Author Topic: Bent brake disk (Read 2605 times)

Johnny340 · « **on:** March 27, 2016, 05:59:33 PM »

Once my front brake heats up it feels on-off-on-off even with a constant lever pull. It's fine when cold but feels like a bent rotor when hot. Can it be turned? Any suggestions?

'81 CB650 single disk.

Stev-o · « **Reply #1 on:** March 27, 2016, 08:26:01 PM »

It could be warped. It is stainless and generally not turned but can be ground. Might be easier/cheaper to find a good, used replacement.

SOHC4 Cafe Racer Fan · « **Reply #2 on:** March 27, 2016, 08:43:01 PM »

Quote from: Stev-o on March 27, 2016, 08:26:01 PM

It could be warped. It is stainless and generally not turned but can be ground. Might be easier/cheaper to find a good, used replacement.

Yep. If it is sticking in the same place consistently, it might be warped. Buy a clean replacement, maybe from from Godfrey that's already resurfaced and thinned.

Johnny340 · « **Reply #3 on:** March 27, 2016, 10:33:35 PM »

Thanks guys! I'm working on finding a replacement for it now.

flybox1 · « **Reply #4 on:** March 28, 2016, 08:01:04 AM »

Quote from: CB750 Cafe Racer Fan on March 27, 2016, 08:43:01 PM

Yep. If it is sticking in the same place consistently, it might be warped. Buy a clean replacement, maybe from from Godfrey that's already resurfaced and thinned.

+1 - great advice!

BobbyR · « **Reply #5 on:** March 28, 2016, 08:06:33 AM »

This is a long shot. Brake rotors can develop hard spots if they have been heated. The hard spots are slicker than the normal spots, like a glaze. You can try sanding them with a coarse sandpaper. This happens a lot with car rotors and causes a pulse. It is mistaken for a warped rotor.

754 · « **Reply #6 on:** March 28, 2016, 08:36:08 AM »

Check it with a dial indicator..

Johnny340 · « **Reply #7 on:** March 28, 2016, 10:21:48 AM »

Quote from: BobbyR on March 28, 2016, 08:06:33 AM

This is a long shot. Brake rotors can develop hard spots if they have been heated. The hard spots are slicker than the normal spots, like a glaze. You can try sanding them with a coarse sandpaper. This happens a lot with car rotors and causes a pulse. It is mistaken for a warped rotor.

This theory is actually supported by the fact that it works perfect when cold. I thought there was something on the pads so I put in a new set and the problem continued. I'll try sanding it first!

754 · « **Reply #8 on:** March 28, 2016, 10:46:09 AM »

See how much runout it has. Will help with the solution....

Johnny340 · « **Reply #9 on:** March 28, 2016, 11:05:01 AM »

Quote from: 754 on March 28, 2016, 10:46:09 AM

See how much runout it has. Will help with the solution....

I'll do that first. Thank you.

754 · « **Reply #10 on:** March 28, 2016, 11:17:45 AM »

If its the one piece thin disc... Like 77/78 F 750....... You may be able to bump it, with a soft hammer or padded 2x2.... I suspect if it took a small hit it would be bent toward the spokes and you would have to hit from the back.... Go real easy

Johnny340 · « **Reply #11 on:** March 29, 2016, 08:15:19 PM »

Quote from: 754 on March 28, 2016, 11:17:45 AM

If its the one piece thin disc... Like 77/78 F 750....... You may be able to bump it, with a soft hammer or padded 2x2.... I suspect if it took a small hit it would be bent toward the spokes and you would have to hit from the back.... Go real easy

According to the dial indicator, it's bent. You are right about which way too! I'll have a go with it when I get back in town next.

RAFster122s · « **Reply #12 on:** March 30, 2016, 01:26:21 AM »

Truedisk can thin and gives great results on their discs.
Might be a solution for discs that develop a hard spot and not bent...

Johnny340 · « **Reply #13 on:** April 19, 2016, 10:56:45 PM »

Quote from: RAF122S on March 30, 2016, 01:26:21 AM

Truedisk can thin and gives great results on their discs.
Might be a solution for discs that develop a hard spot and not bent...

Is Tom at Truedisk still doing this? His contact form on the website doesn't work and an email to him bounced back..

RAFster122s · « **Reply #14 on:** April 20, 2016, 07:05:21 PM »

Johnny, Have you tried giving Tom a call? (734)625-0260 according to his website. He will true only to minimum thickness specs by manufacturer...so, if you want thinner than that you will need to go with Godfrey.
David

Johnny340 · « **Reply #15 on:** April 21, 2016, 09:04:15 AM »

Quote from: RAF122S on April 20, 2016, 07:05:21 PM

Johnny, Have you tried giving Tom a call? (734)625-0260 according to his website. He will true only to minimum thickness specs by manufacturer...so, if you want thinner than that you will need to go with Godfrey.
David

I left a message on that number (who's greeting didn't mention Truedisk at all). Do you have a contact website/number for Godfrey?
Thanks

RAFster122s · « **Reply #16 on:** April 21, 2016, 11:00:26 AM »

Johnny, go to Members and then in page 201 you find Godffrey's user id and details.
he has link to site at bottom
otherwise go to vinmoto.org to find link into Godffrey's area.

Mention the sohc4 list and your id, always good to know where someone is finding you...

David

Johnny340 · « **Reply #17 on:** April 23, 2016, 05:42:00 PM »

Just to end this thread:
I contacted Godfrey and he does a lot of things but grinding one piece rotors like this particular style isn't one of them.
Truedisk must not be in business anymore. No replies to phone messages either.

I never could fully straighten my rotor so I managed to find a good replacement locally from SuperDave for $40. Works perfect. And by perfect, I mean straight with no pulse at the lever but just as anemic as before in terms of power.

Any brake pad brand recommendations for this single disk that might improve performance would be welcomed. (I'm currently trying Bikemaster Sintered pads.)

Powderman · « **Reply #18 on:** April 23, 2016, 07:17:06 PM »

Have you swapped to braided steel brake line yet. Big improvements with that small mod.

Johnny340 · « **Reply #19 on:** April 24, 2016, 08:25:43 AM »

Steel braided line is as great idea. I'll do that next. The lever doesn't feel that spongy but I know that will help out with the power.
As for Truedisk, I tied using the contact form on their website but it didn't work, then I tried an email which bounced back, so I left a phone message with no reply. Yes, weird.

Johnny340 · « **Reply #20 on:** May 19, 2016, 07:23:35 AM »

Quote from: Powderman on April 23, 2016, 07:17:06 PM

Have you swapped to braided steel brake line yet. Big improvements with that small mod.

I just changed to a steel braided line yesterday and polished the caliper piston (among other things) while it was apart. You're right, Powderman, big improvement in power and looks cooler too!

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Author Topic: Bent brake disk (Read 2605 times)