Blue brake rotor bad?

[Anonymous]

I have an '83 GS550E that I recently got on the road again, but the rear brake was sticking. I pried the pads apart and found that the master cylinder was not moving the pads anymore. So I ordered the parts to rebuild them. No problem, I figure, 90% of braking comes from the front anyway, but I continued to tap the rear brake pedal because that is the brake that has the switch I can trust to actuate the rear brake light.
Apparently the master cylinder did somehow continue to move the pads in some, as last Friday while riding on the freeway I noticed some sluggish performance. By the time I got to an exit to get off and pry the pads apart, the plastic cover was actually on fire and the rotor has changed color to bluish. (If you want attention at stoplights, I don't think you can do better than flaming parts.)

So, all the indicated parts are on order and I just so happen to have a spare rotor. (I'm replacing the pads and fluid, also master cylinder cup and cone. I'll see if I can get a new cover, but I'm not hopeful). My question is whether the blued pad is still any good, it still mikes out okay, and isn't warped. I would guess the conventional wisdom is to replace it, but what happens to the metal on an overheated rotor to make it bad?

[Anonymous]

replace

If you've got a spare I'd replace it. By the rotor turning blue you've upset the temper, it's more than likely softened it up. It would work but you don't know the internal stresses built up, it could crack which wouldn't be a pretty sight. Same thing happens when you blue a drill bit while sharpening it, too soft and won't keep an edge...Mike

[Eliseo Monteverde]

Re: replace

If you've got a spare I'd replace it. By the rotor turning blue you've upset the temper, it's more than likely softened it up. It would work but you don't know the internal stresses built up, it could crack which wouldn't be a pretty sight. Same thing happens when you blue a drill bit while sharpening it, too soft and won't keep an edge...Mike

Also don?t forget to check or replace the brake pads.

[snowbeard]

WOW!! sounds like a fun ride I had in a friend's grandmother's car (grandmother driving!) that got it's throttle stuck going down the business side of a mountain, with the engine in gear it was just accelerating constantly (down!) and if we put it in neutral it would rev so fast we were sure we'd blow the engine!! so she braked all the way down the hill, and in the dusky twilight at the (thank god!) bottom of the hill we could see the rotors glowing a dull red!!! 8O 8O

yep, toss it, the temper is shot.

[Anonymous]

Just a quick update. I rebuilt the master cylinder and since the dealer ordered the wrong parts anyway and I had them, I rebuilt the calipers with new pistons. The calipers were quite a mess, and probably needed the attention judging by the gunk and how bad the gasket was in there. After getting it all together and not changing the disc like everybody advised me to, the rear brakes work fairly well. I can lock them up easily enough, although the discs are very badly glazed, everything works like I expected. Thanks for the advice, I'll sand the disc first and then change it if need be. Oh yeah, I did change the pads for some eBay specials.

[earlfor]

Considering you already have a spare brake rotor and considering if it does fracture, its probable you will take a face down side on the asphalt and get run over by the truck behind you, I think its foolish to not replace it.

Earl

Just a quick update. I rebuilt the master cylinder and since the dealer ordered the wrong parts anyway and I had them, I rebuilt the calipers with new pistons. The calipers were quite a mess, and probably needed the attention judging by the gunk and how bad the gasket was in there. After getting it all together and not changing the disc like everybody advised me to, the rear brakes work fairly well. I can lock them up easily enough, although the discs are very badly glazed and everything works like I expected. Thanks for the advice, I'll sand the disc first and then change it if need be.

[Anonymous]

I found some stuff about disc cracks googling, but not a lot of info really. What happens when they fracture? I assume you are saying that the disc can break and somehow get bunged up in the caliper and lock the wheel. Does that really happen?

I guess I'll change my plans and change the disc tomorrow.

[earlfor]

It could happen, but I certainly cant predict it will happen. :-) Why risk it when wearing a truck could be the result. heh heh Consider being on a two lane road, heading towards a turn with oncoming traffic, realizing you're going a little faster than you want, and getting on the brakes only to find the rear disk shatters and the wheel locks. You're going tp slide head on into the oncoming traffic. Its not a risk I'm willing to take for the cost of a rotor.

Earl

I found some stuff about disc cracks googling, but not a lot of info really. What happens when they fracture? I assume you are saying that the disc can break and somehow get bunged up in the caliper and lock the wheel. Does that really happen?

I guess I'll change my plans and change the disc tomorrow.

[argonsagas]

Since you already had a spare rotor, I fail to understand why you did not change it for the burned rotor while you had everything apart.

I could be wrong on this, but I don't see it as likely that the burned one will shatter, unless you poured water on it while it was smoking, thus making parts of it brittle.

Regardless of that, there is no question superheated metal becomes prone to distortion under stress, (both heat and stress are inevitable even with normal braking) and with that distortion, a previously-superheated brake disc becomes prone to either grabbing or skipping, and you cannot predict which one will occur, or with what severity.

We don't know how hot your disc became, or for how long, and we don' t know anything about its cooling situation, only that it is now blue, which suggests a VERY high heat. Discs are supposed to take a high heat, but they are not supposed to be superheated for extended periods.

Since the pads were not releasing, there is also no doubt that a great deal of heat was concentrated in that area, so the disc could not cool down evenly, again leaving room for question about it.

Too many negative possibilities on an important safety item.

For the sake of your own safety, change the disc.

[jimcor]

I can lock them up easily enough, although the discs are very badly glazed, everything works like I expected. .

The fact that they can be locked up easily is NOT indicative of good brakes or a propely operating system. Toss that blue rotor and put on your spare. :roll: