Author Topic: 1978 CB750K front brake rotors - what is "thinned" (Read 2573 times)

SKTP · « **on:** August 06, 2018, 10:38:51 AM »

So I know one of my discs is warped...it drags fairly badly seemingly however I adjust it...so I need new rotors

I was thinking of ordering from Godffery's Garage but was wondering what "thinned" means? I will call Godffery, but I also wondered if the forum had some input...Why would I want thinned rotors? Whouldn't you want as much material on the rotors as factory?

https://godfferysgarage.com/project/twin-disc-rotor-kit-with-calipers/

Bankerdanny · « **Reply #1 on:** August 06, 2018, 11:07:55 AM »

It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.

Airborne 82nd · « **Reply #2 on:** August 06, 2018, 11:46:46 AM »

Quote from: Bankerdanny on August 06, 2018, 11:07:55 AM

It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.

How does that work

slikwilli420 · « **Reply #3 on:** August 06, 2018, 11:52:20 AM »

I would only run thinned rotors with dual discs, but that may not even be necessary. The original stainless these are made from is total garbage by any standard, so thinning and drilling does give them a nice performance boost. The reduced weight will also help with gyroscopic effect as you turn, but on the street you probably wont notice.

MCRider · « **Reply #4 on:** August 06, 2018, 12:13:00 PM »

Quote from: Airborne 82nd on August 06, 2018, 11:46:46 AM

Quote from: Bankerdanny on August 06, 2018, 11:07:55 AM
It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.
How does that work

He meant to say thinner, I'm sure.

Airborne 82nd · « **Reply #5 on:** August 06, 2018, 12:57:10 PM »

Quote from: MCRider on August 06, 2018, 12:13:00 PM

Quote from: Airborne 82nd on August 06, 2018, 11:46:46 AM
Quote from: Bankerdanny on August 06, 2018, 11:07:55 AM
It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.
How does that work
He meant to say thinner, I'm sure.

I know that's why I put the grin just messing with Danny

Bankerdanny · « **Reply #6 on:** August 06, 2018, 12:59:02 PM »

Quote from: Airborne 82nd on August 06, 2018, 11:46:46 AM

Quote from: Bankerdanny on August 06, 2018, 11:07:55 AM
It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.
How does that work

oops. LOL

Airborne 82nd · « **Reply #7 on:** August 06, 2018, 01:01:00 PM »

Quote from: MCRider on August 06, 2018, 12:13:00 PM

Quote from: Airborne 82nd on August 06, 2018, 11:46:46 AM
Quote from: Bankerdanny on August 06, 2018, 11:07:55 AM
It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.
How does that work
He meant to say thinner, I'm sure.

I know that's why I put the grin just messing with Danny

I wish I had a doller for all my typos.
Airborne

MCRider · « **Reply #8 on:** August 06, 2018, 01:10:33 PM »

Quote from: Airborne 82nd on August 06, 2018, 01:01:00 PM

Quote from: MCRider on August 06, 2018, 12:13:00 PM
Quote from: Airborne 82nd on August 06, 2018, 11:46:46 AM
Quote from: Bankerdanny on August 06, 2018, 11:07:55 AM
It means just what it says, the rotor is turned down to be thicker. I had one of his rotors on my 550, I loved it. Eventually my 750F will get the Godffery treatment on both the front and rear.

Between the holes and the thinning the rotor weighs less and cools better. I weigh almost 250lbs and last summer did a long trip through the mountains in Colorado and Arizona and didn't have any issues with lack of stopping ability.
How does that work
He meant to say thinner, I'm sure.
I know that's why I put the grin just messing with Danny I wish I had a doller for all my typos.
Airborne

Ah, me too.

beemerbum · « **Reply #9 on:** August 06, 2018, 02:56:55 PM »

I thought stainless rotors could not be turned in a lathe. Isn't the stainless too springy for turning unlike an iron car rotor?

754 · « **Reply #10 on:** August 06, 2018, 04:36:46 PM »

It is tough to turn, but can also be milled or ground.
But yes tryingvto thinning on a lathe can make you feel like you forgot how to use a lathe.

seanbarney41 · « **Reply #11 on:** August 06, 2018, 05:08:19 PM »

Goddfrey blanchard grinds, if I am not mistaken...SKTP, how would a warped rotor result in dragging? If your brake/s are dragging than they are adjusted incorrectly, something is wrong with your caliper, or your forks are assembled wrong. A warped rotor would result in a throbbing, vibration when the brakes are used.

I had my rotors thinned by Goddfrey. In talking with him about whether my cores would be useable, we found that between the 2 of us, he had only ever seen one rotor that was bent, certainly from some kind of severe impact. These sohc rotors do not warp, wear down, groove or otherwise go bad. Honda certainly wayyyy overbuilt them. That is why you can thin them to nearly half their original thickness...super worthwhile mod imo, especially to the point of a requirement, with dual front discs.

seanbarney41 · « **Reply #12 on:** August 06, 2018, 05:18:14 PM »

Here is what my F rear rotor looked like fresh from Goddfrey's Garage...

KIMG0098 by Sean Barney, on Flickr

scottly · « **Reply #13 on:** August 06, 2018, 09:24:34 PM »

I've seen a rotor that "wobbled" about .015" at the outer edge. Turned out the rotor itself was flat, but the mounting surface of the hub wasn't parallel with the face of the hub on the other side, where it seats against the wheel hub.
The stock front rotors of all the CBs are a nominal 7mm thick, except for the F2/F3, and 650s, which have 5mm thick rotors.

SKTP · « **Reply #14 on:** August 07, 2018, 10:47:45 AM »

Ok...I'm about to buy a pair...is there any reason why I shouldn't? Seems like the best deal on new rotors that I can find

SOHC4 Cafe Racer Fan · « **Reply #15 on:** August 07, 2018, 10:57:33 AM »

I thinned a pair of GL rotors on my 750 before swapping to EBC's (even lighter). It's all unsprung mass that just makes the bike slower to accelerate, stop and turn.

slikwilli420 · « **Reply #16 on:** August 07, 2018, 12:06:22 PM »

Quote from: SKTP on August 07, 2018, 10:47:45 AM

Ok...I'm about to buy a pair...is there any reason why I shouldn't? Seems like the best deal on new rotors that I can find

No reason not to. Question is why you waited so long.

flybox1 · « **Reply #17 on:** August 07, 2018, 12:16:25 PM »

Quote from: slikwilli420 on August 07, 2018, 12:06:22 PM

Quote from: SKTP on August 07, 2018, 10:47:45 AM
Ok...I'm about to buy a pair...is there any reason why I shouldn't? Seems like the best deal on new rotors that I can find

No reason not to. Question is why you waited so long.

One of the best upgrades I made to my K8
You'll need to choose proper hardware to accommodate the added thickness of the 2nd carrier. Either GL hub bolts or new stuff from bolt depot, etc.
You'll need to decide if you'll have Jeff rout the carrier, or do the speedo drive gear mod yourself so everything fits.
You'll need to have your patience cap on when fitting everything, including the proper spacing/shimming of the caliper arms. it takes some gentle persuasion to get it all lined up so the calipers dont bind or squeal.

...but once its done.....

There are a few good threads about it, including one I did with all the detailed hardware I used.

Bankerdanny · « **Reply #18 on:** August 07, 2018, 12:39:09 PM »

I only bought 1 disk for my 550, but with the countersunk the bolt holes so I could update to dual disks later if I wanted. I then used 2 stainless steel washers to shim the bold back out for single-disk use.

seanbarney41 · « **Reply #19 on:** August 07, 2018, 12:54:59 PM »

I think SKTP has already performed the dual disk conversion.

flybox1 · « **Reply #20 on:** August 07, 2018, 01:17:33 PM »

Quote from: seanbarney41 on August 07, 2018, 12:54:59 PM

I think SKTP has already performed the dual disk conversion.

Methinks you're correct... $:-\$

SKTP · « **Reply #21 on:** August 07, 2018, 02:17:28 PM »

Thanks everyone...I'm excited for better brakes. We measure one and it's definitely warped slightly (I forget the number) but I have a CB750 expert who is an airplane mechanic helping me finally sort this bike out. He says it's warped, it's warped

Also yes, I already have double discs...I used the GL bolts and had the heads made shorter to clear. The speedo drive uses two small pins that go into small hole in my hub. It's all in my build thread...

seanbarney41 · « **Reply #22 on:** August 07, 2018, 03:42:05 PM »

OK, but that is extremely uncommon. I have owned over 13 sohc4's and the number grows. I have a good size stack of spares sitting in my shop right now. Non of them are or were warped.

SKTP · « **Reply #23 on:** August 07, 2018, 03:53:58 PM »

Well...I suspect that it happened years ago. It was the very first time I change the front wheel to the Lester. I was pretty nervous because I'd never removed a wheel before..so I swapped it on and only had one brake caliper, but both disks. Then I took it for a test drive. It was early evening and I took off up PCH...something felt wrong, I looked down and the disc was glowing red. I'm guessing this is what caused the warping...

SOHC4 Cafe Racer Fan · « **Reply #24 on:** August 07, 2018, 05:36:15 PM »

Quote from: SKTP on August 07, 2018, 03:53:58 PM

Well...I suspect that it happened years ago. It was the very first time I change the front wheel to the Lester. I was pretty nervous because I'd never removed a wheel before..so I swapped it on and only had one brake caliper, but both disks. Then I took it for a test drive. It was early evening and I took off up PCH...something felt wrong, I looked down and the disc was glowing red. I'm guessing this is what caused the warping...

Glowing red!

MotoGP-style!

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Author Topic: 1978 CB750K front brake rotors - what is "thinned" (Read 2573 times)