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'78 GS1000 Dual Disc Conversion + Lester Mag

  • Thread starter Thread starter mdunn
  • Start date Start date
M

mdunn

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I need some help in my current '78 GS1000 project. I am converting the front end from the single disc to the dual front disc, but am having some problems.

I purchased all the calipers, discs, and forks from a GS750 with dual discs (or so I was told on the add). The bike already had a set of Lester mags with the single brake set-up, but of course the bolt holes were already there on the right side for the second disc. I rebuilt the forks and calipers, installed the second disc and reassembled everything.

The left caliper and disc fit perfectly. The disc is centered in the caliper as it shold be. However, the right disc contacts the caliper on the side closest to the right fork. I did not disassemble the axle and spacers, so they are the same as when I disassembled it. If I loosen the axle nut and move the fork to the right so the disc is in the center of the right caloiper, the threads on the axle would be too short to tighten and get the cotter pin back in.

Has anyone else had these concerns converting to dual disc? Everything I have read on here makes it sound like it is a straight forward swap. It seems like it would be a simple spacer problem, but then I run into the concern with the axle length.

If you have any suggestions or can let me know if you had this concern and what your fix was, I would greatly appreciate it. thanks for your feedback in advance!
 
The rotors for dual disc bikes are smaller than single disc. The LH side fork lower slider is different too, because the disc is different.

You need the fork lowers, both sides, and two of the smaller rotors. Also understand that the 750 forks have smaller diameter tubes than the 1000. Best to stay with the big stuff if you have a 1000.
 
Nessism said:
The rotors for dual disc bikes are smaller than single disc. The LH side fork lower slider is different too, because the disc is different.

You need the fork lowers, both sides, and two of the smaller rotors. Also understand that the 750 forks have smaller diameter tubes than the 1000. Best to stay with the big stuff if you have a 1000.
Click to expand...
I had to get different lowers and rotors to do the conversion on my 1000 conversion.The first gen 750s have 35mm stanchions and the 1000s are 37mm,as far as I know you need a set of 1000E lowers.
 
Thank you for your responses. I went out and measured again. The fork lowers I have are 37mm, so they must be the GS1000 ones. The rotors I have are 275mm in diameter. My current problem is not a diameter problem, it's a spacing problem, meaning the outside of the right rotor is pressing hard onto the outboard pad of the right caliper as soon as I put it on.
 
Where are you at? You can add your location to your signature. Pics would be great. I have 4 pairs of forks that would work for you...
 
mdunn said:
Thank you for your responses. I went out and measured again. The fork lowers I have are 37mm, so they must be the GS1000 ones. The rotors I have are 275mm in diameter. My current problem is not a diameter problem, it's a spacing problem, meaning the outside of the right rotor is pressing hard onto the outboard pad of the right caliper as soon as I put it on.
Click to expand...
Sure you have have the spacers in the right way.Did it wrong on my 85 750 and had that problem:oops:
 
One of the fork tops (stanchion) might be slightly bent. Try loosening it up and twisting the top part of the fork in the triple tree and see it that moves the lower fork leg out slightly.
 
Last edited:
I did not move the spacers from where they were, but that doesn't mean they were right to begin with. I will try to post picures. In the second one, you can see the caliper mount rubs on the disc. Rotating the fork does not help this situation.
Stay tuned for pics. Thanks again for everyone's help!
 
Last edited:
I just read back thru your issue. What is the length of your axle? Maybe it is not original or just a little too short....Hard to tell from the picture angle. If you put your town there maybe be someone is near by you in Ohio. I have a 78 1000 in the garage that I can compare measurements if needed.
 
The easiest would be to give us your disk to disk spacing so that we can compare to our own bikes.
I've had the same issue on my GS 1000 skunk and I believe it could come from the way the front wheel bearings are mounted.
In fact I believe there is an order to mount the wheel bearings;)
The LH bearing should go in first.
This will in practice move the wheel slightly to the left and the RH side disk should no longer touch the caliper.
The issue could also come from the fact that you are not using GS 1000 disks from the same period as the calipers?
If the disks are solid they will only work with the calipers that have the round pads.
 
Last edited:
Thanks John. My outside of disc to outside of disc measurement is 4.650" or about 118mm.

I am indeed using the round pads on the solid rotors. But like I mentioned, it doesn't have anything to do with the pads yet, as it is hitting on the mounting bracket as I tried to show in the previous picture. Hereis a side view of the setup I am using.

View attachment 21401

As far as the axle length goes, being too short would just mean that I need a larger spacer on the right hand side to space the fork lower out farther, and hence meaning the axle would be too short.
 
The spacing of my disks is 117 mm ( outside to outside).
The disks are 4.5 mm thick.
I don't recognize the disks nor the calipers you are using?
 
My spacing is 118 mm outside to outside but my disks are 6.5 mm thick. I have the same disks on mine but the calipers look a little different.
 
David, sounds like your set-up is similar but you said you had different calipers. Do you know which ones you are using? Do you have a pic you could post? I appreciate all the help!
 
Thanks Dave. Yeah your calipers are definitely different than the ones I was sold. Do you know what yours are off of? Thank you for the picture!
 
mdunn said:
Thanks John. My outside of disc to outside of disc measurement is 4.650" or about 118mm.

I am indeed using the round pads on the solid rotors. But like I mentioned, it doesn't have anything to do with the pads yet, as it is hitting on the mounting bracket as I tried to show in the previous picture. Hereis a side view of the setup I am using.

View attachment 21401

As far as the axle length goes, being too short would just mean that I need a larger spacer on the right hand side to space the fork lower out farther, and hence meaning the axle would be too short.
Click to expand...
not completely positive but that caliper in the picture looks like an early GT caliper . Both of my 78 1000's have the same caliper as Dave's
 
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