Topic: 750k GL1000 front end swap question...

[ianbrsn7]

So I have a 76' 750k, I'm doing the GL1000 swap and I'm wondering why the rotor is hitting the forks? The wheels are Borrani 18's, the speedo (accidentally bought to quick) is from a 750 I believe. The rotors themselves, I'm unsure if they're from a GL1000 or from a 750. I know the offset/diameter is different but I'm unsure how to tell which is which. Any help would be greatly appreciated!


https://flic.kr/s/aHBqjBPWCx

Pictures showing what I'm talking about ^^^

[Alan F.]

Subscribed, I've got these parts for my K3 but haven't gotten to it yet.

[newday777]

Welcome aboard the forum ianbrsn7
I haven't done the swap but want to having read about it.
Did you put the GL1000 triple trees?

[ianbrsn7]

Welcome aboard the forum ianbrsn7
I haven't done the swap but want to having read about it.
Did you put the GL1000 triple trees?

Aye thanks! Long time lurker, first time poster.

GL1000 triple trees are in, new neck bearings, the top clamp is from Cognito. Forks freshly rebuilt, etc, etc.

I'm thinking this spacing issue comes down to either the rotors themselves, or the speedo drive. The GL1000 speedo doesn't look any smaller than this one (but i'm only looking at pictures on ebay), and as far as the rotors go... I just don't know how to tell the GL rotors from the CB ones. I don't have another set to compare. Chat GPT says, the CB750 rotors have a low offset and the GL1000 rotors have a high offset along with a bigger center bore.

[Alan F.]

Just did a little looking around, 750 rotors are 295mm or 11.61" diameter, GL1000 are 276mm or 10.86" diameter. So GL are 3/4" smaller diameter.

Not sure about offset, hubs are the same.

And yep, welcome!

[ianbrsn7]

Just did a little looking around, 750 rotors are 295mm or 11.61" diameter, GL1000 are 276mm or 10.86" diameter. So GL are 3/4" smaller diameter.

Not sure about offset, hubs are the same.

And yep, welcome!

So just from a cursory ebay search, it does seem like the offset is deeper on the GL rotors.

CB rotor https://i.ebayimg.com/images/g/VhcAAOSwxplmqVge/s-l1600.jpg

GL rotor https://i.ebayimg.com/images/g/nqIAAOSwtHFmw7pY/s-l1600.jpg

It's hard to see, but it looks as if the GL has a 1/4 more of offset. I'm inclined to believe that's what I have.

I think I'll buy the correct GL speedo drive, as that's the only thing in the system that I know is not from a GL and see how it differs from the cb style. Hopefully it's thinner. If that doesn't work. Maybe buying a cb rotor and having them lathed to the same diameter would be the move?

[seanbarney41]

If you have Gl trees, forks, rotors, calipers you want the gl speedo drive too and axle spacers.  The gl and cb speedo drives actually act as wheel spacers on that side.  I have had a bike with a gl swap for years and I honestly cant remember whether there is any difference in the speedo drive.  What do you have stuck in there for an axle?  It looks like that is what's causing your misalignment.  Axle nut should be clamped by the fork on one side.

[Don R]

 At least some of the GL1000's have the speedometer drive on the left side. I'm thinking they all do.

[ianbrsn7]

If you have Gl trees, forks, rotors, calipers you want the gl speedo drive too and axle spacers.  The gl and cb speedo drives actually act as wheel spacers on that side.  I have had a bike with a gl swap for years and I honestly cant remember whether there is any difference in the speedo drive.  What do you have stuck in there for an axle?  It looks like that is what's causing your misalignment.  Axle nut should be clamped by the fork on one side.

For the axle, it's just a long bolt to check the spacing. (Waiting on a GL axle in the mail, my thought was if it's flat and long enough I'll be able to somewhat test the fitment). So I know the speedo will act as a spacer, and there is another spacer on the gl. I guess I'm slightly confused because if the gl speedo is bigger which it appears to be 1mm-2mm bigger, then I will worsen this problem. But alas, I will get the gl speedo as I goofed buying the cb750 speedo. If anyone needs a 6 hole 750 speedo, let me know. I'm going to measure my rotors to try and confirm they are GL rotors.


The speedo will go on the left side of the hub. I originally had it placed on that side and tested the fitment but had the same problem but on the other fork, so I flipped everything around and the same issue occurred and that's when I took the photos.

[Medyo Bastos]

If you have Gl trees, forks, rotors, calipers you want the gl speedo drive too and axle spacers.  The gl and cb speedo drives actually act as wheel spacers on that side.  I have had a bike with a gl swap for years and I honestly cant remember whether there is any difference in the speedo drive.  What do you have stuck in there for an axle?  It looks like that is what's causing your misalignment.  Axle nut should be clamped by the fork on one side.

Correck


Sent from my iPhone using Tapatalk

[scottly]

What is that hub are you using?

[ianbrsn7]

Okay, so I've figured it out. At least I think I've figured it out, waiting for some parts to come. But, it's not the speedo itself that is the problem, but rather the drive gear and the retainer. So on the 750 the drive gear and retainer are both offset away from the wheel while the GL drive gear and retainer lay flat.

I was missing about 1cm of space on the axle and couldn't figure it out even with the GL speedo, but looking closer at the drive gear and the retainers that's where I'm sure my problem lies. Unfortunately the GL speedo/axle combo I bought didn't come with either the drive gear or retainer. 

[cfairweather]

I work on a lot of GL1000s and have some advice and some information to help.  There are two types of axles used on the 1975-1977 GL1000.  It is best to use the one that has shoulder(s), which keeps the forks positively in alignment.  The earliest axles did not have these shoulders on both ends.  I have some of the earlier versions, but I think I used my last later version.    The 75-77 GL1000 speedometer drive is on the right and the 78-79 version is on the left.  Do not mix any part from a 75-77 front end with a 78-79 version or you will have alignment issues.  The 78-79 disks are thinner than the 75-77 ones.  I have a lot of GL1000 parts, if needed.  Can you post pictures of your front end parts?