dddd

I hope this might ring a bell with some others here who buy and flip good old bikes, since I am seeing a lot of 1990's Pro-Flex full-suspension bikes going up for sale with missing, cracked or melted(!) suspension "bumpers" at extremely low price points (priced for part-out basically, I got the clean model 756 shown below at Goodwill for $30 the other night).
I see aftermarket vendors offering a solid urethane (or coil) spring for $55 per wheel, but at the price points of these used bikes these days I am daring to humbly seek an even cheaper fix.

These were quite high-quality bikes with usable suspension geometry and relatively simple and solid frame pivots.
I also consider a complete fork swap-out in some cases to be a possible best fix for the front suspension (when a good 26" fork with long-enough steer tube is available for cheap).
I used to race these things, and my brother even won a B-class CX championship on the model 856 that I sold to him, so I have to say that I just hate to see these bike's frames being sent to the recycler's only for want of new suspension "rubbers".

So, does anyone here know of a good "hack" for the Pro-Flex suspension rubbers?

crank_addict

Perhaps check the online McMaster-Carr catalog for urethane bushings, size, durameter specs, etc..

The search engine may need polyurethane, bumpers, isolation / vibration dampers, other description.

wesmamyke

Another company offered a rebuild kit that was way more basic than the elastomer replacements. It was sections of reinforced rubber industrial hose, something pretty thick walled with a decent rating. When installed it was smaller diameter than the original elastomer so it looked a little funny but worked great. I did one for someone and tested it around the block a few times, jumped off some curbs etc. Couldn't tell you the name of the company though, the kit was brought in with the bike.

One thing i do recall though is it's not always the elastomers that are the issue. The pivots have these tiny washers on the outside and nobody has ever made replacements. Check that every single piece of hardware and the pivots are in good shape before you even bother.

AngryFrankie

Just a few years ago a kid bought such a frame off of me knowing what you know. I suggested contacting K2 who bought Proflex. He emailed me shortly thereafter to tell me that they sent him the elastomers. Since then, the resident know-it-all blowhard at the co-op insisted that K2 would not help a visitor when I suggested this. Worth a try.
Hack: Decide on the right size tube, cut out the valve section, and wrap it tightly around and around where each elastomer goes, tightly, until it suffices, and secure it with zip ties...and go ride it!

dddd

Thanks, AngryFrankie. I've seen one such hack locally using innertube!


I've seen recently on Ebay what looks like someone selling off all of K2/ProFlex's suspension rebuild stock, including bags of rings and bushings for these old forks and frames. And only $14.95 per kit.
I am not keen to retain the fork except perhaps for road use where a firmer "hack" elastomer would be welcome, snce there is no oil damper just an enclosed grease-dashpot rubber ball damper!
I wish that I had the tooling to just stamp out a stack of rubber washers made from car tire treads, perhaps separated by Belleville washers!
I used to buy the original, pressurized nitrogen foam bumpers for $20 each from the bike shop. These only ever lasted a few years though.

Drillium Dude 

Whoa, how do those things melt? Is it a function of the urethane breaking down chemically, or is it heat-related?

DD

thumpism 

Don't know about melting but they break down with age. If yours are intact you can try nuking them in five second increments to soften them up but they'll re-harden soon thereafter. If you can get replacements you want the pairs of bumpers to have durometer numbers 20 points different in your stack with the higher number piece placed above the lower; like 80 over 60, etc. Proflex referred to those things as "foam springs," by the way.

TheBikeStore

I have used plumbing pipe stops like this one: https://www.zoro.com/cherne-industri...27/i/G0254423/

Mixed results, the first couple of times I used them they worked great. The most recent time it seemed like they had made the rubber softer and I ended up using (2) 2" rubber stops and stuffed (1) 1.5" stopper inside of each 2" rubber stop and they mimic the 60d bumpers rather well. They are black and don't look as cool as the original yellow bumpers, but they work.

Cheaper than the $54 they want for them here: https://www.suspensionforkparts.net/....html?page=all

Cheers,

-Mike

thumpism 

Clarification, please. You say you used two of the 2" with a 1.5" plug inside each of the 2"? And was that repair only on the rear, or did you do a similar fix on the front? I thought I recalled the front foam springs being different sizes than the rears. I sold my old sample 656 to a buddy and the bumpers have bitten it during the intervening years. If your fix works I'll get the bike back from him and give it a try. Thanks for the info.

MiloFrance

If you're on face book, send a message to Fin at Full Factory Suspension. He's a bit of a suspension guru, may or may not have a hack but can't hurt to ask, and not doing him out of any business as you're in the US.

mechanicmatt

Our Noleen Mountain Bike Shocks - Noleen J6 Technologies

Noleen was the next generation of the shocks and they seem to still have components available. I was obsessed with these back in the day.

Reynolds 531 

I probably have many, if you can PM me dimensions.

rosefarts

I put a noleen on the back and Manitou 4 up front. This was on my 855. This was 1996 I think.

If I had that bike today, I'd put a big dowel in there and run it as a hardtail.

TheBikeStore

I only repaired the front fork this way on the bike pictured, but I have repaired front and rear in the same manner in the past. You can get different diameter plugs and fine tune your suspension rate. I stuffed the smaller diameter plugs into the larger ones to add stiffness.

cheers,

-Mike

thumpism 

Thanks!

Darth Lefty 

Is it out of the question to put an actual shock in there?

thumpism 

Real shocks are available but you're looking at about $200 per end. Not cheap. You'd have to be crazy about the bike to want to spend that kind of coin. Sample below for the '96 656 that I sold my buddy.

Proflex Attack/656 P/N Wheel Travel Weight MSRP Genesis Damper 50618 2.5" (63mm) 195 grams $198.00

Genesis installed on Attack frame

cudak888 

Has anyone looked up a source for generic cylindrical elastomers, or at least considered adapting others that are already commercially available (e.g., from a Birdy folder)?

What sizes of elastomers does that ProFlex need? Inner diameter and length of each elastomer would help.

-Kurt

thumpism 

I think I still have a Proflex manual with the bumper specs. I'll try to find it.

*edit*

This is the book I was thinking of and it shows a lot of info on the forks and shocks, including exploded diagrams and dis/assembly instructions, but it does not provide the specs or the dimensions of the foam (MCU=Micro Cellular Urethane) springs. Does call them "spring" in the diagrams.

Incidentally, up to '94 the bikes used single foams at each end but the next year (depending on the model) they began using two foams separated by a plastic washer and the two were about 20 durometer (hardness) points apart; 40 and 60, or 50 and 70, etc., for a more progressive spring action than the single provided. Also, smaller bikes used softer springing for presumably lighter small riders and larger bikes were suitably more strongly sprung.

Darth Lefty 

Does it have to be one of theirs? Look at the yoke on an Ibis, I was thinking there must be some way to do that, maybe with a couple of lathe parts. There have been a lot of shock ends and lengths over the years

thumpism 

It would be easiest if a kludge were not required. Most of us don't have lathe access or talent and carving one by hand out of stock is unlikely for several reasons. If a given bike's shock dimensions and specs were known there is probably one out there that would slip into place painlessly, although at some cost. As usual, making that connection is the crucial aspect.

dddd

Note that a simple shock isn't suitable for the rear, since one end of the shock needs to be solidly mounted to the "seatstay" strut and with only the other end free to pivot.
So the entire strut+shock is actually considered a "strut" which means that it handles side-loads.

The front shock uses a normal two-eye shock, but is very critical about the exact length on the Vector forks. Because the links swing through large angular displacements, the axle path and not just the ride height and spring rate can have huge effects on the bike's handling and on the actuation leverage acting on the shock.

As was mentioned, there are no inexpensive shocks for these, though some of these bikes still turn up with still-functionng original Noleen shocks, some of which feature damping adjustment.
I used a swap-sourced Carbon Vector fork on what turned out to be my best budget build ever, and the fork played really well with the lowly Pacific(!) frame that I based it on. The box-store bike frame featured a great acid-green paint that the decals peeled right off of, and also featured a faux downhill fork so was blessed with a slack steering head angle that made for great fun literally ripping through the manzanita section of Manzanita trail up in the ASRA. I still have it, complete with the wheels I built for it back in 2000.

dddd

Good info there. Oh, and about the special washer that separates the foam cylinders on the longer-travel Pro-Flex shocks, note that adding the washers contains the rubbers from distorting wildly under compression, and also adds firmness since the washer's surfaces control the outward bulging of the rubbers under heavy compression, preventing rubber damage and also preventing bottoming.

So any rubber material used that is perhaps too soft can be firmed up with the addition of washers. Ideally these washers will have a flange around their perimeter, but not necessary if there are enough washers per overall length of the spring stack. The washers need to be of a material that won't wear against the chromed shaft, so hard plastic is ideal, and there mustn't be any gaps at any time for abrasive dirt to enter the inside near the shaft. The challenge is to find a material that is soft enough to control ride height, yet rebounds fully enough to prevent the shock from extending past the free length of the springs and causing gaps. The nitrogen-charged urethane foam really is ideal in this regard because of the compressible gas accounting for most of the rubber spring's volume, and of course a coil spring (like a Speed Spring) also has the travel needed and won't foul the shock shaft with rubbing and dirt.

Darth Lefty 

dddd I can't square the photo in post 1 where the system appears to have a pivot at the front of the shock, the seatstay strut's pivots keeps everything in a straight line, and there's only compression through the shock, which seems normal, and you could make it work just by turning the aft eye of the shock vertical because it's really just a longer analogue of the Ibis yoke I mentioned... to the one in post 17 where the top of the shock is in a socket and it has to take some bending, which seems terrible. (though considering that's what a telescoping fork does all day, maybe not that terrible, but prevents using a regular shock)

cudak888 

OMG moment of the year. I'm looking at it, and I still don't believe it.

-Kurt