Topic: Swapping a 78 supersport dual caliper front end to a 75?

[Ender81]

  Would there be any problems with doing this? It looks like the forks are the same diameter and I've heard I may have to modify the speedometer to read correctly but could someone point me in the right direction on what to do. I didn't see much in a search or the tech pages. Would I need to replace the front wheel or will the two rotors bolt up etc... Thanks in advance.

[kevins750]

the tubes are both 35mm so later model forks will work in early trees..

[Ender81]

 Well that's good to know. I've been doing a lot of searching since I posted and it looks like I can swap them but if I want to keep the spoked rim I will have to machine a set of rotors from an early. What I need to know now is if the speedo will work still and if there is a good way to bolt up the master cylinder.

[JohnG]

I would want to measure the outer and inner distance of the tubes, in both bikes.  By this I mean if you look at the pair of tubes from the front, the distance between them and the distance from the outer edge of one to the outer edge of the other.

If those are the same for the two bikes then the swap should be pretty much trivial. 

A way around it might be to see if the triple tree part numbers are the same for both bikes.

            John

[kevins750]

I think part numbers of trees would be different...I believe later trees has the choke mounted on them, earlier is choke on the carbs...I would think spacing on the early forks is different from the later style...But a measurement would definitely be needed here...79' DOHC had a spoke front wheel(some models), you may try to find one of them..
  Are you trying to use the dual disc late style forks with your stock F wheel?

[Ender81]

I'm trying to use the late model forks with a K spoke wheel. I'm going to look up the wheel now for the dohc and I'll take a look at the measurements tomorrow. I've been told they are the same but double checking has never hurt anyone.

[754]

F lower tree is different, has bosses for log type brake line splitter.
 Discs on 5 are smaller dia, 5 bolt pattern and thinner, so you will have to make or adapt discs, or build a hub copy with 5 bolt pattern and correct spacing..(best idea)

[Ender81]

 Ok great so I have that to work out, what about the speedometer cable? Will it hook right in and read correctly still since I'm not changing the wheel?

[754]

If you want to swap trees, swap as a set, offset might be different

 Speedo drive would work if you use stock wire wheel hub, if you can get second disc on, it may be too big tho.

 If you are careful you might be able to fill 4 of the holes in the F  discs with weld, the redrill to 6 bolt pattern, but the mounting face will have to be remachined, if it warps too much you will have trouble..