Jerking while fully engaging clutch during up-shift

[petrock]

Hey,
Over the past month or so my ride has developed a weird behavior when I'm up-shifting from 1->2 or 2->3 and sometimes from 3->4, but not from 4->5. After up-shifting, I ease on the throttle and let out the clutch lever. When the clutch lever is between 95 and 99% out, the bike will jerk two or three times. Once the clutch is 100% out, everything is fine and the bike runs like a top. It also runs fine in low speed maneuvers while playing with the clutch between 0 and 95%.

It doesn't feel like I'm lugging the motor or something like that, and I have the RPM's up reasonably high but not screaming. Its a pretty sudden, hard and forceful jerking motion, btw, and I can feel a bump/bang in my foot pegs, seat and handlebars when it happens.

I've re-adjusted the clutch (3/4 turn) twice and run an HD primary chain auto-adjuster and SE clutch spring.

Is this an indication my clutch pack is slipping or warped and needs to be replaced? I've got 45k miles on the clock and use my clutch a decent amount, especially in low speed maneuvers and when down shifting.

Any ideas? Thanks in advance...

[jerry34208]

One jerk would lead my to say a warped plate or two in the stack. But feeling two or three jerks and more importantly the way you can feel a bump/bang through the pegs tells me you need exploratory surgery.

A warped clutch just feels like you let the clutch out too fast right at the end of the throw.

[petrock]

Originally Posted by jerry34208

One jerk would lead my to say a warped plate or two in the stack. But feeling two or three jerks and more importantly the way you can feel a bump/bang through the pegs tells me you need exploratory surgery.

More often then not, its one jerk. But on a fairly long ride this past weekend with my girlie on the back, I was getting multiple jerks while in traffic (she doesn't like me to split lanes, even though it is legal in CA). Today, however, while riding to work it was only one jerk again.

What kind of exploratory surgery would you suggest? I assume I should start by checking the clutch pack and make sure none of the plates are warped. If they are fine, what should I look at next?

Originally Posted by jerry34208

A warped clutch just feels like you let the clutch out too fast right at the end of the throw.

You mean it feels like the bike is lugging? How would a warped clutch plate cause that problem? Just curious.
It feels a little harsher then the bike lugging. It kind of feels like, as I let the last 5% of the clutch out, that the clutch pack finally takes hold with a thud/jerk/clunk and the bike continues on its way. Not a push you back into the seat feeling like when you get on the throttle.

Thanks...

[jerry34208]

Sounds like a warped clutch disc or two. Remove the clutch pack. Stack up the steel discs and see if you can shine any light through them from the side. This will show a warp fairly easily. I can't think of anything else that would create such issues. If it were a gear or a bearing it would do it in many different situations. But yours is only when the clutch is being engaged. Bingo, it's the clutch. Beyond that I am out of my league as far as advice. But in any case, first things first and that's where you want to look.

[jerry34208]

Originally Posted by petrock

More often then not, its one jerk. But on a fairly long ride this past weekend with my girlie on the back, I was getting multiple jerks while in traffic (she doesn't like me to split lanes, even though it is legal in CA). Today, however, while riding to work it was only one jerk again.

What kind of exploratory surgery would you suggest? I assume I should start by checking the clutch pack and make sure none of the plates are warped. If they are fine, what should I look at next?


You mean it feels like the bike is lugging? How would a warped clutch plate cause that problem? Just curious.
It feels a little harsher then the bike lugging. It kind of feels like, as I let the last 5% of the clutch out, that the clutch pack finally takes hold with a thud/jerk/clunk and the bike continues on its way. Not a push you back into the seat feeling like when you get on the throttle.

Thanks...

Sounds and feel are very hard to describe with words so don't place too much faith in a particular description. When you have warped disks (and/or warped clutch plates) the clutch is simply not smooth. This shows up first at the last moment the clutch is still allowing slippage but then finally locks up or fully engages. With more than one warped disk the there can be a bit more of a jerkiness to the final engagement of the system. What is happening in a good clutch is all the steel disks and clutch plates are slipping the same amount and that amount of slippage is getting progressively lesser as the lever is released. It's a smooth and evenly graduated process. When there is warp-age, the process is not smooth or evenly shared between all of the disks and clutch plates. The slippage is traded off between the good and the bad disks/plates. Instead of all the disks/plates slipping or grabbing at the same rate, the warped ones are the last to lock (I believe) which further stresses and heats the high spots also causing further warp-age and unpredictable engagement. This is what causes the jerkiness.

With warped clutch parts the amount of jerkiness is unpredictable with each shift because you can never do the same thing the same way every time. So there are different amounts of power being transferred at varried rates of progression but there is most often a telltale "final tug" at the moment of full engagement making a butter smooth transition nearly impossible.

I'm betting your clutch is bad. You may have other issues that are being exposed by that extra hard jerk. But start with the clutch.

[petrock]

Cool. Thanks alot for the explanation. Makes sense. Now to tear the primary/clutch apart.

If it is the clutch pack, which I agree it probably is, any recommendations on clutch packs? Should I go stock or SE or aftermarket?

[jerry34208]

I have SE clutches in both of my builds. After 20K miles & 115 ft/lbs worth of fun on a heavy bike, it began to slip on rare occasions. I added a VPC92 and it's been all good since.

On a 95" the SE will do a good job for another 45K, no worries.

[shoveler]

You can also check clutch plates by laying them on a thick piece of glass one at a time. If you can slip a thin piece of paper under any edge, it is warped.