Issues converting single disc front end to dual disc on 78 GS750

[mattd1205]

im in the process of converting my single disc ‘78 GS750 to dual disc but ran into an unexpected problem. I moved the new forks over and bolted the new rotors to my mags. A PO switched the wire wheels to mags many years ago but didn’t bother switching over the rest of the front end for dual discs. I tried bolting the front wheel to the forks and ran into a couple issues. The first issue I ran into upon the initial installation I noticed the spacer closest to the castle nut sticks out past the fork 2mm or so. The washer that is behind the castle nut doesn’t sit flush against the fork. The second issue I ran into was that the wheel binds when you torque everything to spec (front axle holder nuts 10-18 pound feet and the axle nut 26-37 pound feet). I found that removing the dust cover for the speedometer drive rectifies this but I don’t feel comfortable with this “fix”. The weird thing is I didn’t change the sequence of the spacers and verified against the parts fiche and I made sure the speedo drive was keyed into its proper position. I’m just wondering how this could’ve gone so wrong. Any ideas?

Matt

[GSXR7ED]

Front End Replacement

Matt,

You didn't mention what front end assembly (triples/forks/front wheel/fender) you are using to replace the single disc.

Are you using the same wheel to add another disc?

Reason I ask, I plan on doing the same upgrade to my 1982 750T and using the entire front end from a 1982 GS1100.

The single disc apparatus will be completely removed and a GS1100 front end installed...to include the brake handle/Master Cylinder, braided lines, and all the components that make up the dual disc assembly.

If you're having to modify things to make it work, that may be a problem.

Ed

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[salty_monk]

The older vs newer brake rotors are different thicknesses at the speedo so the dust shield is shorter on the older models than the newer ones...

what front end did you use? I have some 83 GS1100 triples here if they can be of help for comparison or whatever.

[mattd1205]

I’m really ashamed to admit it but I put the rear rotor from my parts bike on the front wheel. Stupid!! I stared at it for awhile and noticed the rotors didn’t match! Doh! No wonder the spacing was off. I put the matching front rotor on my wheel and everything bolted up as it had before.

Ed: in answer to your question, I have a 1978 GS750EC parts bike so I pretty much transferred the entire front end to my daily rider which is a GS750C. The wire wheels for my GS750 are long gone so I used the mags that I bought it with.

salty: I noticed that on parts fiche that they did swap them out. It looks like my parts bike and my rider have the same spacer. The big problem was me not paying attention to which rotor I installed. Oops.

thanks for your help fellas and happy new year!
Matt

[salty_monk]

Yeah the rear rotor is also thicker at the spider... I’m glad you got it sorted Happy New Year!

[mattd1205]

Yeah the rear rotor is also thicker at the spider... I’m glad you got it sorted Happy New Year!

Thanks Salty! Happy new year to you as well!

matt