Drum In Hat Brakes

Posted by Spencer on May 4th, 2012

Changing up the format a bit here folks. Decided I can give back to the internet by posting some how-to type stuff.

To kick things off, I want to bring up Drum In Hat brakes. I first learned about these the hard way when attempting to change the rotors on my 2006 Jeep Liberty.

And here’s the disclaimer: I Am Not A Mechanic. Everything here is just an account of what I’ve witnessed. When attempting home vehicle repairs you risk damage to the vehicle or yourself. Always take proper safety precautions. I suggest using the buddy system too- you’ll need someone to drive you to the store for that part you forgot!

Drum In Hat is an interesting concept. It’s basically like having a disc brake AND a drum brake together in one compact unit. The disc brake is what’s used when you push down on the brake pedal, actually providing the stopping force for the vehicle. Meanwhile, the drum brake lives inside the disc “hat”, and that’s used for the parking a.k.a. emergency brake.

This design seems to be used by a lot of heavy duty GM trucks and, apparently, my Jeep Liberty. I have found no clear explanation of why they use this system as opposed to just discs or just drums. From what I’ve been able to gather through researching online, it seems to be that they’re heavier duty, able to prevent “roll-aways”. I suppose if you have a lot of weight in the truck or trailer and you park on a steep hill, that would be pretty important.

The problem I encountered was when I went to replace my rotors. They were stuck and absolutely refused to budge. Heavy duty lubricants like PB Blaster did nothing, neither did attacking it with a sledge hammer. Which, by the way, you probably shouldn’t do (especially if you planned to reuse those rotors).

The reason for the hold up was that the shoes within the drum brake mechanism were pressing so tightly against the inside of the rotor (which acts as the outside of the drum assembly), it wouldn’t budge.

There is one way, and ONLY one way to get the rotors off, and that is by loosening the drum shoes by way of the star-wheel adjuster. What is a “star-wheel adjuster” you ask? Frankly a star wheel is just a euphemism for “tiny gear”, driven by a screw. That connects to various levers that push the brake shoes out against the drum hat (in this case the inside of the rotor), keeping them tightly adjusted. The star-wheel is designed to turn in only one direction: tighter.

So what you need to do is turn that star-wheel in the opposite direction, to loosen it.

Easier said than done.

First, on my Jeep, it was extremely hard to locate. There’s a tiny oval opening on the vehicle-side of the hub, covered by a little rubber plug. Once you pull out the plug (don’t lose it!), you’ll have to crawl underneath the vehicle and look through it at an angle with a flashlight. Eventually, you’ll find this mechanism up in there.

Actually adjusting it is pretty tricky too. I had a set of drum brake tools I picked up from the hardware store, but they were totally useless. What worked was a flat-head screwdriver. Position the screwdriver on one of the tines of the star-wheel gear, and push it up. The gear will move up and a little to the back. Don’t worry, it’s mounted on a spring, so it’s meant to have a little play. You’ll hear a click each time you spin the gear up a notch. Doing this freaks me out, I was very concerned that I might be stripping the gear. But after clicking it up/back several notches, I observed no visible wear. And best of all, the more I clicked it back, the more the rotor was able to wiggle on those shoes, until eventually, it pulled right off.

Once you’re finished with whatever maintenance you needed to do, you don’t have to worry about re-adjusting the star-wheel. It’s a self-adjusting mechanism. First, put that rubber plug back in you took out earlier. Then all you have to do is pull the emergency brake a few times, and you’ll feel it tighten back up. Easy enough!

Posted in How To