Correct 77 GS750 dual disk set up? Help!

[rotcod66]

I read though older post and did not find any one covering this issue, Any help would be great!
I am rebuilding my 1977 gs750 from when I was a teenager. I am doing a full ground up restore of the Super bike I built in 1984. I want to improve the brakes I have. I am going to drill out the rotors and rebuild everything else in the brake system. Back in the day I put on spoked alloys, bought the right side fork slider, disk and caliper. Now that I am looking to improve the brakes that were always so so bad, I see that the left side caliper sits up higher on the fork slider than the one the right side and the brake pad does not fully engage the rotor. Long long story short, I have a spare front end, less calipers (dual disk off 78 w/mag wheels) I checked to see if one slider is different than the other and they are too! (Same as what I have on my 77). The mounts on the right side slider sit about 1/2" lower than on the left side. I check my caliper mounting and discover that the spare bike had bigger diameter rotors that my 77. The forks I have from both bikes are exactly the same. The bigger disk off the 78 sits perfect in the left side caliper (higher mounting) and the smaller disk works perfect in the right side (lower mounting). The disk are much different (Thicker, bigger diameter) so I don't want to run one of each and I can?t figure out the correct set up. I thought it should be in the caliper mounting plates on the left side since the stock 77 single disk used the higher mounting and bigger disk. I just bought a left side caliper off e-bay with a obvious different mount (thought it would lower the caliper on to the smaller disk) and if falls in the same darn spot! HELP! Does anyone know what the correct combo is? Should it be the 2 smaller disk and a different left side caliper or lower slider? Or should it be the 2 bigger disk with the different caliper or lower slider on the right side?
Thanks in advance for any input.

 

[tkent02]

You are right, to do this correctly you need both fork sliders from a dual front brake 750. My 750/1000 had the same thing you do, one caliper not engaging the disc completetly. With good brake pads it stopped really well anyway so I never bothered to fix it. No one ever noticed it but me.

 

[rotcod66]

I though maybe when I bought the new right side lower (Back in 1984) I must have got the wrong one. I have the front end i got off a complete parts bike i bought years ago and it was a dual disk bike. The sliders are the same as what I have, one mount is high and one is low. The strange thing is this bike had the larger disk. unfortionatly when I moved I stipped some things off the bike for spares but I guess I disgaurded the Calipers with the rest of the bike. i think there must be a caliper with a different mounting bracket that aligns the caliper in a different spot.

 

[tkent02]

No, it's the forks. On a true dual disc brake bike, both discs are the same size, the mounting bosses are on the correct place for the smaller discs, on both sides.
Your parts bike was a converted one too.

 

[rotcod66]

Hmmmn thats a thought. The only thing is, the right side can not work with a bigger disk and the same calipers. It will not mount, the bigger disk gets in the way. This parts bike was a runner when I bought it. I wounder if there was a version with both big or both small disk.

 

[tkent02]

Yes, dual disc bikes came with two small discs, and the appropriate forks on both sides.

The big disc and the big disc fork is only for single disc bikes.

 

[rotcod66]

Do you have an extra left side slider with the lower mounts? I will gladly trade two with the higher mount holes... Arg this is killing me. I just want to get this front brake set up done. I cant seam to find any of the right parts to make this work. What bike do you have?

 

[tkent02]

I have…. several. No 750s right now, but I may have some forks. I'll look tomorrow.

Another choice possibly would be fork sliders from a 650G or 650E, they came with two brakes and the same 35mm forks that you have. I don't know if it would fit on your fork tubes or not, maybe probably?
The 650 came with the later style calipers, they work much better anyway.

You could also get the front end from an 850, but it has 37mm forks so you would need the whole thing.

 

[rotcod66]

Thanks, I was just looking at that twin pot set up. Very cool! looks like a fair amount of work though.

 

[tkent02]

Yes, but it stops great! You still need two small disc forks to do it.

 

[rotcod66]

Arg, those darn small disk forks!

 

[mattfeet]

Why not do the saltymonk conversion and use two newer Concours calipers and CBR F3 rotors?

 

[rotcod66]

I guess the problem is I have two different sliders, So even with the Salty monk set up I have issues with each side being different. I have yet to see the left slider with a lower mounting lug. I may go that way one I figure out how to get them equal on each side.

 

[tkent02]

If you did the Saltymonk conversion on just the one small disc side you would have adequate braking for a 750, if you used good grippy pads. At least good enough for temporary use until you find the other fork leg, much better then the single disc 750 ever had with it's original brake.

I am actually thinking about doing that on my 550, just to save a little unsprung weight.

 

[rotcod66]

I keep hoping someone will post pictures of a 77-79 GS750 with both side mounting lugs in the same position. This way I will know what fork leg to look for. I still think there is a way to get there with another caliper. I just can't figure out how this second parts bike I have was running the two large disk. Like I said somewhere in my move I dis-guarded the set from that bike.There was a caliper mounted on the right side and it can not be the same as the ones I have on this bike. This has the round pads.

 

[chuck hahn]

Just get a set of 78 750 forks and discs, put in the divider valve and be on the road.

 

[rotcod66]

Update: Last week bought 82 gs650 forks with correct mounting for calipers. I will rebuild and use the 750 uppers for correct length. I wanted the upgraded brakes so I bought 96 zx600 dual piston calipers and master cylinder,96 Honda F3 full floater disk and the Salty monk adapters for disk and calipers, $82 delivered. Easy to install! I needed the right side spacer from the gs650 to get disk centered. I am running spokes wheels and it Looks bad ass! Thanks for all the input.