GS tranny in a GT750 box

tz375 · Post by **tz375** » Mon Mar 30, 2009 10:32 pm

Allan,

I discounted the GS550 but it did have a 6 speed transmission. I have no idea whether it was a slightly scaled down 750 or if it was smaller overall.

It's hard to make meaningful comments without having one here to look at, but I suspect the box would have to be sped up to take the forces. By running a numerically lower primary ratio, the gearbox rotates faster and can handle the reduced torque a little better.

It's certainly worth looking at. If anyone has a 550 trans and clutch and shifter they'd like to send me, I can work out if it would work.

Suzukidave · Post by **Suzukidave** » Tue Mar 31, 2009 7:27 pm

Tonite while playing around with the GT clutch inner basket to get it to fit further onto the the GS clutch support shaft i discovered a real duh thing .. the reason the GS bearings looked like they needed changeing out to the GT bearing because they looked to be too big and wouldnt seat was the GS bearing have a small pin that must fit into a hole in the saddle in the GS cases and this pin was keeping the bearing from seating down . So anyways rotate the bearing so this pin is out of the way and the GS tranny bearing fit right into the GT cases perfectly

. Anyways also working with the clutch inner basket to get it to fit 7mm further on the GS shaft i didnt really want to just lathe out the splined area the 7mm so what i did was to file and grind down the splines so they matched the splines on the shaft and that got me the 7mm i needed , the inner basket fit the GS shaft in the exact spot in the outer basket as it did with the GT shaft

tz375 · Post by **tz375** » Tue Mar 31, 2009 8:06 pm

Dave,

That's good news. It will take about 30 seconds with a Dremmel to make a recess for the pin. And does that first gear work OK with the oil pump like we suspected it would?

Suzukidave · Post by **Suzukidave** » Tue Mar 31, 2009 8:27 pm

Drops right in

and still has a smig of lash

Post by **Suzsmokeyallan** » Wed Apr 01, 2009 7:09 am

Dave thats excellent news, and no big long detailed work we discussed will be needed now.
Good thing i ordered my GS750 transmission a few days ago, i might now need another one too.

tz375 · Post by **tz375** » Wed Apr 01, 2009 4:42 pm

Have you looked at a BMW K1200 box? It's awesome (apart from a minor peg design issue) and it's compact and it's also casette style.

The bevel output shaft for shaft drive is a minor inconvenience, but it is so compact.

Suzukidave · Post by **Suzukidave** » Wed Apr 01, 2009 9:31 pm

Uh .. neat , but i think for now i will use the 49$ GS750 tranny http://cgi.ebay.com/ebaymotors/BMW-K120 ... 240%3A1318

tz375 · Post by **tz375** » Wed Apr 01, 2009 10:44 pm

No, No. Not the old flying brick. I mean a 2007 k1200R - the 150HP thing. It has a full cartridge box.

Of course it is designed in a way that makes for no replaceable parts and a replacement is available for only $3512 plus tax and shipping. It's all needle rollers and tight tolerances.

Pity that third gear dogs get rounded off and that destroys the shift fork. etc.

I realize that they used pegs and slots in gears rather than sets of undercut dogs to keep it slim, but what were they thinking? A GT box, or a GS box, would last longer.

Glad to hear you have cost effective way to bring first and fifth slightly closer.

Suzukidave · Post by **Suzukidave** » Fri Apr 03, 2009 8:48 am

Leave it to BMW to turn out a bike really different .

pjmcburney · Post by **pjmcburney** » Thu May 21, 2009 5:27 pm

Suzukidave wrote:Anyways also working with the clutch inner basket to get it to fit 7mm further on the GS shaft i didnt really want to just lathe out the splined area the 7mm so what i did was to file and grind down the splines so they matched the splines on the shaft and that got me the 7mm i needed , the inner basket fit the GS shaft in the exact spot in the outer basket as it did with the GT shaft

Hey Dave,

I've tracked down a GS 'box for my next GT engine rebuild - cost about US$50 on fleaBay and even with postage across the ditch it works out about a third of what I'd have to pay for one here.

After reading this thread, you've convinced me it's a viable modification, and I didn't have a real good GT 'box to use anyways.

I'm thinking I'll replace the pinned bearings with new un-pinned ones and drop the GS 'box straight in, using the GS shafts.
This gives me advantages with the output shaft, but (of course) I'm going to have to sort out the input shaft...

I was wondering if you have any pics of the mods you did to your clutch basket?

I have a couple of GT baskets lying around to play with - I don't necessarily want to use the GS straight-cut gears and/or the GS basket if I don't have to, and I don't have those parts (yet) anyway.

Any and all info greatly appreciated

Thanks
Paul

Suzukidave · Post by **Suzukidave** » Thu May 21, 2009 6:45 pm

Paul , i havent done the mods to the input shaft to shorten it but you can see from this picture the differences in the splined length and total length between the 2 ( top one GS )

Suzukidave · Post by **Suzukidave** » Thu May 21, 2009 7:00 pm

To get around the splined section not allowing the stock GT750 clutch basket to seat far enough in the back side of the basket needs to be back cut or shaped to fit on all the way

tz375 · Post by **tz375** » Thu May 21, 2009 9:11 pm

Dave,

Yes, that's the bike my son has and it's a very interesting motorcycle with over 150HP on tap. I rode it last time I was down there and have to tell you that the part throttle fueling made it a pain to ride slowly at tiny throttle openings.

He tells me it's great if you open the taps further, but it wasn't my bike to crash so i took it easy. It's hard to be smooth though.

I hope you do a better job that Honda, BMW or Bimota on the EFI system.

pjmcburney · Post by **pjmcburney** » Thu May 21, 2009 11:24 pm

Dave,

Thanks for the info.

I'll go down the same path as you and modify one of my GT baskets to suit.

I might drop the whole shebang off to a mate who has access to a lathe and get him to remove the required amount from the basket - I don't trust myself with a Dremel and/or file.

Question - what about the oil hole on the GT shaft where the basket sits, did you have to drill another or is it not an issue?

Cheers
Paul

tz375 · Post by **tz375** » Thu May 21, 2009 11:31 pm

Paul, Sounds like that might be a good idea. How does teh GS get oil into that needle roller bearing and bush?

I also checked the gear ratios in a GS750 trans and not surprisingly, it's identical to a late A model GT750 apart from a slightly higher first gear. 2 through 5 are identical to a late model GT. It brings the ratios slightly closer overall and reduces first to second jump but will need a few more revs to get it moving off the line.

Primary ratio is much lower though (higher numerically) as the motor revs faster than a GT