Pantour hubs - elastomer replacement?

Bikes
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Turns out the Bike Friday I collected has a Pantour front suspension hub (only one hit on tarck, one more than I thought there’d be!)

I was expecting to find a degraded elastomer in it, but worse, there’s nothing at all. So the hub settles to the highest rim position where the brake pads can’t quite reach fully and can drop down when unweighted.

Any suggestions on either a replacement elastomer source (vehicle bushings?) or something to fill the internals and lock it into one position? Failing that I’ll need to rebuild with a normal hub.

Most hits online are >10Y old and replacements were a problem even then, but I have found the service manual and some people cutting up blocks of elastomer (shore 40-50 ish) or using thudbuster spares.

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That’s a cool weirdo hub. I would try and cut some elastomer blocks to test it out. If the thing has been out of production for a decade or two, presumably, any NOS elastomers would be degraded and useless by now, no?

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Definitely not expecting to find a dusty old NOS unit, but it would be nice to know the intended dimensions.

I’m not sure where I should even start looking for blocks of elastomer. lots of flower petal shaped motor couplings out there. Might drop into an auto parts place and look for the largest suspension bushing I can find to start cutting up

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They sell elastomers in rods and blocks. Not sure what material is ideal but here’s PU. If it’s good for skateboard bushings it should work.

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Ah, great, i was searching by durometer value and for other types of elastomer and not much was coming up but there’s massive amounts of PU in all kinds of form factors.

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(T)PU is also 3D printable, so if you can get dims or a model you can have a new one printed. I can’t see anything at that link but found a potentially similar thread with the following:

Plastic - Iglidur H370 - Unflanged
Specific Gravity 1.60 g/cm3.
Operating Temp 240 C short term / 200 C long term.
Tensile Strength at 20 deg C = 135 Mpa.
Hardness 82 Shore D (DIN53505).
Tolerances listed are after H7 Pressfit.
Nom. ID (d) (mm):: 7.938 (0.3125 inch)
Nom. OD (D) (mm):: 9.525 (0.3750 inch)
Length (s) (mm):: 9.525 (0.3750 inch)

it also looks like the elastomers themselves are rectilinear blocks that get wedged to fit into the hub:




so there may be an opportunity to DIY some chunks of material to test, then print shaped blocks that securely fit the cavity

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Yeah i found those threads too, I’m unsure if the block is supposed to run the full width or if it’s smaller lengths on one or both sides.

Would love to find a photo of an original elastomer, but i guess I’ll just wing it, erring on the side of too stiff.

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wild assumption based on the photo of the blocks above, they seem to be a thick and thin cut from what may be a common square extrusion size— maybe 3cm?

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Oh, were those photos from a post about the hub?! I thought they were just example elastomer images! That’s very helpful, thanks, i didn’t turn those up earlier (there was a forum with some attached images but i didn’t create an account to access them)

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those are Pantour elastomers from a Japanese website that is sold out; the orange are regular and green are heavy

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What a wild idea! If you can figure out sizes should sandwich a few different duros to alter spring rate…. For science!

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I suspect you’re putting a lot more thought into elastomer material selection and sizing than the original designers did

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Having dealt with elastomer bushings back in the day, my recommendation would be to fill it with epoxy.

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The 3dp TPUs are harder Shores but you could print them at a lower density to make them softer, you know, for science the dither.

For lulz I’d be looking at chunks of artist’s pencil erasers.

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yes it looks like a chunk of square material jammed into the cavities; making something the actual shape or with different infill might offer some tuning. or install a sleeve where you want the axle neutral position and pour a new two-part PU but that’s a little riskier and messier

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naturally they would be imported from Japan!

I’d really just start slicing up squares of things with razor blades and putting them in there to goldilocks this shit

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If the rotation of the two axles is fairly rigid there probably isn’t a real wrong answer

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Heh, possibly.

image
I totally glossed over this when looking at the manual previously. Two small blocks on one side only, should be very easy to carve different length pieces to affect the squish.

The hub bore of mine is different to the schematic but I think ~20mm radially, and some value axially (either 20mm or longer for more resistance) then cut to fit the space between the axle and shell will do it.

Ordering some ~75A PU and ~60A silicone blocks in 50x50x30mm to commence the dither!

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Too hard and too large, but this is GoodEnough.

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I was thinking that perhaps it’s less of the elastomer compressing but more making it deflect…

So by having a thinner block that could deflect in 3 point bending, that might perform better, eg:

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