Hello all, the brake sensor has gone off on my rear brake pads and I would like to follow octaneguy's DIY writeup on replacing the pads on all 4 corners of my 04 Mini. The car has 56K kilometers. Is it necessary for me to replace the rotors at this time as well, or can i just slap on some new pads and sensors? My experience with other vehicles is that you can replace the pads once before you have to replace the rotors - but I have never owned a european car before. Can I just replace the pads? Thanks guys.

 

You will get different answers, but the real issue is rotor thickness. If the rotor is too thin it needs to be replaced.

When I did my pad change at 30K the rotors did not need replacement. Others have needed to. In my case the pads were not worn and I simply was changing to Hawk ceramic pads to get less dust.

However, rotors are cheep and replacement will not harm a thing. I just helped a fellow MINI owner do rear brakes and the rotors were $30 each from Autozone.

 

I think you will find a near consensus that the rotors either need to be resurfaced (i.e., turned) or replaced at your kilometer-age.

 

OK thanks for the input. I think I will look into the cost of resurfacing the discs before I go replacing them all.

1 more question - I purchased the front breake sensor, only to find out the rear sensor is the one that has worn through - does anyone know if it is possible to splice the front wear sensor into the rear one?

 

Replaced the rear pads on my '04 Cooper at 76,000 kms., the rotors were within spec. thickness so I left them, no problems experienced. Went with Hawk HPS pads, and followed the Zeckenhausen Racing bed-in procedure. All is well, less brake dust, and about $90 cost. Will do the fronts myself soon. BTW, I chose not to replace the sensor wire, I just taped the wires together to close the circuit, and zip-tied to the rear suspension. This extinguished the dash light, and now I will have to do my own checking for wear...

 

Don't turn the rotors (resurface).
Rotors do not take to being turned now a days. This will likely cause them to warp. Besides the cost to replace is only a little more than having them turned.
If the current rotors are in spec then just put the pads on, if not get new rotors.

 

What is the spec for rotor thickness?

 

Minimum thickness (MIN TH) is stamped on the brake disk body. Spec is: front 20.4mm, rear 8.4mm

Invest in a micrometer if you will be doing your own brakes and want to maximize rotor life, otherwise just replace them. Modern rotors are not designed to be resurfaced, but are as light as practical to reduce weight, as are many other components, in the interest of fuel economy.

 

A quick question concerning rotors and the sensor. Do any domestic outlets

like Autozone carry OEM style rotors or do I have to go to someone like Moss

Motors? Regarding the sensors, do they have to be replaced each time the

pads and/or rotors are replaced or can they be reused? And a ballpark price

on each. Thanks

 

Sorry, no "concensus" on this at all. If anything, the CW with today's cars is that you don't resurface simply because the rotors don't have enough extra metal to allow it. So you either leave the existing ones on or you replace.

It varies from car to car and driver to driver, but I typically do 2 or even 3 sets of pads to a rotor replacement.

- Mark

 

Yeah...whatever...

Maybe it's acceptable, but I'll never put new pads against an old, worn rotor surface. Just seems so unnecessary to be cutting all of those grooves and imperfections into the new pad material. C'est la vie.

It's a nice excuse to shop for new rotors.

 

You can go to Autozone or the like for rotors. Even TSW who sells rotors says they are all about the same.
You can get them from Autozone for about $30 each vs. others for almost $100.
Pads are a different story. Don't by cheep pads from Autozone.

 

Well I took the front brakes off this weekend, and the discs appear to be too worn to reuse. There is a lip around the outside of the disc that prevents the new pads from sitting completely flush on the disc. So I think I have to replace the discs.

Oddly enough, the lip does not look any worse than what I see in octaneguys' brake pad writeup. Maybe if I was using OEM brake pads I would be able to reuse the discs, but the Akebono pads I bought touch that lip and I don't think it would be safe to reuse the discs. I don't think resurfacing is an option either, as the min spec on the front discs is 20.4 mm and that does not really allow for any resurfacing.

 

The lip is normal and is the reason you have to rock the caliper a few times to retract the pads enough to get the caliper off. But the new pad should be sized properly to fit inboard of the lip. One reason I tend to use the OEM pads, at least for street applications.

Rotor wear is very dependent on driving conditions. It's possible you can wear the rotor beyond spec in one cycle of pads.

- Mark

 

There is a lot of mis-information on this thread. Let me introduce some "good" information for you all.
1.) You ABSOLUTELY can turn rotors, even cross-drilled and slotted, no matter what anyone tells you. Maintaining minimum thickness is the key.
2.) 20.4 mm is the starting thickness for the front rotor on the '04. 8.4mm is the starting thickness on the rear rotor. (SEE FMSI manual) Not the minimum thickness. Minimum is really up to the facility/shop doing the turning. You will not find a minimum thickness listed because of liability issues.
3.) ALL OEM rotors come out of the box, needing to be turned, so that they will be true. They are never perfect.
4.) Request a fine turn when getting rotors turned. Every facility/shop can do it, they must slow the machine down, which they don't want to do. This will give a smoother finish, creating fewer "pores" to be filled. This will create better braking power and increase the life of the pads. The rotor should look like it did new.
5.) It is a good practice to turn or replace rotors with every long term brake change. They do slightly warp, and this puts them back true again. However, seeing as you should turn brand new OEM rotors anyway, if you don't need to buy them, don't. Just have them lightly turned.
6.) Higher end, more expensive rotors are typically true out of the box, but not always.

Hope this helps.

Mike Jr.

 

I haven't seen the factory service manual, but when I pulled out the micrometer to check my rotors yesterday my rears were at 9.1xmm - 0.7 thicker than you claim the starting thickness to be (fronts were 20.35). I think I remember seeing "MIN THICKNESS xx.x MM" (or some variant of that spelling) on the rotors where xx.x matches up to what you said it the starting thickness.

 

I think there might be a mis print in the FMSI. The OEM rotors are stamped with a MIN thickness of 20.4 in the front. Rears are 8mm

Please do not use any rotor that is less then 20.4mm in the front or 8mm in the rear.

 

Hey 101101,
That may very well be true. I am simply stating the minimum starting thickness guidelines from the Friction Materials Standards Institute, which is the organization that is used as the basis for the US friction industry. The FMSI dimensions come from the manufacturers. Yes, they can be a little thicker, I have been told they are as thick as 22mm new, and that is entirely possible, and with some wear your rotors may still be thicker than 20.4mm. The thickness of the pad is based on the FMSI numbers as well, and there have been some cases where we discovered that we could add some mm's to a pad, but there has to be a guideline for all of us to use. At the thickness your rotor still has, it sounds like you have a good bit of life left in them. Thank you for making me clarify, I should have been more specific in my original post. Nice catch.

Mike Jr.

 

Very good information here from all. Personally, I always replace rotors when installing new pads. Pads and rotors form a mating surface over time and there is a lot of forces involved in their operation (heat too!). Material is removed from both surfaces by design throughout their lifetime (that is what all the dust is). Brakes are something that your life could depend on and not a place to go cheap...

 

Sorry I quoted the wrong value for the rear brake disk minimum thickness. I've corrected the earlier post for future readers and reiterate here: the minimum thickness for the rear disk is 8.4mm, max machining limit 0.8mm, wear warning at 3mm (pad thk), surface roughness of disk face 0.5 to 3.5 Rau, disk dia 259mm.

Front rotor same as rear except: dia 294mm, min thk 20.4

 

i'm a track rat that currently uses the same rotors w/ street and track pads. i mic my rotors when i change pads. i replace them when they approach 10% loss in thickness. i'm on my fourth set of front rotors and third set of rear rotors w/ 28k on the odometer (including the swap to bbk and larger rear rotors). i'll switch to track only rotors w/ the death of this current set.

 

Well, I replaced the rear brakes the other day and the rear rotors were OK, so I reused them. The front ones have too big of a lip to be reused, however. The pads are not flush on the disc so I dont feel comfortable reusing them. Maybe after a few miles the pad would wear down on the edge and fit properly, but I dont think that is a good idea. So I will replace them. Im not even going to bother turning them because new ones are like 50 bucks each.

 

I've NEVER heard that you routinely have to turn new rotors.

- Mark

 

It was normal in the old days, with drums.

 

I am looking at the Bentley service manual right now and it has a table for brake rotor specifications. It says:

Front brake rotor thickness:
New: 22 mm
Wear limit: 19mm

Rear brake rotor thickness:
New: 10 mm
Wear limit: 7 mm

I am planning on replacing my MCS's brake pads this weekend and will not be replacing (or resurfacing) the rotors. My fronts are at 20.5 mm and rears at 8.7 mm. 58K miles on the car.