niswanger

Hey gang,

I picked up a nice 1997 Specialized Rockhopper late last year and when I tore down the forks one of the elastomers was shot so I started looking and boy was that a frustrating experience. One shop in NM sells a new (suspect NOS) pair for $55 plus shipping. So I started measuring and searching on density and firmness and determined that solid polyurethane rod in the 50A durometer range would be idea and a solid rod that is 3/4" thick and at least 10" long so I can make a pair by cutting it. Well, even then there really wasn't anything economically available so I started a conversation with a poly ebay seller "kpreneurethane" and he hooked me up with a 24" 50A solid 3/4" dia poly rod for $37 shipped (took 30 days). Here's how that turned out:

mtnbud

Interesting! I am looking forward to your long term impressions. I seem to remember my original elastomers came in a three part stack with three separate densities.

I replaced my elastomers with Speed Springs when the elastomers failed years ago. The springs are still going strong. I don't know if they're available anyplace anymore.

Rage

Wow, great fix.
I’ve actually been looking for those springs mtnbud mentioned for a while now. Last saw them on eBay three or four years ago but they seem to have vanished off the face of the earth since then.
Might have to go with that same fix if I can’t find the springs. My concern is durability, tho.

niswanger

I'm not a plastics engineer, but that solid 50A durometer polyurethane rod I used as replacement elastomers (not the springs) are certainly more durable than the stock elastomers. The real question is does it perform like the OEM/Stock elastomers...so far these shocks have been working better than when I got them with that one bad elastomer and years of not being serviced.

niswanger

There were so many darn version of even the same model RockShox back in the late 90's early 2000's so yeah I recall the ones with separate stacks from internet research. So far that are great. I'm about to cut another pair from the left over I have but add another 4mm for a total of 120mm long vs the 113mm long stock one I replaced. Seems I could use a little more pre-load on the elastomer. I'll keep these 116mm in a zippy for future maintenance or when a buddy needs a set.

freeranger

Not the only one who converted to Speed Springs. My old threaded fork, with springs, is somewhere buried up in my shed. Getting the non-specific elastomer thru ebay was a good idea-and probably easier (and less expensive) than finding a "genuine replacement" part.

niswanger

Again stock elastomer in this RockShox Indy XC was 113mm...figure it might have been 115mm new, cut first pair at 116mm and they work great, but cut the second pair at 122mm and installed...BAM! Nice, tight and firm just how I like it!

Darth Lefty 

This is interesting. I thought the point of the old MCU (multicellular urethane, not Marvel cinematic universe) is that the open cell foam gave it damping just like a sponge. If it's not foam isn't it just a bouncy ball?

niswanger

Best I can gather is for the slight improvement on compression dynamics you give up a whole lot of durability. Polyurethane 40-80A durometer was still used in these shocks back then because it performed near as well as MCU and was more common material (used in industry bushing fab a LOT). Can I tell the difference in performance?...no, the shocks seem to function a hell of a lot better with these poly elastomers. But yeah MCU was the premium material, it's just once the outer shell was compromised it starts to disintegrate quickly.

Kapusta

That was my experience.

I did once replace some MCUs with elastomers that I think were poly.

Did not work all that great. Super bouncy. Also felt like the spring curve was much sharper.

The fork was some late 90s Manitou.

Maybe they work better in some forks than others.

FastJake

Nice work! A bit off topic but are there replacement bushings available for these? They wear out, causing wobble in the fork (rocking under braking like a loose headset) which only gets worse over time.

Everyone in the world seems to hate these forks but I love mine. I put a NOS Indy on my main MTB I built up a few years ago. They're lighter than just about anything and they work great, IMO.

niswanger

About the only place I know if in the US is this site: https://www.suspensionforkparts.net/...rock-shox.html Again, I didn't want to pay $64.50 for one set, so opted to buy 24" of 3/4" 50A duro polyurethane rod from ebay and cut 2.5 sets (5 total bushing/elastomers) for $35.

Kapusta

If anyone does bushing replacements on those, it would be these guys: https://www.risseracing.com/suspension_service.shtml

They don't list the Indy, but the Mag21 and RS1 are listed, so they clearly have ways of handling some pretty old stuff. Whether it is worth it is a different question.

An Indy is a fine shock if you suddenly find yourself in 1995.

niswanger

That makes sense and the part I replaced which I have called by the defined name are elastomers and they are in the uppers (from the top adjustment captive nut > adjustment slider stack > spring head seat > spring > spring foot seat > elastomer head seat > elastomer

Best I can guess is what ever the part if it is like a dense rubber then poly rod in the ~ same firmness (duro) cut to the same dimensions and machined (drilled out etc.) as necessary might work?

HorizDropPlz

by chance did you ever see and blocks or brick shaped of similar poly. I'm looking for some to make an elastomer for a vintage Moxey Suspension seat post I recently bought. I need it to be 1.25 - 1.5" thick then at least 2" wide and at least 3" long.

roccoatl

Thanks for the post and the video Roy!

I contacted kpreneurethane (Paul) and was able to procure a 3/16" inside diameter x 1" outside diameter x 12" long 60A polyurethane tube to restore my vintage '93ish Tai Huei MIT forks. I'll be sure to use a box cutter (and not a PVC pipe cutter) for size adjustments.

2old

Don't think anyone mentioned this, but Suspension Fork Parts has specific elastomers for many fork models. I procured a set (about $50) for a '95 (AIR) RS Judy and they were of supreme quality. Plus the owner is available by email or phone.

roccoatl

It's a great site (suspensionforkparts.net), but the cost was a factor for me. They charge $65.50 (incl. shipping) for one elastomer kit vs. $62 (incl. shipping) for material to produce three sets from the ebay store (search kpreneurethane).

Suspension Fork Parts will sell elastomers identifying specific brands, offers a warranty, and also includes lubricant. The route I've chosen is more akin to DIY since no one sells anything specifically for the retro shocks (Tai Huei) on my two bikes, and I'm not particularly educated as to what will or won't work.

JB450

A bit of a thread revival, but just wondering if you still have this fork with the DIY elastomers? How's it going?

niswanger

My son rides it every day to/from high school. They work like new ones. I would make them 1/4" longer, we now run the adjusters all the way tight. I think if they were a bit longer we wouldn't have them fully tightened. We also relieve them during long per of non use.

JB450

Excellent! You went with 50a durometer, how do you find that for your weight? If you don't mind me asking.

I'm going to buy some for a retro mtb build I have going on (it's the first mtb I bought back in 2002) and just wanted to get something that wasn't too soft for my considerable heft haha