2nd gear thumping . . .

[HCorn]

I have an intermittent issue I thought was related to my new shock.  However, I was able to repeat the issue.

When I am in 2nd gear and sort of idling along (2500-3500 rpm) I can feel repeated thumping in my right foot, presumably coming from the tranny (like a flat spot in the tire).  This doesn't happen during acceleration or deceleration, even through that rpm range.  It doesn't happen in the other gears.  It only happens, like when taking off from a stoplight but slowing due to traffic, when the engine is in that gray area between acceleration and deceleration.

I'm theorizing that my 2d gear cog either has worn a bit and has too much play or perhaps a bad tooth.  And when the tranny is unloaded the gears slap a bit or chatter.  The bike only has 21K.

I don't plan to do anything unless it gets worse as it is a very minor annoyance.  If it is a worn cog, I assume the only practical solution is to swap trannies and it certainly isn't that big of an issue.  Unless you fine folks tell me otherwise.

(Edited to clarify the symptoms)

[frankenduck]

Yes, with tranny problems the best answer is usually to swap them.  Expensive parts inside and much labor to replace them.

If you do do a swap then get a 90 or later unit as those have the hardened splines.

Any K75, K100, K1 or K1100 tranny will bolt right up.

K100, K1 and K1100 trannies have a slightly taller 5th gear - 1.61 vs the 1.67 gear ratio of a K75 tranny.  All of the other gears are the same.

[mystic red]

Pretty unusual at 21K. You runnin' synthetic gear oil?

[HCorn]

I've only had the bike for 3K miles.  Not sure what the PO's were running.  Nothing looked unusual with the fluid last time I checked.  It definitely is isolated to 2nd gear.  Other than "feeling" it with my foot, it doesn't seem to effect anything.  Doesn't pop out of gear or anything like that.  I thought it was pretty unusual too given the mileage.  I was kinda hoping people would say it's normal, but I didn't think that would really happen, :biggrin:

As long as it doesn't get significantly worse, I'm not too concerned.  But I worry it might be foreshadowing something bigger down the line.

[mystic red]

Change it and run a synthetic. Those tranny's are tough. Not smooth but tough. Even JO can't trash one. Syn may smooth it out.

[frankenduck]

90/140 Mobil 1 with some Guard Dog moly additive.

The trannies aren't as tough as Mystic Rod thinks.  If you stomp on them hard enough enough times you'll eventually bend the shift fork.

Johnny has supernatural motobricking skills and is the smoothest K shifter on the planet.  Just ask him.

[wmax351]

I'm planning to try Redline Shock resistant gear oil next change. Fluid friction of ~75w-90, but film thickness of 75w-250+. Seems like it should smooth it out a bit.

http://www.redlineoil.com/product.aspx?pid=44&pcid=8

[HCorn]

Thanks for the info.  I checked my notes, and I haven't changed the tranny fluid yet.  Although I had a shop due the spline lube and he may have changed the tranny fluid.  It's real clean.  But it can't hurt to try new fluid.

But since it is limited to 2nd gear, I do think it is something mechanical.  Although I haven't totally ruled out the kickstand vibrating and hitting the muffler.  But I would think that would happen in several gears unless it is some unique harmonic.

Not sure how that all is supposed to look, but the tolerances are real tight between the muffler, kickstand, clutch cable.  Plus, my muffler can be shifted a little even though the clamp is tightened down.  Not sure if this is normal.

Now that I can replicate the noise, I'm hoping it is just  matter of time before I can find a definitive source.

[frankenduck]

I'm planning to try Redline Shock resistant gear oil next change. Fluid friction of ~75w-90, but film thickness of 75w-250+. Seems like it should smooth it out a bit.

http://www.redlineoil.com/product.aspx?pid=44&pcid=8

There's plenty of decent synthetic gear oils out there - Redline, Royal Purple, Mobil 1 - or, if you need a sticker too, Amsoil.

[wmax351]

I'm planning to try Redline Shock resistant gear oil next change. Fluid friction of ~75w-90, but film thickness of 75w-250+. Seems like it should smooth it out a bit.

http://www.redlineoil.com/product.aspx?pid=44&pcid=8

There's plenty of decent synthetic gear oils out there - Redline, Royal Purple, Mobil 1 - or, if you need a sticker too, Amsoil.

Definitely. All work well.

I figured I would give it a try, and was ordering some of their zzdp break in additive for my R75/5.

[conybeare]

90/140 Mobil 1 with some Guard Dog moly additive.

I've always used 75-90 Mobil 1 synthetic, mostly because that's what is commonly available in stores... what's the difference in terms of performance/shifting between -90 and -140?

[WayneDW]

.

  Plus, my muffler can be shifted a little even though the clamp is tightened down.  Not sure if this is normal.

Mine was like that too.  I took the muffler off and found that the "donut" gasket was missing.  I ordered one and it tightened down much better with it in place.

[DRxBMW]

90/140 Mobil 1 with some Guard Dog moly additive.

I've always used 75-90 Mobil 1 synthetic, mostly because that's what is commonly available in stores... what's the difference in terms of performance/shifting between -90 and -140?

75/140 full synth gear oil shifts so much smoother when it's HOT.

Miraculous concoction, to the point, I will never go back to 90 weight.

I'm NOT a big supporter of brand loyalty but the BMW gear oil is a better quality. Bill's a cheapskate, used Wally World synth gear oil in his K 100. What a difference a year later,read worth the extra money spent for the good stuff. 

[frankenduck]

The moly additive makes a difference too.  After several hundred miles it had "sunk in" to my LT and made the tranny noticeably smoother.  I use it in all of my Ks now.

[HCorn]

I replaced the transmission oil with Mobil1 75/90.  There was nothing remarkable about the old oil - still had the honey color, but did have a decent amount of metal sparkle to it and some fuzz on the drain plug.  But really, nothing I considered out of the ordinary.  Seems to shift a bit nicer, but I'm probably splitting hairs.  The short of it is it didn't seem to make much difference to 2nd gear.  But I'm also getting a bit more comfortable about it.  It doesn't jump out of gear or make strange noises and I think it has probably been this way since I got it.  I'm just a bit more in tune to it now.  The fact is, it only happens in probably <1% of my riding.  I'll just keep an eye on it.  I think after a few hundred miles, I can hopefully start ignoring it  :neener:.

[johnny]

greetings hcorn...

final drive guard dog molly...



gear box guard dog molly...



j o

[frankenduck]

JMHO but I don't think you need different bottles to mix with different gear oils.  That's just what the moly is suspended in.  I'd just go with the 75/90 for both.  (Which is what I do.)

[HCorn]

Just to sort of close out this thread (albeit without resolution) for future reference.

I did replace replace the exhaust donut (needed it and quieted and secured the exhaust).  But the problem clearly must be in the tranny somewhere.  To further clarify the symptoms:  there is no sound, but feels sort of like a flat spot in the tire; it only happens in second gear and mostly between 2500-3500 rpm; by 4000 it is essentially gone; under load (heavy acceleration) it really can't be felt ; it really can only be felt with my heels pressed against the stays (I'm really duck toed) - if my feet are solely on the pegs I really can't feel it.

What really has me stumped is why the symptoms aren't felt through the entire rpm range and why it is decreased as the load is increased.  I will update if it gets worse or if I figure it out.  Until then, I'm riding it out.