Making a Cushier Cush Drive

[Greg Field]

Engine braking is notoriuously hard on all the splines of a Guzzi. In my day job selling Guzzi parts and my morning job fixing Guzzis, I see so many hammered splines that I normally recommend that Guzzi riders avoid engine braking altogether. This is especially true for all the early (and some late) Guzzis that lacked a cush drive in the rear wheel. Even on those with a cush drive, I recommend against engine braking unless you are sure the cush drive is actually functional. I've seen a ton of them that are so rusty that they do nothing at all to absorb shock.

 

A few weekends ago while swooping through the delirious roads around Mt. St. Helens I found myself compression braking out of necessity because the roads were so beaten up and frost-heavey and washed out, with patches of gravel in the washouts. After 50 or so miles, I just gave up trying to avoid compression braking and learned to enjoy it again and decided that I would allow myself its pleasures, but only on the Ballabio. And I decided that if I was going to compression brake, I'd seek to limit the damage by better making sure Billy Bob's cush drive was as good as it could be.

 

The V11 Sport's cush drive is almost identical to the cush drives on the other Guzzis. It works OK when it is properly lubed but quickly siezes up from rust if neglected. And its action can be vastly improved with a little modification of its parts. The cush drive consists of a main dive-spline plate with six vanes on its backside, 12 rubber wedges to absorb the shock, and a retaining ring fastened to the wheel by six buttonhead screws.

 

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.

 

 

The photo above is actually after re-assembly but shows the brutalized buttonheads.

 

 

The photo above shows the vanes on the back of the cush-drive plate. Each vane rests between two rubber wedges in the wheel hub, providing cush under the go and slow regimes. As on most Guzzi cush drives I've ever disassembled, this one was all rusty and on the verge of siezing up. In the i.d. of the center hole is a spiral groove that's supposed to hold grease to keep it all lubed. Instead, it was packed with rust and was fretting away at the mating flange on the wheel. Again, after just over 2 years in service. The picture shows it after I'd cleaned off the rust.

 

Also, the rubber pucks themselves had all the give of chome-moly steel. There is a way to soften them up, though, so they do a better job absorbing shocks: Drill holes in them, as shown in the photo below.

 

 

You can drill them with normal twist bits, but the better way to do it is with an improvised hollow drill, which cuts a core sample from the puck. I improvised one by using the hollow punches that came with an el cheapo gasket-punch set I got from Harbor Freight years ago. These cut a neat hole and have a slot in the side, which makes them sef-cleaning, as shown below.

 

 

I like to make my drives even cushier by leaving out half the puck pairs. Some might be concerned that this puts too much strain on the three vanes that slip between the three remaining pairs of pucks. Certainly, it does put extra strain on them, but I think they are tough enough to handle it, and I haven't seen nor heard of any any failures in cush drives so modified. What it does give you is a cush drive that works so well the bike feels smoother. And it causes more of the shock loads to be taken by the rubber of the pucks, rather than the steel of your splines.

 

 

So, then you just grease everything well. I use Redline synth grease on the steel parts, and dielectric silicone grease on the rubber. Then, put antisize liberally on all the retainer buttonhead screws so they do not sieze again, fit each screw with a new schnorr washer, fasten it all together, install it on the bike, and go for a ride. There's a change you can really feel. Rubbery and smooth. And you'll sleep better knowing your bike's splines are protected well.

[tikkanen]

Hi Greg,

 

thanks for sharing and enlighting us all

 

It seems like I'm one of those 'bad guys' who just love to use the engine brake; just love the sound when the big roar sets in and scares the living s*** out of the other com(m)uters (one or two m's??)

 

So far I haven't observed any flaws on my 2002 Scura, but I'll have a chat with my mechanic next time I have my rear tyre changed. I'll show him your 'How-to-fix-a-cush-drive' with your permission, of course.

Better safe than sorry, you know (and YOU do!)

 

Nothing better than a tip-off from a real pro like yourself - thanks again!

 

Cheers

Søren

[Guest ratchethack]

Bravo, Greg! Please allow me to throw my appreciation on the pile.

 

I would sorely miss relying on engine braking, and don't intend to give it up! Thanks for the superb write-up and great photo's. I did exactly this about 3 years back and was immediately rewarded by a perceptibly smoother driveline feel, not to mention the satisfaction of knowing that spline and all driveline wear has been substantially reduced, all the usual rust accumulation (of 22K miles at the time) inside the collar of the forged steel web that acts as grinding compound has been removed, and that the collar, which is machined with a helical groove obviously put in there to retain grease (yet comes dry from Mandello) has grease in it for the first time.

 

A discussion on this from 2 years ago here: http://www.v11lemans.com/forums/index.php?...c=5323&hl=#

 

This seems to be yet another example of one of those proven (per your compadre Dave Richardson) and sensible procedures that will draw ridicule from those who lack either imagination and/or knowledge, and/or motivation and/or effort level, and/or appreciation for one of those recommendations of the Pro's that goes back many decades.

 

Having replaced my stock "pie plate" retainer screws with locktited stainless after chiseling the old ones around to get 'em out, I find it a simple and easy task now to have the pie plate off every other tire change for a look-see and re-lube as necessary.

 

Hey Dave -- you can remove probably 10X more unsprung weight by drilling-out cush drive blocks than by using your cu$tom titanium wheel bearing spacer! Take out every other block and make it probably 100X!

 

Best go sparingly on the grease, Gents. Any excess will be flung out on the wheel.

 

Well done, Greg.

 

EDIT: Holy Moly! Redline extreme pressure assembly lube with "Red Moly"??

 

Gotta give this a whirl. . .

[dlaing]

Looks like an opportunity for someone to whip out a thousand of those bumpers in a nice soft Urethane, maybe 50 durometer on the soft scale, and sell for a modest profit.

Or maybe some other elastomer would be more appropriate.

 

 

Hey Dave -- you can remove probably 10X more unsprung weight by drilling-out cush drive blocks than by using your cu$tom titanium wheel bearing spacer! Take out every other block and make it probably 100X!

 

Who was it that sold the wheels with no cush drive? Was it OZ or Dymag?

It does seem like the cush drive should be better engineered.

Titanium springs in place of rubber bumpers?????

But we need damping.

Sorbothane???

[Guest ratchethack]

Looks like an opportunity for someone to whip out a thousand of those bumpers in a nice soft Urethane, maybe 50 durometer on the soft scale, and sell for a modest profit.

Or maybe some other elastomer would be more appropriate.

. . .

Who was it that sold the wheels with no cush drive? Was it OZ or Dymag?

It does seem like the cush drive should be better engineered.

Titanium springs in place of rubber bumpers?????

But we need damping.

Sorbothane???

Um, here we seem to be going again. . .

 

Now this is just me, but I hardly think so. Greg has just illustrated a zero-cost procedure that's been successfully proven and recommended by the Pro's for many decades. Do you have a problem with the stock rubber blocks that seem to have exactly the desired properties according to the Pro's like Greg and Dave Richardson, Teo Lamers, et al , for decades, once drilled-out? Titanium springs in a cush drive?! We need damping in a cush drive?! Sorbothane?! Just my opinion, but regardless of how exotic (or otherwise) the material used, I b'lieve your suggestion would be tough to find any market for wotsoever (at any price), considering the cost of development, testing, tooling up, and marketing something with such a tiny (and shall we continue to make every effort to be sensible here and admit -- obscure ) intended market, that would evidently offer ZERO possible advantage over wot Greg has been so kind to present here.

 

BAA, TJM, & YMMV

[docc]

Hazards of the internet: every time I think I've got my Sport well sorted something new gets added to the list. This sure looks like time well spent.

 

Er, but "shnorr" washers? Waazzzat?

[Guest ratchethack]

. . ."Shnoor" washers? Waazzzat?

Thin, conically-shaped spring-steel washers with serrations on their bearing surfaces for "grip".

 

From MG Cycle:

 

B2836/6 Schnoor washer, 6mm, hardened lock washer, various applications 0.35

[dlaing]

 

Also, the rubber pucks themselves had all the give of chome-moly steel. There is a way to soften them up, though, so they do a better job absorbing shocks: Drill holes in them, as shown in the photo below.

 

I realize "all the give of chrome-moly steel" is an exaggeration, but rubber is a less than ideal material for the job in my opinion.

Maybe if you got it loaded with silicone grease before it had hardened it would stay soft like Ratchet's.

But I am sure there are many that never got lubed, that are so hard that drilling won't give them much cush without risking the durability of the rubber bumpers.

By the way, which splines are in danger of failing if I don't do anything?

[Guest ratchethack]

I realize "all the give of chrome-moly steel" is an exaggeration, but rubber is a less than ideal material for the job in my opinion.

. . .I am sure there are many that never got lubed, that are so hard that drilling won't give them much cush without risking the durability of the rubber bumpers.

Um, (Part II), what's your opinion and your certainty above based on, Dave?

[dlaing]

Um, what's your opinion on this based on, Dave?

Watching rubber go hard over the years.

On my Guzzi I have seen it happen to every piece of rubber that I can see, except of the gel grips that are obviously made of the right material for the job.

 

 

By the way, which splines are in danger of failing if I don't do anything?

The anterior longitudinal guzzichondriacandectrum?

[Guest ratchethack]

Watching rubber go hard over the years.

On my Guzzi I have seen it happen to every piece of rubber that I can see, except of the gel grips that are obviously made of the right material for the job.

How many entirely different rubber formula compounds do you s'pose there are? How many varieties d'you s'pose a Guzzi has on it? D'you s'pose the compound used in say, hoses or tires, for just 2 examples, are the same compounds you'd find in a cush drive?

 

Fascinated now, enquiring minds (well, you know). . .

[Greg Field]

Dave:

 

Yes, rubber does harden over time. That said, I think these wedges start life hard and just stay that way. I've got bags of new ones on the shelf here, and they are as hard as the ones I removed from the wheel of a 1974 850-T a few months ago.

[belfastguzzi]

So far I haven't observed any flaws on my 2002 Scura,

 

I fear for your eyesight Soren:

how many fingers am I holding up?

 

I know 2002 Scuras are almost flawless, but surely there must be something slightly amiss, somewhere?

 

Anyway, just wanted to say that my 2002 Scura showed the same signs as Greg reports, when I did this disassembly at fairly low mileage. The good thing was that I was able to get it apart, but when I tried more recently, in order to inspect the greasy situation, It was stuck tight. That was despite the prior anti-seizing. Must try heat next time, as suggested. For that reason, be cautious when you give it to your mechanic because the job could be more prolonged than expected.

 

As for rubber, while it pains me greatly to agree with Ratchet , it seems to me to be the flexible and shock absorbant and relatively cheap stuff for this basic job. More expensive urethanes may put up with more extreme stresses but that's not called for. The design of the wedges could have been beter tuned, but as with other Guzzi parts, fine tuning is left to the end-customer (and his box of mallets).

 

Oh, a terrible headache has just come on: where's my tub of Ratchet-salve?

[Guest ratchethack]

. . .while it pains me greatly to agree with Ratchet

. . .Oh, a terrible headache has just come on: where's my tub of Ratchet-salve?

The salve -- oooh, the SALVE! Feeeeeeeeeeeeeels so sooooooooooooothing!!!

 

And yet the salve masks the tenacious ravages of the infection in process , does it not??

 

BFG, once you acquire the habit of facing, then chasing down the most horrific and ghoulish of bizarre hallucinations, and stake them to the earth with a wooden stake, rather than habitually tolerating their odious presence, it becomes easy and routine -- sorta like a sport. . .

 

. . . I find it as relaxing and satisfying as sporting clays . . .

 

Over here, the command is, "Pull!", followed shortly by, "bang!"

 

Many's the dastardly, demonic germ of a festering delusion that simply needs killin' these days. Best abort their development whilst they can still be nipped in the bud . . . Deep down, BFG, you know that somebody's just gotta do it. You're welcome.

 

Confronting phantasms, though increasingly unpopular these days, is highly recommended for clarity of thought, providing great freedom from all manner of lunacy and baseless frivolity and folderol that seems to gum up the minds of so many and then spread uncontrolled. . .

 

Unfettered naïveté , so cute in children, left untempered by reason and unchallenged, becomes a horrendous Class 5, Free-Floating Menace in adults. . .

 

As has so often been proved throughout history, an ounce of prevention is worth a GREAT BIG BUCKET o' salve. . .

[Pierre]

...

 

A few weekends ago while swooping through the delirious roads around Mt. St. Helens I found myself compression braking out of necessity because the roads were so beaten up and frost-heavey and washed out, with patches of gravel in the washouts. After 50 or so miles, I just gave up trying to avoid compression braking and learned to enjoy it again and decided that I would allow myself its pleasures, but only on the Ballabio. And I decided that if I was going to compression brake, I'd seek to limit the damage by better making sure Billy Bob's cush drive was as good as it could be.

...

Greg, don't you find this enhanced "rubbery" action you're recommending interferes with the "feel" needed to "back er' in" and throttle steer through corners? A tough performance vs longevity call IMHO. I'd personally hate to give up impressing the neighbors as I throttle steer into my drive way, just to save a few splines. Whadaya' think?