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View Full Version : GS kicks back from 4th to 3rd under acceleration (sometimes)



The_Veg
05-11-2009, 02:22 PM
Sometimes when I'm accelerating through the gears (especially if I'm being a bit 'spirited' with the throttle) I'll shift into 4th and the box will then immediately kick back to 3rd. This has NEVER happened with other gears, and it does not always happen during spirited accelerations- but the fact that it's only 4th/3rd and has happened often enough to notice keeps nagging at my mind. Should I be worried?

planepaul1949
05-12-2009, 05:04 PM
I certainly wouldn't like it. Understanding why this happens may help you modify your shifting practices a bit.

In the same vein as "the knee bone is connected to the shin bone.........", the gearbox shifts by converting rotary motion into linear motion. The shift spindle (lever attached) links to a cylindrical shift drum, whose cammed slots carry the shift forks linearly to engage the appropriate gear. There is only a spring-loaded roller arm that keeps the shift drum positioned in any gear (or neutral). So, when your transmission jumps form one gear to another, it is because a side force is acting against the shift fork. That side force is from incomplete engagement of the gear in question. The edges of the gear dogs/slots are in only partial engagement, and the shift drum is not fully rotated into gear. Also, the detent roller arm is not centered in the shift drum's cammed slot. The side force overcomes the spring strength, and the shift drum is sent back from whence it came.

I will just say that the event you describe is potentially damaging to the gearbox. Excessive wear, chipping, or outright breakage can occur to the gears or shift forks. I've seen it many times on other brands. So, you want to avoid this like the plague.

Incomplete shifts are typically a result of the shift being attempted too quickly, as in "spirited". You need to slow your shift lever movement rate down slightly in order to allow the gear slots an opportunity to achieve alignment. And "slightly" is the keyword. I time my shift lever actuation as a function of engine speed at the shift point. That is, in lazy around-town riding my shifts are relatively slow. I quicken my shifts as I go "more spirited", because all of the rotations are happening faster. I've never missed a gear on my '05 RT. By the way, don't listen to the guys on the forum who advocate "loading the shifter". They don't understand what they are doing to the gearbox, or don't care.

One last thing. To be on the safe side, whatever gear you're in for a while, if you can, roll the throttle off once to allow for any incomplete shift to complete itself. Unloading the gearbox lets the shift roller spring do its job.

Good luck.

Paul in CA

The_Veg
05-13-2009, 01:35 AM
So how come it doesn't happen with any other gears?

planepaul1949
05-13-2009, 03:52 AM
Can't say exactly, but I can take a guess. 1st to 2nd, and 2nd to 3rd, the ratios are the most widely spaced. You will catch engagement more quickly than the higher gears. By the time you are run up in 4th gear, you're probably out of the "spirited" mode. That leaves 3rd to 4th as the problem child.

You're welcome.

Paul in CA
'05 R1200RT

sit
05-13-2009, 04:10 AM
My GS, me really, gets an incomplete shift once in a very great while from 4 to 5. And also from 5 to 6 more often. Just did 800 miles last weekend and used all the gears and ony did it once going into 6. My fault, was half assing the shift and trying to be quick with it. Have learned for the most part to make 4-5 and 5-6 shifts nice and smooth and deliberate. Head space still gets me once in a while though.

The_Veg
05-14-2009, 12:53 AM
Also I did 'especially' on the spirit, not 'always.' It has done it during somewhat calm riding, just not nearly as often as when I'm being zoomy.