Solution to chattering, clunking, rattling of front Pagid brake pads

[ChrisH]

I have Pagid blue brake pads. I like the performance, but I would get clunking, chattering, rattling, buzzing sounds, and wanted it gone. It could get pretty loud sometimes (sounded nasty), and would immediately go away even with light brake pressure. This behavior in brake pads is well known when the pad’s backing plate is slightly too small for the calipers in the dimension between the edges of the backing plate that are forced against the inside of the calipers when you brake (not the piston side, but the ends). This is illustrated in the first attached picture. Many brake pad sets come with clip on shims to fill this gap and stop the clunking, chattering and rattling, but I couldn’t find any such shims for the Pagids. Also, they were small enough that the anti-rattle spring on the caliper couldn’t keep the pads forced to the top of the caliper, thus allowing the rattle. It has been noted before at this forum that the Pagid blue front pad material was slightly smaller than stock. What had not been noticed was that the backing plate was also smaller in the most key dimension.

Here are some measurements:
Stock front pad backing height: 3.042 inches = 77.25 mm
Pagid front pad backing plate height: 3.008 inches = 76.41 mm
Difference: -0.84 mm (Pagid backing plate smaller than stock)

Installed gap from force bearing surface to caliper with Pagids: 1.18 mm
(anti-rattle spring removed for measurement. Measured with feeler gauges.)

The clunking occurred at low speeds, and appeared to be due to the pad being pushed to the top of the caliper at one point in the rotation of the wheel, then, at another point in the rotation where there was less friction between the pad and the rotor (maybe due to some slight run-out in the rotor), the pad would fall back to the bottom of the caliper (or at least as low as the anti-rattle spring would allow). This was the initial symptom.

Eventually, the pads started rattling, chattering and buzzing sounds, still generally at low speeds. It was sometimes quite loud, and embarrassing when driving in crowded parking lots. I was concerned that it might also cause wear on the load bearing surfaces of the caliper. I did try bending the anti-rattle springs a bit to put more pressure on the pads, but that didn't solve the problem.

So, I wanted a shim on the upper force bearing surface that was on the order of 0.84 to 1 mm thick. (0.84 would give me a remaining gap the same as the stock pads.) I also needed a way for the shim to reliably stay in place. I finally decided on making a simple angled backing plate that would look like the back of the pads themselves, with holes for the pad retainer pins. This is shown in the second attached figure. I used some galvanized mending plates (used to join boards – the holes are for nails) that I had in my garage, which is 0.92 mm steel (I think the steel was cold rolled). I used the pads themselves to lay out the shape and the angled piece dimensions. I cut it mostly with tin snips, and with some help with a Dremel tool with a cut-off wheel for the part between the retainer holes. I cut back the material in the area of the retainer holes to make sure that the anti-rattle spring would push against the pad backing plate, not the shim. I drilled the retainer pin holes slightly larger than the pad’s holes. I made the bend using a vice and a hammer, and tried to flatten the piece as well as I could with the hammer.

The view as mounted in the caliper is shown in the third attached picture. Note that I made the shim to fill in the gap on the upper edge (as mounted in the caliper). This helps to force the pad back against the anti-rattle spring so that the spring works better.

I have had them on the car for about two weeks now. All the clunking, chattering and rattling sounds are gone. I did have an issue initially that the brakes were a bit spongy on initial braking after a time gap. I think this was due to the shims not being completely flat, and thus pushing back against the brake piston a bit when the brakes were off. So, I went through an exercise like the normal brake padding bedding procedure, where you get up to about 60 mph and then brake hard, doing that repeatedly. The brakes get pretty hot, which softens up the shim material. I figured that after doing that a while, the steel shim would flatten out due to the force of the piston while the material was hot. And, it worked! There is no spongyness anymore, and the brake feel is as good as ever.

My only residual concern is that the shims may not fit when the pads are new. My pads have been on my car for about a year when I put on these shims, so there was room between the piston and the back of the pad for the shim plate. It would be nice to have a solution which was just on the upper force bearing edge of the pad.

Now, if only the sellers of the Pagid Blue pads would provide shims with them for the Elise.

[luxige]

OK, I'm impressed!

[ChrisH]

I had considered numerous other ideas for attaching shims. I originally preferred they just be on the upper edge, or a small angle piece that didn't overlap the piston on the back. I considered attaching them with a high temperature glue (like JB Weld), spot welding (but I don't have a welder), short flat head screws attached to the backing plate, and cutting notches in the pad backing plate and cutting and bending tabs on the shims to fit into the notches. In the end, I decided the method I used was the easiest to implement, most secure, easiest to reverse, and non-destructive to the pad itself. And, since I wasn't completely positive the shim would fix the problem, the method I used seemed to make the most sense for the first attempt.

[apk919]

Nice work! I'm wondering why I never had that problem... I went through 3 sets of Pagid Blues before switching the Hawk HT-10s.

[ChrisH]

Originally Posted by apk919

Nice work! I'm wondering why I never had that problem... I went through 3 sets of Pagid Blues before switching the Hawk HT-10s.

Did you save any of the old front Pagid pads? Maybe you could measure them and see if they were the same size as mine.

[apk919]

Originally Posted by ChrisH

Did you save any of the old front Pagid pads? Maybe you could measure them and see if they were the same size as mine.

Yes, I have all my old brake pads... I'll measure one later and report back.

[apk919]

OK, I measured a few pads... they were all between 76.65 and 76.70 mm

[ChrisH]

So, 0.25 to 0.29 mm more than mine. I wonder if that was enough to keep them from chattering.

I wonder how much variation Pagid's manufacturing process creates, or if they contract it out to multiple other companies.

[Mr. Know]

Originally Posted by apk919

Yes, I have all my old brake pads... I'll measure one later and report back.

How odd...what possesses you to keep them??

[apk919]

Originally Posted by ChrisH

So, 0.25 to 0.29 mm more than mine. I wonder if that was enough to keep them from chattering.

I wonder how much variation Pagid's manufacturing process creates, or if they contract it out to multiple other companies.

I wonder about the manufacturing process too... if they use a punch press to make the backing plates, wear on the die might account for tolerance variation...

Originally Posted by Mr. Know

How odd...what possesses you to keep them??

Two reasons... first, I always keep my last set of pads as spares when I go to a track day (and because I do a lot of track days I rarely let the pads wear more than halfway). Second I was getting uneven wear on the rear pads, and I wanted to see if it was consistent (it is, and I assume it has to do with the single piston design).

[ChrisH]

I kept my stock pads just in case I might want to compare third party pads to them some day. And, it turned out I did.

[ChrisH]

One other method I considered for dealing with this problem was to put a small steel tube (possibly a little flattened) over the cross arms of the anti-rattle spring. This would effectively increase the height of the arms, thus allowing them to push the pad up to the top surface and stop the chattering. However, I wasn't sure if the spring would be damaged (bent or overly stressed and weakened) when they pad is pushed to the bottom when braking when going in reverse. I decided that filling the gap would be the best thing to do.

[Frank Amoroso]

Kudos for having the chops to identify the issue and then execute on what appears to be a 'simple,' yet elegant, solution.

FWIW, I never had the problem with the 1-2 sets of Hawk HP+ or multiple sets of Pagid Black that I've run.