Rotor thickness.

So my internet search skills suck. I have been searching the intarweb yo for an hour trying to find min. thickness specs for the front rotors on my new (to me) 90 CR-X DX. I can find any tourque spec I want but no rotor thinckness specs. ARRGH! Anyone mind looking in their manual?

On a related note can anyone reccomend the factory manual over the Haynes or Chilton one?

Most of the rotors I've worked with had the minimum specs cast into the rotor. The Haynes manuals I have are better for wiring than the Chilton manuals. I usually go with the Haynes.

Min spec is 0.748"

In the future you can go to http://www.bendixcatalog.com/Application.aspx?b=B and then punch in your application

in line with the OP's question... is .005 too much to take off the rotors of a CRX that's used exclusively as an a-x/track day car (loss of heat absorbing mass is the worry)

.005? it's hard to get a clean cut less than .010 unless you have very good equipment and are starting with a dead-true rotor. Usually rotors lose .020-.040" from machining.

That said... I view minimum thickness specs as just a guideline. I've gone well under with with no worries.

I also only machine rotors if there's a pulsation, and that's always the Previous Owner's Fault. Install a rotor with zero runout, don't hold your foot on the brake after coming to a stop, and you've just eliminated 99% of the pulsation problems in the world.

Just replace them. Probably $20 - $25 a piece. The last thing you want to do is machine them even close to min. tolerance. The thinner the rotor, the more likely they are to warp. Especially when you hit a puddle when those rotors are hot.

Rock Auto, Raybestos 96147DR, $16.87 each plus shipping. Autozone 31029B, $21.99 each. Bet you can't turn them for less than $10 each.

Nowadays it's around $15 a piece to turn.

rotors don't warp through usage*. 99-point-a-whole-friggin-lot percent of "warped" rotors simply have an uneven transfer layer of friction on them, and the pulsation felt through the pedal and through the chassis is torque variation, not thickness variation, due to that uneven transfer layer.

*yes, i made a sweeping generalization there.

Good, cause I was about to say the same thing.

Uneven rusting will pulse the peddle, but that's from negligence.

AngryCorvair wrote: rotors don't warp through usage*. 99-point-a-whole-friggin-lot percent of "warped" rotors simply have an uneven transfer layer of friction on them, and the pulsation felt through the pedal and through the chassis is torque variation, not thickness variation, due to that uneven transfer layer. *yes, i made a sweeping generalization there.

Interesting, pretty sure this is what's going on with my car. How does it happen, and can it be fixed without replacing parts?

I think it comes from improper bedding. Slapping on new rotors and pads and driving like normal. The pads will heat up and transfer some of the friction material to the fresh rotor. Then you go into Wal-Mart. The pad still is transferring material to the disk, just in that one spot. That spot is now extra "sticky." When you come out of the store and drive, then brake, its sliiiiiide-grab-sliiiiide-grab-sliiiide pulsations.

Stop Tech's web site has a great section on brake bedding. I use cheap crap Vato-Zone's on the Caprice, and using their procedure worked awesome.

Not sure if there is a free fix. Maybe pull the pads, hose down the rotors with brake cleaner, and scuff both sides with steel wool?

Appleseed wrote: I think it comes from improper bedding. Slapping on new rotors and pads and driving like normal. The pads will heat up and transfer some of the friction material to the fresh rotor. Then you go into Wal-Mart. The pad still is transferring material to the disk, just in that one spot. That spot is now extra "sticky." When you come out of the store and drive, then brake, its sliiiiiide-grab-sliiiiide-grab-sliiiide pulsations. Stop Tech's web site has a great section on brake bedding. I use cheap crap Vato-Zone's on the Caprice, and using their procedure worked awesome. Not sure if there is a free fix. Maybe pull the pads, hose down the rotors with brake cleaner, and scuff both sides with steel wool?

I try to bed in the pads per as best I can, but I live in a city (fairly high traffic area at that) so it's a bit tricky. I suppose I could do it at 3am next time around...

I'll have to check out the Stop Tech site. Though I am somewhat happy to hear that it might not be warped rotors - I'm running half-way decent stuff, NAPA blanks with their mid-level ceramic pads (PBR), so I was rather grumpy when they started acting warped a few months ago.

Thanks Mith. I asked because I was giving the CRX a once over and wanted to know that the rotors were within spec. The pads are about 80-90% so I will wait until I replace the craptastic tires and wheels. I too have run rotors under spec on a street car but only with near full life pads so the calipre piston wont extend far enough to cant and bind in its bore. Rotors used to be much more expensive than they are now.

The_Pirate wrote:

AngryCorvair wrote: rotors don't warp through usage*. 99-point-a-whole-friggin-lot percent of "warped" rotors simply have an uneven transfer layer of friction on them, and the pulsation felt through the pedal and through the chassis is torque variation, not thickness variation, due to that uneven transfer layer. *yes, i made a sweeping generalization there.

Interesting, pretty sure this is what's going on with my car. How does it happen, and can it be fixed without replacing parts?

I've had good luck fixing rotors with a bad spot of pad transfer material by just re-bedding them in - once everything gets hot enough that any loose trash / old friction material sitting on the caliper lights on fire, you've gotten them hot enough to remove the "sticky" spot and place a nice even layer of pad material on the rotor. 5 threshold stops from 30-5, then 5 from 40-5, 50-5 and then at least 5 stops from 60-5 or until you get massive brake fade, then drive around at least 10 minutes without hitting the brakes at all if possible to allow everything to cool nice and evenly. Do not apply parking brake when parking after this is done. New pads and rotors are going on the 944 turbo tonight, bedding them ought to be fun I should probably re-install the brake cooling ducts I found in the pile of parts the owner included while I'm there.

In reply to porksboy:

No problem. We carry Bendix at work so that's where I got the link from. It's a great resource; it's how I found that 91 CRX rear rotors would be near perfect to convert my Opel to rear discs.

In reply to pigeon:

Yep, sometimes just going through the bedding procedure properly will fix it.