Guys, I have few mates with K75's
One of them said his felt a bit 'revvy' and asked me if he could fit a K100 final drive
to his to give a higher cruising speed at lower RPM.
basically, I dont know. they look very similar and I know the RS has a different ratio
to other K100's, thats about it.

Any ideas?
Thanks

I believe this is feasible without any modifications but If you take a 1985 final drive, you must replace the shaft too. The 1985 splines has 15 teeth and the 1986 and up has 16 teeth.

I might be wrong, but thought the early ones had 15 (the shaft part had 16) and the later ones have 21 (and 22 in the shaft part).

Hi Guys
I have a final drive for a k75 which has a ratio of 11/34 the ratio of my r80 rt was 11/37 and my current bike K100rs needs a final drive can have a ratio of 11/32 or 33 the k75 has a diffrent number of splines making the two non-compatable.

How many splines does the input shaft have?

Hi Renez
Greetings from South Africa.
Though my eyes are not so sharp if seems that the 1984 k100rs has 18 splines and the k75 has 17 splines making one spline diffrent.
I am following up to see if I can get the drive shaft and thereby make the k75 final drive compattable to the k100.
Cheers
Joe

As far as I know the earlier ones had 15 or 16 splines (depending on if you count the inner splines or outer splines of the connection) to be later replaced by a 20/21 arrangement.
My '84 has 16 splines on the connecting shaft, so 15 on the output from the gearbox and 15 on input from the cardan.

Hi Rene
I will count them again to see if they are the same. I will take the shaft out this weekend and count the splines on the gearbox side as well.
Have a good weekend
Cheers
Joe

And you! Have a good one.

Hi Rene
Yes itr was really wet but the job is done.
On double counting you are correct the old final drive is 16 splines and the k75 final drive is 20 splines so it seems to be a case of the old and the new.
I could not locate the circlip that holds the drive shaft in it's place. Is it inbetween the universal joint? I it a round clip or can I get in with a circlip pliers?

Well I am trying to get the k75 shaft from george which is about 500 km away and as you know couiers and such are dickky out here so it come back to who you know but I am hoping to get the shaft by the end of the week.
Cheers
Joe

Hi Joe, you see progress, good one!

The circlip that holds the shaft is a steel ring around the outgoing shaft of the gearbox. If you look into the shaft you should see a recess for the ring to clip into.

I'm still a bit puzzled as to what you want to do as the splines on both the gearbox and the final drive are the same and you can't split the shaft. So if you earlier had a '16-spline' set-up you can't just fit a 20-spline FD by fitting a 20-spline shaft as it won't fit on the gearbox end (which than still has 16 splines). Or am I missing something?

Hi Rene
Here in Africa unorthodox repairs are the order of the day and decades of sanctions have resulted in a culture of engineering workshops who will make it work no matter what!
So the current plan is to split the k75 shaft & the k100 shaft on a lathe, then a coded welder will weld the shaft to the exact length of the old shaft and walla a shaft that will fit my new diff and my gearbox this will also result in a diff ratio of 11/34 which is approx 500 rpm lower, which will be halfway to a touring ratio of 11/37 which will result in a slightly better fuel consumption and a small loss of excellaration on pull-away.
But lets see if we can make this a reality.
Regards
Joe

Hi Joe,
Over here we would call that Kiwi ingenuity seems the same thing exists there.

Where I live in Auckland the SA accent is probably the second most frequent accent from overseas the first being UK English. Sadly for SA many excellent Doctors, Architects & Engineers are coming here and are being snapped up into the NZ work force.

We have a large number of South Africans working in my office (we are the largest Consulting Engineers in NZ), they are all mature very senior staff, what a disaster for their ex country to lose that calibre of people.
Regards,
K-BIKE

to kbike
That sounds about right.
good on you mate regards
Joe