Transmission Clunks

Hi, folks. I am in the valley of decision here, and could use some advice. My transmission clunks really bad when shifting, it sometimes misses between third and fourth unless I shift hard with my foot, but the biggest problem is that the bikes clunks/jerks during acceleration.

I have gone through all electrical and everything checks out. The bike runs great and smooth, coil output checks out, clutches great, etc.

I can really feel the clunking between my footpegs. So I am assuming my transmission needs to be re-built.

I'm just learning how to work on my own bike, and I'm really hesitant to dive into a transmission. Is this something best left to a mechanic experienced in vintage bikes? How difficult is it for a novice, but mechanically inclined?

Finally, if it is the transmission, considering my symptoms, what could I expect? Gears chewed up, or just adjustments?

I'm pretty troubled by this, and could use some directions.

Have you checked the play in the drive chain and the condition of both sprockets??

Am also thinking drive chain.

Might be kinking. Can usually determine by just examining and manipulating the chain by hand.
Kinked chain may also feel hot after a run.

Lubing the chain might help, but may need replacing.

i was getting the same kind of problem a few weeks ago until i readjusted the chain tensioners to get it back to where it should have been, i was only about one tick off on my adjusters, that and a good lubin rid me of the vibrations.

Thanks, Guys. I just posted to a previous thread I had posted about this in the Electrical forum as I initially thought it was rooted in coils, IC igniter, or some other electrical source.

It turns out to be a simple source - those brand new Dyna sparkplug wires I had installed were unshielded wires, and since my bike is a 1981 with electronic ignition, it requires shielded cables.

Once I had corrected this last night, the problem I now thought might be transmission-related, completely went away, and the bike runs great!

However, it stills shifts kinda "clunky", so I still want to address that, but obviously that doesn';t require splitting cases and rebuilding transmission. Is there a known fix to this clunky shifting?

Norseman wrote:

...stills shifts kinda "clunky...Is there a known fix to this clunky shifting?

Perhaps clutch is failing to completely disengage while operating foot gearshift lever.

Has clutch push rod been adjusted to allow the proper slack? Too much slack could prevent the clutch from completely disengaging while shifting gears.

Would also check for and correct any excessive slack in the clutch cable at the handlebar lever, as this too might prevent the clutch from completely disengaging while shifting gears.

Thanks, Guys. I did check alignment of rear wheel, and checked both sprockets - all checks out. I have adjusted the chain and clutch (2mm free travel at grip) exactly according to manual, although I tightened the chain to 1" travel instead of 1.25 as the manual suggested.

One thing I did notice, when I tightened just a little bit more to 3/4" travel, the shifting was a lot smoother and less "clunky"., but I took it back to 1" so I didn't screw up sprockets and drive. Was I too careful here?

Also, in addition to the "clunky" shifting, I have also noticed that there is "slop" in engine to drive. This sounds weird, so I'll try to explain. Say I'm in second, rounding a corner. I let the throttle go to cruise, then give it a little gas. The bike kind of clunks/jerks like there is slop in the drive. I don't know how else to explain it. My question is could my chain be that worn that even when adjusted to 1", the play or slop in chain could cause this?

Or is it a worn or previously abused tranny? The bike does shift real good, has never popped out of gear, and I think the few times I have missed a shift is my own fault for being to quick or soft on the shifter.

One last way of explaining is if I cruise aling in third going say 35 miles, and start to play the throttle by letting down and then giving gas repeatedly, the bike clunks back and forth like it has excessive play between engine and tranny. Is this common and not an issue, or should it be addressed?

By the way, the bike has 12K miles on it and has been very well maintained.

Post edited by: Norseman, at: 2007/09/02 23:42

Post edited by: Norseman, at: 2007/09/02 23:46

Norseman wrote:

My transmission clunks really bad when shifting, it sometimes misses between third and fourth unless I shift hard with my foot, but the biggest problem is that the bikes clunks/jerks during

The first thing I would do is look for wear or damage around the shift lever. An improperly seated or worn shift lever case hole will perhaps cause a misalignment of the rest of your shift mechanism.


What did you do to inspect the clutch? Checked thickness and warp of plates according to factory minimum specs? It's also good the check the clutch basket for grooving, which will prevent the plates from moving laterally at the proper rate.

...I can really feel the clunking between my footpegs. So I am assuming my transmission needs to be re-built.

You might have worn shift forks/shift cam.

...How difficult is it for a novice, but mechanically inclined?

If you are good at following the book without losing patience and skipping any steps go for it.

...Finally, if it is the transmission, considering my symptoms, what could I expect? Gears chewed up, or just adjustments?

What does your Clymer manual say? Mine has a nice section on inspecting the shift cam, shift forks, shifting pawl, and dogs for wear.

have you looked at the rubber damper in the rear wheel, maybe its worn

I have noticed that after a few years of using Castrol Act-EVO 10W-40 in my 650 SR that the shifting went from stiff and clunky to silky smooth. I've only put a bit over 2000 miles on in that time and have changed the oil once each spring.

YMMV.

Thanks for the heads-up on the oil, Nate. I have been using Valvoline 20W50 for motorcycle since I bought the bike (1000 mile ago). Do you know if Castrol offers Act-EVO in 20W50? If so, I'll make the change next oil change (which is pretty much now LOL).

I may have a slightly worn shifter case hole as I have noticed an occasional oil drip from that area under the bike. It's either that, or a failing oil seal. While the bike only has 12K miles on her, seals that are 26 years old obviously have a propensity for failing... So much for the "clunky" shifting.

The continuous clunking in all gears during acceleration was not caused by the tranny, but rather a problem with misfiring caused by a problem in the ignition system. As it stands today, it appears my IC Igniter is failing, and is returning extremely high readings when performing the "Igniter Out of Cicuit" test in the manual. For example, on one set of wires I should be reading 200 - 500 ohm, I'm getting 1,000 ohm resistance. I am waiting on a call from an expert recommended by the good folks at Z1, but we're pretty sure the Igniter is causing the problem.

I appreciate all the good advice and posting from all you guys!

Walter

How about checking this out ?
Grab a few rags or an old pair of gloves and with the bike on the stand and in neutral ,
Grab the rear sprocket and see if you can move it back and forth (clockwise & anticlockwise)
Does it move much ?
It should not ,
Does it clunk ?
If it does , the dampers are done .
From the age ,just dried out ,
I ALWAYS fill in the voids with RTV .
Much smoother ride even on a good running bike.

I have NEVER heard of an IC box "kinda" failing .