Author Topic: 78 GL to 75 750F0 compatability (Read 1269 times)

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.

Bankerdanny · « **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.

dusterdude · « **Reply #2 on:** May 26, 2018, 04:13:04 PM »

One of the neck bearings is different too iirc

Sent from my R1 HD using Tapatalk

Cougars750F0 · « **Reply #3 on:** May 26, 2018, 04:46:48 PM »

Well I would sure love to find a way to make it work.

fill in the holes on the rotor and then drill a six hole? nope that could warp

trading stock never the less. I have mags wheels as well as spokes so I'd need to keep the six hole. Thanks.

Cougars750F0 · « **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

American Locomotive · « **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.

Cougars750F0 · « **Reply #6 on:** May 26, 2018, 06:34:10 PM »

I'll need the six bolt roror.

Bankerdanny · « **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.

scottly · « **Reply #8 on:** May 26, 2018, 10:41:19 PM »

What is the diameter and thickness of the GL rotor?

Bankerdanny · « **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.

American Locomotive · « **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?

Bankerdanny · « **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'.

Cougars750F0 · « **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?

Bankerdanny · « **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.

Cougars750F0 · « **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

754 · « **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.

American Locomotive · « **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?

Cougars750F0 · « **Reply #17 on:** May 27, 2018, 02:01:18 PM »

Slightly different

much stronger I'd love to see them work.

Bankerdanny · « **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

scottly · « **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.

754 · « **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.

Cougars750F0 · « **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

Cougars750F0 · « **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

American Locomotive · « **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.

Cougars750F0 · « **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.

scottly · « **Reply #25 on:** May 28, 2018, 07:40:52 PM »

Quote from: Cougars750F0 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

The 275mm 550 rotors will bolt right on in place of the 750 rotors. You can have them thinned to 5mm to work with the GL calipers (or the superior later two piston calipers).
The width of two rotors on a 750 wheel is less than the width of a 750 F2/3 comstar with twin rotors, so I assume the same holds true for the GL wheel. Since the calipers are mounted to the inside of the lugs on the fork legs, spacers can be used to move the calipers inward to line up with the rotors. Is the GL axle the same diameter as the 750?

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Author Topic: 78 GL to 75 750F0 compatability (Read 1269 times)