trany swap

smokin · Post by **smokin** » Sat Nov 14, 2009 1:24 am

I got a transmission to replace the older (72) one that has a problem , when I put the newer trans (year unknown) in it has a tight fit doesn't turn freely like the older one and harder to shift, both trans look the same gears seen to be binding, is this a problem with swaping out tranys.

tz375 · Post by **tz375** » Sat Nov 14, 2009 9:23 pm

If we are talking GT750, then the answer is No. All years of gearbox are interchangeable.

IS one of the selector forks on the wrong shaft?

Which shaft is tight, input or output?

Which bike?

smokin · Post by **smokin** » Sun Nov 15, 2009 10:41 am

it's a 72 gt750, when I swap out the trany it's hard to turn by hand both ways and shift both ways i can't see where it is binding because everthing is so tight, put the old trany in no problem, could it be that the old trany has worn down or are all the transmission suppose to drop and turn freely with very little adjustment.

Post by **Suzsmokeyallan** » Sun Nov 15, 2009 11:31 am

Theres surely a problem somewhere, you need to re-check it carefully. If necessary remove the selector forks and see if the new shafts spin freely.
A couple of things to pay closer attention to are if the bearings are sitting properly into the grooved shims on the new shafts.
Normally the shafts just drop right in with no hassle, so can you feel backlash on the gearsets despite the tightness, if so its possibly you have an end clearance issue.
Did you try the new shafts by themselves in the bearing holders to see if they spin freely
Did you try one new and one old shaft assembly as a pair to see what happens also????
Theres so many questions to ask here without actually seeing the situation firsthand.

tz375 · Post by **tz375** » Sun Nov 15, 2009 5:55 pm

Allan is absolutely correct. The shafts should spin easily.

A couple of possibilities:

End bearings are not pressed on far enough - carefully measure old and new across the bearings

One of the gears in either back to front or on the wrong shaft - compare to your old shafts to be 100% sure

Second gear may need to pressed on slightly further on the input shaft - compare with the old shaft.

Make sure that everything spins freely before assembly. If it's free outside the cases and binding when fitted, check the individual gears and see what is tighter. See if you can determine what is tight.

Assuming the locating pins and half moon retaining clips are all in place and in good condition, there isn't much that can bind - unless it's GS trans instead of a GT - that would do it.

Do the two look identical or what differences can you see between old and new

Post by **Suzsmokeyallan** » Sun Nov 15, 2009 6:26 pm

How about a few photos???? those may help somewhat.

smokin · Post by **smokin** » Sun Nov 15, 2009 9:41 pm

Spent all day on this and found what the problem is the two gears on the left lower and upper (large and small) and the two on the right lower and upper are binding, took the right gear that first shifts into out and it would spin a little tight but it was easy to move, when I put it back in it wouldn't spin. The transmission are the same they fit in like they should and turn freely one set at a time but when you put them together there's binding, I switch the newer first gear and the larger gear over to the old shaft and it still was tight ( the larger gear is what's binding) I can swap out the gears but I need the bearings on the left side can't get it off is it pressed on?

tz375 · Post by **tz375** » Sun Nov 15, 2009 10:02 pm

OK. That sounds like someone has mixed gears from different years. As you may already know, they ratios were changed on some of the gears and they must be swapped as pairs.

It would be helpful if you could count all the gears on each shaft. Please start with the front shaft that goes inside the clutch and start from the clutch sides, so we know which is which. Then count the rear (output shaft) starting at the clutch side and ending up on the sprocket end.

Then I'll be able to tell you what gear set you have and what is wrong.

There is one other possibility and that's Suzuki had some sort of issue with one pair of gears that had to be matched to the crankcase and it is quite possible that you have a combo that doesn't work. It related to backlash to reduce transmission noise and involved First and second driven gears on the output shaft.

They used a color coding and there should be a color paint splotch behind the clutch which has to be matched to the right color on the gears. Bulletin GT-3 dated May 1, 1975 which refers to Service Bulletin GT-29.

Let's start with a gear count and work from there.

smokin · Post by **smokin** » Mon Nov 16, 2009 10:39 pm

http://i772.photobucket.com/albums/yy1/ ... C00823.jpg http://i772.photobucket.com/albums/yy1/ ... C00824.jpg

The trany on the left is the older and the right is the newer one, both gears are the same the gear on the right is the one that's binding, both trans are the same.

Gear count right to left starting with the clutch side 13,24,22,26,19
Drive side right to left 37,27,30,24,33

No color code on the clutch or gears engine #166xx

Post by **Suzsmokeyallan** » Tue Nov 17, 2009 7:37 am

When you say the gear on the right is the one thats binding i take it you are referring to the largest gear on the output shaft (lower shaft in pic) on the new gearset.
If so, thats first gear, can you count the teeth on both of these largest gears and the matching teeth on the main shafts. Just from looking at it the one on the right appears larger.
If you slip that bearing off, its not pressed on, the gear comes of easily for checking against the other one.

tz375 · Post by **tz375** » Tue Nov 17, 2009 8:41 am

Thanks for posting those pictures. That gear is first and both are 37 teeth. The gear sets are the same J-K-L and are not from a later A or B.

I suspect that the first gear is a fractionally larger fit. It was first and second that Suzuki changed and offered as matched sets with the crankcases.

I would try swapping the 37t first gear from the old to the new set and see if that fixes it. If not, second gear will have to be swapped (19/33) but the 19t gear is pressed on. If you have to swap a second gear, try just the 33t gear from old to new and see if that works.

smokin · Post by **smokin** » Tue Nov 17, 2009 10:08 pm

I have tried to swap first gear (new to old) and same problem, the tooth count and measurements are the same can't measure between the teeth, the gear fit is like 1/1000 larger I don't need to swap out first or second what I really need are the bearings on the left side, can I press them off from the left or do I have to take the trany apart, I was hoping to just drop another trany in but that's not going to happen.

tz375 · Post by **tz375** » Tue Nov 17, 2009 10:50 pm

The bearings on those shafts are not on very tight and can easily be pressed off and replaced. The two small diameter bearings are never very tight and often just slide off. The two larger bearings are much tighter fit on their shafts, but still press off quite easily.

As I understand what you're saying, both 37T gears are tight on the new shaft when it's in place, but not on the old shaft.

I would be looking very carefully at the shaft itself up close at the shoulder that the gear rubs against to see if there's a rough spot or something. It sounds like that section of shaft between the bearing and the gear is too short. the most likely reason for that is the bearing at the other end not being pressed on far enough, causing the whole shaft to be pushed to one side and pinching that gear.

There may be a shim behind one of the bearings that's too thick or should not be there.

smokin · Post by **smokin** » Wed Nov 18, 2009 11:27 pm

Thanks Tz and Allen for all the help, the newer 37t is binding on both shafts so switching the gears and shafts probably won't make a difference, first gear seems to be slightly larger but I don't need it I wonder if this is an early model problem? I'll swap out the bearings and everything should be good to go. Thanks

durgam · Post by **durgam** » Tue Nov 24, 2009 12:31 pm

Sorry to interject so late in the game. if the 2 37t gears both are tight on the shaft, than maybe you have a bent shaft. if the gears turn free for a 1/4 or 1/2 turn and than bind up, it may be a bent shaft. my 2 cents.