I have a question. Is it worth cutting the rotors on the Q or should I just replace the rotors every time I change pads. With such a heavy car like the Q with such tiny brakes, I would think that cutting the rotor and making it thinner would cause even more loss of braking power due to increased heat buildup.
The Q needs some 14" rotors up front!!!
Brake service
Even at their thinnest, rotors still have maybe 90-95% of their as-new mass. Probably more cost effective to ensure your brake fluid is new, since you can see a 50% performance drop with bad wet fluid.
Turning and resurfacing are the same. The tech will cut just enough (.001-.015") off each face of the rotor to get it true. The error of the machine plus the error in the mating surfaces plus the error in the bearing all have to add up to less than .0028" on both sides of the rotor. Amazing to me that it can be done at all. A sheet of paper is about .0035" thick!
Turning and resurfacing are the same. The tech will cut just enough (.001-.015") off each face of the rotor to get it true. The error of the machine plus the error in the mating surfaces plus the error in the bearing all have to add up to less than .0028" on both sides of the rotor. Amazing to me that it can be done at all. A sheet of paper is about .0035" thick!
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Brake pads have 6-7 mm of useful thickness and rotors have 1mm [wear limit].......... so pads should wear out every 20,000 miles to minimize impact on rotors.
Unfortunately owners don't want to spend the money to replace pads and clean and service the system.......thus we get harder pads that last too long.
The usual amount [average] we cut off each rotor face to true is more like 0.005"..........have seen some that need 0.015-0.020".
It all tends to wash either the pads wear them down or they warp enough to be cut into uselessness in 40,000 miles.
1mm = 0.03937"
I have tested a few Q with off car lathes and no matching of rotor locations. The average typical brake job is way outside the spec when assembled.........something like twice the spec or 0.005" but they feel much better because they were 2,3,4 times this when brought in for service.
Most don't want to pay to replace the hub and wheel bearings.
Unfortunately owners don't want to spend the money to replace pads and clean and service the system.......thus we get harder pads that last too long.
The usual amount [average] we cut off each rotor face to true is more like 0.005"..........have seen some that need 0.015-0.020".
It all tends to wash either the pads wear them down or they warp enough to be cut into uselessness in 40,000 miles.
1mm = 0.03937"
I have tested a few Q with off car lathes and no matching of rotor locations. The average typical brake job is way outside the spec when assembled.........something like twice the spec or 0.005" but they feel much better because they were 2,3,4 times this when brought in for service.
Most don't want to pay to replace the hub and wheel bearings.