given their different mode of operation.

Illlustration of Girling caliper parts:

Image

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Amskeptic
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Re: Front Brake Pad Shims

Post by Amskeptic » Sat Oct 08, 2016 7:39 am

vwlover77 wrote: Is having 2 shims per pad going to be a problem?
Nope.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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