Making a Cushier Cush Drive

[Dan M]

I'd sooner go through the trouble of molding urethane than go after the major project of removing the bolts. Once you have gone that far, why not order the superior part if it existed, or make it yourself if it is easy to do.

I have had some limited experience with plaster, polyester, alginex, and silicone casting, but never urethane. I am certainly more frightened of taking on removing the buttonhead screws in my bike that is more than twice the age of Greg's 2004, than I am frightened of replacing the simple rubber cush with urethane.

Makes me crazy to think that such a clear simple solution is viewed as a major and risky endeavor.

 

Greg is a professional wrench+++ and his experience was,

"The first step was to take it apart. I used my usual technique for buttonheads (which stip easily): 1) heat on the head of the screw for one minute with a MAPP gas torch; 2) insert the appropriate sized allen socket into the screw and give it a wallop with a hammer to shock it loose; and 3) turn out the screw with a ratchet wrench. Two of the screws were loose already. Two others cam right out. The final two took 45 minutes of heating and pounding and cursing. I finally had to drive them out by chiseling a shoulder into the buttonhead and driving them around with a punch. Both fought every turn of the way. It wasn't loctite; it was corrosion between the threads. This on a 2004-model bike that has been in service just 26 months."

I guess my clear solution may be to let it be, although I am curious as to just how hard these chrome-moly steel hard rubbers really are.

 

I too am a professional wrench. After decades of doing this sort of thing here in the rust belt, removing stubborn fasteners has become second nature. As with many soft OE fasteners, once you go through the trouble of removing them and replacing them, a little care on installation & a dab of anti-sieze will keep them servicable for years without the anguish. With me, unless it is the dead of winter and I don't have much to do, I prefer to get the bike back on the road ASAP. While I like to tinker with my bikes, I'd rather be riding them.

BTW, I never said risky. I'm just for keeping things simple and reliable. From my experience, those two terms are usually synonymous

 

 

My theory, Dan, to pick up on an earlier comment, is that there are many people who simply aren't happy when the current overall level of grief, antagonism, and anxiety in their lives falls below a certain "pre-programmed" level. When this happens, they quickly act by whatever means is most convenient and close at hand -- consciously or sub-consciously -- to bring their grief level back up to wot they're most comfortable with. I think of it as the Grief Level Optimum. Some seem to have their GLO settings much higher than others. . .

 

This condition is easly cured with a revolver.

[dlaing]

 

No. Just because you can move it more after contact is made, it does not follow that there is more free play. Free play is exactly that: an amount of non-contact. Softening the cush drive only blurs the boundary.

 

That seems kind of like measuring your height by the puffiness of your hair.

Following that definition, I contend there is no freeplay in the drivetrain, as everything is in contact.

[Guest ratchethack]

That seems kind of like measuring your height by the puffiness of your hair.

Following that definition, I contend there is no freeplay in the drivetrain, as everything is in contact.

Dave, I beg your pardon, but your contention is poorly informed and entirely incorrect. Mike is exactly right. In any sequentially shifting constant-mesh transmission, there is, and must always be "free play" or "driveline slack" or "driveline snatch" or wotever words one chooses to call it. Without some degree of this "slack", it would be impossible to shift this kind of transmission.

 

As Pete has discussed many times, the design of the "old" 5-speed box used half the number of shift dogs and engagement slots in the sliding muffs of the V11 6-speed box. IIRC, the old design was a 3-dog setup, and the V11 six-speeders use a 6-dog setup. While the 3-dog design made for a slicker and swifter shifting box, it must've created a walloping huge driveline slack. The increased driveline slack due to the more than doubling of the distance between dogs and engagement muff slots created an opportunity for increased inertial loads and proportionally harder slamming engagement between dogs and muffs. This very quickly made mincemeat of the case hardening of the parts. Without a cush drive in the wheel hub on bikes with this transmission, it was a formula for schrapnel Italiana on a short fuse. Once the case hardening was worn off, the parts would quickly self-destruct. As in all engineering designs, there are trade-offs that are struck. IMHO the 6-speeder has not only *ideal* ratios, beautifully matched to the torque curve of the motor , but the driveline slack is neither more nor less than what it should be for all practical purposes.

 

The gap between shift dogs and sliding muffs can be directly and very easily measured. Since there are virtually no other sources of slack in the driveline of any measurable amount, this is the same as a measurement of the total driveline slack. With the bike in first gear, the dog-to-sliding muff gap in the first gearset amounts to 70 mm of fore-aft movement at the rear wheel. This is by no means excessive for any motorcycle with a constant-mesh transmission.

 

Now cushioning both ends of impact resulting from this gap in each of the 6 gearsets is wot we've been talking about here. On one extreme, where a neglected cush drive has been allowed to rust up solid (as has so often been reported, per Jack's post #50), this makes for a dramatically "clunky" driveline, creating excesively jarring shifting load impacts, and for the most part, resulting in rapid destruction of transmission, clutch hub splines, driveshaft splines, wheel hub splines, U-joints, etc. -- everything in the driveline.

 

A properly functioning cush drive softens up the effects of the fore-aft engagement impacts between shift dogs and sliding muff slots. This eases the impact loads on everthing in the driveline, significantly increasing the service life of all the parts and providing much smoother operation.

 

Improving the operation of the cush drive as we've been discussing in this thread has ZERO to do with driveline slack, as Mike posted above (post #60).

[dlaing]

Dave, I beg your pardon, but your contention is poorly informed and entirely incorrect.

No, it is not.

The problem is that it is absurd to measure driveline slack without including the flexibility of the rubber.

If you completely removed the rubbers you would have more freeplay, right?

If you drill holes in the rubber you have more freeplay, unless you do the technically absurd thing and measure from the point of contact of the rubber, that is always in contact.

If you measure between the rubber and metal it is zero, unless you squeeze a feeler gauge in there, in which case you could come up with some useless number.

If you measure the slop in the gears with a feeler gauge, you will get real numbers that if you add them all up, they would amount to total slop in the gears that does exist, and I am not contesting that, but the gears are constantly touching, so if contact equals zero freeplay, there is no freeplay, again absurd.

If we make an analogy to suspension:

topping out = point of freeplay when decellerating

bottoming out = point of freeplay when accellerating

YOU DO NOT MEASURE BOTTOMING OUT AT THE POINT IT HITS THE RUBBER BUMPER, YOU MEASURE IT WHEN IT BOTTOMS OUT.

 

 

Improving the operation of the cush drive as we've been discussing in this thread has ZERO to do with driveline slack, as Mike posted above (post #60).

You are wrong.

It increase the slack.

[Guest ratchethack]

Improving the operation of the cush drive as we've been discussing in this thread has ZERO to do with driveline slack, as Mike posted above (post #60).

. . .You are wrong.

It increase the slack.

Hmmm.

 

If Mike, Greg, and Y'ers Truly are wrong and it is you who is correct here, it must be that those who've allowed their cush drives to rust up solid have considerably "improved" their driveline slack in the process -- eh, Dave?

 

Well, that's something completely different alright. . .

 

 

. . .But unfortunately, it's also completely wrong.

[Dan M]

Hmmm.

 

If Mike and Y'ers Truly are wrong and it is you who is correct here, it must be that those who've allowed their cush drives to rust up solid have considerably improved their driveline slack in the process -- eh, Dave?

 

Well, that's something completely different alright. . .

 

 

. . .But unfortunately, it's also completely wrong.

 

 

Dave is confusing slack / free play (an air gap) and cushion (a rubber or mechanical spring, regardlesss of how soft) Making it softer doesn't increase slack it just...makes it softer.

 

Is this the right place for an argument?

I just told you.

No you didn't.

Yes I did.

No you didn't.

Yes I did.

[Guest ratchethack]

Dave is confusing slack / free play (an air gap) and cushion (a rubber or mechanical spring, regardlesss of how soft) Making it softer doesn't increase slack it just...makes it softer.

Dan, Dave has already confused the function of a cush drive with that of a shock bumper and tried to equate the two. N'er the twain shall meet, but leave us not even hint at a defense of this here. The use of terminology here seems fraught with danger. Let's not throw more fuel on this driveline vs. suspension confusion conflagration by introducing "air gap" (aka Luftkammer, per Wilbers fork spring setup) when discussing driveline slack -- or Dave could well be off in the weeds again on yet another rabbit trail. . .

[Dan M]

Let's not throw more fuel on this suspension vs. driveline confusion by introducing "air gap" (aka Luftkammer, per Wilbers fork spring setup) when discussing driveline slack -- or Dave could well be off in the weeds again on yet another rabbit trail. . .

 

No intention of confusing Dave. Actually, Luftkammer translates as an "air chamber" &

Driveline slack is caused by clearance or a gap between meshing components.

Further, there is no intention of causing confusion to our UK brothers, who are always told to "mind the gap"

[pete roper]

I'm still perplexed????? Why would you bother going to elaborate and expensive lengths to cure a problem that can and has been addressed for thirty years cheaply and effectively in the way Greg, Ratchet and many others have done? It's not like it's not tried and true. I'm sure that Greg isn't it's a miracle cure that he's invented, he's simply been decent enough to do a photo essay and explanation of the process for us and post it up. I simply can't understand why it's causing such rancour???

 

Pete

[Dan M]

I'm still perplexed????? Why would you bother going to elaborate and expensive lengths to cure a problem that can and has been addressed for thirty years cheaply and effectively in the way Greg, Ratchet and many others have done? It's not like it's not tried and true. I'm sure that Greg isn't it's a miracle cure that he's invented, he's simply been decent enough to do a photo essay and explanation of the process for us and post it up. I simply can't understand why it's causing such rancour???

 

Pete

 

You're abslutely right Pete. I just found it amusing. I'll stop now. We can move on to the pros & cons of waxing the underside of fenders to reduce drag & heat caused by the turbulent airflow created by modern directional tread patterns.

[Skeeve]

Further, there is no intention of causing confusion to our UK brothers, who are always told to "mind the gap"

 

What, did the Tube authorities finally break down & upgrade the loudspeakers in the announcement system? I always thought they were saying "Mwaaa' na' MAP!"[1]

 

Ride on!

 

[1] Spoken like one of the "adult voices" in one of the Charlie Brown cartoon features.

[Skeeve]

I'm still perplexed????? Why would you bother going to elaborate and expensive lengths to cure a problem that can and has been addressed for thirty years cheaply and effectively in the way Greg, Ratchet and many others have done? It's not like it's not tried and true...

 

Pete, Pete, Pete:

 

It's not whether or not the solution is practical or inexpensive: it's whether it's elegant that matters! Carving up bits of recycled hockey puck is never elegant; using the correct modern material that was unavailable or prohibitively expensive to the original project engineers 40 years ago & has just never been updated, now, that's elegant!

 

In all fairness to Dave Laing, I must admit that I'd rather have a turnkey solution in hand to the issue. I mean, after going to the [apparently not inconsiderable] trouble of busting open the Moto Guzzi cush drive vault, I'd rather have a set of six urethane replacement wedgies of defined & calculated squishiness set & ready to drop in & button back up than have to muck about drilling holes in the old hockey pucks, guessing all the while as to final squishiness [technical term ] and whether they were even or not.

 

OTOH, I'm notoriously impoverished & perforcedly thrifty thereby [some have gone so far as to call me "cheap," of all the nerve!], so as appealing as a properly calibrated of 87A durometer urethane wedges may be, I'm anticipating that it just isn't going to happen at my preferred price point. Drill bits, some sillycone grease, and a shop vac to clean up with - those I already have...

[dlaing]

I'm still perplexed????? Why would you bother going to elaborate and expensive lengths to cure a problem that can and has been addressed for thirty years cheaply and effectively in the way Greg, Ratchet and many others have done? It's not like it's not tried and true. I'm sure that Greg isn't it's a miracle cure that he's invented, he's simply been decent enough to do a photo essay and explanation of the process for us and post it up. I simply can't understand why it's causing such rancour???

 

Pete

Why is it causing such rancour when I simply suggested using polyurethane in place of the chrome-moly steel hard rubber?

What makes anyone think using urethane more elaborate and expensive than taking my bike to the dealer and paying them to do the work Greg did?

Nobody is rancourous about Greg's suggestion.

Some have reservations about the number of holes drilled and one person has reservations on how it effects control of the bike, but no rancour.

All the rancour comes from the folks that think polyurethane is a bad solution, and that have the notion that increasing slack won't increase slack...a notion that boils down to selective misleading semantics and what you consider slack.

Slack to me is the difference between the engine and the wheel as it is being accelerated and deccelerlerated.

It can be measured statically by freezing the rear wheel with the engine in gear and seeing how far the engine will turn from one direction to the other.

The actual measurement will vary depending on how much force you use.

But drilling holes in the rubber will increase how far the engine will turn at the typical force that we see when accelerating and deccelerating.

This is an increase in slack.

I really don't understand why nobody understands this

So, I give up.

Maybe if I do the urethane upgrade I'll post how elaborate and expensive it was.

But until then, go ahead and toot the virtues of drilling steel hard rubbers.

It is not a completely bad idea, unless you over drill the rubbers or throw the wheel balance off too much.

I guess wheel balance will be something I'll have to get right if I do the urethane....I had not thought of that earlier

Have at it you rancourous geezers

[docc]

 

This is an increase in slack.

I really don't understand why nobody understands this

 

I get it. Even with the very slight increase in 'play' or whatever, the softer end points have got to be desirable. A slipper clutch for the perforcably thrifty.

 

The motor mounts on my Volvo and the suspension bushings on the Cherokee are all upgraded to urethane. I can see this as an elegant alternative to swarfing the bench with rubber slag.

[mike wilson]

 

Now cushioning both ends of impact resulting from this gap in each of the 6 gearsets is wot we've been talking about here. On one extreme, where a neglected cush drive has been allowed to rust up solid (as has so often been reported, per Jack's post #50), this makes for a dramatically "clunky" driveline, creating excesively jarring shifting load impacts, and for the most part, resulting in rapid destruction of transmission, clutch hub splines, driveshaft splines, wheel hub splines, U-joints, etc. -- everything in the driveline. <_>

 

 

But particularly, in this case, the wheel hub splines, which are piddly little affairs seeming designed to fail. If you look at the design of the small block system (which has its own flaws....) the drive is connected in a much more substantial way.

 

Note part 16 here: http://www.isdal.dk/images/mc/lario/rear_transmission.htm

Which at one end has the crown wheel bolted to it and at the other fits into the gaps between rubber blocks in the wheel hub: http://www.isdal.dk/images/mc/lario/wheel_rear.htm

 

I haven't been able to find a similar view of the big block rear wheel for comparison but it seems to me that a redesign to the small block system would be time better spent than farting around with rubbers. As it were.

 

That seems kind of like measuring your height by the puffiness of your hair.

 

Good analogy. If you want to _look_ taller, a bouffant hairstyle does the trick. But you are really exactly the same height. Just the boundary has been blurred.

 

If you could make the entire drive train out of some soft polymer, yet retain dimensional stability, the driveline slack would remain the same as with steel and alloy. But it would feel rather cushy........