1978 GS1000 single disk to dual disk upgrade

[Hoomgar]

I have acquired a set of front fork tube lowers for my bike from an 80's GS850. They seem to be the same dimensions as the ones on my 78 in every regard except one thing.

The two mounting holes for the brake calipers are about 1/4" to 7/16" lower than the ones on my 78 tubes. The mount points for the fender are exactly the same. I am guessing that the disks for the dual disk setup bikes were smaller maybe?

It looks like the single solid disk on my 78 is about 12" and the disks on the front end of the 80 GS1000 I have look to be about 11"?

Does anyone know, does that seem right? If the disks were in fact smaller then of course the calipers would mount closer to the axle.

I just am not sure.

[shaftzuki]

You are correct - the dual disc setups do employ smaller diameter discs than the single disc setup ...

Are you going to need any other parts?? I think I have some useable twins around here somewhere ... 8O 8)

[Hoomgar]

You are correct - the dual disc setups do employ smaller diameter discs than the single disc setup ...

Are you going to need any other parts?? I think I have some useable twins around here somewhere ... 8O 8)

Thx Mark. I was hoping that was the case. Here is what I have then to do it:

the two lower fork tubes
the two sloted disks off the front on an 80 GS1000
the two calipers off the 80 1000
the hoses and spliter off the 80 1000
new pads for both calipers

Will I need a different master cylinder? Or is the one on my 78 good enough?

[SqDancerLynn1]

You should change the master to get the correct fluid rate/size. Dual disks are smaller & thinner than single disks

[Hoomgar]

You should change the master to get the correct fluid rate/size.

OK then I guess I better start hunting.

Mark, do you have one you could part with?

Or anyone for that matter.

[shaftzuki]

You should change the master to get the correct fluid rate/size.

OK then I guess I better start hunting.

Mark, do you have one you could part with?

Or anyone for that matter.

As a matter of fact - I do have one lying around ... somewhere :?

It's all yours if you want it - don't think it was in bad shape, but you should probably rebuild (or clean really good). 8)

[Hoomgar]

You should change the master to get the correct fluid rate/size.

OK then I guess I better start hunting.

Mark, do you have one you could part with?

Or anyone for that matter.

As a matter of fact - I do have one lying around ... somewhere :?

It's all yours if you want it - don't think it was in bad shape, but you should probably rebuild (or clean really good). 8)

Email is forthcoming. Thx Mark