How common are HH-rated shoes (and pads)? Centric parking brake shoes

[slacktide_bitog]

4th gen F-Body (Camaro/Firebird/Trans Am)

Centric parking brake shoes for these cars are HH! I have never seen HH in any pads or shoes for any car before, OEM or aftermarket. EBC's website says they're essentially only found on motorcycles (EBC doesn't make any drum brake shoes). That's why it's so surprising to me. Part number 111.07840, FMSI # S784
Bosch is also HH
Dynamic Friction is GH
Power Stop is FF
I couldn't find the friction rating on Wagner and Bendix shoes, nor I could find the rating of the OEM shoes.

Centric was the cheapest and shipped from the same warehouse as other parts I needed, so Centric is what I got.

The 4th F-Body (and some other GM cars and trucks) use a weird parking brake shoe design. They're not like normal drum shoes with the scary springs and everything. Instead, they're shaped like a horseshoe, a C-shape with both shoes on the same ring. They seem less scary to work on than normal drums and shoes.

The only problem is that the shoe lining, the friction material area, is so thin, noticeably thinner than drum brake shoes normally are. Are parking brake shoes normally that thin? I don't have much experience with rear discs that use separate parking brake shoes. Maybe they made the shoes HH to compensate for the thinner shoe thickness

 

[chemman]

Call me "strange" but for some reason I measure and record the thickness of the friction material before installing disc pads or brake shoes on my vehicles.

The friction material on the rear shoes for my '92 Olds & '99 Buick are just under 7mm thick. The friction material for the parking brake shoe on my '99 Silverado & '04 TrailBlazer is just over 2.5 mm thick. Unfortunately, I did not record the friction ratings. I used Wagner ThermoQuiet shoes in these applications.

So yes, the parking brake only shoes friction material does indeed appear to be much thinner than regular brake shoes friction material in these applications.

 

[Tman220]

In the end.. That is the parking brake. They are not designed for standard braking and do not need a thick friction material.

 

[eljefino]

I suspect it's a "problem solver" for a compromised design.

When GM invented the X/A-body cars in 1980, they discovered at the last second that the e-brake didn't hold on that San Fransisco hill they test such things on. So they put stickier rear service brake shoes in those cars. Shoes, that on the first stop of the day, locked up the rear axle.

 

[doitmyself]

I thought that Timmastertech's recent explanation of parking brake shoes requiring more bite was excellent: https://bobistheoilguy.com/forums/t...commendations-on-brand-s.333036/#post-5550230 ....But, it seems that the OP i.d.'ed some aftermarket parking brake shoes with higher friction (good find).

" Go for dealer parking brake shoes. The reason for that is there is a huge difference in friction characteristics needed for park brake shoes vs regular brake shoes that most if not all of the aftermarket does not pick up on. Park brake shoes need a friction material with a massively high coefficient of static friction so the park brake holds. This is an undesirable characteristic on a regular brake shoe as it would make the brakes grabby. Most aftermarket brake manufacturers use the same friction material for park brake shoes as regular brake shoes which leads to park brake shoes that dont work the best. "

" Drum brake cars have far larger shoes (more surface area) than a park brake shoe does and they also wear into the radius of the drum which a park brake shoe never really (should) have a chance to do. More surface area and more clamping force and the park brake holds. Same with a rear brake that has the park brake integrated into the caliper, significantly more clamping force can be generated which can overcome the friction characteristics of the pad. Park brake shoes are tiny without as much clamping force and need all the help they can get "

 

[GlennDa5id]

Latetst brake pad friction publication. You can see how common HH pads are. My 13 Volvo has OE pads from ATE which are HH. They stop very well. HH seems high!

https://ameca.org/wp-content/uploads/2020/10/AMECA-List-of-VESC-V-3-Brake-Friction-Material-Edge-Codes-October-16-2020.pdf

 

[CharBaby]

Yes, most parking brake shoes are thin. They don't need to be on the thicker side.
If you install these shoes, make sure they hold the car to your liking under some throttle input.