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Discussion Starter · #1 · (Edited)
So, I’m gathering parts to swap in a dual disc CX/GL 500 fork into my 82 CX500

Looking at the motofaction fork chart, it shows that the US 81-82 CX500 came with 35mm fork tubes, while the AU version of the CX500 (presumably the one with dual discs, which also came in Europe) came with 33mm… Is this correct?

Yet, according to the chart… all GL500’s came with 35mm fork tubes.

Am I reading this correctly?


So then, if I want to keep my current trees (which should fit 35mm tubes), I’d need dual disc fork tubes from a 81-82 GL500 (asp 35mm), which would maintain stock geometry… Correct?
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Most CX500s have the same 33mm forks. Only the '81 and '82 CX500 Customs have 35mm forks with a leading axle.
While the GL500 also has a 35mm fork, the fork spacing is determined by the steering yoke. If you mount the GL500 forks in the CX500C yoke, the resulting spacing might not accommodate the GL's dual-disc wheel. If you're making the swap, you'll want to use the GL yoke, too.
 
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Discussion Starter · #3 ·
Ahh okay, so the GL500 yoke/stem is identical otherwise, and will bolt right up?

GL500 78-82? Or just 81-82?

And do you know if they come with the 30mm calipers or 32mm?
 

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Discussion Starter · #6 ·
Ahh right, sorry for the redundancy.

So just need to swap in the 81-82 CX 35mm fork uppers into the 81-82 GL lowers, and fit into a GL yoke, so the GL wheel bolts in, got it.

Now could this setup work with 32mm twin pot calipers and the larger 295mm discs?
 

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Ahh okay, so the GL500 yoke/stem is identical otherwise, and will bolt right up?

GL500 78-82? Or just 81-82?

And do you know if they come with the 30mm calipers or 32mm?
There was no GL500 before 1981.
I believe the stems are close enough. I know they use the same bearings. Not sure about the length.
I'd use the brakes from your front end donor.
 
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Discussion Starter · #8 ·
So that would just come down to which bracket can correctly position the twin pot 32mm calipers (CB900C, CB750F and 82 CB650C) onto a 295mm discs.

Has anyone done this with GL forks?
 

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Discussion Starter · #9 · (Edited)
Ok, so just use the 30mm twin pot calipers, and call it a day?

Indeed that would be easier and likely work well, but somehow I’m still curious… I must make things difficult for myself in the name of customization, uniqueness and possibility of marginal optimal performance o_O
 

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Discussion Starter · #10 ·
So referencing this post:


The 32mm CB900C (750F and 82 CB650) calipers should bolt up to the CX500 fork lowers using the brackets from the included list of potential donor bikes).

And since we know the mounting hole diameters are the same as the GL, these calipers/brackets should bolt right up to the GL fork lowers as well, correct?
 

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So just need to swap in the 81-82 CX 35mm fork uppers into the 81-82 GL lowers, and fit into a GL yoke, so the GL wheel bolts in, got it.
Do you know if the custom uppers are the same length as the GL500 uppers? Same applies to the lowers. Which springs do you intend to use?
 

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Discussion Starter · #12 ·
Somehow I assumed the length of the fork lowers were the same on both the CX and GL, and only the uppers were longer on the GL (with longer springs).

Good point though, I’ll do some digging to assure the lowers are the same length after all.

Regarding springs, I was going to use Progressive or Racetech springs, along with cartridge emulators, so if the fork lowers are indeed the same, I’d just choose the springs made for the CX500.
 

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And since we know the mounting hole diameters are the same as the GL, these calipers/brackets should bolt right up to the GL fork lowers as well, correct?
That's a poor assumption to make. The bolt holes might be the same, but the spacing could very well be different.
 

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Discussion Starter · #15 ·
I assumed the mounting holes are the same per info in the post/link I referenced in post #10

BlindStitch mounted a CB900C caliper directly to the CX500 fork, since they share the same bracket as the 81-82 GL500, I assumed it would bolt up.

Indeed I’ll double check the distance between bolts.
 

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Discussion Starter · #16 ·
In a way, that’s what I’m doing… Using the same calipers that came on the CB750F (twin pot 32mm, along with the 295mm discs), only bolting those to 81-82 GL500 fork lowers and 81-82 CX500 uppers… in a GL yoke.

… or at least, that’s the plan.
 

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Discussion Starter · #17 ·
Hey KLCruiser, do you know whether your calipers have the 30mm or 32mm pistons? And the diameter of the discs?

Your set up has the shorter bracket, so would be a load of info to confirm whether it’s possible to run the 32mm calipers with the shorter brackets (that fit the CX and GL).
 

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Discussion Starter · #19 ·
Thank you!

So, Im realizing my plan won’t work… Im thinking in order to fit the 295mm discs would require calipers which use the longer bracket, which will not bolt onto the CX/GL fork lowers.

And since I’m trying to retain stock fork geometry, I’m confined to the 35mm fork tubes.

So, looks like I’ll have to go with the twin pot 30mm calipers for the dual disc setup after all.

Can 2mm larger pistons really make that much of a difference anyway?
 
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