Leave shim(s) off rear brakes?

I was unable to do my last brake job myself (2013 TE), so paid a mechanic. That included new rotos, calipers, etc..

Today I noticed that the rear brake (one side) is missing an outer shim. There could be more missing but I haven't pulled the wheels.

Here's the mechanic's reply:
There's nothing wrong or anything to be concerned about.Sometimes I will leave that shim off if it's not fitting properly meaning if it's slipping around because when they slip off in the caliper they start to cut the rotor. But if you are concerned you can bring it in and I'll put them on for you. But it will not affect your breaks working properly in any way.

Any thoughts?

 

Never heard of them "choosing" to leave it on or off before. The shims will not affect functionality but they do prevent noise.

 

Change your mechanic for not informing you the first time then coming up with reasons not to do it the second time.

 

Probably won’t keep the brakes from working in the short term. But besides possible additional noise, quality shims probably keep the brake pistons from digging into the backing plate of the pad. The oem shims are “slippery” compared to the pad backing steel. I would imagine that plays a part in allowing the pad to shift back and forth slightly over the piston as brakes are applied and released. Without them, the piston would probably “grab” the steel of the steel pad backing, instead of allowing some sliding to occur. The small front to back movements of the pad might be transfered to the piston, which would wear out the caliper bore.

OEM shims are also more corrosion resistant than the usual steel. Without them, the piston might wear into the backing steel of the pad, then they might get “welded” together with corrosion if it sits for a period of time. They’ll probably break loose on the next use, but it might get worse and worse and cause wear on the piston.

They probably skipped the shims because they fit like crap. Oem shims on aftermarket pads may fit poorly as well. This is why I prefer oem pads with matching oem hardware. Not to mention, the oem material is probably much better (better coating and/or treatment on the hardware). The better materials for oem hardware might explain why they are on the pricey side.

 

Did you supply the parts or did you buy them through the shop? What brand are the pads and rotors? The mechanic exercised judgment if he's indeed presented with ill-fitting parts. If the new pads didn't come with shims and he's forced to re-use 11 year-old OEM shims, those fingers could've fatigued after several installs and removals.

The shims' only function is to reduce noise. If you grease all the metal-on-metal contact areas, the shims aren't necessary for as long as the grease is present.

 

^In the Canadian North, grease isn't sufficient. I just use anti-seize on the rotors to eliminate squealing. Wait 15 minutes between coats. Add a few drops to the brake fluid reservoir to keep the master cylinder lubricated:

 

Man, you missed it. April Fools Day was two days ago.

 

^Toyota left its April 1st press release up. I'm not sure if it's a joke or not: https://pressroom.toyota.com/toyota-prius-wins-2024-world-car-design-of-the-year/

 

Wow. That is comedy, but I think they're serious. Makes me want to go over to the Prius forum to see how they're modding them out. I'm sure it's sick.

 

No need to leave off shim. Did he also leave off that pad support hardware?

 

That’s a good point that I would want to verify. Especially since they omitted the shims with the excuse that they didn’t fit. Chances are, the clips fit poorly as well. In my experience doing various cars over the years, if the shims didn’t fit well, the clips were just as bad.

 

Yeah, get a new mechanic. Ugh man!

 

wtf!! You can be serious!?!?

 

^I know what I'm doing! I've seen it on TacomaWorld!