Mechanics

CROSSED DRILLED ROTORS

2000 Cadillac SLS

Brakes problem
2000 Cadillac SLS V8 Front Wheel Drive Automatic 108000 miles

I've put crossed drilled rotors on all 4 wheels last winter and now 7/26/10 the mechanic says they maybe the cause of my shimmy problems. He does'nt know if he can cut these rotors. My Q is, can they? Or they trying to force me into buying new rotors? Is this normal lifetime for rotors. I love the crossed drilled, especillay in the rain and snow, here in PA. They bring my 2 ton Caddy to stop in a hurry. I don't ride my breaks at all, i'll drift to a stop before I use them. But, when i'm on the highway, I have to watch out for city drivers and Sunday drivers. Stopping from 70 to 40 mph is verrrry important to me.
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Thunder
July 26, 2010.



Hi thunder. Welcome to the forum. The holes in the rotors have no affect on how they're machined. They don't improve stopping directly either. There is less surface contact area, but the difference is negligible. What they do is improve cooling which reduces gasing of the friction linings which reduces one type of brake fade. Mountain driving is where you'll really notice the difference.

As for the shimmy, when does it occur? All the time or just when braking? Does it shake the steering wheel or do you just feel it in the seat? It is real common for new rotors to warp and once they're machined, they generally don't warp again. This is especially true of Chinese rotors. There's nothing wrong with them except cast iron parts made here are " aged" for 90 days before the final machining. Chinese rotors are cast, packaged, and shipped. The aging takes place on your car.

If the shimmy occurs all the time, have the steering and suspension components inspected by an alignment specialist. GM vehicles eat ball joints faster than most other brands. Also look for a broken belt in a tire. You will feel that at all speeds. Often you will see the steering wheel oscillate back and forth as you drive through a parking lot. Warped rotors can do the same thing if the calipers aren't sliding freely on their mounts, but usually you'll only feel that when braking.

Caradiodoc

Caradiodoc
Jul 26, 2010.
Caradiodoc, thank you for your response. I notice 3 things this morning driving to work. 1. i need a front end alignment (pulls hard to the right) 2. It get a slight shimmy when driving between 50-65 3. My right front shakes hard (and the steering wheel)when braking at these speeds, like when exiting off the highway (down grade). i inserted a pic of the rotors.


http://www.2carpros.com/forum/automotive_pictures/55386_cross_drilled_rotor_2.jpg


Tiny
Thunder
Jul 27, 2010.
Good observations, but a broken tire belt can cause a pull too along with a shimmy. A quick test that only works with front-wheel-drive cars is to observe the pull during hard braking. If it pulls to the left during braking and right during acceleration, look at the tires. Switching them side-to-side will make the pull change directions or in some cases, go away.

It is also possible for a tire to just pull for no apparent reason, but they don't suddenly start doing that. They will do it from day one. Rotating them front-to-back eliminates that pull, and they can stay there until they're worn out.

Also consider a binding inner cv joint. They will cause a shimmy under moderate acceleration but usually not at the higher speeds you mentioned. An inspection is the place to start. Start with the cause of the pull. Once that's solved, then see if the shimmy is still there.

Caradiodoc

Caradiodoc
Jul 27, 2010.
What about the rotors? Can they be cut? I'm having new tires put on tonite. $880 tires+install and tire insurance. Excuse me while I bend over. LOL!

Tiny
Thunder
Jul 27, 2010.
Absolutely. I mentioned that previously. The cutting bit skipping over the holes is no different than skipping over rust spots. Holes mean nothing to the brake lathe. The only exception would be when the rotors reach the minimum legal thickness. No mechanic will risk his professional reputation by cutting them thinner than allowed. Besides the legal ramifications, less metal means they will heat up faster.

It is also strongly advisable to machine the fattest rotor down to the same thickness as the thinner rotor. Keeping them the same thickness on each side, (within around.010" or less), means they will always be near the same temperature. Years ago with big heavy rear-wheel-drive cars, we never gave that a thought, but now with lighter cars, unequal thickness rotors often leads to a severe brake pull when the brakes get hot. It's due to the changing coefficient of friction of the linings at different temperatures.

Caradiodoc

Caradiodoc
Jul 27, 2010.
I had 4 Bridgestone Turanza Serenity tires, a front-end brake job and alignment done yesterday. What a difference! Unbelievably quieter and smoother ride! (Then the Kanook performance tires). This got rid of 90% of the shimmy & shake. I think i'm still going to have to have the rotors turned to get rid of the problem completely (more $). Thanks for your help caradiodoc.

Tiny
Thunder
Jul 28, 2010.
Dandy news. Sorry for taking so long to reply back. Verizon can't seem to figure out how to do e-mail so they finally gave up and switched to Frontier. I'm just now getting some e-mails from three and four weeks ago!

Caradiodoc

Caradiodoc
Aug 22, 2010.
No prob. After a couple of weeks, I guess my new tires wore down to their true roundness and the shimmy stopped. Now my chk engine light is on. The guys at Tire plus did a diagnoses and said it was the knock sensor and I would have to take it to the dealer because its located under the plenum. Any idea of the cost?

Tiny
Thunder
Aug 23, 2010.
Sorry, can't help with that. I do know some Caddies also have the starter on top of the engine under the plenum. Makes sense to me! By now I'm sure most mechanics are experienced at disassembling engines to get to previously easily-accessible parts. My best guess is you can expect a bill in the $200.00 - 300.00 range. Knock sensors aren't terribly complicated but GM is rather proud of their parts and they aren't afraid to charge for them. I would hope my guess leaves enough dollars for around 2 1/2 hours of labor.

Be aware too that they will likely want to perform their own diagnostics before replacing parts. That might be a good thing as it shouldn't take very long to verify what Tires Plus found. If the original diagnosis was wrong, that will save you from having to pay for installing the wrong part. There could also just be a problem with the wiring or a connector and not the sensor itself. The diagnostic codes just get you to the circuit or system with the problem, not necessarily the exact part.

Caradiodoc

Caradiodoc
Aug 23, 2010.
What's the question?

Caradiodoc
Sep 24, 2010.