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Author Topic: 78 GL to 75 750F0 compatability  (Read 1271 times)

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Offline Cougars750F0

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78 GL to 75 750F0 compatability
« on: May 26, 2018, 03:10:00 PM »
Just picked up a 78 GL fork with triples, brakes and rotors and wanted to know if the 78GL will be compatible with my 75 750F0. I would like to be use to run my 750 wheel sets. Thanks for your help.
« Last Edit: May 26, 2018, 03:14:16 PM by Cougars750F0 »
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline Bankerdanny

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Re: 78 GL to 75 750F0 compatability
« Reply #1 on: May 26, 2018, 04:11:00 PM »
The 78 GL used Comstar wheels not wires. The Comstars use 5 bolt rotors I believe, not the 6 used by the wires of the earlier GL's and your F0. You might be able to use your wires if you can find 75-77 GL1000 rotors.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline dusterdude

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Re: 78 GL to 75 750F0 compatability
« Reply #2 on: May 26, 2018, 04:13:04 PM »
One of the neck bearings is different too iirc

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Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #3 on: May 26, 2018, 04:46:48 PM »
Well I would sure love to find a way to make it work. ;D fill in the holes on the rotor and then drill a six hole? nope that could warp ;D trading stock never the less. I have mags wheels as well as spokes so I'd need to keep the six hole. Thanks.
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #4 on: May 26, 2018, 05:28:15 PM »
Wait a second... will the early 75 to 77 rotors work? is the bearing difference a deal breaker? Inquiring minds want to know ;D
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline American Locomotive

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Re: 78 GL to 75 750F0 compatability
« Reply #5 on: May 26, 2018, 06:03:19 PM »
My '76 F0 appears to have ~78 GL1000 forks on it. My bike has Comstars front/rear, which I like better than the wire wheels anyways, and I have 5 bolt front rotors. I bought it with the forks, so I'm not sure what the PO did to put them on, but it definitely is possible.
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Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #6 on: May 26, 2018, 06:34:10 PM »
I'll need the six bolt roror.
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline Bankerdanny

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Re: 78 GL to 75 750F0 compatability
« Reply #7 on: May 26, 2018, 10:28:13 PM »
It could just have an F2/3 front end and wheels since those years used the same style Comstar as the Goldwing.
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline scottly

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Re: 78 GL to 75 750F0 compatability
« Reply #8 on: May 26, 2018, 10:41:19 PM »
What is the diameter and thickness of the GL rotor?
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Offline Bankerdanny

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Re: 78 GL to 75 750F0 compatability
« Reply #9 on: May 27, 2018, 07:45:24 AM »
I could be wrong, but I think that the GL rotor centers have different dish too because of calipers being fixed to the back of the fork leg rather in front of the leg and mounted to a moving arm.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline American Locomotive

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Re: 78 GL to 75 750F0 compatability
« Reply #10 on: May 27, 2018, 09:30:58 AM »
Quote from: Bankerdanny on May 26, 2018, 10:28:13 PM
It could just have an F2/3 front end and wheels since those years used the same style Comstar as the Goldwing.
I have air fittings on my forks. I don't believe the F2/F3 forks had air fittings?
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Offline Bankerdanny

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Re: 78 GL to 75 750F0 compatability
« Reply #11 on: May 27, 2018, 10:04:21 AM »
True, but I don't think the '78 GL1000 did either. It is a common 'upgrade'.
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #12 on: May 27, 2018, 10:14:45 AM »
A Google search shows the 77 GL rotors being a six hole with a deeper dish. Will they work? And what about the bearing difference?
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Offline Bankerdanny

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Re: 78 GL to 75 750F0 compatability
« Reply #13 on: May 27, 2018, 10:20:25 AM »
Yes, I believe so.

A Cycle World review from 1978 says the forks are externally the same as the 1977 wire wheel versions. So using 75-77 rotors should allow you to use your existing wheels. I think you also need to source 75-77 brake calipers, the 78 used different calipers and rotors than the 75-77's.
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #14 on: May 27, 2018, 10:52:47 AM »
Well that's better news. I picked up everything for $50.00 so I'm not completely out now I just need to research the calipers and bearing differences ;D
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline 754

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Re: 78 GL to 75 750F0 compatability
« Reply #15 on: May 27, 2018, 11:31:36 AM »
Often you can grind the weld off stem and push it out and swap.
But if stem to tree is bigger it won't work without machining a shim bushing.
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My next bike will be a ..ANFOB.....

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73 836cc.. Green, had it for 3 decades!!
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Offline American Locomotive

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Re: 78 GL to 75 750F0 compatability
« Reply #16 on: May 27, 2018, 12:49:58 PM »
Quote from: Bankerdanny on May 27, 2018, 10:04:21 AM
True, but I don't think the '78 GL1000 did either. It is a common 'upgrade'.
Do you know the lengths of the 750F forks, so I can compare them to what I have now?
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Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #17 on: May 27, 2018, 02:01:18 PM »
Slightly different ;D much stronger I'd love to see them work.
« Last Edit: May 27, 2018, 02:03:06 PM by Cougars750F0 »
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline Bankerdanny

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Re: 78 GL to 75 750F0 compatability
« Reply #18 on: May 27, 2018, 04:53:12 PM »
If you have calipers measure the diameter of the fork tubes. I believe the 750 tubes are the same 35mm as all other sohc 750's while the GL is 37mm
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline scottly

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Re: 78 GL to 75 750F0 compatability
« Reply #19 on: May 27, 2018, 08:27:10 PM »
Quote from: Cougars750F0 on May 26, 2018, 03:10:00 PM
Just picked up a 78 GL fork with triples, brakes and rotors and wanted to know if the 78GL will be compatible with my 75 750F0. I would like to be use to run my 750 wheel sets. Thanks for your help.
Once again, what is the diameter and thickness of the GL brake rotors? Honda 750 rotors (except the F2/3) are 295mm (11.6") in diameter, and 7mm (.276") thick. Honda 550 rotors are 275mm (10.827") in diameter, and the same 7mm thick. 
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Offline 754

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Re: 78 GL to 75 750F0 compatability
« Reply #20 on: May 27, 2018, 10:06:01 PM »
GL rotors are Smaller than 750, maybe same as 550, but they have more offset and the spokes of the centre's look a bit different.
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Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #21 on: May 28, 2018, 09:55:14 AM »
Quote from: scottly on May 27, 2018, 08:27:10 PM
Quote from: Cougars750F0 on May 26, 2018, 03:10:00 PM
Just picked up a 78 GL fork with triples, brakes and rotors and wanted to know if the 78GL will be compatible with my 75 750F0. I would like to be use to run my 750 wheel sets. Thanks for your help.
Once again, what is the diameter and thickness of the GL brake rotors? Honda 750 rotors (except the F2/3) are 295mm (11.6") in diameter, and 7mm (.276") thick. Honda 550 rotors are 275mm (10.827") in diameter, and the same 7mm thick.
I thought your question was for American Locomotive. The GL rotor that I have is 275mm in diameter and 5mm thick. They have a 4mm minimum thickness were my 750 rotors are 6mm minimum thickness. The center hole is also smaller than my 750 rotor the GL rotor is 5.6mm and the 750 is 5.8mm. The offset for the 750 is 2.1mm and the GL 2.6
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A

Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #22 on: May 28, 2018, 10:05:46 AM »
Quote from: Bankerdanny on May 27, 2018, 04:53:12 PM
If you have calipers measure the diameter of the fork tubes. I believe the 750 tubes are the same 35mm as all other sohc 750's while the GL is 37mm
The GL fork that I have is 37mm
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Offline American Locomotive

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Re: 78 GL to 75 750F0 compatability
« Reply #23 on: May 28, 2018, 02:02:36 PM »
I can confirm my 750F0 has GL forks - they measured at 37mm. I wish I could be of more help, but I have no idea what the PO did to get them to work. I presume he must have changed the steering stem bearings to make it work, and used later F1/F2 wheels.
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Offline Cougars750F0

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Re: 78 GL to 75 750F0 compatability
« Reply #24 on: May 28, 2018, 03:21:58 PM »
Yes the comstar wheels work they have a five bolt pattern I need the six for aftermarket mags and spoke wheels.
« Last Edit: May 28, 2018, 03:23:36 PM by Cougars750F0 »
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1970 Honda / Yoshimura 810 with ported head, 1968  Honda CB450 5 speed European model, 1973  Triumph Bonneville 750 twin carburetor model, 1975 Honda 750F0 Super Sport, 1977 Honda 750A
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