Disc Brake turning minimum allowable thickness

Wonderwagon

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Pulling this out of my other post about the the Disc salvageability for a quicker response.
Drum and rotors are the same are the same, max .060. you can go .030 on one side and .030 on the other but no more than .060.

Dave

Reconciling Dave's Lux post and FSM, my understanding follows: each face should be no less than .030 for a total of .060. The .060 is less the cooling slots cast in the rotor?
The FSM states on 5-55, that the total Disc thickness should be 1.25-1.24, but no less than 1.20. I ask because I have access to digital veneer calipers, yes micrometer dials are accurate to .01mm, (might have dropped a zero); but if my measurement is closer to 1.20 total thickness or less than .030 per surface the Rotors, are scrap metal. There is surface rust, but no scaling, so a deep re-surfacing probably will be needed.

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25-30 years ago the countries on the Western Pacific rim got into the business of producing and marketing rotors for REAR AND FRONT WHEEL DRIVE CAR. The average prices of rotors at that time went from $90- $120 per rotor to $30-$40 per rotor and pretty much stayz the same today. The average price today iz $12- $15 a piece to just turn them and many of the FWD carz are produced to specs that NO ONE will or can legally turn them today, same with drumz. Why would you bother just because you can? Even if you can and keep them within spec, I'd think you'd be rolling on a time bomb? It's like asking how much you should Pay for a helmet in the motor cycle shop when you buy your 180 MPH Crouch Rocket, and the salesman asks you how much iz your head worth? Just my .02, Jer
 
Pulling this out of my other post about the the Disc salvageability for a quicker response.

Reconciling Dave's Lux post and FSM, my understanding follows: each face should be no less than .030 for a total of .060. The .060 is less the cooling slots cast in the rotor?
The FSM states on 5-55, that the total Disc thickness should be 1.25-1.24, but no less than 1.20. I ask because I have access to digital veneer calipers, yes micrometer dials are accurate to .01mm, (might have dropped a zero); but if my measurement is closer to 1.20 total thickness or less than .030 per surface the Rotors, are scrap metal. There is surface rust, but no scaling, so a deep re-surfacing probably will be needed.


You are correct. The .030 on each side is assuming a new full sized rotor. Most rotors that have been run long enough to wear out the pads have at least .010 of wear, so the max you can turn them drops accordingly. You are also right that most rotors today are not worth the cost of trying to turn them as rotors at or near the legal limit are much more prone to breakage or warping, so why take the chance. A note on replacement rotors made overseas need to be checked to be sure that they run true and show no signs of warping even though they are "new". I have run across several that were junk right out of the box.

Dave
 
Thanks Davea Lux, for your insight. Self-edification, one reason; the other is if there was still enough material on the rotors why not turnem and use them one more time, if safe. However from what the digital calpiers are showing, at best marginal, and they would need a heavy resurfacing to clean up. Hope, this is of help to others, for me it has been. Some pics to entertain.

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Thanks Davea Lux, for your insight. Self-edification, one reason; the other is if there was still enough material on the rotors why not turnem and use them one more time, if safe. However from what the digital calpiers are showing, at best marginal, and they would need a heavy resurfacing to clean up. Hope, this is of help to others, for me it has been. Some pics to entertain.


FYI, the measuring tool you are using is measuring the high side of the rotor thickness. Brake shops usually use a point type measuring tool placed in a groove or other defect of the rotor. This give a more accurate picture of the minimum thickness of the rotor after it has bee turned to remove the defect.
 
Yes, I agree, so the veener calipers may be showing more due “averaging“ over the length of the jaw. Rather than the points used on each side of the micrometer. Still the rotor marginal at best, one side.029, total thickness1.2440.
 
This is the correct way to measure, even if the wrong tool is used. You should measure several places around the rotor like cutting it into a pie so you can get a thickness variation measurement. Thickness variation and runout with a dial indicator once installed are the common measurements used to detect hub/rotor problems. Thickness variation alone should be OK with a used rotor.
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This is pretty much useless and incorrect, but I can see it used to prove out a rotor that was over machined on one side. That is a common mistake made by someone trying to save parts... don't want that in brakes.
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Bottom line with parts like this... They don't get better with age. You have new rotors available, don't waste time on trying to save these old ones. Deep pitted rust like you have will be hard on equipment (cutting bits) and most knowledgeable folks doing this for a living wouldn't even consider hurting their equipment to cut these... and yes there also will be many shops that will try.

If you feel bad about using the Centric brakes, which I have no personal experience with, you can have new ones "cleaned up" by a shop that uses a Pro Cut lathe. The Pro Cut will cut them on the car and gives the smoothest possible results. I do agree that it is incorrect to have to cut a new rotor, but the manufacturing tolerances don't even match the Pro Cut results once installed.

This is a training video, but may help you understand the machine I am talking about. Also nobody should ever start cutting and then tell you they can't finish the rotor... they either can't measure correctly or got too lazy to do so.
 
I agree wrong tool, but, if they were closer to FSM spec. I would take them to the macHine shop for a measurement with the correct tool. With the improper tool I checked around the complete rotor and the measurement didn't get any bettet, either in total cross section or on either rotor surface. Final question the, bearing race does not get removed from the rotor, because a new one is included with the new bearing? Have not seen bearing grease crystallized so completely since I did pipeline maintenence. Davea Lux, Cantflip, thanks
 
I agree wrong tool, but, if they were closer to FSM spec. I would take them to the macHine shop for a measurement with the correct tool. With the improper tool I checked around the complete rotor and the measurement didn't get any bettet, either in total cross section or on either rotor surface. Final question the, bearing race does not get removed from the rotor, because a new one is included with the new bearing? Have not seen bearing grease crystallized so completely since I did pipeline maintenence. Davea Lux, Cantflip, thanks
Bearings are cheap too, when shopping find your part numbers... you will find that in many cases it is cheaper to buy a cup and cone set rather than just new cones. There are some of us who will knock the new cups out of a rotor brand we don't trust and install the cups from the brand name bearings we do trust. If you do this, be very careful not to damage the cups driving them in and they install a little easier if you stick them in the freezer for an hour before installing them. Driving the new cups isn't difficult but will be a lot more force than you would think, don't get crazy with this.

If your new bearings are cheapies, don't even bother replacing the cups... there are arguments both ways on this subject. I've had success both ways.

The biggest thing I want to get across to you or anyone else reading this later... don't fool around with old stuff that you don't have to. When parts are not available I understand folks trying to save what they can. With current parts availability like you have, use the spindles and replace everything else to the best quality you can find. If you have doubts, save your old parts... a good idea until after you're sure the new stuff is working correctly. With brakes there really isn't a good enough, they work correctly and are safe or they are not safe... no middle ground to work with.
 
Being frugal, was not in the plan for this system. It appeared as though the races/ cups stayed with the rotors, and new ones are included. Double checking. BTW the passenger side rotor, has similar numbers as drivers, so both will be replaced.

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Being frugal, was not in the plan for this system. It appeared as though the races/ cups stayed with the rotors, and new ones are included. Double checking. BTW the passenger side rotor, has similar numbers as drivers, so both will be replaced.
With all the work you have done... I wasn't thinking of you as cheap here. :thumbsup:
 
I agree wrong tool, but, if they were closer to FSM spec. I would take them to the macHine shop for a measurement with the correct tool. With the improper tool I checked around the complete rotor and the measurement didn't get any bettet, either in total cross section or on either rotor surface. Final question the, bearing race does not get removed from the rotor, because a new one is included with the new bearing? Have not seen bearing grease crystallized so completely since I did pipeline maintenence. Davea Lux, Cantflip, thanks


You are welcome. A lot of the new rotors that have been imported from Asia have new races installed which are also made in Asia. I have never liked the idea of mixing and matching parts from more than one manufacturer when it comes to bearings. That includes bearings that are made here. If I had a good bearing in my rotor when I took it off, I am probably going to take a brass drift and drive the old race from the old rotor and re-install it in the new rotor. I know that I have mated parts that way.
It is always a bad idea to put a used bearing on a new race. If you are going to use the new race, you also need a new bearing. As far as the imported bearings go, some are probably as good as any that are made here. Unfortunately, some are very poorly made and fail quickly, the so called peanut butter bearings. Since I hate having to do a job more than once, I use US made bearings and have had good luck with them.

Dave
 
Cantflip, no hurt feelings, Davea Lx wish the races were salvageable the grease is like hard dried maple syrup. Thanks both for help. Next step is to try and get the spindles blasted while in LA.
 
If you buy new they will need trued, I would run them first getting them hot a few times then have them trued. If they do not pulse they are probably okay, truing would still be better. The cups in aftermarket rotors should be removed and immediately scrapped, same with Chinese bearings, there is no need to use those impending failures when Timkens are available made at a state of the art facility in Ohio.
I have definite opinions on your rotors but you should follow the above recommendations for doing it correctly.
 
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