MTB front shock problems

biomech

hi all

At the end of a recent spin on the mountain i noticed my shocks were getting a bit stiff. im riding a Trek 3900. last years type i think, not the disc brake type. ...
Got it home and cleaned up but couldnt see any major issue... left the bike upside down and had the boots and wiper seals moved up the stanchions for cleaning and next thing a load of water poured out of the shocks... Pumped the shocks a few dozen times until it stopped.
After finishing the service i took it for a short spin and the shocks seem to be back to normal... Have i done damage to my shocks?? Any one else have this Problem??

Thanks in advance

bio

mossym

how long was the water in there? i'd be worried about rusting..(but i am no expert on shocks)

biomech

its hard to know... ive been for a few wet spins over the last few weeks but only noticed problem during last spin.. i usually check for shock performance at start of every spin by just bouncing around on the spot. got about an egg cup of water out of one side and about half as much out of the other... noticed some damage on chrome inside the wiper seal on the side with more water alright... bit rough under my nail when i scratch... might explain how water gets in that side.. Ive no mud gaurds?? would mud gaurds help??

rob1891

Sorry to say this, but do yourself a favour and buy a new fork. Your Suntour fork has no proper sealing/oil bath, you are supposed to keep the stanchions lubricated with teflon oil and the seals greased which is somehow supposed to stop water ingress. This is a cheap short cut to a fork that works in a bike showroom but nowhere else.

I honestly don't think it is worth the time and effort to keep your kind of fork running. Ride it into the ground and then spend as much money as you can afford on something by Rockshox (Recon/Reba/Revelation ... in order of expense). Or find a good fork going second hand (pre 2007 marzocchi forks can last forever and ever).

To revive the fork for now dismantle, grease bushings and oil stanchions with a teflon lubricant. Or take it to the shop you bought from and complain, they'll likely explain that the fork isn't really good enough for proper MTB and do nothing on warranty for you :-/

rob1891

biomech wrote: »

... noticed some damage on chrome inside the wiper seal on the side with more water alright... bit rough under my nail when i scratch... might explain how water gets in that side..

If the surface of the stanchion is damaged it is going to wear out the bushings more quickly, once the bushing are worn out, the fork stanchions are going to move a bit inside the lowers (still relatively safe, but annoying, it will feel like the headset is loose). It will also permit water to get past the seals more easily, but I'd guess that water gets past those seals pretty easily anyway, in fact the boots may have trapped water which would aid the corrosion. The stanchion cannot be repaired effectively, particularly a chrome one. See what you can find about it on the web, most people won't go to the effort on such a fork though ...

Most people do not use mudguards while mountain biking, I wouldn't consider it a factor.

The fork should be very simple to dismantle, internally it isn't much more than a spring. Just make sure you do it up the way it came apart, you don't want it to collapse on a trail!

biomech

Oh ya was not under any illusion that i had shocks worth repairing or taking back to the shop.. ... they def gonna be ridden into the ground... rest of the bike is only just about holding up also.... bike shop owner knows exactly where i ride and he just gonna say "well wat did you expect"

Would it be safe enough to strip these down so for a good clean??
Do these forks need a cup of oil like the rock shox??? or just a light oiling prior to reassembly??

Thanks a mill for your help

:)

rob1891

I'm pretty sure this model of fork doesn't have an oil bath, they run dry with just lubrication at the seals/bushings and whatever you spray on the stanchions. So not like a rock shox. There is a brief manual and exploded view here:

http://www.srsuntour-cycling.com/SID=sib4dcb129199c489c91586f4055de31/index.php?screen=sh.detail&tnid=1641

Which should give you an idea of how to dismantle it and were the grease/oil should go. Grease would be on bushings, teflon oil on seals and stanchions it seems. WD40/GT85 might perish the seals, so be sure to use the right kind of oil.

It is a lot of maintenance to do on the fork though, start eyeing upgrades ;-)

biomech

nice one... had found that site while i was waiting.... will rip it tonight and see how i get on.... just need to stay on the go till HR at work get the finger out and set up the bike to work scheme... lazy muppets.... after that itll be one big upgrade.....yippee i cant wait...

thanks very much for your help...

bio

concussion

Mud sprung - rainwater damped forks I had the same thing happen on my first crappy forks, besides the water squirting out of them at every compression I got a few months out of them before they started rocking back and forth ominously. Splash out on a pair of RockShox or Marzocchis, they'll last you years.