Steering Coupling Disc 211415417 (coupler)

[Wildthings]

What is important is that each pair of adjacent holes on any couple has high ohms, opposite holes do not matter. No clue what the lower limit is ohms wise, but it may well be lower than any of the readings you are getting. In some failed couplers you can see a copper wire that ran from bushing to bushing, so the resistance would likely have been on the order of 0.05 ohms.

[germansupplyscott]

All holes on Vewib, adjacent and diagonal, were the same, about 650 Ohm.
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[kreemoweet]

A simple ohm test on a coupler sitting on a desk may not be entirely relevant. There are many who have reported horn honking (due to excessive coupler conductivity) only when turning, or otherwise placing stress on the coupler. In my own resistance measurements, I've found that putting pressure on the metal sleeves with the ohm-meter probes will substantially reduce the resistance (on some couplers). This squares with the theory that the unwanted coupler conductivity is caused by excessive graphite content in the coupler rubber, as graphite is somewhat conductive, and the conductivity is pressure-sensitive. Some old sewing machine speed controls were simply a stack of graphite disks in the motor electrical circuit, and putting mechanical pressure on the disks made the motor run faster, due to decreased resistance.

IOW, an actual in-use test may be necessary to evaluate the suitability of any given coupler design for use in early bay busses.
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[raygreenwood]

[SGKent]

winner is Ray with an answer of carbon black. Compressed it is used for electric motor brushes, spot light cathodes and anodes, and many more conductive uses. Graphite is carbon black when it has been compressed to the point the molecular structure changes. Diamonds are the next step of compression. One never uses pencils around open electronics - the dust is conductive. Burning (oxidizing) carbon black, graphite or diamond yields CO2 and any impurities in it. Ironically, both carbon black and graphite are good conductors, diamond is not. Using graphite in an electric lock like on new cars can destroy the electric components inside.

I don't remember if my bus horn honks when the bus is off, or whether my 1971 did either. I can visualize the science where turning might decrease the resistance. 650 ohms at a running voltage of 14V would create about 1/3 watt drain. 650 ohms at a sitting voltage would create about a 1/4 watt parasitic drain if the horn is armed when the bus is off.

Ohm's Law is E=I/R so I=E/R which is 14V/650 Ohm's = .022 amps. Power (watts) is P=(V2)/R which calculates at about 1/3 watt when running at 14V.
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[raygreenwood]

[borninabus]

from page 31:

[germansupplyscott]

[raygreenwood]

So....here we are. 33 pages in....many different versions tried, all but a few fail in one way or another.

Across all of this discussion, we have no real specifications other than:

1. Must not conduct electricity
2. Must not be too soft
3. Must not be too hard
4. Must fit correctly.

Because no one has ever found (to my knowledge) a blueprint/spec sheet/CAD print of the original coupler.....no one has really defined the real specs of this thing.

I keep saying this. The specification of rubber cannot be done with a curl test in someone's hand. Sure, being able to wrap around a hotdogs is OBVIOUSLY too soft ....but otherwise, I can find reinforced rubber/elastomers that can curl that much in the flat plane....but in the opposite "plane" ....they are hard as a rock.

The measurements for rubber need to include type of rubber, density of that rubber, durometer of that rubber, modulus of elasticity and tensile strength. Until all of that gets involved....and rubber that passes the unscientific "bend test" in someone's hand....may actually fail compression tests (squishes out too much), may fail modulus/tensile strength tests (too stretchy).

I can test for type or rubber, durometer and to a crude extent....stretch out or rebound.

So, let's change tact....and start somewhere else and define what this part should DO before we worry about what it should be made out of.

1. We say it should "give" some. How much? Do we mean just twist wise, torsionally when you turn the steering wheel?....or do we also allow vertical/axial flex like when you pull in and out on the steering wheel? How much for each?

It is my observation....that this coupler only needs to flex a little bit in the flat plane....torsionally...when you turn the steering wheel....mainly as a buffer to not overload the steering gearbox and slam the gears together.

2. It needs to be non conductive....that's a given.

3. It needs to absorb/arrest vibration. I see this as a a big function right?

Question: a few pages back I commented that I "thought" that part of the reason this is a soft coupler was so that it would rip/tear during an accident. Wildthings noted that this is probably not that important given the rest of what goes on to the front end in an accident.....and OK...I agree. I see his point.

So....given all of that....why could this coupler not be made of a stack up of reinforced but flexible plastic like nylon or UHMW in the middle with a layer of rubber on each side on the outside?

About 10 pages back I posted a sketch of just how this could be made and actually made pretty cheap and easy. About the only thing it would not accomplish is to be "breakaway" in an accident.

Ray

[Wildthings]

I suspect on a lot of couplers the engineering consists of buy a piece of conveyor belt for a reasonably cheap price, then shape it and sell it. Similar couplers were used on many rigs of the era and there were likely dozens of domestic manufacturers at one point, but slowly companies left the market and remaining production moved over seas, and more expensive product were replaced with cheaper ones. Hopefully someone will make a decent replacement coupling well into the future.

[metahacker]

is there any need to look further than the Lares?

[raygreenwood]

[borninabus]

[advCo]

FYI the Lares 209 is back in stock on RockAuto.
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[rob.e]

I fitted the Lares coupler back in 2022.

I removed it at the weekend - no issues but i just wanted to check it out - no visible issues with wear, still looks like new.

it does feel a bit more flexible than i think it was when it was new. i don't have a new one here to compare unfortunately.

i've fitted an old one from my "stash" temporarily and i've orderd one of the bus-ok couplers to compare.

i'll do a short comparison video when the bus-ok one arrivives.

I've done prob 7-8k miles on the lares coupler btw.
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[Jason0115]

[Wildthings]

The rebound is just from your tires and suspension loading and unloading, and not from the coupling, while the up and down motion seems excessive and potentially worrisome.

[Jason0115]

[raygreenwood]

[Wildthings]

How about a shot that shows the cords in the coupler well. Maybe Lares is using some other belting than what they had been using?

I have a fairly new coupling on the bus and a new spare, both of which carry the VW logo and seem to be A-1, but if I were looking for a replacement I might get the hole measurement that VW uses and hit a wrecking yard with a bunch of oldies but goodies and see if I could find a coupler with the same hole spacing that I could potentially salvage the rubber disc from.