In house research: flex donut coupling improvements

[trw99]

What's the latest on your endeavours, David?

Tim

[billwill]

I think it would be best to leave them white; to clearly indicate that they are an improved variety.

[elansprint71]

Due to personal issues I have been unable to post on this thread until now.

[Elanman99]

Due to personal issues I have been unable to post on this thread until now.

So the pills the doctor gave you did work!

[lotustastic]

What's the latest on your endeavours, David?

Tim

Tim,

Thanks for asking. I did complete another prototype over the holidays using a slightly different material. The bonding to metal bosses, interleaves remains excellent. I did construct a basic rig for testing full droop angles, etc. as a static installation but I need to improve this. The new donut flexes at full droop deflection without issue, but needs a bit more flexibility as compared to the current rubber donuts. So, I'm going back to the "white chocolate" formula ( ) which is softer and more resilient. As long as the next prototype displays the same bonding strength, then I believe I have something worth going forward with. I will have to commission some additional bosses/metal bits to be made so several donut sets can be made. Based on the properties, It is my feeling that these new donuts will have less "wind up" but still produce good dampening effects for the driveline and overall drivability as well as provide greater durability/longevity. The best gauge for them will be an actual road test with the donuts in an Elan, which is the only way to determine the "feel" or cushioning/dampening effect through the whole driveline, but my Elan is not ready for that yet (engine in reassembly stage).

Later,

David

[Ianashdown57]

I wonder if I might ask a question as you clearly know a great deal more about rubbers etc than I do!

Can a NOS donut be considered safe to use or has the passage of time ensured that the rubber has deteriorated to the point of being unsafe? I believe they have been stored reasonably well and not left in bright sunlight etc.

I'm asking because I have one or two NOS joints and I wonder if they could provide a datum point for your testing. If you think there may be something useful to be learned, I'd be happy to send one.

Ian
SoCal

[DJ908]

Ian

If the couplings are marked with the brand name Metalastic or Rotoflex then I would use them. This is a photo of one of the four still on my car, one of the three originals.

Not yet showing any great signs of distress after 47 years and near enough to 100,000 miles of motoring. Only one on my car has been changed and that was because in changing a rear wheel bearing back in 1969 we had to cut through one of the bolts holding one of the couplings on and damaged the coupling.

I am however following this thread with some interest for finding original rotoflex couplings will be difficult indeed although like you I have a couple of originals in my stock of spares.

Robert

[lotustastic]

I wonder if I might ask a question as you clearly know a great deal more about rubbers etc than I do!

Can a NOS donut be considered safe to use or has the passage of time ensured that the rubber has deteriorated to the point of being unsafe? I believe they have been stored reasonably well and not left in bright sunlight etc.

I'm asking because I have one or two NOS joints and I wonder if they could provide a datum point for your testing. If you think there may be something useful to be learned, I'd be happy to send one.

Ian
SoCal

Hi Ian,

Thanks for the message. I don't know how old your NOS donuts or what their appearance is but the expected "life" of the rubber is greatly dependent on the usage, storage conditions, heat cycles, humidity, etc. Traditional rubber formulas from the past don't do well in UV and exposure to the elements helps degrade parts to failure. If your parts have been stored well, then they may function fine for a while, however I would inspect the entire areas especially around the metal bosses closely for visual cracks, separation from the metal before using. I appreciate the offer to provide a donut for testing, this may be helpful. If nothing else, I would appreciate to see a picture of one which you stored for a visual comparison. I am performing some uv/weathering testing on materials as I have some newer NOS donuts and I've noticed some slight hairline cracks around the metal bosses on some. Perhaps it was stored in excessive heat. Seems to be a common failure point as the rubber bond to the metal fails due to moisture intrusion, heat cycles, etc. Traditional rubber matl's don't have as high abrasion resistance or resistance to fluids (oil, fuel, water) as compared to newer polymeric materials. My intention is to address the weak points with materials and design in the improved donuts.

Thx

David

[john.p.clegg]

David
It's four o'clock in the morning but just came up with a thought,you say the bonding of the material to the metal is a problem.would piercing the metal and allowing the "rubber" to flow through help?
In line with Colins adding lightness.

John

[lotustastic]

David
It's four o'clock in the morning but just came up with a thought,you say the bonding of the material to the metal is a problem.would piercing the metal and allowing the "rubber" to flow through help?
In line with Colins adding lightness.

John

Hi John,

Yes, your thought is spot on. That's one of the improvements coupled with a better bonding agent.

David

[billwill]

I've often wondered if a safety ring could be embedded in the centre. A ring made of steel hawser wire.

[Chancer]

What bonding process are you using, if its a high temperature vulcanisation press with the components given the requisite pre-treatments then you stand a chance or replicating the original quality but its an exacting process with many variables and even the professionals who have been doing it 50 years make significant scrap.

If you are using a chemical bonding process then unless something new has been invented then I fear you might produce something like the Indian made gearbox mounts that I bought nearly a decade ago, poorly fabricated and prepared metal (not saying yours would be) making a glued sandwich with the rubber, it lasted all of one hour in service.

Editted, I cant expect anyone to measure up to a factory producing OE Equipment using high capital value machinery, significant R&D investment etc so its unfair to compare what you can produce at home with what was made by Metalistik in the 70's and 80's.

However what is being produced these days is far inferior and I'm sure your goal is to produce better than what is available and I wish you every success.

[trw99]

David et al

I hope this is helpful, and not too presumptive of me, as a synopsis of where David is right now. It is taken from David's earlier posts but re-arranged to show what he is aiming for and where he has got so far.

AIM
To see if I can maintain the dampening effects in the Elan driveline, reducing vibration, harshness, wind up and prove a much longer service life than those rubber donuts available today

MATERIEL
Polyurethane, which is very resilient, tenacious and tough and should withstand constant flexing and stresses

1st PROTOTYPE
Improved reinforcement and superior material properties, improved elongation, peel strength, weathering, etc. It has bonded bolt bosses and reinforcements and is circular. The design addresses common failure points and should greatly reduce the disadvantage of rubber degradation by atmosphere, chemical attack, temperature cycling. Coloured white

2nd PROTOTYPE
Has a tougher Pu rubber grade and much improved bonding to the metal interleaves. It flexes at full droop deflection without issue, but needs a bit more flexibility as compared to the current rubber donuts

3rd PROTOTYPE
I'm going back to the "white chocolate" formula which is softer and more resilient and which will hopefully display the same bonding strength

David, please do correct me if I have any of this wrong. Good luck as you go forward, this is a most interesting project.

Tim

[Chancer]

I notice that the original 40 or 50 year old doughnut shown on DJ908's photograph is not even one of the reinforced interleaved parts, it looks like a standard Hillman Pimp item, that just shows how strong and durable the original parts can be, if correctly made the elastomer should fail before the rubber to metal bond.

[elj221c]

it looks like a standard Hillman Pimp item

How rude!

I had a few Imps in my time. No pimping I'll have you know!

Seriously, I seem to remember that they were a different size.

I am up for correction. (If you see what I mean!)