Drive line slop. More discussion.

[Ramblin Man]

So while removing my relay arm I took a look at my universal joint to make sure it was in good shape. It was fine but I started looking at just how far the drive shaft rotated from lock to lock in first. The drive shaft rotates at least 30 degrees.

As first I thought it may be slop between the middle drive shaft and driven shaft that I could shim out but there is no way that that much play could be caused by the tolerences between those gears. Lash between thos gears is something like .1mm.

Futher listenning with a stethescope reveals the lock to lock clunk is comming from somewhere nere the center -center right part of the motor.

So, what I'm getting at is that the slop everyone talks about is not in the drive shaft, rear end or middle gears, its somewhere in the transmission or possibly between the output shaft of the tranny and the middle drive shaft. Maybe even between the crank and clutch input shaft.

That's a lot of places to look.

 

[Ramblin Man]

So I got with some of the V-Max guys and it appears that the home of the biggest portion of drive line slop/lash is actuaully the dogs in the tranny gears. That would seem reasonable because if you shift gears and repeat the slop test you get different numbers.

So what are our options?

1. go on as before and learn to love it.

2. Add power commanders, adjust spring tension, adjust cables etc...

or what about this?

Does not the FJR's rear wheel contain a drive cusion? What if we could get a drive cusion made out of a softer material? Something that would absorb more of the on-off transisition. After all I think thats what everyone is really looking for. Just a little more cusion to help smooth things out.

I do know someone who works with urethane and they use several materials of different durometer. I don't know if any would be soft enough but I'll certainly look into it. They don't injection mold but for this I'm sure casting would be fine.

Obviously this is one of those things that isn't really broke and doesn't need fixing, but neither is the position of the handle bars, size of the rear rack, factory CO levels, fuel capacity, windcreen size, lack of a hugger, seat comfort, absense of cruise control, softer suspension, etc.... So don't start bitching because I'm throwing gas on fire that should't be burning in the first place.

A new drive cusion is the only mod you can make without splitting cases that would have any effect on the actual mechanical "to the road" transition between off and on throttle.

If there are any real rubber experts on the forum that want to jump in please feel free. I know what kind of rubber I think would work, but I don't know if it exists.

 

[Groo]

I know what kind of rubber I think would work, but I don't know if it exists.

Flubber?

 

[twowheelnut]

Ramblin' Man - English for maywannayamaha? :grin:

 

[jestal]

I think if you check you will find that all motorcycles have that "slop" you are talking about. It is in the gear dogs. There is more "slop" in the lower gears since those are the ones that get shifted hard and fast more often so there is a wider window for the gear dogs to hit. Makes a bigger target when powershifting.

You don't notice the slop as much on bikes with a chain drive due to the inherent chain slack. For the lash in the drivetrain to transmit a clunk on on-off-on throttle maneuvers the chain has to be tensioned from the slack position to taut and that takes a lot of the slop feel out. Look at the chain sagging between sprockets and imagine that to take the chain taut it has to be pulled straight which takes energy and time that tends to mitigate the lash feel. Shaft drive, even with cush drives, transmits the shock pretty directly so you feel it more.

Changing the cush drive durometer is likely to be a futile exercise. If it gets softer the lash will crash thru the rubber even further and come to an even more abrupt stop when it runs out of room. In addition the added travel built in with softer durometer material will add to the lash, not decrease it. Harder cush drives or higher durometer rubber is likely to just make the lash takeup harsher and harsher. Might decrease the travel some but will make the take up much more obvious. Been there and done that on drive axles in cars in the past. The cush drive is mainly to prevent clanging noises and broken parts from metal to metal contact. It isn't going to fix drive line lash.

The only time the lash is really annoying IMO is at low speeds and trying to maneuver with on-off-on throttle doing parking and U turn type of things. There is a simple and easy way to forget about drive train lash on a shaft drive bike. When you drive into a slow speed maneuver simply open the throttle slightly, lock it by sliding your thumb/finger onto the switch pod so the throttle doesn't move at all. Control your speed by dragging the rear brake and there will be no lash as there is no need to modulate the throttle. Use this in any sort of tricky maneuver or on loose gravel or whatever and forget about the lash. It cannot hurt a thing. The rear brake is powerful enough to stall the engine at an instant if need be to stop fully and it can handle the heat from low speed dragging indefinitely. The worst it can do is to wear the rear brake pads that never wear out anyway.

EVen with notchy, jumpy carbs or injection and poor driveablity at low speeds and tons of lash a bike can be ridden quite smoothly at low speeds by dragging the rear brake to control speed and keeping the throttle cracked slightly. In fact, this is an even safer way to ride in those situations as you have instant "power" available by letting go the brake where a throttle movement to get power is not likely to yield instantaneous power. Use the rear brake. I always figured that this was why motorcycles had rear brakes after trying to ride the 78 XS1100 with large CV carbs, lean emission tuning and a shaft drive much like the FJR has....LOL.

This little trick is MUCH easier to learn than trying to re-engineer the drive line lash out that you will never be able to engineer out anyway....LOL.

 

[ShinyPartsUp]

"The only time the lash is really annoying IMO is at low speeds and trying to maneuver with on-off-on throttle doing parking and U turn type of things. There is a simple and easy way to forget about drive train lash on a shaft drive bike. When you drive into a slow speed maneuver simply open the throttle slightly, lock it by sliding your thumb/finger onto the switch pod so the throttle doesn't move at all. Control your speed by dragging the rear brake and there will be no lash as there is no need to modulate the throttle. Use this in any sort of tricky maneuver or on loose gravel or whatever and forget about the lash. It cannot hurt a thing. The rear brake is powerful enough to stall the engine at an instant if need be to stop fully and it can handle the heat from low speed dragging indefinitely. The worst it can do is to wear the rear brake pads that never wear out anyway.

EVen with notchy, jumpy carbs or injection and poor driveablity at low speeds and tons of lash a bike can be ridden quite smoothly at low speeds by dragging the rear brake to control speed and keeping the throttle cracked slightly. In fact, this is an even safer way to ride in those situations as you have instant "power" available by letting go the brake where a throttle movement to get power is not likely to yield instantaneous power. Use the rear brake. "

+1

This technique plus a deft hand on the clutch works wonders.