BrakeFilter: Do I really need to turn the rotors and replace the calipers?

October 24, 2006 4:07 PM

BrakeFilter: Do I really need to turn the rotors and replace the calipers?

My brakes are squeaky and need work. The mechanic said the whole shebang needs to be replaced, which I in theory have no problem with, but the car is a beater and doing all this work rapidly approaches the cost of the whole car.

So if I were to replace just the pads, do I face a safety hazard? Am I safe in doing this and driving the car for another 18-24 months?

posted by Andrew Brinton to travel & transportation (7 comments total)

Brakes work by squeezing the rotors with the pads. Both the rotor and the pads are worn down over time. As they wear down, the pads and the rotors develop grooves together. If you simply replace the pads alone, you present a new and flat pad to the grooved rotor. This mismatch can greatly reduce brake performance. When they 'turn' a rotor, they are putting the rotor onto a lathe, and then cutting the faces of the rotor with a tool until the rotor is perfectly flat again. This makes the rotor and new pads match up again. The good news is that turning rotors isn't very expensive at all.

However, if the grooves are really deep, or if the rotors are already worn thin, then you can't turn them. It's because there isn't enough metal left to cut off the faces to make them flat again. At this point, you have to buy new rotors.

As for new calipers, I'm not sure why your mechanic believes they need to be replaced. I would ask why, and ask if it because of a defect or broken part, or if it is simply policy.
posted by tumble at 4:23 PM on October 24, 2006

If it has been a really long time since these brakes were worked on, the calipers may be seized. It would surprise me if, say, all four of them were seized... That's the only reason I can think of why any would need to be replaced. Definitely ask what the reasoning behind that is.
posted by autojack at 4:29 PM on October 24, 2006

get a 2nd opinion - it sounds like this mechanic is ripping you off with un necessary work.
posted by ptm at 4:37 PM on October 24, 2006

I’m not a mechanic... just a former, long term slackass shadetree mechanic, but I think I’ve been in your shoes (no pun) more than once. If you put off doing a brake job for way too long after the squealing starts you can wear away enough of the sacrificial friction material from the pads to put their metal underpinnings into contact with the rotors when you hit the brakes. This grinds shallow grooves into the rotors that you can easily see and feel. I did it to a couple of VWs and a Porsche 914.

I just replaced the pads and everything was fine, except that the new pads never lasted very long - I don’t know, maybe two years.

As to replacing the calipers, I don’t know. It sounds excessive to me, but brakes are pretty important. Do yours just squeal, or do they do other nasty things?

If you’re lucky a real mechanic might respond. You should post your car’s model and age.
posted by Huplescat at 5:03 PM on October 24, 2006

tumble gave a good explanation of how disc brakes work from the pad and rotor perspective. The calipers are the parts that hold the pads in position on either side of the spinning rotor, and more importantly, contain movable pistons or cups, which convert the force transmitted by the brake fluid into squeezing force on the pads, that actually stop your car. Calipers eventually develop leaks in the rubber cup seals that hold back the brake fluid, or they get full of dirt to the point the pads can't be squeezed reliably when brake fluid pressure is delivered. In either case, you can't get full stopping performance from them, regardless of the condition of your rotors and pads. Calipers can be rebuilt in the field, but it usually costs more in mechanics time and parts than just exchanging them for rebuilt units, which are done in factories, with tooling and equipment that is faster, and allows full function testing off the car.
posted by paulsc at 6:16 PM on October 24, 2006

My dad owned his own shop, which I worked in for several years. If your rotors and/or calipers are screwed up, you will probably be unable to stop soon. Both paulsc and tumble have explained the process fairly well.

Rebuilt calipers were a staple in brake jobs in my dad's shop. Unless the car is new (sounds like not) rebuilt ones are probably going to be what you get (and they are perfectly fine). Additionally, rotors have a tolerance, and some people are more willing to try to get a good one out of an old one than others, because there is a point where they are too thin. Ideally this mechanic should be able to tell you what is specifically wrong with your brakes, and if the calipers are truly screwed up, he can probably show it to you up on the rack (ditto with the grooved/effed up rotors).
posted by Medieval Maven at 6:30 PM on October 24, 2006

IANAM, but I've changed rotors/pads many times on a few old beaters. Can't help with the calipers, other than to say get a second opinion. Also, if you know someone who buys/sells cars as a side-job, ask them for a recommendation for an honest mechanic.

If you want to do it yourself, here are some things I've found (Midwestern US prices):

1) You'll pay about $20 for pads that have a lifetime warranty.
2) You'll pay about $10/15 per rotor to have them turned, if they can do it. Pepboys is the only place around me that does it.
3) You can probably get cheap rotors for about $25/30.
4) I understand that you have to do *something* with the rotors when you change the pads (either turn or buy new).
5) If the rotors just won't come off, you can either slam them repeatedly with a hammer/mini-sledge, or heat them up somehow.

Have fun.
posted by claytonius maximus at 8:31 AM on October 25, 2006