Gearbox technical question - BMW Luxury Touring Community
 
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post #1 of 9 Old Aug 28th, 2013, 10:11 pm Thread Starter
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Gearbox technical question

We have discussed previously here about clutch problems and the fact that our first geasr ratios are quite tall. I am thinking of making a project around reducing the gearing in first gear, but need some answers to the following questions in order to decide whether or not this could be a "goer". It looks to me from the cutaway drawing that first gear set is at the rear of the gearbox, could someone confirm this please ? That being the case, does the electric reversing gear train engage with the fourth gear ratio driven gear ? What I'm wanting to confirm is that in any first gear set modification, the reverseing function won't be compromised, and that the modification (manufacture and install 2 new gears) will be technically possible. Then the challenge will be to find a project gearbox in Australia.
Just checked the specs, first gear ratio is stated at 2.050 : 1. I make that gear teeth numbers of 20 on the input shaft and 41 on the output shaft. can someone please confirm those numbers also ? Thanks.
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Dennis
1987 Yamaha TY250R
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post #2 of 9 Old Aug 29th, 2013, 12:29 am
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Re: Gearbox technical question

Reverse has it's own gear on the output shaft. Not sure if there is room in the case for a different ratio on first gear. Didn't we go through this a few months ago?

John
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post #3 of 9 Old Aug 29th, 2013, 1:02 am Thread Starter
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Re: Gearbox technical question

I commented some time back that it may be an option John, I'm wanting to get some potential show stoppers confirmed before I commit to hunting down a gearbox. I have a contact in a gear design company and can source a gear manufacturer. If it is too cost prohibitive then I won't pursue it of course, but it would be nice to do as I can see quite a few benefits.

Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
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post #4 of 9 Old Aug 29th, 2013, 8:10 am
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Re: Gearbox technical question

If you change the first gear ratio you may find going into second awkward, big rpm change going into second, end up in second at a lower rpm than "normal", most boxes are close ratio and the rpm change gear to gear is the same

Gary
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post #5 of 9 Old Aug 29th, 2013, 8:27 am
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Re: Gearbox technical question

I wonder if there might be more intrest in a lower gear set for the R1150GS trans.?

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post #6 of 9 Old Aug 29th, 2013, 5:31 pm Thread Starter
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Re: Gearbox technical question

In standard form, the ratio difference between 1st and 2nd gears is extremely small at 2.050 : 1 for 1st and 1.60 : 1 for second, it's really noticeable when shifting that the bike almost decellerates if you shift into second gear and don't gas it. In comparison, K100 gearing is 4.50 : 1 in 1st and 2.96 : 1 in second. Those bikes never ever toasted the clutch and could be ridden quite slowly whist still having resonable spacing between the gears, argueably they were a little low in 5th if anything. I would be aiming to have a 1st gear ratio change to around 2.9.: 1 but it may not be possible due to restrictions in the casing.

Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
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post #7 of 9 Old Aug 29th, 2013, 8:37 pm
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Re: Gearbox technical question

I really don't have any problems with the gearing of my LT. I would be far more interested in a once and for all clutch fix solution. Like redesigning the entire clutch system and making it a wet clutch. Then if any of those seals fail it wouldn't matter. Perhaps a clutch like most other bikes use, then seal the seam between the engine and transmission. Could it be done? I don't know. But it would be nice to replace a clutch only because it is worn out and not because some seal leaks all over the dry clutch plate.

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post #8 of 9 Old Aug 29th, 2013, 10:04 pm
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Re: Gearbox technical question

It's not difficult to get a wet clutch on an LT.........

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post #9 of 9 Old Aug 30th, 2013, 12:00 am Thread Starter
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Re: Gearbox technical question

Lowering the 1st gear will preserve the clutch, the rest of the "wet clutch" problems are from leaking seals and failed clutch slave units, so no real reliability problems with the dry clutch itself other than a short life. As for converting to a wet system, unfortunately the operating principle is totally different, ours spin at engine speed, typical wet clutches spin at the speed of the primary reduction, very much slower than the crankshaft, so oil churning is not a problem.

Dennis
1987 Yamaha TY250R
1991 Aprilia Climber 280
1988 K100RT (the pack horse)
2005 K1200LTE Light yellow metallic
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