High rev clutch slipping, 94 Wombat

[matt glascock]

Hello friends, here's the scoop. 1972 M94 Wombat. I rebuilt and blueprinted the clutch using updated friction disks and steels from Strictly Hodaka and filed the washboarding on the clutch cage (fine triangle file and NOT Dremel, Captain ). Removed all existing shims from under the clutch disk. I Replaced the pinion bushing and thrust washer. Remaining parts appeared serviceable showed no unusual wear. Safety wire reassembly. Clutch was smooth as butter. Now, I'm almost consistently experiencing what seems to be a slipping of the clutch at about 75% WOT. In other words, at somewhere around the 75% WOT range, the bike will rev out and lurch. Coming off the gas allows the clutch to engage and can keep going. I'm planning to inspect the clutch components unless this symptomotology suggests I'm barking up the wrong tree. I'm hopeful the problem is not deeper in the drive train. As always, many thanks!

[Hydraulic Jack]

Sounds like clutch slippage to me. Since you were just in there, my hunch is the disc count isn't right for that clutch hub. The differing model clutch hubs look quite similar and parts can swap back and forth, but they didn't all use the same clutch discs and disc count. Having too few discs in the pack can create the exact symptoms you describe.

The only other thing you mentioned was removing all shims. This may or may not be correct for your situation. I would revisit the shim process when putting things back together.

[racerclam]

if you had to remove all the shims to get the release lever free play something is wrong like Jack said , doing that is what you do as clutch wears but never down to zero shims , if you missing a plate that would be like having all the plate wore out.

Rich

[taber hodaka]

How much free play do you have?------Clarence

[matt glascock]

Thanks fellas. You are correct, Rich. There was a 0.5 and 2 x 0.2 mm shims under the disk prior to the rebuild and with them in after the rebuild, there was zero free play. In fact, I could barely pull the clutch lever. Perhaps I'm operating under a misconception here but I thought the addition of shims was to account for plate wear and therefore, wouldn't be needed with fresh plates. Jack, you bring up a very valid point. This bike was a textbook mutt with a unknown array of DPOs so it may not even be the proper clutch cage. I'm reasonably sure I installed 4 friction and 3 steel plates, but I'll have to look at the build sheet for the bike when I get back to the shop. I may just pull the clutch out of my other M94 for confirmation of a proper clutch basket. Its sure possible I could have whiffed on the disk count or order. I've done sillier things.

[matt glascock]

Hi Clarence. Free play is roughly 3/16" now. Disengaging, shifting, engaging, and launch are smooth. No strange sounds. The slippage only occurs at speed.

[Bill2001]

I don't know wet multiplate clutches, but here are my thoughts based on dry single-plate.

What is the width of the "friction zone", that part of the clutch travel that you can slip the clutch in? In other words, the start of where it starts to release tp where it is fully released, and vice versa. This friction zone should be 1/8" to maybe 1/4". If that friction zone is very narrow, that suggests that the clutch plates are worn. On my Wbat, the friction zone is less than 1/16", and I suspect that it is very worn. But I don't know what it should feel like.

Your clutch slipping at high speed is unusual and may be an important clue. It should slip at low speeds.

My 2c, FWIW.

[BrianZ]

Are you certain the clutch is slipping? I have had bikes that jump in and out of gear causing the symptoms you describe. This could be a worn out or maladjusted shifter mechanism.

Brian

[matt glascock]

Bill, you highlighted the part of this I can't figure out. Why the slippage at high speed? Like you, when I have experienced clutch slippage, its typically during acceleration from standstill when strain on the drive components are maximal. I'm trying to wrap my head around an RPM based reason for the slippage. I'm probably a bit rough on clutch components as I always have a finger or two on the clutch lever and slip the clutch purposefully and frequently. Maybe the higher RPM context for the slippage will resonate with someone. I'm going to start with disassembly and inspection. Thanks Bill.

[matt glascock]

Thanks for the comment, Brian. I did install new springs and ball receiver when I replaced the clutch components and everything worked fine initially. This bike did duty as an MX bike in its previous life and the gearing has been changed to a closer ration than on my stock M94. Lord knows what demons are lurking in there! At least its behaving like a clutch slippage issue. I will take a look at the shift adjustment when I get the bike on the lift. That would be a nice and easy fix. Its a rev change ala clutch slip more than the crunching/sickening sound of a shifting maladjustment, but you bring up an excellent point.

[michael_perrett]

A clutch will slip in high gear first, since that is when there is the most resistance.
Mike Perrett

[matt glascock]

Agreed, Mike. Usually under acceleration in my experience. This problem here occurs near the end of the rev range which doesn't make sense to me.

[Hydraulic Jack]

If the clutch doesn't have the correct discs, is worn out, or has the wrong springs, its clamp force is impaired. Slippage due to reduced clamp force isn't speed related per se, but rather load dependent. Usually happens in the higher gears under acceleration where the engine hits its torque peak and it trying it hardest to accelerate the mass of the bike and rider. It may have a light feel to the clutch lever, which is something that IMHO Hodaka wasn't noted for. This clutch was described as butter smooth, and for me that's a clue. "At the end of the rev range" is where I would expect to find slippage on a trail bike that doesn't have a killer torque peak, like an MX bike does. Take the clutch out and measure the cage depth and disc count. You may have an Ace 100 clutch basket stuffed with later discs and the build height is wrong. You should not start out without shims in order to get the right free play. If this was a 40 year old clutch I would say it is worn out. Since it is newly rebuilt, I would say it has the wrong combination of parts.

[matt glascock]

Ding ding ding ding! Again, you are correct, Jack. I pulled the culprit clutch and a known properly functioning clutch from my other M94 and found that the malfunctioning clutch had a cage that was a little over 1mm shorter. It must have been lapped at some time. I'm not familiar with loss of height as a typical wear and tear pattern as opposed to washboarding at the point of plate engagement with the cage teeth. Additionally, even though I dressed the washboarding, it had already redeveloped to a noticeable extent. Disk and plate counts were correct. Fortunately I have spare cages that will be serviceable with a bit of file work. I'll rebuild one and report. Many thanks to all.

[matt glascock]

Clutch rebuild finished and...whew...just in the nick of time apparently. The screws were warping. Who knows how close I was to a complete clutch explosion. The clutch operates perfectly now. A good object lesson here - never underestimate the power and reach of the DPO. Thanks to all!