Bicycle Mechanics - Curse of the forks?

Hi, here's a challenge for you engineers out there. I've had a problem with two sets of forks that no one can find an answer for, even the manufacturers. It happens with the Manitou SX's I have on my current Specialized Stumpjumper, and it happened with the Pace RC36's I had fitted to my previous Kona Explosif. A friend with Pace forks also had it. What happens is that during the course of a ride, the forks get noticeably less responsive and "slower", especially over lots of small bumps (baked-hard vehicle tyre marks etc). It takes about an hour of this kind of terrain for this to happen. Then, overnight, with no servicing or maintenance, the action of the forks returns to normal. Changing the oil/grease etc doesn't help. (My) logic says something must be heating up during the ride, causing friction, and cooling back to normal at night, but an engineer friend says this wouldn't happen to the extent that I would be able to notice any difference. And in case you're thinking it's just me getting tired and imagining it, it's not ... I've tested it on friends. I might have thought something was happening to the elastomers, except that the Pace forks only had one tiny elastomer. Any ideas? :confused:

Thanks in advance, Bryan

Hi , when the forks were seviced what condition did the elastomers appear to be in ?, I would try replacing them as elastomers do deteriorate with age and the sx is fairly old now ! . I hope when it has been serviced that "judy butter" or something not lithium based was used as a lube .. there realy is not much that can go wrong with basic internals such as the sx ! , Heat ,I think would not enter into it, so whats left ?? ELASTOMERS ..as these provide your compression and rebound damping ..as they have natural rebound damping qualities ..if they are tired and worn out ,then the fork would show signs of feeling slow .. this is most likely the culprit !! replace them ..

My thoughts are that perhaps a seal is providing more interference when it heats up, as it would with the friction from heavy use. Maybe you could overhaul the thing-perhaps there are some "high temperature" seals available, like those used in certain automotive applications. Keep in mind, though, such seals will likely leak a bit when cold.

Thanks for the advice so far, guys. My original thoughts were against the elastomers being the culprit, as I said the problem was just as great on my Pace forks (and those of a friend) and those forks had steel springs, with just one little elastomer which I think was for "top out"(?) only. However, it's obviously easy to change the elastomers and I might do that to see what happens. I'll ask about the high-temperature seals.

By the way, if anyone else has ever had this problem, I'd be interested to know. I can't believe it's happened to me on both my last two sets of forks and no one else suffers from it! If you go on a ride where your forks are aborbing a load of high-frequency hits, check them for plushness before and after, and see if there's a difference. I know it sounds silly, but you might not notice until you check - you might just think it's arm-fatigue. My friend didn;t notice until I pointed it out. That made his day :D

Cheers, Bryan

I've just had a problem with a 2nd hand pair of Pace Forks getting stiff during the course of a long day's ride. I thought it was just a knackered set of ofrks, but maybe not.... I'll see how they are tomorrow evening.

Does anyone have a service manual for Pace EVO R36 forks?

Sorry if it's bad form to resurrect a thread this ancient, but just in case anyone has a similar problem and finds this thread in a search, I came across this is my Fox Talas manual today and it caused an "Aha!" moment:

"Thermal expansion rates can cause the bushings to close in on the upper tubes causing high friction and binding during normal operation. Correct bushing clearance is critical to prevent binding of fork during normal operation."

Which is presumably why Fox make their forks with so much play in the bushings. So it looks like the problem I had with my Pace and Manitou forks becoming less plush over the course of a ride was due to friction/heat, and this was enough of an issue for Fox to notice and do something about it. I'm surprised that at the time I had the problem, Manitou seemed never to have heard of such a thing happening.

Bryan - better late then never to solve a mystery.