fork swap

[bowzer]

More out of looks than necessity I'm thinking about fitting dual discs to my new 78 gs750. I know someone who has the front end from a 1980 850.
Will the tubes fit my trees?
If not, are the steering heads the same so I could do a complete swap? What about length?
I don't want to screw up anything. (rake & trail) I can get the cast wheels with it along with all the calipers and discs.
Will the rear wheel fit?
I know I can make everything work somehow, but I'm just looking for an easy swap on this. There is plenty of other work ahead of me. Also when it is all apart, is there a conversion for the head bearings? From my days wrenching on the Brits, I remember a needle or roller bearing conversion? Much better than all the little balls, at least on them.
Very cold right now, so I'm just planning and gathering parts. Thanks

 

[8trackmind]

More out of looks than necessity I'm thinking about fitting dual discs to my new 78 gs750. I know someone who has the front end from a 1980 850.
Will the tubes fit my trees?
If not, are the steering heads the same so I could do a complete swap? What about length?
I don't want to screw up anything. (rake & trail) I can get the cast wheels with it along with all the calipers and discs.
Will the rear wheel fit?
I know I can make everything work somehow, but I'm just looking for an easy swap on this. There is plenty of other work ahead of me. Also when it is all apart, is there a conversion for the head bearings? From my days wrenching on the Brits, I remember a needle or roller bearing conversion? Much better than all the little balls, at least on them.
Very cold right now, so I'm just planning and gathering parts. Thanks

Fork tubes on the 850 are 37mm. Yours are 35mm. So they won't fit.
The bearing issue is another story. I'm sure someone has tackled that one...

Guys?

 

[tkent02]

I believe the fork tubes are 35mm diameter on both models, one difference is the leading axle forks on the '80 which may be part of the reason the '77 - '79 bikes work so much better on dirt or gravel roads, etc. In Chicago this may not concern you much.

 

[bowzer]

Ok cool, it appears they are different sizes. Is there a direct swap for dual discs? I would change springs, seals and powder coat anyway, I just don't want to fab. too much stuff.

 

[8trackmind]

Ok cool, it appears they are different sizes. Is there a direct swap for dual discs? I would change springs, seals and powder coat anyway, I just don't want to fab. too much stuff.

It depends. The early model with single disc may have the slightly narrower triple tree. (like the 550) If so, I have a solution. Go here.

If it is in fact wide enough, you're set.
Be aware that the single disk bikes used a larger brake rotor, so you will need BOTH lowers, and two rotors. The single disk master cylinder uses a 14mm bore, the dual disk model uses a 5/8 bore, so you need to source one of those as well.

The ideal setup to find would be off of a 81, 82 GS650 E or G. They use 35mm tubes. They are the same length as what you have now, use better calipers, slotted rotors, and are not leading axle. The calipers are easier to rebuild than the earlier models, and the pads are cheap.

Second choice would be 79 GS750E parts.
You can mix and match rotors from various years. You can also use different calipers from most models as long as they are not leading axle.

 

[bowzer]

I just assumed I would need both lowers and the matching rotors. I knew about the master. Thanks for the info, at least now I can keep an eye out for stuff. I'm really just planning now (because it's 3 degrees) but I will gather whatever parts I can and begin to tear into it when it warms up.