Something no one else has mentioned (including me):
If the rotors are non-vented:
- Older vehicles can usually be turned down once if they are not grooved
too deeply
- Newer non-vented rotors should be considered throwaway.
If the rotors are vented
If they have worn evenly, they can be turned as much as .060, which is
2 -3 rounds. A good rule of thumb is, if the chamfer or bevel at the outer
edge is gone, the rotor should not be turned.
The bevel/chamfer test is also good for brake drums.
It's OK to leave a groove or two in a rotor, like where the pad rivits
have machined a deep groove. Long as the faces are parallel and smooth.
Most drums and rotrs have a minimum spec for thickness cast into it. If
not, a parts store can look it up. Generally, it's .090 for drums, .060 for
vented rotors, and .025-.030 for non-vented rotors.
Note that some late-models have a composite rotor, which means the center
"hat" is stamped steel, while the outer is cast iron. These can
theoretically be turned, but they are cheap enough most people don't bother.
Most parts houses do not have the adapters anyway, and they will screw up
the rotor and possibly not admit it. Just buy a new one.
A quick way to tell a composite rotor: The edge of the "hat" where it
bends 90-degrees from the mounting surface will be rounded. Full cast rotors
are squared off in profile.
Rex Burkheimer
J-CON Coordinator, WM Automotive Whse Fort Worth TX
Texas Region SCCA FC #19 SRX7 #39
rex@txol.net rex@ceoexpress.com
"There is pleasure sure in being mad which none but madmen know." John
Dryden
----- Original Message -----
From: Tim Mullen <Tim.Mullen@trw.com>
To: <shop-talk@autox.team.net>
Sent: Monday, February 21, 2000 11:14 AM
Subject: Re: Turning brake rotor
>
> I agree with Phil and the other's. Don't turn rotors unless you really
> have too. I "reused" rotors with groves in them, with absolutely no
> roblems.
>
> I find if strange that all the ads for "brake jobs" on the TV and
newspaper
> always include turning the rotors/drums in the price. It seems to be the
> standard practice. I guess it will help in the bedding-in of you new
brakes
> sooner, but at the overall longevity of the rotors/drums - that much less
> metal to wear off...
>
> I once had a problem with pulsating brakes on a car still under warrantee.
> I could get the pulsating while just using the parking brake, indicating
> the rear drums were the problem. I pulled the front wheels, and measured
> the run-out, parallelism, etc. and every thing was within spec. (almost
> perfect in fact). So, the car went into the dealer. I explained what the
> problem was, gave them my measurements, etc. The result? They
> turned the front rotors, and I still had the pulsating. By the time it
was
> all done, they had ground off enough of the front rotors that I had to
> buy new ones at about 40,000 miles, along with the rear drums that they
> never did fix...
>
> Tim Mullen - who likes to do his own work - so it gets done right...
>
>
>
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