QUICK QUESTION re: brake pad change

[jbripps]

Hi all,

I am surely becoming more of a DIY guy, so I'm going to change brake pads in the near future. I'm waiting on the Feroda pads from our host.......hurry Wayne!

Anyhow, I'm aware that the discs will need to machined/turned, and I know not got go below the minimum thickness.

I guess my main question is......when I'm at a DE, I see tons of guys swapping out their pads.....and it does not appear that they are turning rotors/discs. Won't that warp the discs very rapidly. Am I missing something?

Any input and feedback would be appreciated. Also, I'm attending the a free brake pad change workshop through my PCA club in Melville, NJ on Saturday, March 13...... anyone care to attend? You can be my guest, and check out a club activity.

regards,

[jbripps]

shameless bump........there's gotta be someone with input.

thanks,

[RickM]

Hmm, opinions will most likely vary and I'm no expert but I've changed plenty o pads. My take is that turning the rotor will do two things...first remove any glaze that may have developed which will inhibit heat dispersion. Second it brings the surface back to afford the pad as much surface area as possible to contact.
My rule of thumb for a street application is usually to turn the rotors on every other pad change. There are a few factors that I consider, such as time between changes, squealing, bearing change, rotor condition (obvious), type of pad compound used etc.

I can't really speak for the racing crowd but I'm sure they'll chime in.

[na2ub]

You don't need to have your discs machined between pads. There are only two things to check on you discs (I do neither - reasons stated below). One is to check for thickness (micrometer, see porsche specs or the disc specs for minimum allowed thickness). Two, warpage, aka runout. I am not exactly sure how to check for this, but with a similar measuring device, checking the amount of deflection as you turn the rotor one rotation.

If your rotors are warped - you must replace
If your rotors are below mimimum thickness - you should replace
The only reason to have them turned, is if the are grooved from letting your brake pads go to low. This simply restores a full, even contact surface for the new pads.

The reasons I dont check:
You will know if your rotors are warped because the car will shimmy when you step on the brake. You will know when your rotors are to thin, because they will warp. I never let the pads wear all the way down, and grind the rotors, so I never get my discs turned.

(EDIT) I suppose RickM has a good point. You might want to get them turned if they are glazed or discolored.

Clear as mud?

[vash]

i didnt turn mine. i think if you stay on top of the pad changes, and do it before you get any metal on metal contact, you will be fine. your pads will probably wear out slower if you do turn the rotors, but i bet even that is miniscule.

cliff

[Superman]

It's a good idea to "break the glaze," but that's not easy. You have to use something fairly aggressive. If rotors need to go to the machine shop, grinding them is better than "turning" them, particularly if they have been used. The cutting edge will skip over spots that have been heat-hardened if you 'turn' them. Again, just break the glaze. If you can.

[David]

There's some good brake info on Wilwood's web site. The main point they make is that it's best to bed in new pads with old rotors and new rotors with old pads. This is better for optimum brake function but not neccesarily for optimum brake quietness.

[jbripps]

Hey all,

Thanks for creating a mental tug-of-war for me. It seems that the opinions are split. 101 projects advises turning them, as well as the staff at PP, however, many say don't worry unless they are worn or grooved. Let the debate continue. I know it's not that big of a deal to get them turned, but why bother if I don't have to?

thanks again,

[vash]

when you take your tires off, you will see how easy it is to pop the pads out and put new ones in. on the other hand, when you take a look at the fancy wrenching (not hard) needed to take the rotors out for a nice turning you will see. it is like the big fat anchor dude on the side of the mental tug-o-war that saying "rotors look great, no turning needed... this time".

[RickM]

Where the heck is Kurt? I'd swear he's be in here setting us straight.

[aj88cab]

Originally posted by unfixed
it is like the big fat anchor dude on the side of the mental tug-o-war that saying "rotors look great, no turning needed... this time".

That's what you say the second time you do the brakes. The first time it's more like "WHAT THE F....."!

[JavaBrewer]

Originally posted by unfixed
when you take your tires off, you will see how easy it is to pop the pads out and put new ones in. on the other hand, when you take a look at the fancy wrenching (not hard) needed to take the rotors out for a nice turning you will see. it is like the big fat anchor dude on the side of the mental tug-o-war that saying "rotors look great, no turning needed... this time".

Yep. My Carrera differed from the 101 Projects SC in that the soft brakeline connected to the hard brake line through a welded tab to the strut - not to a clip that could be pulled free. To replace a rotor you need to remove the brake caliper which will force you to disconnect the hard/soft line (to avoid pinching the hard line). You will need a special wrench (crow foot?) and then bleed the brakes when finished. I replaced the pads w/o touching the rotors - they were pretty new - no worries, wobbles, or squeeling.

[howiee]

Haven't done it on the p-car yet but on my Honda's I just sanded the rotor with 80 grit sand paper to rough it up and give the new pads something to grab on. If they aren't warped don't loose valuable metal by getting them turned. Like na2ub said, they will warp when they start to over heat from being too thin. Never had a problem and I auto x'ed my Honda's. Not the same abuse as DE's but still harder on brakes than your average daily drive.

[gr8fl4porsche]

I stopped turning rotors years ago. If your rotors are bad enough to need turning then get new ones. My previous experience is that when you turn rotors, they will warp soon. I quickly sand the surfaces with 80 grit paper on a D/A and set in new pads. Never had a problem yet.

[RickM]

Some lightly turn new rotors as well. I never have but I know people that do.

[randywebb]

Originally posted by 125shifter
There's some good brake info on Wilwood's web site. The main point they make is that it's best to bed in new pads with old rotors and new rotors with old pads. This is better for optimum brake function but not neccesarily for optimum brake quietness.

http://brakepads.wilwood.com/03-tech/index.html#Anchor-Note-63116

[ZOA NOM]

+1 for no turning until wobbles.

[Jack Olsen]

I'm no brake expert, but Carroll Smith says it's a myth: rotors don't warp. The pulsing phenomenon is from pad material building up on the rotor.

As a data point: I've only ever had rotors turned or ground if there was enough metal-on-metal contact to make grooves. And I agree with the idea that it's probably cheaper to just replace most rotors rather than turn or grind them.

I've got six years on my 930 front rotors, right now (which is good, since they're over $400 a set). My rotors have never been turned or ground. They're still within spec, and I've never had any issues with uneven braking within them. I use Porterfield street and race pads and I switch back and forth all the time. I make sure new pads have had a chance to bed before a track day, but that's about the sum of it.

[rnln]

Has anyone ever seen this? Very cheap brake rotors. I wonder how are they?
http://cgi.ebay.com/ebaymotors/Porsche-911-84-89-OEM-Replace-Front-Brake-Rotor-SET_W0QQcmdZViewItemQQcategoryZ33564QQihZ019QQitem Z8075732187QQrdZ1QQsspagenameZWD1V
ebay item# 8075732187

[SWISSMADE]

If you feel any pulsating on the brake pedal when braking...turn the rotors. If they have visible or tangible ridges on them...idem.
If none of the above, don't bother.

Mike.