New front forks?

[jagarra]

I am getting ready to start the restoration project on my 74 90/6 and need the forums opinion on the stock front forks, especially the brakes. Found a complete front end off a 77 R100RS available, with triple clamps, 40MM tubes with the calipers for a decent price. Will this front end fit the 90/6, also, do I have to change hubs for the dual disks or are they already drilled for a pair of disks.

thanks,

gg

[dougie]

I believe the OEM 1977 tubes are 36 mm.

[jagarra]

Dougie,

You are indeed correct, found a site selling replacement
tubes, looks like all 70s were 36mm. Now the question remains
is dual discs worth the $$ from stock 90/6?

I do have set of 6 piston calipers from a Kawasaki, but then have to find lowers
and make adapters. Probably that is too much brake anyway.

Thanks
gg

[Seth]

So the question is, are you really doing a "restore"?
I'm assuming you want to keep it close to stock, use period pieces but get some upgrade in braking.
Those ATE calipers aren't the greatest. The 77RS front end uses blue anodized calipers, but otherwise are the same as the 40mm calipers on other models. The R90 calipers probably have 38mm pistons.

The bigger issue is the Master Cylinder. You'll get a big improvement with a handlebar mounted master. I have a single disk master drilled with 2 outlet ports for the dual disk stock calipers on my 77RS. The braking is improved over the stock dual disk, but still not great. But you can't tell the difference by looking at the bike it's been modified.

If you step up to the later forks with the other style ATE or Brembo brakes, you'll also need to change wheels (snowflakes?), as the spokes hit those brakes.

[Duane Ausherman]

I am getting ready to start the restoration project on my 74 90/6 and need the forums opinion on the stock front forks, especially the brakes. Found a complete front end off a 77 R100RS available, with triple clamps, 40MM tubes with the calipers for a decent price. Will this front end fit the 90/6, also, do I have to change hubs for the dual disks or are they already drilled for a pair of disks.

thanks,

gg

Maybe we have a different definition of "restore" but for me it means putting it back to stock on the dealer's floor. If you wish to install accessories that were available from the factory, that is still part of restore. It could have been ordered that way. The R90/6 was listed as available with dual disc brakes. I never saw a single disc model come with the dual disc in actual fact. It could have been a marketing ploy, or an error.

You certainly are doing the right thing to do something about those rotten single disc brakes. On my daily rider I just used the /5 fork with the drum brake. It is far superior, but takes more skill. I never liked the heavy handling of the dual disc on the R90S.

It is "your" bike so do as you wish. Maybe what you are doing should be called "rebuild" rather than restore.

[chasbmw]

In the uk many single disc bikes were specced with twin discs, I agree with Seth on the MC issue. If your bike has the smaller 14mm wheel spindle then your front wheel won't be a straight swop into the later forks, otherwise apart from detailed changes in the internal damping there is not much differances between the sets of forks.
Dual discs are worth it!

[jagarra]

Well it sounds like changing over can be a pain. I do want the bike to look stock
with subtle changes for better handind and braking. Since this bike is an early 73 it probably has
the smaller front axle, now I guess you're going to tell me it not a matter of different bearingss
and spacers, but a new hub. I guess the best course now is to tear it down and consider simpler options
and retain original brakes,

Just as a curiosity factor. I have seen a number of R65 front ends on eBay, are these even an option as the a axle
position is further back than stock?

thanks,

gg

[mattcfish]

There are K Bike front ends that will bolt on as well. Just to add food for thought.

[Major Softie]

There are K Bike front ends that will bolt on as well. Just to add food for thought.

I believe that creates wheel issues unless you want to go to mags.

[dwire]

For my own education here, what is stock on this vintage? Still the self-actuating style drum?