When to replace the Rotors

[B-Doon]

Quick Question regarding the rotors on my 72. They are stock, do not have any scarring, but the outter lip is slightly higher than the rotor surface...These rotors appear to be stock(original to this vehicle)...Is it time to get new ones?

Secondary question....if I need to/decide to replace the rotors, what parts need to be replaced when removing the hub to get the rotor off? Can any of the hub parts be reused?

thanks,

Brian

72inka

[cj]

The difinitve way to know if you need to replace the rotor is to take a measurement of the rotor thickness(at the thinnest point). If it's too thin, replace them.

Cris

[Pierre]

Rotors are cheap enough. It also depends how hard you drive the car. The harder you drive it, the smaller the ridge before you replace.

There are no other parts that need replacing when doing rotors. But you may want to get new pads and bed them in.

BMW rotors do not get turned.

[Emyers]

02 rotors are not very expensive. However thay can be turned provided you do not exceed the minimum thickness. The number is usually engraved on the edge of the rotor. The main issue arising from turning is you remove "meat" and the rotor is more prone to warping if driven hard.

Earl

74 02Lux

02 M Roadster

72 Volvo 1800ES

[ChuckR]

i just did my rotors. seemed cheaper to buy new than take them off, drive them to a machine shop, and have them turned. the only thing you'll need is a way to torque the hex head bolts that hold it onto the hub. pretty easy. you can check your bearing at the same time and clean and re-grease. get a new cotter pin too, that is usually the most difficult part of any project i have ever done! those darned bent up cotter pins.

chuck

[76duece]

Chuck, I hope you don't think I'm not your 02 buddy anymore. I only spent one day with my other 02 buddy, thats not cheating is it? I would have loved to help you out with the bearings.

Larry

[TobyB]

If they don't look 100% new, spend the $25.

You do need a new wheel seal, and if you don't know when your

bearings were regreased, it might be a good idea to clean and repack them.

Make sure to leave the nut 'almost loose' in front.

And if you don't know how old the calipers/seals are, I'd put new

seasl in them. If the inside of the bores are rusty, that can kill your nice new

rotors...

Nice, properly functioning stock brakes are quite good indeed...

t

[B-Doon]

Thanks for the advice Toby!

I was initially rebuilding my left front caliper with the seal kit (car was pulling hard upon breaking). That's what prompted my initial question regarding the rotors. I ordered new rotors, and plan to do both at the same time....however, I won't be rebuilding the right side as it was replaced less than 2k miles ago...

Brian

72inka

[MikeWooldridge]

Anyone know the thickness minimum for the '02 rotors?

TIA

Found it:

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,145834/highlight,rotor+thickness/

[B-Doon]

Toby et. al,

Do you know about these paper'ish felt pads that go between the pad and the cylinders in the caliper? There were some on the car, but they seemed pretty chewed up. Not sure what they are, or where to get them. They are paper thin and stiff....any idea if those are needed, what they are called, and if they are readily available? I checked real OEM and my haynes manual, but there was no mention of them.....

I appreciate the help! THis is my first time doing brakes....normally I leave it up to the pros, but I new the caliper was going to need work, and it would be easier/cheaper to do it myself...especially knowing project creep would take hold once I got in there....

Thanks!

Brian

[Pierre]

Those are anti-squeak anti-rattle shims. My brakes have not had them with no adverse effect, even on my track vehicles.

[02sahara]

Let me extend this topic a bit as it seems to overlap:

 

Something's off with my front brakes and I do believe the discs / rotors are warped:

1. I hear a dragging noice on the left front wheel when driving. All the time, so no rusty discs or debris. And it has a certain frequency, so not a constant tone. (See point 4.)
2. Felt both rims after 30 mins drive: Both get noticeable warm, the left one hotter. (Do car rims always get warm with standard breakings?)
3. During breaking the car stumbles; noticeable at low speeds immediately before coming to a halt.
4. Right front spins almost free, but drags slightly, but noticeable at one point (10% of the surface).
5. Left front spins not free at all, drags stronger 80% of the surface and gets a little less dragging (or non? hard to notice) for 20% of the surface at a single point. (Supports point 2.)

• (Some months ago I replaced the pads; made sure they move free – but not sure if I checked if the rotors are spinning freely. Probably afterwards when I pushed back the pistons and it was fine ...)

Usually I would say: Replace the rotors, they are warped, and fine. But with the strong dragging left side and especially the more dragging surface, than free spinning surface of the disc, it leads me to the question, if it is rather (or also) a caliper piston issue?

 

Is that hard to tell or does anyone have strong opinions about that? Would be happy if someone could confirm that this might only be the rotors(!). 

 

Meanwhile I thought about a big vented brakes upgrade IF I would need to replace or rebuild the calipers, cause it seems that little more effort and hardware would do the upgrade. But it also does not seem to be a complete bolt-on solution, which I probably wouldn't do then ... so how easy/often to discs get warped?

Edited August 11 by 02sahara
Symptom added

[Son of Marty]

It sounds like a caliper problem, When you replaced the pads did all the pistons retracted easily? if they did suspect the flex lines, how old are they? When they hoses break down they allow brake pressure to extend the piston but won't release the pressure when you take you foot off the brake pedal. As for the disc's themselves a quick runout measurement will tell if they are warped. 

[Stevenc22]

unbolt the caliper on the bad side and see if the rotor spins freely. If it doesn't, it might be wheel bearing problems. If it does, then you probably have a caliper issue. See if the pistons move freely and are in good condition. No point in replacing pads and rotors if you just going to burn them out because of different problem.

['76mintgrün'02]

My front brakes were dragging due to rust in the caliper bores.  The seals are set back around a quarter of an inch and that outer part gets rusty, causing the pistons to get hung up.  I scraped the rust out and the problem went away.

 

As mentioned, the flex lines could also be the problem, if they're swollen shut and not allowing the pressure to bleed off. 

 

If you pump the pedal and they hang up, then crack the bleeders and they free up, then the hoses are probably the problem.  If they're still dragging after cracking the bleeders, I'm betting on rust in the bores.