Cush Drive- What's its Function?

T95 · Jul 7, 2011

I am trying to understand the function of this system.

Do the rubbers soften the shifting or reduce vibration?

Or was this system put into play simply to allow the wheel to be removed from the frame while the hub stayed in position?

Is it worth it? Unfortunately, I have only read about the problems with the system and the potential for additional aggravation. Ultimately I am trying to decided if I should be looking for a cush drive hub and drum to lace up rather than my bolted system.

Stumped,
Gary

Torontonian · Jul 7, 2011

It's to lessen the "shock" to components involved. Wallet excepted.

Hobot · Jul 7, 2011

We know the reason for Norton cush drive pegs and wimpy cushions, but question remains, why bother, as plenty of reports of racers to street Cdo lasting a long time w/o any. On hand some report breaking drive train until a cush installed. ??? Makes perfect sense to me but not if its actually significant w/o changing design away from Norton like I have on Peel.

rvich · Jul 7, 2011

It is really nice to be able to pull the rear wheel off without removing the chain. I am not familiar with the bolt up system but I assume it doesn't allow this. The cushions are just there to take up slack I believe.

Russ

1up3down · Jul 7, 2011

Heinz Kegler told me that when he worked for the east coast Norton importer, Joe Berliner, that they were experiencing a rash of gearbox warranty claims, in addition to broken frames. Heinz said Norton told them to just ship the entire bikes back to England rather than strip them in New Jersey for the frame redos.
The gearbox problems were entirely due to the snatch and lash caused by no give in the drive train. Heinz said he wrote England with his recommendation to install rubbers in the rear hub to "relieve" this problem, as he put it.

DogT · Jul 7, 2011

rvich said:
It is really nice to be able to pull the rear wheel off without removing the chain. I am not familiar with the bolt up system but I assume it doesn't allow this. The cushions are just there to take up slack I believe.

Russ

The 68-70 is the same, you can pull off the rear wheel without taking off the chain and associated parts. I think the cush drive just gave it some slop so the drive assembly was not so hard on the gearbox and primary. I remember a BSA I had, had a cam arrangement with a spring that did the same thing, but that was a 50's vintage.

I haven't had any problem with my non-cush drive, but I don't thrash it.

Dave
69S

Jeandr · Jul 7, 2011

I broke two gearbox shells, one layshaft and one mainshaft on my 69S before I sold it. It was fine with the stock Avons (called "savons" or soaps) because they would just peel rather than stick. It was when I switched to K81s that the problems started, those tires stuck to the road so the shock was taken up by the transmission with catastrophic results. A cush drive would have prevented the failures.

Jean

frankdamp · Jul 8, 2011

The cush drive was supposed to smooth out the firing impulses of the engine and give the final drive an easier time.

T95 · Jul 10, 2011

1up3down said:
Heinz Kegler told me that when he worked for the east coast Norton importer, Joe Berliner, that they were experiencing a rash of gearbox warranty claims, in addition to broken frames. Heinz said Norton told them to just ship the entire bikes back to England rather than strip them in New Jersey for the frame redos.
The gearbox problems were entirely due to the snatch and lash caused by no give in the drive train. Heinz said he wrote England with his recommendation to install rubbers in the rear hub to "relieve" this problem, as he put it.

Vary interesting to hear the reasoning behind the the cush drive! Do you recall where specifically the damage was occurring in either the frames or gearboxes. As I stated above I was running around for several years without the cush drive. Considering the frame is stripped and the gearbox will soon be rebuilt now is the time to look for damage, although I don't recall any gearbox problems and my frame seems sound.

I got to ask, how many of you would swap out the non- cush for the cush?

nortriubuell · Jul 14, 2011

Had a Norton years ago that had the "non-cush" type rear wheel. I didn't have any problems, and a guy from Finland bought it in 1996. However, knowing what I know now, I would not use the "non-cush" type rear wheel on any Norton I own.

willh · Jul 14, 2011

As I see it the earlier bikes had a cush clutch so no cush wheel was needed. Pre-unit BSA motor I had had something rigged up on output shaft of engine. Today's dirt-bikes, running slippery knobs on the street isn't a problem, but put sticky street rubber and hub or gearbox pay the price. Norton's got to have some give somewhere, slippery tires, slippery clutch, or cush drive, if not and you hammer it like it was stolen somethings gonna give.

yellow750 · Jul 14, 2011

Cush Drive? Call me old fashioned but I think there is a clue in there somewhere......could the cush drive CUSHION the DRIVE. As other posters have said you are asking for trouble if you use hard acceleration regularly without a cush drive as something will have to give out in the end be it a snapped chain or even catastrophic gearbox failure. Although if you have a more restrained riding manner it would be entirely possible that no problems would be encountered as very little stress on the whole drivetrain assembly.

Clanger · Jul 4, 2016

willh said:
As I see it the earlier bikes had a cush clutch so no cush wheel was needed. Pre-unit BSA motor I had had something rigged up on output shaft of engine. Today's dirt-bikes, running slippery knobs on the street isn't a problem, but put sticky street rubber and hub or gearbox pay the price. Norton's got to have some give somewhere, slippery tires, slippery clutch, or cush drive, if not and you hammer it like it was stolen somethings gonna give.

Yes, if you go back to the Dominators they had cush rubbers in the clutch centre. I don't know when that was stopped - perhaps with the introduction of the diaphragm clutch?

Most bikes have some cush somewhere, very often in the rear wheel a la Commando.

Dances with Shrapnel · Jul 4, 2016

From the Clymer manual

1961-1970 Sprocket/drum assembly bolted to rear hub
1971-1974 Sprocket/drum assembly separated from rear hub by thick cush drive buffer and thin cush drive buffer
1975 Sprocket/drum assembly separated from rear hub drive rubber and drive rubber

I cannot recall what the 1975 drive rubber was made of but my recollection is that the 1971-1974 cush drive buffers were some very hard and tough plastic like material - not rubber.

There are instances a Norton big twin run in anger with solid drivetrains w/o problems; one in particular has been race campaigned for 30 years. The cush drive referred to in the Clymer manual is likely to mitigate a metal to metal fretting while allowing a quick release of the rear wheel for service.

The only Norton gearbox failures I am familiar with came from Commandos with the so called "cush drive" so go figure. Maybe the additional drive line slop contributed to the problem. Again, you need something there to prevent metal to metal fretting.

comnoz · Jul 5, 2016

When I was racing I did not have a cush drive anywhere for several years. I broke trannies regularly.

Then I changed the rear wheel to a Honda wheel with a cush drive. I still broke trannies regularly. No difference that I could see.

When I first assembled my FI bike I used a Triumph rear wheel with no cush drive. I used that for around 50,000 miles with no problems.

Eventually I went to a MK3 hub with the cush drive [hard as a rock] thinking I might make the bike smoother,
I couldn't tell the difference.

After I went to the belt rear drive I found a soft cush drive was needed so I made my own cushions from a soft knobby motocross tire and fit them in the MK3 hub..

The rear belt does not provide near as much cushion effect as a chain. You can not stretch a belt at all without damaging the glass strands in the tensile strip.

Dropping the clutch and doing a burnout was no problem but clicking the trans into gear with a dragging clutch would shock the belt enough to cause failure. Installing a soft cush cured that.

Now that I have gone to using the carbon fiber belt it seems to be much more immune to shock damage. Jim

acadian · Jul 5, 2016

It's certainly a piece of "poor mans" technology that's endured, my 2011 Speed Triple has a rear hub cush arrangement similar in design to the clutch centre rubbers on my T120/T140 bonnies... Oddly enough, when I went to replace the engine sprocket on speedie last year I discovered the factory sprocket also had hard rubber inserts in its inner portion... the replacement I bought did not however, and when I questioned the distributor (local trumpet dealer) I was told the factory "rubberized" ones were not available as a retail part, but that it wouldn't be a problem...

still not sure what the point of the rubbers in the engine sprocket were, but I've had no issues with the non rubberized replacement...

gripper · Jul 5, 2016

A lot of Jap bikes have a rubber collar on the edge of the front drive sprocket, I think to quieten them down a bit. Replacements rarely have them. I've run a bolt up rear sprocket/hub on my 1970 Commando for 41 years. A recent advantage is I can use a 520 sprocket set from a Dommie and fit an o ring chain. The bolt up sprocket does not need a bearing In it either. (though that bearing on the cush drive version will help the true running of the sprocket/drum)

BillT · Jul 5, 2016

Clanger said:
Yes, if you go back to the Dominators they had cush rubbers in the clutch centre. I don't know when that was stopped - perhaps with the introduction of the diaphragm clutch?

Most bikes have some cush somewhere, very often in the rear wheel a la Commando.

Yes, exactly.

My G80, G15 and Ranger all have the Dommie/Atlas style clutch with the cush rubbers in the hub of the clutch. My Commando and '06 Speed Triple (sold) have the cush in the rear wheel assembly. Speedy had a 5-blade cush in the rear hub, very similar to the 3-blade cush of a Dommie clutch hub. The Commando puts out maybe 60 HP, The 1050 speed Triple put out 129 HP (albeit as a relatively smooth 3-cylinder).

My basketcase G15's cush rubbers were gone, and the tabs on the clutch discs were hammered to about half their original width.

Whether it's to reduce drivetrain shock from firing pulses, or the reduce the shock of clutch action on the final drive, cush drives serve a function. If it wasn't needed, why would a manufacturer engineer it?

Dances with Shrapnel · Jul 7, 2016

BillT said:
If it wasn't needed, why would a manufacturer engineer it?

Great point!
https://m.youtube.com/watch?v=rp8hvyjZWHs

Trust me.

acotrel · Jul 8, 2016

Loved the video. One thing I've noticed about engineers during many years of working with them - they don't handle UNCERTAINTY very well. Everything seems to be plugging numbers into formulae and believing the answers.

Cush Drive- What's its Function?

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