QuestionI just replaced my front disc brake pads and rotors (on 1995 Subaru Legacy, if it matters). I couldn't fit the calipers on the rotors with the shims between the pads and the calipers, so I left the shims off. I'm pretty sure that I pushed the calipers pistons all the way in.
The old pads each had two shims. The new pads each came with one shim on them. First I took the outer shims off the old pads, put them on the new pads over the shims that came on them, put the pads and shims in the calipers and tried putting the calipers on the new rotors. They wouldn't fit, so I removed the outer shims and tried again. They still wouldn't fit, so I took off the inner shims that came on the new pads and then the calipers fit on the rotors. This happened on both sides.
My questions now are: Do I need the shims? What function to they perform? The brakes work fine and don't make any noise. Would it make sense to try putting the shims in now that the new pads are well-seated?
AnswerHello Brad,
To answer you question, the shims keep the pad and puck square to hit the rotor flush
they also help with brake noise issues...rear brakes can squeek bad, especially in reverse. While you do not have to use shims, it is highly recommended you do to ensure that the pads hit the rotors evenly, thus reducing the uneven effect you see with brakes that are worn down or missing the shims.
Shims are designed to fit with brand new pads, however, aftermarket pads and shims do not always do this, which is why many people end up throwing them away and not using them. I recommend using OEM Pads and shims as they were designed to work the way the vehicle manufacturer intended them to be used. Some good OEM brake makers are:
Textar
Pagid
ATE
and Jurid
Some aftermarket brands i recommend staying away from include:
PBR
Metalmaster
PBR Delux
i recommend staying away from them because they don't deliver the same performance as the OEM pads do. The PBR Deluxe pad is an organic compound pad which means it really is not suited for heavy use as they tend to fade and wear quickly in anything other than leisurely driving.
The PBR Metalmaster, or "rotor-eater" as myself and many other technicians call them, are a semi metallic compound but are very hard and will eat through rotors quickly. European pads are all semi metallic compound as this is what the cars in europe were designed to use.
OEM pads do dust more than others but this is a moot point in my opinion as safety is more important than a clean wheel. In my experience I have had excellent results from ATE pads. I also like to use the same brand for both the front and the rear in order to keep braking balance in check. Rotor condition is also very important and they are usually pretty inexpensive so it makes sense to replace them as well when doing a brake job.
Here is some more information about what shims are and what they do, in-case you are still wondering.
Brake shims are thin layers of rubber or metal that fit between the brake pads and the rotors to correct small imperfections that cause brake noise. They function just like shims in cabinetry: If the kitchen floor of an old house is a little crooked, the cabinet installer will add a couple of thin, wooden shims to level out the cabinets. Brake shims work much the same way to adjust otherwise normal brakes.
On the most basic level, for many new vehicles with new brake parts, brake shims function as anti-rattle pads. They keep the pads and rotors from banging against each other or squealing. Some brake part kits come with the shims already attached to the brake pads; some come with separate shims that have adhesive backings, which need to be affixed to the back of the brake pads. Other shims must be purchased separately and attached to the pads with double-sided tape.
In any case, brake shims are easy to use and install, and they can make a big difference in the way that the brake parts work together. While most are made from rubber, it's possible to upgrade to something like titanium brake shims.
Titanium brake shims:
Brakes are tested under extreme conditions. Titanium brake shims work as heat shields to maintain braking power.
When brakes are under stress, they get hot. Real hot. Just think how hot the brake parts on a racecar get when coming out of a straight stretch to enter a corner. Rubber can quickly turn to goo in that situation, or in any heavy braking scenario. The heat created from the friction of the hard-working brakes can actually boil the hydraulic brake fluid, which even further reduces stopping power. That's where titanium brake shims come in.
Titanium brake shims work like heat shields to prevent the heat of the braking effort from affecting the other brake parts. Manufacturers often use a titanium alloy in the brake shims to keep costs down, as titanium can be very expensive.
While rubber brake shims can be stuck to the back of brake pads using two-sided tape, titanium brake shims are usually secured by other means. They often have holes at the top and thread onto the caliper pins. They still fit between the brake pads and the rotors, but they function less as noise dampeners and more as heat shields.
Keeping the brake parts as cool as possible means a longer life for brake parts and fewer brake fluid changes.
Good Luck, I hope this was helpful.
Thank you.
