Rear Brake Rotor Not Flat


Information and questions on GL1200 Goldwings (1984-1987)
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rjames
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Rear Brake Rotor Not Flat

Postby rjames » Sat Mar 21, 2015 8:25 pm



I'm in the process of rescuing an '84 GL1200 Aspencade that sat for years, only has 27,000 miles but lots of neglect. I was bead blasting the rear brake rotor and discovered it was obviously not flat. I put a steel straight edge across it and there's about an 1/8" gap in the center. The gap is consistent when checked in several places. Is this normal? There's plenty of meat in the wear surface and no signs of overheating. The brake pads that were on it look fine and could be reused. What's the deal? - Rjames



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themainviking
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Re: Rear Brake Rotor Not Flat

Postby themainviking » Sun Mar 22, 2015 6:27 am

As long as the gap is consistent, the rotor should work alright. It would seem that some force was put on one side of the disk, either in the center or around the complete outside. It might wear the brake pads unevenly, but should still get the stopping job done. It also might be a manufacturing anomaly.
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roadwanderer2
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Re: Rear Brake Rotor Not Flat

Postby roadwanderer2 » Sun Mar 22, 2015 7:42 am

themainviking wrote:As long as the gap is consistent, the rotor should work alright. It would seem that some force was put on one side of the disk, either in the center or around the complete outside. It might wear the brake pads unevenly, but should still get the stopping job done. It also might be a manufacturing anomaly.


personally, I would be a little leery about using that rotor. anytime you have a rotor that's not perfectly true round, you could wind up with a pulsation or a "wobble" when you apply the brakes. if it were mine, I would not hesitate to replace it. on a car, its not that dangerous, but on a bike, that could present a problem.

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Re: Rear Brake Rotor Not Flat

Postby tom84std » Sun Mar 22, 2015 8:53 am

If it's a radial groove and not a warp, it should be fine. I read your post a couple of times and I believe you're talking about an even groove around the entire circular surface. If that's the case, the new pad will eventually conform and you should be fine, especially on the rear. If warpage or it's uneven then as was mentioned in a previous reply, it could cause some pulsating.
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Re: Rear Brake Rotor Not Flat

Postby bustedwing » Sun Mar 22, 2015 5:16 pm

Some brake shops will turn your rotor to true it up and it's a lot cheaper than a new one.
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Re: Rear Brake Rotor Not Flat

Postby roadwanderer2 » Sun Mar 22, 2015 6:07 pm

if your thinking about having that rotor turned, go to your local Honda motorcycle dealer and get the specs for it. there's 2 different specs for the rotor, the minimum thickness spec and the "discard" spec. if its still thick enough to be turned, that's ok, but make sure its not at or below the "discard" specs when its finished. if it goes below the "discard" spec, get rid of it and get another rotor. a rotor that's at or below "discard" specs can be cause problems.

below is a pic of what can happen to a brake rotor that is too thin. notice all the cracks in it. I don't think you would want this to happen on your bike. I know this is a vented rotor, but the same thing can happen with a solid rotor as well. if there's one thing you shouldn't skimp on its your brakes, your life is worth more than using a rotor that's questionable.

stuart.
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bustedwing
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Re: Rear Brake Rotor Not Flat

Postby bustedwing » Sun Mar 22, 2015 9:20 pm

1 agree 100% with Stu, if you know someone with the tools to measure the rotor that is the most accurate way to go. Once you get the rotor to run straight, then with new pads, they will last longer and work better.
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Re: Rear Brake Rotor Not Flat

Postby roadwanderer2 » Mon Mar 23, 2015 2:03 am

bustedwing wrote:1 agree 100% with Stu, if you know someone with the tools to measure the rotor that is the most accurate way to go. Once you get the rotor to run straight, then with new pads, they will last longer and work better.


I would take measurements from 3 different spots on that rotor to be sure it was still turnable. listen, I know about brake systems, I have/had my SAE certification from Wagner brake institute as part of my training for my job. I NEVER go cheap when it comes to my brakes or the brakes on my wife's or anyone else's vehicle that I work on. you life and the lives or others depends on good brakes. its nice to be able to ride a bike, but its even nicer to be able to stop it safely.

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Re: Rear Brake Rotor Not Flat

Postby rjames » Mon Mar 23, 2015 3:33 am

Ok, it looks like the rotor is heat warped and I'm going to have to replace it. Anyone out there have a good rotor for any year GL1200 for sale? Thanks for the replies- Rjames

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Re: Rear Brake Rotor Not Flat

Postby themainviking » Mon Mar 23, 2015 6:31 am

rjames wrote:Ok, it looks like the rotor is heat warped


Well, that changes the entire scope of the thread. Yup, replace it.
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Re: Rear Brake Rotor Not Flat

Postby roadwanderer2 » Mon Mar 23, 2015 6:52 am

smart move rjames.

stuart.

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roadwanderer2
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Re: Rear Brake Rotor Not Flat

Postby roadwanderer2 » Mon Mar 23, 2015 7:24 am

rjames wrote:Ok, it looks like the rotor is heat warped and I'm going to have to replace it. Anyone out there have a good rotor for any year GL1200 for sale? Thanks for the replies- Rjames


rjames, I have some friends that run a motorcycle salvage yard near me, if you want, I can find out from them if they have a rotor for your bike if you cant find one from someone in here. let me know and i'll find out for you.

stuart.

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Re: Rear Brake Rotor Not Flat

Postby WingAdmin » Mon Mar 23, 2015 11:11 am

bustedwing wrote:Some brake shops will turn your rotor to true it up and it's a lot cheaper than a new one.


Very few brake shops will have a lathe capable of turning bike rotors. Bike rotors are much harder steel than automotive rotors, and are made not to wear like automotive rotors. You will need a specialized shop that does bike rotors if you do want to have it turned - but it's very likely it's either below spec now, or would be put below spec by turning it.

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Re: Rear Brake Rotor Not Flat

Postby roadwanderer2 » Mon Mar 23, 2015 11:49 am

WingAdmin wrote:
bustedwing wrote:Some brake shops will turn your rotor to true it up and it's a lot cheaper than a new one.


Very few brake shops will have a lathe capable of turning bike rotors. Bike rotors are much harder steel than automotive rotors, and are made not to wear like automotive rotors. You will need a specialized shop that does bike rotors if you do want to have it turned - but it's very likely it's either below spec now, or would be put below spec by turning it.


agreed 100%. its not worth the risk. just replace it.

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Re: Rear Brake Rotor Not Flat

Postby bustedwing » Tue Mar 24, 2015 1:07 pm

I agree that some rotors are beyond saving. But some can be turned and as long as it is within specs it can be re used. I have done this several times with my Gold Wing rotors, and when you pay$15 to clean them up versus ??? I don't know how much a new rotor costs, but I'm sure they are not cheap. Save the money as long as you are safe.


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