GS tranny in a GT750 box

Post by **Suzsmokeyallan** » Tue Sep 29, 2009 9:57 am

That photo shows just how much further out the GS sprocket is by the corresponding old link rub marks on the shifter shaft. This update gives you the opportunity to either machine or add accordingly to reach the desired position of the chain centreline,,,that jobs looking excellent there Dave.

Suzukidave · Post by **Suzukidave** » Tue Sep 29, 2009 9:57 am

diamondj wrote:I guess the question I should really ask then is if anyone knows if the straight cut crank gear off the GS would work on the GT crank? The 750 cranks turn up on ebay often for not a lot of money although shipping is a killer:

I think the spacing between the 2 gears are different on the GS vs the GT requiring a special set of primary gears ?

tz375 · Post by **tz375** » Tue Sep 29, 2009 12:31 pm

The 77- 79 GS shaft is 10mm longer overall than a GT shaft
80 on, GSX750 shaft is 21mm longer and both require the same modifications.

For people who want to use a GT rear wheel, a GT output shaft can be used with a GS first gear plus GS input shaft shortened and modified for a seal.

The later the GT box, the better the ratios, but this mod works with them all.

Post by **Suzsmokeyallan** » Tue Sep 29, 2009 2:54 pm

Heres what the output shafts look like stripped and standing upright and next to one another.
Most of the extension is in the thread of the GS shaft, and while the first gear part is cross drilled the hole really needs opening like the GT one for better oil flow to keep that bushing better lubed.
Dave you will be happy to note this GS gearbox had 8 section ball bearings.

GT shaft on top

GT shaft on the right

Suzukidave · Post by **Suzukidave** » Tue Sep 29, 2009 3:08 pm

Hummm , Allan that second picture showing the collars shows the amount i had to machine off but what troubles me now is how the GT collar moves the 4th gear farther over .. i didnt notice that before but is still lines up nicely with its matching gear on the input shaft in my engine case ? Can you post a full length picture of the GS / GT shaft standing so we can see how the snap ring grooves line up ?

tz375 · Post by **tz375** » Tue Sep 29, 2009 3:14 pm

Dave,

It's all set out here.

http://pinkpossum.com/GT750/Transmission/GS750.htm

the key photo is

The extra width in those last two gears makes up for the amount they are shifted.

Suzukidave · Post by **Suzukidave** » Tue Sep 29, 2009 3:33 pm

Thats right you did those measurements Richard , i was about to go to http://pinkpossum.com/ to look over again your research . So it looks like all is still ok as the difference is in those wider gears . My new setup seemed to shift OK on the 1/2 case when testing .

Tom Garcia · Post by **Tom Garcia** » Tue Sep 29, 2009 3:43 pm

And I thought I was Dr. Frankenstein... Guess I need to start getting up earlier if I'm to get a leg up on you guys....

Post by **Suzsmokeyallan** » Tue Sep 29, 2009 3:44 pm

Dave the gear in that wider location may just be that, a bit wider. Its the sliding selector so run a check on its width compared to the equivalent GT one.

Post by **Suzsmokeyallan** » Tue Sep 29, 2009 5:24 pm

I took the output shaft apart grabbed my vernier, some carbide cutters etc and spent a little bit of time on the lathe. The camera really shows how the hardened material of the shaft behaves when it meets the carbide cutter bit, but then again thats a real closeup so any little detail is visible.
Hey Dave heres step one of the output shaft alteration for the oil seal.

Suzukidave · Post by **Suzukidave** » Tue Sep 29, 2009 7:24 pm

Looks great Allan , your carbide cutter left a crisper edge at the base of the cut than the grinder i used .

Post by **Suzsmokeyallan** » Tue Sep 29, 2009 8:36 pm

I tried some stones i had spinning clockwise in the tool rest to the counter clockwise spinning shaft but it wasnt doing it for me so i stopping wasting time with them and went for the carbide high speed stuff.
The insides of this shaft was quite hard and it took a lot of passes to get it close to the final dimensions, then the final setting of correct ID was a try test, try test ritual.
You can see i also put a wide transition chamfer to the holes edge for the fun of it.
To do this shafts end from start to finish and make it all correct and tidy took about an hour, not too bad IMO.
Did i happen to mention i use a four jaw independent chuck, try that for centering up stuff quickly,,LOL

Post by **Suzsmokeyallan** » Wed Sep 30, 2009 11:25 am

And here we are on a trial fit of the finished output shaft in some less than clean cases, the flange by the sprocket bearing has been machined back and the oil hole for 1st gear opened and chamfered across the shafts length.
Plus i swapped the spiral bushing from the GT to the GS first gear as it had a tighter clearance, and all it took was a socket and the press to transfer the bushing.
Now to look at the clutch shaft for shortening the threaded side and machining the oil seal groove plus the clutch inner basket taper on the rear facing side

Output shaft completed

Larger hole for first gear bushing just like the GT shaft and wide flow chamfer.

tz375 · Post by **tz375** » Wed Sep 30, 2009 3:26 pm

Allan, That's great news that we got it right and it can in fact be duplicated.

That's one more myth busted and the solution out in the public domain. Now almost anyone can change the transmission to gain the advantages of a taller first gear and later sprockets. And your GS trans is in very good condition.

That's not a bad bit of machining by the way.

How's that VFR/Bandit project coming along now? Maybe the GS main shaft will give you more room to work with on the drive chain though I think you had worked through most of the issues IIRC.

Post by **Suzsmokeyallan** » Wed Sep 30, 2009 3:55 pm

Today i took another GS gearbox output shaft i had and tried another plan of attack for altering it to fit into the GT case.
Instead of cutting back the outer side of the flange as Dave and i did on my first one to narrow it , i spun cut the ball bearings inner race portion that faces the flange.
This is actually easier to do than aligning the shaft in the lathe and cutting the flange on the shaft since its easier to set the bearing up against the chuck face and grind away to your hearts content.
The inner race locks itself up due to the grind dust coming off from the cut so you dont have to keep it held, just hold the outer race in the jaws.
Given the fact these gearbox bearings hardly ever go bad its not a big deal to do this alteration and have it last the life of the engine, plus its very easy to make another one if need be.

This gearbox is really for the bike you speak of Richard even though i had the alignment more or less solved with the stock GT shaft. Its nice to have the modern output shaft design of the GS and the fact you can now machine any sprocket of that design to create the offset you require.
Now ive got to go and cut the oil seal rebate in the other end of this shaft, ill be back in about an hour or so.

Caliper laid across the bearing showing how much of the inner race was removed to allow the shaft to go across to its correct location.