Brake Rotors-Replace When ?

My Porsche 930 technician says that I need to replace the rear brake rotors, which he quoted @ $330 each.

I did a search here on the bulletin board, trying to find out at what point one can no longer turn the rotors and replacement is necessary. I found lots of pertinent data, but nothing exactly as to when they must be replaced. Anyone have any input ? This is for a 1986 930.

Your brake rotors have a minimum thickness which any other owner could give. If it is close to or below this thickness or if you show signs of heat cracking of warping, it is time to replace. That price seems very high. There is some labor getting the rotors off. Rotors for that car could be had for $75 to $100 for one. Any other posters with a similar car, feel free to chime in with actual prices. If this fee inlcudes new pads, which you will need, for the back brakes, then it is somewhat more reasonable

In the Pelican online catalogue:

911 Turbo Front - $136.15
911 Trubo Rear - $142.55

Each. They are easy to install. I tend to 'turn' rotors when I put them on to make sure they are straight. The best brake machine shop in town charges $10.50 each.

There are wear limits you can find in spec books for example, to see if yours are worn, They are also printed on the rotors themselves.

Here's a tip: Feel the edge of the rotor. The outer edge. The pads will have dug into the rotor leaving a taller lip at the edge. If this lip is anywhere near as tall as a dime is thick, your rotors are thin.

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'83 SC

This is the same guy that thought your oil filter was too dificult for you to change, right?

I guess you must be a bit concerned about his advice and prices, not to mention his hand going into your back pocket on a too-frequent basis, lately, huh?

I suggest you put the tail of your car up on jack stands, pull off both rear wheels, and look ... all rotors have the min. thickness markings cast into them in English! Changing, or turning them and reinstalling, then bleeding the hydraulics, is an easy procedure, one you can do yourself!

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Warren Hall
1973 911S Targa

Thanks guys ! I went into the Pelican parts listing early this a.m., then posted the message. The pricing sure did seem high, it being exactly $312.13 each from the dealer. Figured I might not be seeing right, when looking at Pelican Parts pricing, therefore thought I'll just post a message. You then have verified what I saw price wise. The mechanic claims these rotors come right from Porsche , and that they will not ship until they have money 1st so "everybody" prepays via a credit card. Once they arrive, you cannot return for whatever reason. Well, seems a little strange here. Why not ship, billing them through the dealer, then bill me when the work is done, like everything else ? That's raised a little red flag and now really has me wondering ! ( perhaps some other source ? )

Yes, Early S Man, this mechanic is also my oil filter expert ! After seeing the 60 seconds it took to screw off the old, oil up the gasket on the new one, then install , I thought this is easier than changing any other filter I do routinely, be it my wife's Lexus, either of our Corvairs, my 4X4 pickup, Ford 9N tractor, or garden Cub cadet tractor. I almost said something, but just let it pass. Actions speak louder than words -as in I don't need to return for service.

My mission this weekend will be to pull the rear tires off and examine, like offered in your replys. I guess the car has somwhat intimitated me , at least initially, but now I beginning to see some of this stuff is not that bad at all, in fact some of it very straightforward !

Again, I really appreciate everyone's input.

Orph, this is a good and accurate bit of wisdom you are gaining. Mechanics charge too much and often do a mediocre job, or worse. Really. Not all, but many. there are even a few that are dangerous to your car, in addition to your wallet.

If you have a caliper to measure, you can see if they are too thin. Rear rotors may not have as much wear. Mine don't. If they are not too thin, they can be 'turned' if you wish. If you can be without the car for a day or so, just take them in to the brake shop and they'll tell you what can be done. They cannot, and will not, cut them too thin. And as Warren says, this is a good timne to bleed the hydraulinc system and install new pads if necessary.

Here's the Big Smile: if they're not too thin, you can turn the rear rotors, install new brake pads and bleed the system for under $100. This is probably more than the mechanic would have done for $500 or $600. Or more.

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'83 SC

orph,

Before you try to pull off the rotors, should they need turning or replacing, you will need a metric flare-nut wrench set -- Craftsman has a nice set. Why, because you have to remove the calipers from the trailing arm first. Don't try to loosen those fittings without a flare-nut wrench ... much aggravation and damage will result!!! Vise-Grip pliers do NOT remove brake-line fittings without severe damage!

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Warren Hall
1973 911S Targa

Is a flare nut wrench the same as an open-ended wrench? I've seen the term a lot of places, and I've been using my metric open ended wrenches successfully so far (except for a small blood-blister under my fingernail after changing the fuel filter ). Is there a feature of flare wrenches that regular open-ended wrenches don't have? Or are they the same thing?

Thanks,

Olivier
82 SC

Flare nut wrenches are a little different than open-ended wrenches. They are more like the standard box-end wrenches that touch the bolt/nut on all sides for less slippage, but they have an open area in the very end so that the wrench can slide over the tubing that connects to the nut. They work well on brake lines and fuel lines.

MarkH

Olivier,

The big problem with brake line fittings is the environment the live in ... high temperature heat cycles, lots of water splashed on them, so rust and corrosion is inevitable. The nuts and fittings are not hardened, so open-end wrenches tend to round them off when applying the high torque required to loosen them! I have seen dozens/hundreds of damaged fittings over the years. Flare-nut wrenches give the best chance of loosening without damage. I also recommend a dab of anti-sieze compound on the fitting when reinstalling ... to make things easier the next time you do work on your brakes!

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 09-10-2000).]

Thanks guys,

Now I know what you're talking about, like box-end wrenches with small cuts in the side. Maybe I'll ask my wife for a set for my birthday. I've been watching this blood blister slowly grow out with my fingernail after catching it between two open ended wrenches while loosening the fuel filter. That definitely required a lot of torque! Almost as much as the tip of my finger is rated for.

Olivier
82 SC

I'm guessing you have hi-torque fingers. Mine are measured in inch pounds rather than foot pounds.

Orph,

Sounds like your mechanic is trying to get too much money from you. I would take them off, take them to a garage, and have them turned/surfaced. This should cost $30-40 per pair.

Bill

And if you really want super rotors for just a few bucks more, ship them to Cryogenics for a very reasonable treatment and double their expected life!

Thanks for all the valuable information guys ! I pulled the wheels off, located the minimum thickness imprint in the hub, then measured . Guess what-I'm above the minimum.
I checked pads, and they ran 4mm-6mm, so new sets were ordered from Pelican, for both front and back .

I'll no doubt run through these, then look at the rotors once again.

Diverdan-What does Cryogenics do, that makes the rotors so much better ?

I am not a Cyrogenics expert but here is what I know... Cyrogenics is a computer controled process that gradually bakes the rotor under high tempetures. In increments of 1 - 2 degrees. The process is then reversed to cool the rotor. This process is suppose to change the molecular construction of the rotor resulting in a harder longer wearing rotor.

Joe A