Help! Issues with Hawk Brake Pads

[Kccampro]

Anything using Hawk HP street pads? The OEM pads have an integrated shim that wraps around the side of the pad as pictured and the Hawk pads do not. As a result the overall length of the Hawk pads are just under 1/8" less than the OEM pads so there is a slight gap in the caliper and the pads aren't snug. Is this how its supposed to be? I want to figure this out before I both everything back together. Thanks!

[MightyMouseTech]

Will the pad shim come off the old pads?

[Kccampro]

That was my first thought, but it looks like the backing shim is integrated with the pad. Doesn't look like they can be separated.

[Ginger_Extract]

Originally Posted by Kccampro

That was my first thought, but it looks like the backing shim is integrated with the pad. Doesn't look like they can be separated.

Mine got baked off from track use. They can, and will come off. A bit of pad play shouldn't affect performance noticeably. Have you tried installing them as is?

[Kccampro]

Not yet, wanted to see if people thought it would be OK that there would be pad play

[MightyMouseTech]

A little play is not such a bad thing. Allows them to expand more before they seize in the caliper. Only real drawback is that you will get a click noise when you change direction and step on the brakes. Back up, step on brake....click......drive forward, step on brake....click. If they are REALLY loose you will get a higher pitched clunk from the suspension over bumps.

[fe1rx]

I agree that a bit of play is not a bad thing, however too much will result in extra wear on the phenolic insulators at the end of the pistons (a known weak point). The shims also provide some thermal isolation for the piston boots. As Ginger_Extract says, if you track your street pads they will get hot enough to cook the adhesive bond that holds the shims on and they will come off easily. I suggest saving the OE shims and using them with your track pads.

I made my own stainless shims (waterjet cut out of stainless sheet) for the front and the back. They are the same thickness as the OE shims, but I wrap around only one end of the pad (the side that sees thrust force under forward braking) so I have a bit more clearance for thermal expansion. You could achieve the same thing by cutting off one of the wrap-around ends on the OE shims.

The heat of braking also melts the paint on the backing plate. It sticks to the piston boots and will damage them. To some extent, the shim protects the boots from this. It is actually a shame that Hawk paints its brake pads.


Rear Shims:



Rear Shim with Pad:



OE pads have shims that wrap around both ends and which provide a close fit in the caliper. Race pads lack shims and so are a rattling fit in the caliper (about 2 mm clearance when cold). Some additional clearance is required for the race pads vs. street pads because they expand more under their potentially higher operating temperatures. Rather than using thinner shims that wrapped both ends, I used the same thickness as the OE shims but only wrap around the thrust end of the pad, providing essentially 1 mm additional expansion clearance. Using the shims removed from OE pads you could achieve the same thing by cutting off one of the legs on each shim.



I took a similar approach with the front pad, first installing the titanium shim:



Then adding the stainless shim:



The bent end of the shims is always located at the top of the caliper so that it carries the torque reaction thrust from the pad:



Changing back to OE pads, I noticed several things. At the rear to brake heat was sufficient to melt and partially burn the paint used on the pads. The melted paint is messy and tends to glue the piston boots to the shims.



I took this opportunity to glass bead blast the pad backing plates and shims to remove the paint residue so that next track day this should be less of an issue. Next time I install new race pads I will blast the paint off the back of the pads before I install them the first time.



At the front, brake temperatures were obviously higher and the paint was largely incinerated rather than melted. I used no compound between the brake pads and the shims. All the residue is from the paint on the backing plate, or from the singed piston boots.



The new piston boots I installed are now singed and damaged, despite the shims.



Lack of heat colours in the shims indicates that they did not get excessively hot, but the piston nose design puts the boots directly in contact with the shims at all times. This is not really ideal as it cooks the boots. The residue of cooked boots can be seen on the stainless steel shims. A piston nose design that put a small air gap between the pad/shim and the boot would be preferable, but we are stuck with what we have got.



Don't use any anti-sieze or brake quiet products between the pads and the shims as this will just add to the mess when operating at racing-pad temperatures. You still need anti-sieze on the ends of the pads where they slide against the caliper body though.

[OLEK135i]

http://hardbrakes.com/

[fe1rx]

Originally Posted by OLEK135i

http://hardbrakes.com/

The Ti shim I used up front is from Hard Brakes. It doesn't wrap around the ends of the pad so doesn't address the "excessive" end gap issue. At least when I got mine, they didn't offer shims for the rear (and there really is no need for them at the back).

[OLEK135i]

I use Hawk DTC-70 on the track in the front. Never had an issue. Sometimes the brakes will make a chonk sound when backing up. Similar to what Mightymouse mentioned earlier in the thread.

[Kccampro]

thanks everyone for the feedback, i really appreciate it.

[DSSG]

I put on the Hawk Ceramic Pads, Yellow Box, and I haven't had any problems or strange noises.

My Hawks came with metal shims, and I used a brake pad shim lubricant on both sides. I understand that earlier made pads didn't, but Hawk later added them.

The pads work well as far as stopping goes, but I'm disappointed with the amount of dust they throw off.