From N to 1st: Transmission thunk.

[DannyMotor]

I'm used to this on my old dirtbikes... it's a common thing... get on, start it, kick it into 1st, THUNK, the chain slaps a little, and you're good to go.

But the 78' GS750 is doing it too. Clutch cable feels good, engagement is about 1.25 inches off the grip (enough so I can double-finger the clutch) and it's not hard at all to pull.

The oil is Rotella SAE10w-40, full to the "F" mark on the case. The bike was sitting, not running for about a year, and then void of oil for about 6 months or so. The clutch doesn't slip what-so-ever.

It gets "slightly" better when warm... but to not feel it at all, the revs have to be up a bit. Also, with down-shifting, it likes to be blipped a little before engaging the lower gear.

No transmission noise, griding, clunking or anything.

Just didn't know if this was a normal trait or if it's something that can be 'adjusted' out of it.

 

[tkent02]

It gets "slightly" better when warm... but to not feel it at all, the revs have to be up a bit. Also, with down-shifting, it likes to be blipped a little before engaging the lower gear.

The clunk is normal, but what happens if you don't do the downshift blip?
It should just click right in gear regardless of what you do with the throttle. Smoother with the blip, but it should work fine either way.

 

[MisterCinders]

Heh, my bike always chunks into gear from neutral. I thought all bikes did.

 

[tkent02]

All constant mesh bikes do as far as I know. The big beemer you can't even hear it, just feel the lever move up from your toe. Shifts when you are moving are another story, just about always a loud clunk. I'll take a Japanese transmission and it's first gear clunk any day.

 

[DannyMotor]

Sub 40mph, and sub 3000rpm, it'll clunk when down shifting from any gear to any gear... I may need to snug up the cable a bit more.

Japanese transmissions are normally so smooth was my worry. My Triumph... Crap, that thing clunks in any gear as well. My fiance's 92' Yamaha Seca II 600, however, will just pop through the gears without batting an eyelash. Just simple "click" and done.

 

[koolaid_kid]

MY GS does it when it is cold and stops after it warms up. My GPz has never done it, but the tranny is a bit different with backcut gears.
The chain slap should be looked into, your chain may need to be adjusted.;

 

[Nessism]

It will do it worse if the clutch is dragging. Some warpage of the plates may not even be noticeable under normal riding, but will show up with a clunk as described or may make neutral hard to find from a stop.

 

[DannyMotor]

Nope, neutral is easy... it wasn't at first, but that's because I had over-filled the bike with oil... (whoops), now that the level is set, I can hit neutral from 2nd or 1st no issue.

Letting the clutch out slowly (or riding/dragging it) is smooth as silk. I haven't tried shifting through clutch dragging, as I don't intend on bending a fork... but it will 'quick shift' or clutchless shift 100% OK on the way up to 5th. I have NOT, nor intend to quick-shift down... unless they make a slipper clutch for this thing... haha.

 

[tkent02]

It's easy enough on the gears if it's done right.

 

[kawfeedave]

Motorcycle transmission don't use synchros like a car. The synchro in a car is a smooth ring that contacts a similar ring on the next gear, just before they engage. The two rings making contact will tend to even out the speed difference (if any) between the two gears before they mesh. The faster gear will slow down a touch, and the slow gear will speed up a little, and everything is cool.

Bikes use dogs to engage the gears, and there is no 'smoothing' of any kind in the transmission. Gear dogs are either engaged or not, end of story. So when you get a 'clunk', those are the dogs hitting each other at a higher-than-normal speed.

If your clutch is dragging, even a little, it will cause the input shaft to the tranny to spin when it should be freewheeling, and when the spinning, loaded gear locks into the stationary first gear, you get the clunk. If you can, try sitting on the bike facing down a slight incline, clutch in, tranny in neutral. Let the bike roll forward a foot or two, and then toe it into first on the roll, you should get less of (or no) clunk at all. In that case, you know your clutch is dragging, and needs adjustment/attention.

 

[DannyMotor]

... this I knew... I just though, since it was Japanese, and a lot of the Japanese bikes I've ridden have very little lash when shifting into first... that this one wouldn't be as clunky as it is.

But, it is! Just as long as nothing's wrong... riding like I stole it just became a lot easier.

 

[kawfeedave]

... this I knew... I just though, since it was Japanese, and a lot of the Japanese bikes I've ridden have very little lash when shifting into first... that this one wouldn't be as clunky as it is.

But, it is! Just as long as nothing's wrong... riding like I stole it just became a lot easier.

But this isn't lash we're talking about. Lash is the slop in the driveline, and when you roll on/off the throttle, the lash has to be taken up before the bike will accelerate or engine brake. When you have a big delay there, that's lash.

This is something else, it's a speed differential between the gears when they engage, and the one you describe points to a clutch that is not fully disengaging. Most bike will 'clunk' if you grab the clutch lever and quickly pop it into first. Even if the clutch is fully disengaged, the input shaft might still be freewheeling when you engage first, so you get a clunk. If you pull the clutch, and give the input shaft some time to freewheel and come to a stop, you should have much less (or no) clunk at all.

Ride it like you stole it if you want, but your clutch needs some attention and you can do it now, or later on the side of the road somewhere.

 

[tkent02]

How high is it idling?

 

[tatu]

If you pull the clutch, and give the input shaft some time to freewheel and come to a stop, you should have much less (or no) clunk at all.

You have to pull the clutch in for longer when the oil is cold, another way around it is to start in gear with the clutch pulled in. For me (when I remember) its hold the clutch and snick it in when the shafts have stopped rotating because it's harsh on the dogs. Fine when its warm.

 

[DannyMotor]

Alright, I'll try that in the morning. It thunks less when warm, as stated. But I like the idea of testing the freewheeling, and doing the neutral roll test.

It's idling at 1100rpm, but I'm also dealing with a weird air leak/lean/hanging idle issue when it's warm. But if I'm keeping the revs under 3500rpm, it seems fine otherwise. I did just adjust the new chain too... seems to have stretched some in under 200 miles already.

There could be a couple clutch plates stuck together due to it sitting for so long. I'll ride it... do a few tests, and if it continues, next oil change I'll pop the cover off and see if I have any issues hardware wise.

I'll fiddle, and fiddle again.

 

[Guest]

Mine has always clunked like that, sometimes it can come from the oil drag on the clutch as well. Heavier the oil the worse it seems to be.