HELP! Spacing issues - swap GS650 forks to 77 GS750, speedo drive width???

[Chuck78]

So I got the only pair of Dual disc non-leading axle forks that I could find at the local junkyard and modded them out extensively with a tarozzi fork brace, emulators, stiffer springs, etc.

Now I went to assemble my bike tonight and the same hub with the original spacers that worked on the 750 forks now are too wide to fit in the 750 with 650 forks! The triples were both spaced at 175mm center to center, so I assumed they would work. Both are 35mm fork legs. I would imagine that the mag wheels would be the same hub width as the spoked wheels, same offset and all especially since the GS650E at least (rare non shaft drive version) did come with spoked wheels.

I was hoping that someone on here could measure some spare speedo drives off of other GS's and tell me if any that were 1978+ or 1980+ were narrower than the older 77 - which is about 32.46mm from outside to the inside portion that contacts the wheel bearing. I need something that is about 30.5mm. I have two right side spacers, one which makes if fit but the wheel is offset 2mm to the right, and the the 77 GS750 spacer which is 2mm too wide to work. Hoping to not have to make a panic run to a machine shop to have them try and mill my speedo drive and a single axle spacer. I will go to the junkyard Monday and try and track down the parts, but I am not sure if they exist!

So either the spacers are the same and the 81 GS650GT hub is narrower, or the speedo drive and spacers came in different widths, because the GS650 forks are 4mm wider than the 77 GS750 despite having the same 175m spacing up top on the triples... Bumming, and I gotta have this bike ready for a 6 day road trip by Wednesday night!!!! HELP!!!!

[Chuck78]

I do remember seeing some different parts listings for 77 vs 78-79, so I think maybe my 77 fork is possibly the anomaly??? PLEASE HELP ME FIGURE THIS OUT ASAP!!!! Machining the spacers to a width that I dictate to the machinist worries me as far as my margin of error and potential fork stiction

[mrl1000l]

Sorry I don't have speedo drives to measure, and I'm not familiar with your forks. Good news, I am familiar with making things work.

Jam the axle through the forks without the wheel and mark the insides of the axle where it meets the fork. You are measuring the total inside width of the forks. Now take the axle and jam it through the hub and mark where the axle comes through to get the total width of the hub. Subtract the hub width from the total width, divide by 2 and you'll get how much spacing each side of the wheel needs to be centered. Account for the speedo drive offset by measuring the width of the speedo drive using the same method. Then either machine down existing spacers, or just have some new ones made.

That's what I would do if I were in your position.

Best of luck,
Ross

[Chuck78]

a machine shop was my last resort, as I am really worried about getting the exact proper width with zero stiction/binding in my fork legs. the local vintage Japanese motorcycle junkyard does have a box full of speedo Drives and spacers so I am headed there after work

[gsrick]

Eric wanted me to post this;

It would help immensely if you could post some pic's of both the 650 and 750
fork lowers, but I suspect that all you needs to do is mount one of the axle
hub/spacer with the flange inboard on one side. Just like I had Rick suggest
for me in the other thread that was shot down as being a wrong picture in the parts fiche.

As I found placing the '83 1100GK forks/triples in the '79 750, some of these forks have different mounting spacing (closer to or further from the rim) for the axle hubs and the calipers.

I have also found that some forks just need to be slightly forced wider at the axle by a smidgen to be in perfect alignment. (axle hub/spacer flange inboard on one side

ERIC.


This is the parts fiche Eric is refering to. You can see how the spacer #8 is positioned on the right side with the flange ont the axle nut side instead of being inboard.

I have found when swapping '82 1100GL tune fork rims to my '80 1000G, that I had to play with a combo of spacers from both, because I had a simular situation mounting the rear wheel. Going from 2.5"x17" to 2.75"x16" No matter what spacer combo used, it was either a little too wide or too narrow to fit the swingarm properly.

The spacer at the wheel bearing was the culprit, though they were identicle width where it met the bearing and the dust cover were different for each wheel. I wound up keeping the dust/bearing surface spacer that came with the TF wheels, which made it too narrow, but by using an axle nut washer next to the inside of the swingarm instead of outside it lined up perfectly. I had to find another washer for the outside.

It's good to have some spare parts bikes hanging around.

BTW I had a problem like yours when putting '77 750 mags in place of my wires on my '78 1000C, I had to use the spacers that came with the bike instead of doing the same thing on a 750 even swap(wire for mags) were it was needed to keep the spacers with the wheels.

Hope this helps, good luck.
Rick

[Chuck78]

I was able to use a belt sander table to shave it down 2mm on the outside down to .05mm accuracy for trueness. now I noticed that my wife's GS 550 wheel is offset a similar amount in the fork! using my stock spacers I was too wide for the fork on both sides however.