warped rotors - Page 2 - PeachParts Mercedes-Benz Forum

Tomguy · #16 06-25-2006, 01:32 PM

I don't know how other MBs are, but on a 108/109/111/112, if improper torque caused warping of rotors, the hub would also become warped. They are bolted together quite well.

Also, if improper torque caused rotor warping, wouldn't it also cause the WHEEL ITSELF to warp as well? They're mated flat and tight against each other with a LOT of force. If one warps, the other will have to warp as well.

kramlavud · #17 06-25-2006, 03:42 PM

Quote:

Originally Posted by Tomguy

I don't know how other MBs are, but on a 108/109/111/112, if improper torque caused warping of rotors, the hub would also become warped. They are bolted together quite well.

Also, if improper torque caused rotor warping, wouldn't it also cause the WHEEL ITSELF to warp as well? They're mated flat and tight against each other with a LOT of force. If one warps, the other will have to warp as well.

Tom, you make a good point; If the wheel or hub were distorted by improper torque, then perhaps you would experience the same 'shudder' without application of the brakes. Of course if the runout is minor, then the elasticity of the tire may mask it. Regardless I am yet to be convinced that improper torque will deform a rotor. Anyone?

Mark

MBtech21 · #18 06-25-2006, 09:25 PM

Quote:

Originally Posted by Bob Weir

Thanks to MBtech21 for a very good explaination.

However, I have a few questions...

MBtech21 wrote:
< Second one is what tom was talking about- actually, its not pad deposits that usually cause this- it's the pad ripping material from the disc. Usually occurs when the car sits for a while- with the metallic materials in pads now, it is a given that they will corrode to the rotor with very little time/moisture involved. You jump in the car, put in drive and RIPPP..... away goes some rotor surface(and pad surface)- this can be driven out of the car, at least on an MB, by braking hard, or using the sanding pads, >

Note: 11,000 miles on 4 new rotors & pads. After my 94 e320 sat for about a month, I discovered an accumulation of material on both sides of both rear rotors from the leading and trailing edges of the pads. I hand sanded with 400 grit until the disk surface feels smooth. After about 500 miles of city driving, a slight thumping still is present.

Is it more likely the rotors or the pads?
Why just the back and not also the front?
About how may miles would it take to drive/brake it smooth?

Until 1964, my father had a 2 bay "Gas Station" - the kind that fixed most anything and have been converted into mini-marts. He taught me; mount the wheel, attach each lug nut in a star pattern with a speed wrench (didn't have an air gun in those days) and then again in the star pattern, use a 1/2" breaker bar to tighten each to a squeek.

Other than using a torque wrench instead of a breaker bar, isn't this still the prescribed method?

Bob

The rears take longer to 'fix' as they don't do much braking.. hence why the rear discs on MBs corrode first.
As far as the sandpaper goes- MB has made special tools for years that are basically brake pads with sandpaper on them to 'surface' rotors- far as I can tell, it is regular sandpaper like you would get at Home Depot.
I guess every one missed my point- tightening them to the wrong torque wouldn't warp the discs, but tightening them wrong WOULD!! Your father was right, if you tightened the wheel like that and had wrong torque on each bolt- no problem with warpage- however, very few do it like that any more, so you get the scenario I described.

t walgamuth · #19 06-26-2006, 05:40 AM

if you look, when tightening a steel wheel you will see that the parts around the bolts indeed does flex a bit. because of the shape of the wheel, with the rim being such a large mass, if the center is warped a bit here and there the flexibility of the overall wheel will absorb the differences and no effect will noticable.

now with an aluminum wheel because of the mass of metal around the hub area, the flexing is a lot less noticalbe, but it will be there too.

you know, "if you drop a feather on an anvil, it will deflect....it will be hard to measure though".

tom w

mayr71 · #20 08-06-2008, 02:39 PM

I have a 95 E320 and there is an issue with my 7k old rotors (call it "warped" or not) they make a pulsating sound. My MB mechanic says my calipers are fine, but the lug nuts were too tight and he said it was the lug nuts being too tight.

My MB mechanic has over 30 years of experience so he appears to be an authority to me on the subject.

What else am I to think? Calipers are operating fine so I need to chagne teh rotors again and torque the lugs equally to the required spec.

G-Benz · #21 08-06-2008, 02:50 PM

As far as the tire shops using torque wrenches versus impact wrenches, that is mostly due to protecting the alloy rims, which CAN warp if improperly torqued.

Using torque wrenches to eliminate warped rotor complaints may only serve to placate customers.

I don't buy the warped rotor theory either...I'm more inclined to believe that a bad caliper or pad can create issues that would appear that the rotor is warped (i.e., high vs low spots measurable with a caliper), but I believe visible damage such as scoring would be present.

pmckechnie · #22 08-06-2008, 07:25 PM

Well, I have no degrees in any field but I do know that uneven torque on the lug nuts where some are TOO tight and some are TOO loose will cause the rotors to warp. It is not immigrant but takes 3 or 4 weeks of normal driving to happen. A trip to the mountains and getting the rotors extremal hot will cause it to happen sooner. We replaced the pads and turned the rotors for a gentleman and all was good. He later had a new set of tires installed at a tire shop. About a month latter, he came back to us with a pulsating brake peddle. We took care of the problem. About 2 months later he returned with the pulsations again. Again we took care of the problem. Another 2 months later, same problem. This time we ask a few questions. Have you had your tires rotated or anything? Well, he got a lifetime rotation with the new tires. We ask that the next time he had his tires rotated if he would come by ASAP and let us torque the lug nuts correctly. He did, and had no problems for the next 6 months. We lost so much money so we could keep a customer. He then believed what we were saying about the torque being very important that he took all the receipts we have given him (we make a receipt for our files and for the customers files even if it was free) to the tire place and demanded that they pay us a fair amount for all the work we had done that they had caused. Believe it or not, they paid us the labor for 5 brake jobs and one set of rotors. What we learned from all of this is that lug nut torque is very critical and needs to be the same on each lug nut and applied in a star pattern. This is only one of many stories about this problem we have had.
science and education may disagree, but real life tell a different story. Did you know that science says it is impossible for a bumble bee to fly but the bumble bee proves them wrong every day.
Paul