Topic: swapping '78 CB750 fork on CB550

[charlie27]

Hi,

looking to go with dual disc brake and considering using 78 CB750 forks.  Both are 35mm tubes and I believe use the same axle - is that correct?

I was also wondering how much longer the 750 fork tubes are than 550.

I am also going to lace up an 18" rim over the 19" and can slide the forks up in the triple clamps short of contacting lower triple clamp when the forks bottoms.

comments?  suggestions?

thanks

[crazypj]

750 forks are about inch and half longer.
I would use them at stock height with an 18" rim
You don't need to swap forks for dual disc on 550 though, just get the caliper and arm then change master cyl (unless you mean 750F2 or DOHC ?)

[charlie27]

thanks

the 550 forks I have the uppers are very rusted and new fork tubes are much more than what I would pay for a decent set of '78 750 forks.  I also think the calipers that go on the 750 fork are much better than the 550 caliper that only have 1 active piston.

Are the disc diameters the same for 750 fork with appropriate calipers?

[kerryb]

I had '78 750k forks on my '77 550.  I had them dropped in the trees about an inch.  (my handlebars wouldn't permit any more)
I rode it this way for awhile.  I liked the way it handled and it stopped fine with one '78 750k caliper on it.  (I try to avoid panic-type stops)
Now I have 550 forks on the same bike, with the same 750 caliper, the 550 caliper looked a little smaller but I haven't measured the piston yet.  I can't feel any difference in handling, it's still good in that department.  I still have wheels from a 750 on it.
It's still just too much fun to worry about it.
Yours sounds like a good plan, I say go for it!

[srbakker]

Are the brake calipers compatible or do you plan to use F brakes as well?

[charlie27]

I think I will need to sue the 78 F brake calipers that I beleive have 2 live pistons.

I need to see what diameter disc works with that.  I have a brake master cylinder to work with this set up already.

[charlie27]

the 78 750F forks have the brake calipers that mount on the rear of the fork leg.

does anyone know if the the 550 disc diameter and offset will work with the 750F fork and caliper?

else do I need to get different disc with diameter and offset that will work and have the bolt pattern to bolt on to the 550 hub?

I tried to look at parts fiche and the front axle is the same part number but disc is different PN.

thanks

[hondawade]

what size is the axle for a 1975 cb750 k5?