Eating rear wheel Cush drive rubbers

My Mk 2a is eating rear wheel cush drive rubbers. A new set just put in lasted about 200 miles and, with the rear brake on, I now have 1/2" of play at the OD of the tyre. It's the third set I've put in, so something is obviously amiss.

I've stripped the rear brake and checked the sprocket bearing, it looks and feels ok.
Thick side of the Cush rubbers are on the drive side.
Hub is not getting got, so no brake binding.
I fitted a new chain and sprockets at the last fitting of Cush rubbers, the chain was bad but the latest set of Cush rubbers has worn again.

So I've now got the primary stripped out wondering if the mainshaft or sleeve gear is bent, but there's nothing obvious. I've had a RGM belt drive fitted for the last 20 years or so and everything in the primary looks like it's turning true.

So I'm wondering if there is a way I can check alignment of the front to rear sprocket ? Or if anyone has any other suggestions of what I can check?

Cheers

My orginal crush rubbers lasted for over 30 years the newer ones aren't the best and they seem to wear out in a few weeks, since replacing my orginal ones I have gone through 2 sets of rubbers since, but the last set seems to be hanging in there, maybe you got a bad batch of rubbers, I think our mate Hobot is making his own using old tyres, some of the newer parts today don't seem to be up to scrach comparpered to 40 years ago, the quility doesn't seem to be there.

Ashley

Just a thought;
Are you using some type of lube that may be non-compatible to the rubbers? I know they can be a little difficult to get the last ones in.
What do the cush drives look like after they have been "eaten"?
Ride On
Dave

I sawed some out of an old tire, your looking for about 10mm thick. I bet they last a long time

ashman said:

...I think our mate Hobot is making his own using old tyres...

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I remember him talking about cutting them out of car tire sidewalls.

If your rear brake is dragging, it will melt them in no time. { I found out the hard way }
I don't put lube on mine. I grind off the 2 ribs where they bear up against the hub. Makes it easy to get the rear wheel of and on. Mine seem to last quite a while. Have done about 20,000 mils on one set so far and the are only warn a little.
Dereck

Clearly those making the rubbers out of old car tyres have the test facilities available to check they work correctly and are not GREATLY increasing the shock loads being shoved into the rear chain / gearbox and primary system greatly increasing the risk of gearbox etc failures...........Or are they so brain dead such thoughts never occur to them? Mind you when one reads about brain deads who do not even hear or feel their rotors tearing themselves apart and owners who publish on these pages pictures of gearbox sprockets so badly worn they are toothless.....

J. M. Leadbeater said:

Clearly those making the rubbers out of old car tyres have the test facilities available to check they work correctly and are not GREATLY increasing the shock loads being shoved into the rear chain / gearbox and primary system greatly increasing the risk of gearbox etc failures...........Or are they so brain dead such thoughts never occur to them? Mind you when one reads about brain deads who do not even hear or feel their rotors tearing themselves apart and owners who publish on these pages pictures of gearbox sprockets so badly worn they are toothless.....

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Please share with us how tire sidewall wouldn't be a FAR BETTER choice for that application. :idea: :?:

The Buckeye Rider said:

Just a thought;
Are you using some type of lube that may be non-compatible to the rubbers? I know they can be a little difficult to get the last ones in.
What do the cush drives look like after they have been "eaten"?
Ride On
Dave

Click to expand...

Thanks for the reply Dave, no I don't use any lube - a bit of jiggling and it just slides in. (Oh gawd, that sounds rude, but you know what I mean I hope!)

The rubbers have heavy indentations in them from the paddles and look like they are plastically deforming rather than elastically deforming. The first set had disintegrated completely, but this was after a long (8 year) lay up so I kind of expected that. The last two sets have flattened to the point of needing replacing again in less than 200 miles.

Pictures here (I think)

[url=https://goo.gl/photos/QLXc7wRPuUZprqX98]https://goo.gl/photos/QLXc7wRPuUZprqX98
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[url=https://goo.gl/photos/nySzGbuTyRfMwFxL6]https://goo.gl/photos/nySzGbuTyRfMwFxL6
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Cheers
Steve

kerinorton said:

If your rear brake is dragging, it will melt them in no time. { I found out the hard way }
I don't put lube on mine. I grind off the 2 ribs where they bear up against the hub. Makes it easy to get the rear wheel of and on. Mine seem to last quite a while. Have done about 20,000 mils on one set so far and the are only warn a little.
Dereck

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Thanks Dereck,

I'm pretty sure the hub is not getting hot, although I've heard of this before. I'm wondering if I just got unlucky with a dodgy batch of rubbers (which seems a bit like clutching at straws) so I've ordered another 'genuine' set from a different supplier. Maybe the norton logo in the plastic bag will make all the difference..... :wink:

Steve

I replaced the ones in my bike when i rebuilt it after it had been stored for 30 years ( in dry conditions). The old ones were rock hard so i assumed they had hardened with time the new one (can't remember where I got them) were also rock hard in fact I cut a little off (as another poster has said) in order to fit the wheel. 3000 miles so far and they are still a very tight fit with no sign of wear.

Are they ment to be so hard ? They surely offer very little shock cushioning effect.

It has been a while since I installed these parts, but they seemed to be made out of plastic rather than rubber. Nasty little pieces of plastic, with hardly enough thickness to do a good job of shock absorbing. The cush drive rubbers in Madass's rear hub looks like it would do a much better job, whatever they are made of.

Stephen Hill

Stephen Hill said:

but I they seemed to be made out of plastic rather than rubber. Nasty little pieces of plastic, with hardly enough thickness to do a good job of shock absorbing. The cush drive rubbers in Madass's rear hub looks like it would do a much better job, whatever they are made of.

Stephen Hill

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More plastic than rubber is my recollection.

Just my opinion here but they are only there to facilitate a quick release of the wheel from the drive chain/sprocket/brake drum assembly and have little (if anything) to do with providing cushion other than mitigating a metal to metal fretting of a two piece rear wheel assembly. I put this "cush drive" legend in the same bin as "Super Blend" bearings.

Sounds like the OP has some poor quality or off spec bits or maybe there's some serious wobble or run out on the wheel or brake/sprocket assembly. Need to check both.

Dances with Shrapnel said:

Stephen Hill said:

but I they seemed to be made out of plastic rather than rubber. Nasty little pieces of plastic, with hardly enough thickness to do a good job of shock absorbing. The cush drive rubbers in Madass's rear hub looks like it would do a much better job, whatever they are made of.

Stephen Hill

Click to expand...

More plastic than rubber is my recollection.

Just my opinion here but they are only there to facilitate a quick release of the wheel from the drive chain/sprocket/brake drum assembly and have little (if anything) to do with providing cushion other than mitigating a metal to metal fretting of a two piece rear wheel assembly. I put this "cush drive" legend in the same bin as "Super Blend" bearings.

Sounds like the OP has some poor quality or off spec bits or maybe there's some serious wobble or run out on the wheel or brake/sprocket assembly. Need to check both.

Click to expand...

Yes they do seem like plastic. I'd wondered why no-one has developed a PU version of these. I've had PU replacements for the suspension bushes on my moggy thou and they've lasted donkeys years.

I've used a straight edge on the front to rear sprocket and all seems OK. What I didn't do was stand on the rear brake lever when tightening up the rear wheel spindle (which I'm told I should have done).

I've also discovered tonight that my clutch basket has a 1/16" run out, perhaps suggesting a bent main shaft but I'm unsure if this might result in problems at the Cush drive. I've not noticed any excessive vibration etc.

Onder said:

http://www.accessnorton.com/cush-drive-what-its-function-t10153.html

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Yes, that thread is all over the place with conjecture, hearsay, and ramblings. Nothing coming close to definitive there.

I know at least one Norton Featherbed racer that has campaigned with a stock Commando gear box w/o a cushion drive for better than three decades w/o a gearbox failure. All of my race bikes run w/o anything that comes close to looking like a cushion drive component and I am rather heavy and ham-fisted at times while riding the bike - no gearbox problems. I personally broke a 74 850 gear box multiple times back in the day with the so-called cushion drive - though it was with Barnett clutch plates and a Drouin (pronounced ruined) supercharger.

One could easily make the argument that because one has so much slop in the drive train (with the little plastic thingies) that it is harsher on the gear box.

If one wants to see something of a cushion drive, have a look at the 70's vintage GRIMECA rear hubs found on Ducati's. They incorporated a huge rubber spider in the rear drive hub.

The Dominator rear hub so called cush drive was simply a CHEAP way to end up with a Q.D. rear wheel. In use within a few thousand miles the plastic lumps compress so much that the 3 ears on the chainwheel / brake hub were rattling around between them with LOTS of back lash putting god only knows what shock loads into the transmission system. Of course someof youwill have noticed the Classic Racer bumphabout Tony Hayward and the polyurethane lumps heflogs for the cush drives on the BSA / Triump 3s..... Wonder if he flogs them for use in the Mk3 rear hub rather than the proper rubber type material originally employed...... I assume Mr Hayward researched the use of the new material and did testing before flogging them.
As for comments about the gearbox ...remind me when the gearbox was originally designed and what it was designed for use with....If you go using a gearbox designed for use with a 500cc single cylinder engine producing no more than 25 ft lb of grunt in the late 1920s and then use it on a lump producing getting on for twice as much grunt you should NOT be suprised when things go BANG. The fact that they do not often go BANG is testiment to the LARGE safety factor employed by the designer in the late 1920s OR the fact that owners these days no longer know how to use the throttle..... in an attempt to preserve engine life??
Wakefield book..' GEAR LUBRICATION ' ....Page 106 .... ' Fig 75 shows the Burman 4 speed gearbox in which the gear train is compressed into a widtrh of 3 1/2 inches...... The box is guarenteed for 50 b.h.p. at 2,500 clutch shaft r.p.m' . As I rember Norton gearbox history Norton originally employed a Sturmy Archer gearbox manufactured by Raliegh which when Raliegh decided to get out of the gearbox business to concentrate on cars they handed over to Burman and apart from changes to trhe clutch lift mechanism and casings over the decades this became the AMC box which then became known as the Norton box. One vintage friend reminded me last night that Burman gears were manufactured from a direct hardening steel whilst AMC / Norton were manufactured from EN36B a case hardening gear steel which gives a good shock resistant core.
Playing for a moment......50 b.h.p. at 2,500 r.p.m. gives a torque of 105 ft lb. With a 2 to 1 primary ratio this equates to a max torque output at the higher rpm rotating crank of 52.5 ft lb. Assuming the designer employed a x 2 safety factor for his gearbox design calculations then the gearbox was designed for motors producing 26 odd ft lb at the crank. Remind me what torque a 750 or 820 Commando can produce at the crank .....on a good day with a tail wind.... Clearly the original designer employed a MUCH greater safety factor......but tis no suprise to me that not only did the factory Commando motors prove so unreliable but as Mr Peter Williams also found out the gearboxes were no better and oriders must of prayed that they failed whilst going in a straight line rather than through the twisty sections with a Manx rock face on one side and a Manx thick dry stone wall on the other.....along with a pub within easy walking distance!! Of course Mr Williams found the main shafts were deflecting resulting in gears incorrectly meshing ...the rediculous weight / mass of the clutch was NOT helping being so far away from the gearbox sleeve gear main bearing and that the idiot who changed the primary reatio from the 2 -1 as used on the Atlas to one that increased the torque being shoved through the poor old box did NOT help either.... Mr Williams if I remember correctly employed a CORRECTLY fitted gearbox main shaft support bearing behind the clutch...reduced clutch mass considerably and increased gearbox r.p.m. to reduce torque through it. I assume Mr Williams did not relish the experience of a totally locked up Commando rear wheel having the seat drop off was bad enough....Remind me who forgot to do it up!! And for those who waffle that Commando gearhboxes give no problems the retired NVT people I have talked with on the subject over the decades all stated that they did give problems and all gave the following reasons.....1. The primary ratio used. 2. The rediculous weight / mass of the unbalanced clutch especially of that vastly overweight bronze plated lump . 3. The increased torque of the 820 motors.
Question. Which gearbox cluster did they employ on the rotary Norton race bikes ?

Nater_Potater said:

ashman said:

...I think our mate Hobot is making his own using old tyres...

Click to expand...

I remember him talking about cutting them out of car tire sidewalls.

Click to expand...

I was corrected that he used car tires for his cush rubbers. 'Sorry, Steve!

That's probably the path I'll go when/if my originals go bad.

Nathan

Nathan, I don't see how you will ever wear them out with that unreliable engine and transmission. ...

Glen

I use rubber cut from tires for my cush drive also. The replacements available today are just not up to the job. Jim