rcommbikes 

Greetings.

This rear bumper on a Trek 2100 has begun to deteriorate as shown. I can’t find one on eBay or just by googling Trek 2100 bumper or elastomer. If anyone knows where to get one, I would appreciate a reply. Has anyone else seen this and is there any fix other than replacement with OEM part? Hate to trash the bike.

As usual, thanks in advance for your comments.

Fred

HillRider

Have you contacted Trek directly? They might have replacements or suggest a substitute. If they have no options, ask about a replacement frame under warranty or at a much reduced cost under their "crash replacement" policy.

DorkDisk

I remember those; Trek called it "SPA (Suspension Performance Advantage)." I call it BS.

To be more helpful, maybe you can take the part out and have it fabricated.

cyccommute 

You might contact Suspension Fork Parts. I don’t see anything that is a direct replacement but they may be able to suggest something that will work.

cyccommute 

Not “BS”. It’s similar to a Moots YBBeat. Even the travel is similar…about 20mm. That’s not enough to squish much while riding but just enough to take the edge off of impacts. I have a YBBeat for bikepacking and it does make a difference. Moots uses a spring mechanism that is more robust but elastomers aren’t that bad a choice.

DorkDisk

well familiar with the "softail" concept, not sure about this implementation of it. Al chainstays that flex sounds wrong but the frame has held up

cyccommute 

While aluminum wouldn’t be my first choice, I’ve seen other aluminum frames using the softtail idea. Salsa made a mountain bike with it.

rcommbikes 

Well Trek told me the part is not available and that I could file a non-warranty claim through a dealer. The benefit would be a 30 or more percent discount on a new bike. I don’t want a new bike and my dealer says he can’t get any bikes anyway.
Now, I’d like to take the bumper out and I have several options to replace it. The problem is I can’t figure out how to remove it. Theres a 5mm short set screw that is removed from the bottom. After removing the brake, it’s clear that the elastomer has a metal tube that extendsinto the hole, but that is not threaded. I can’t find any purchase for allen wrench or screwdriver up inside and as far up as they can go. I may have to take this to the mechanic’s forum. I can push the rear triangle down and get about 2-3mm opening. That’s where I see the tube...
Any ideas?

Crankycrank

Have you tried looking into the top of the seat tube? There may be access to some kind of nut or bolt that releases the shaft. Also I would be surprised if there isn't an elastomer out there that already has the dimensions to fit your bike. The problem is finding one the has the proper stiffness/durometer rating since we probably don't know what that is. The car world uses elastomer bushings in various parts of the chasis and they are used in a million other applications. Try plugging the dimensions into a general search. Also try YouTube as there are tutorials on making your own that aren't expensive and you could even experiment with different stiffnesses.

rcommbikes 

There’s only a hole into the rear triangle inside the seat tube. Can’t really get any tool into it. It’s about the same diameter as the hole on the under side. Was gonna ask our dealer friend, but he’s closed today. Will keep you posted. Maybe I’ll call Trek.

rcommbikes 

So here’s what I got from Trek. Unfortunately two reps that I talked with said it was “before their time” and they had no details about HOW to access internal parts, in what order or with what tools. I replied asking them to perhaps find an old dude who could fill me in. Is there access under the paint on the upper frame tube? I see a circle there..... And a nut B??

Crankycrank

I would say try screwing a bolt into the threads that had a cap on them and pull. From the drawing it looks like the only thing holding the shaft in place is the brake mounting bolt.

jccaclimber

I'm making some assumptions, but that's actually a really helpful diagram. If I had to guess:
You remove the rear brake and set screw E first. At that point you can remove F by threading a screw from the top and tapping it out. Note, when re-installing this I'd secure a brake on before putting set screw E back in.
At this point shaft D should be free to come out. It may require threading something in the bottom and giving a bit of a pull, but there are a few other options if that doesn't work.
Once D is out I'm guessing the bushing, C won't be far behind.
I suspect that nut B is just there to retain A, which looks to be a guide bushing for shaft D.
If I was forced to guess I'd also guess that the 55/45/65 next to the bumpers are Shore A durometers for bushing C, which will be useful if you want to have a new one made. The other good news is that the bumper in that diagram looks like it's just being used in compression, not also keeping the back of the frame aligned like for example an engine mount.

rcommbikes 

LBS gave me a hand. I was afraid that the end of the tube was somehow anchored in the carbon. Not! I really don’t care about the suspension, so I’ll have a friend skilled in lathe at work make me one out of a nice solid piece of rock maple. Plus, I’ll have a beautiful one-off custom bike! Thanks for all of your help and thanks to Dave at the Bike Zone. Here’s a picture in case anyone else has a similar question on the forums.

jccaclimber

I wonder if your Trek contact would be willing to provide a .step file of the bushing to archive into this thread before all knowledge of it is lost? I wouldn’t normally ask for that sort of thing, but it sounds like they aren’t interested in supporting the design with parts at this point.

The solid maple is going to increase the loads through you seat stays as you hit bumps, but we’re pretty far off the reservation already, so it may not be worth worrying about. I agree that it will look nice, post a picture when you’re done?

You could also probably put a maple sleeve over an elastomer tube and get a bit of both worlds. I’m assuming your buddy has a wood lathe, but if it’s a metal lathe, rubber is really easy to machine with a tool grinder, or when very cold.

rosefarts

For what it’s worth, I heard rumors in the 90’s that public athletes we’re doing this on their ProFlex.

In that case, the yellow hunks of wood satisfied the sponsors without the creaking and compression problems of the bumpers.

So it’s not unheard of to use wood.

Question about the frame, can it fit 28 or even 32 wide tires? If it can, it could be a really bad road or easy dirt road bike. If you’re stuck with 25 or less and it’s a pure road bike, the wood would be cool.

I made a yo-yo from Purple Heart once, I still have it. You could also machine a highly polished piece of aluminum to fit too.

Darth Lefty 

The part isn’t anchored in the upper end of the assembly, so if you replace it with something rigid it’s going to get pounded when it turns around from top out to compression. And if you can make it out of wood, it seems like you can just as easily make it out of rubber.

The original might have been MCU and that’s hard to source but lots of other kinds of rubber exist. The suspension bushings mentioned above seem like a good start, or a cork. You could play with molding something… forum member @iab posted a couple years ago how he made brake hood replicas.

I think it’s amazing that Trek found you that drawing, all these years later.

JoeTBM 

How about a big rubber cork like used in a science lab drilled out to fit the shaft.... try this yahoo search https://search.yahoo.com/search?p=Bl...%3Asb&ei=UTF-8

I found items like this, lots of different sizes available

sch

At mcmastercarr a search on elastomer springs brings up: https://www.mcmaster.com/elastomeric-die-springs/
and it looks like one in the 'high load' section designed for 300-400# loads might be a dropin replacement.
Mcmaster shipping can be a bit high but you will get it delivered within 48 hrs. Cost in the $12-16 range
for one with OD ~1-1.2".
On further study the high load are 40 durometer, so depending on your weight and the routes you ride
perhaps the 'ultra high load' bumpers might be a better choice with durometers of 55.

Camilo

I hope OP posts a follow-up with photos!

Gonemad

I recently replaced the elastomer on my 2005 Klein Reve V, which has same rear triangle suspension system as the OP, aka SPA. Used a 1.25" length of polyurethane rubber tubing that I got here. I bought two 6" pieces about three years ago, one 40A and the other 60A. I didn't replace the original elastomer at that time because it wasn't in that bad of condition when I removed it back then. Cutting this stuff accurately is a real pain it the ass! Muffed up a few cuts using a miter box and saw before I figured it out: securely clamp the long section of the tube to the box, hold the other end steady without deforming it and patiently saw through it. After cutting, I sanded each cut end with emory cloth laying on a flat surface to get it reasonably flat and perpendicular. Anyways, below is what I ended with using the 60A tubing. Seems to work perfectly. BTW if you need this replacement elastomer part, you are probably far better off buying it here than fabricating it as I have, especially if you don't have the tools to cut it.



Sorry I didn't post this earlier, but thought this info might be useful none the less. BTW, I love that bike, put a Shimano 105 ten speed grupo on it about 3 years ago.

Edit: I wouldn't trust using a piece of wood as a replacement for the elastomer as discussed above. There are HUGE shock impulses that go through that shock linkage if you are traveling fast when you hit even modest bumps in the road. Thus I imagine that over time the wood may fail and it could be rather ugly when it does.

rcommbikes 

Slow to finish up this thread, but the project was on the back burner. The tip to go to Suspension Fork Parts was right on and I bought the elastomer spec’d for the Klein Reve. The bike is back on the road. A friend turned a replacement part out of cherry on his lathe. I installed that with a piece of rubber to ensure a decent fit. It did not fit perfectly because of play in the rear triangle and I decided it would just be a hard ride. Photos attached. Thanks to everyone who commented here.

jccaclimber

Glad to know it's back in service and doing nicely. For anyone who wants to cut a piece of elastomer in the future (for example, to match the taper), they cut much better cold (really cold) if you're on something like a lathe, and they grind well with an open wheel. Sure you could do it on a rotary grinder, but freehand (or around a pencil or something) on a bench grinder is easier than you might think after even a little practice.

Lazyass

I bet you could have found a spring the correct diameter. I've always liked softtails. In the 90's I had a Pro Flex MTB and there was a kit to replace the elastomers with springs.

canopus 

You could probably make a mold from the old part (clean up/fill in the outside portion a bit) and pour some polyurethane bushings.