What caused inboard front disc brake pad to score the rotor?

[Bill Crowell]

Chrysler large single piston front calipers.

I'm trying to figure out why the inboard pad kicked its shim halfway out from behind the pad (until the shim hit something and could go no further) and scored the inside face of the rotor.

Did the shim let go first and cause the pad to do weird things? Or did the piston fail to retract correctly and make the shim jump out of place?

How exactly would you check to see if the piston is retracting correctly on single-piston calipers?

Thanks very much, everyone!

 

[rumblefish360]

I’d say a bad glue job for a lack of better words allowed the steel backing shim/plate on the pad to let go.

A rock or small metal shard was the most likely item that made the 1 in a million jump off the road and became stuck between the brake pad and the disc.

The caliper should be easy to compress with a C clamp. The amount it retracts while working on a driving car is a very small amount. Feeler gauge amount. Not a 1/8th or 1/16th of an inch but smaller. Mostly a pressure relieving.

I’d say that a helper would depress the brake pedal and physically show you that it’s clamping the disc. Try and shake it. Then release the brake pedal and you should see the caliper physically relax but no major pad retraction happens. You should be able to move the caliper.

 

[Dana67Dart]

I'm trying to figure out why the inboard pad kicked its shim halfway out from behind the pad (until the shim hit something and could go no further) and scored the inside face of the rotor

Are you saying the shim that should be between the piston and the pad got to a place where it could touch the rotor.?

That's a lot of movement.

I agree that the shim ( anti squeek device) lost it's grip over time, and probably walked with every pedal application a tiny amount till it got to the sweet spot and was grabbed by the rotor and folded.

It's also possible that the anti squeek wasmis aligned during installation.

Post some photos.

 

[missing linc]

I've seen an inboard pad kicked before due to the rotor being undersized, but never a shim or anti rattle clip.

 

[cudamark]

I'm having a hard time visualizing how the squeak shim made it all the way to the rotor. Did you put the pad in backwards? Photos please.

 

[Bill Crowell]

I'm having a hard time visualizing how the squeak shim made it all the way to the rotor. Did you put the pad in backwards? Photos please.

OK, guys, and let me thank you kindly for your helpful replies.

The shim between the pad and brake piston came loose, its attaching tabs got all bent up, and it rotated until the front edge of the shim hit the rim and started rubbing on it. Here's a picture. I then discovered that the inboard side of the rotor was totally scored up.

So is it important to glue the shim securely to the back of the pad with Brake Quiet glue? If the shim comes loose while I'm installing the pad, do I need to re-glue it?

 

[Bill Crowell]

So is it important to glue the shim securely to the back of the pad with Brake Quiet glue?

While I was installing one of the inboard pads, the Brake Quiet let go and the shim came loose. Do I need to remove the pad, re-glue it and let the glue dry before proceeding?

 

[Dave999]

OK when you say shim are you talking literally about a very thin pice of spring steel
or the metal brake pad backing?

that looks like the brake pad backing has come off the pad..

brake pads have a backing with keyed ears that fit into the groove either side of the flaoting caliper or if its a KH i think they have pins through...so am assuming this is the claw bracket floating 1 pot caliper that takes pads like these Fits Dodge / Mopar 1973-83 Various Models New Brake Pads Raybestos D123 D86 D269 | eBay

in which case 1 pad has a Z shaped spring to keep it in place and 1 as you can see has little ears on it
the hole lot is held togther by 2 plates that press the cliper and its pads into the bracket
suspect either detached pad from steel backing or you have something missing

 

[Tooljunkie]

That looks like outboard anti-squeal pad. The brake pad tabs were loose, allowing pad to shift around. All this anti-squeal stuff can be more trouble than its worth. And in some cases, not very effective

 

[cudamark]

So is it important to glue the shim securely to the back of the pad with Brake Quiet glue?

While I was installing one of the inboard pads, the Brake Quiet let go and the shim came loose. Do I need to remove the pad, re-glue it and let the glue dry before proceeding?

Sure, give it a try.....why not? Frankly, I've never had one come loose. Many pad sets don't even use one. On those, I just use the Disc Brake Quiet glue.

 

[Bill Crowell]

Newbie take-aways from installing new pads in big Chrysler single-piston front calipers:

Rockauto is quite a bit cheaper than O'Reilly or Autozone, even after shipping, and the parts arrived in one or two days, thereby saving a trip across town to the parts store.

You need to bend the tabs on the outboard pads so they fit on the caliper nice and tight; tight enough that you've got to use a C-clamp to get it on. You'll probably have to hit the tab with a hammer to bend it.

Put just the slightest bit of high-temperature brake lube on the ways, where the tabs on the pads move.

Renew the anti-rattle hardware. I thought my old hardware was OK until I compared it to new hardware. My old stuff was all bent up, and I didn't realize it.

You're going to have to buy a pad-spreader tool to make the piston retract enough to get the new pads over the caliper. Those tools are not cheap! Why do they charge so much? Because they CAN! (I know you can move the piston in with a C-clamp, but that is too redneck for me!)

Install those rubber band O-rings on the adapter ways! They come in the brake hardware kit. I really like what they do for firming up the caliper movement.

After you install the new pads, hit the brake pedal several times before you drive away! You gotta get those pistons back out there where they belong before you're going to get any pedal.