GS tranny in a GT750 box

[tz375]

We need pictures and details. Please and lots of them. We have a couple of GT racers on here and always want to hear about what worked for others.

[Cyzygy]

TZ,
I have many pics of the conversion but unfortunately I don't know how to post them and I'm too old to learn. If some one can post them for me I will email them the pics .
Bob

[water cooled]

...is this Bob Prior...?

[Suzsmokeyallan]

Richard, Dave and I have loads of photos, and I even put up two videos on the shaft alteration on You Tube quite a while ago.
It was Dave who spotted the top cover guide screw issue and notified me about it. I would have as well if I had tried fitting the top case, but I was concentrating on the lateral clearances within the shaft ends and the shifting, using the only a lower case half.
Up to that point I did two pairs of transmission gear sets and then cleaned and oiled the parts and stored them away for some engines I plan to assemble with the modded transmissions.
If you want photos just check with Dave or me.

[Old School]

After skiming through the posts, I have a question. What would be involved to swap the output shaft and how much would it space out the sprocket? I am asking so that I could run a wider wheel.

[oldjapanesebikes]

Richard, Dave and I have loads of photos, and I even put up two videos on the shaft alteration on You Tube quite a while ago. .

And of course the video is also at this link - just scroll to the bottom of the page:

http://oldjapanesebikes.com/mraxl_GT_Re ... video.html" onclick="window.open(this.href);return false;

[Suzsmokeyallan]

Thanks for your excellent work at your website Ian, its good to know you have that link there for viewers to see the videos.

Old school you cannot just swap the output shaft, you have to use both shafts from the GS750 gearbox and alter them accordingly.
The teeth on the GS "primary" or clutch shaft, namely the first gear pinion, are also different than those of the GTs and so they have to match those of the "output" or secondary shafts gear teeth.
Basically this means: on the GS transmissions the primary shafts first gear is smaller in diameter and tooth count and the secondary shaft first gear is bigger in diameter and tooth count.

You should also never mix up gearsets that have mileage on them, unless you are going to replace them in mated/matched pairs. If you do mismatch used gears you run the risk of whining and other shifting issues.

As a final note, on the GS and GT, the primary shafts first gear is part of the shaft so it cannot be swapped out.

[tz375]

Thanks for the offer Allan. I have copies of those pictures plus I have a set of shafts here that I converted. I'm always interested to see what others have done and how they did it and in this case the OP is talking about a class of Vintage drag racing that I don't know much about, so that's also interesting to me.

[Old School]

Thanks for your excellent work at your website Ian, its good to know you have that link there for viewers to see the videos.

Old school you cannot just swap the output shaft, you have to use both shafts from the GS750 gearbox and alter them accordingly.
The teeth on the GS "primary" or clutch shaft, namely the first gear pinion, are also different than those of the GTs and so they have to match those of the "output" or secondary shafts gear teeth.
Basically this means: on the GS transmissions the primary shafts first gear is smaller in diameter and tooth count and the secondary shaft first gear is bigger in diameter and tooth count.

You should also never mix up gearsets that have mileage on them, unless you are going to replace them in mated/matched pairs. If you do mismatch used gears you run the risk of whining and other shifting issues.

As a final note, on the GS and GT, the primary shafts first gear is part of the shaft so it cannot be swapped out.

Thanks for that. So with the swap, how much will the sprocket be offset?

[Suzukidave]

Thanks for that. So with the swap, how much will the sprocket be offset?

Look back to page 5 it shows a sprocket on a out put shaft and you can see the old marking on the shifter shaft from the chain dragging .

[Old School]

Thank you. I did see that one, I am looking at a wider wheel and I would feel easier knowing the actual measurements just to see if it is doable before spending any money.

[Suzsmokeyallan]

oldschool, Do you know where your engine sprocket needs to be with the wide rim/wheel you plan to use?
If so copy this value into a measurement taken from the output shaft bearing to the back of the engine sprocket and let me know what that spacer distance is.
I have a SSSA setup with a five inch wide rear rim and its got plenty of room on the shaft, however I did do some work when I was setting that up so that the stock output shaft could have still worked.

[Cyzygy]

Took my GT to our local drag strip yesterday. The only down side to the GS transmission conversion for my application is I need to slip the clutch a little further out to prevent the engine from bogging. I expect this to be less of a problem as I dial in more power and the bike and rider loose more weight . Once under way the 2nd gear shift being closer is real good. I have a 2.4 to 1 Barton Motors 1st gear but I feel that would have been too tall for my application. The reduced thread length on the transmission input shaft is less of an issue for me as I'm using straight cut primary gears.
Thanks again to ALL who contributed to this topic.

[tz375]

That's good to hear. For the strip you might be better off with a lower overall gearing with maybe 1 less tooth at the front.

Is that Barton straight cut primary noticeably noisier than stock?

[Cyzygy]

TZ 375,
The Barton Motors straight cut primaries are very quiet, no noisier than stock helicals. This surprised me as I was expecting them to be much noisier.