Loss of damping in rear shock

[ChrisEyles]

I was out on Dartmoor this afternoon, and on one of the long, out of the saddle climbs I noticed my rear shock felt a little different from usual. There seemed to be a little less preload (the back end was bobbing more) and a fair bit less damping, with a slight audible knock when the shock was topping out. For the rest of the ride it felt OK on the downhills but a bit too squishy on the climbs, and the reduction in damping, while not massive, was definitely noticeable.

I'm pretty clueless about servicing suspension units (I can dismantle an elastomer/spring based fork to re-grease but that's about it).... is it possible a seal has blown on the shock? I didn't see any oil on the shock body or piston, which I'd have expected if this was the case. The offending shock is a "shockworks" unit on a late 90s not-particularly-high-end Marin, with no damping/rebound adjustment that I can see.

Is it possible to revive this sort of thing with a garage overhaul? If so that'd be ace... but if not the bike was so cheap (£20!) that I don't think I'd be interested in replacing with a better, modern shock so I guess if that's the case I'll just ride it to death 'til it fails all together.

Any input much appreciated!

 

[ufkacbln]

It would be nice to be able to link to a service manual for the unit, or something similar

Can you post the make / model of the shock?

 

[ChrisEyles]

I can't find any details about the shock online in any of the usual places. Bikepedia doesn't have an entry for the '97 shoreline trail. The closest it's got is for a '98 east peak, which is listed as having a 4" shockworks unit. Having had a little look around on retrobike I believe "shockworks" might have been owned by Marin, or at least they were OEM kit on pretty much all the FS bikes from this era, even the higher end ones like the mount vision.

Here are a couple of pics. You can actually see a tiny bit of oil and gunk on the central rod, which I guess isn't great news. Even worse, the only writing on the shock other than "shockworks" reads "pressurised unit; do not pierce, burn, or service".

It's annoying as the shock was working really quite nicely for the first few rides I took the bike out on, and now the damping is totally shot. I will admit to not treating it gently, but equally I didn't subject it to anything I wouldn't do on my rigid bike so I'd have thought it would have been able to cope.

 

[Crackle]

Unfortunately it doesn't sound good. Even if it's serviceable, looks like getting the parts might be a problem. Looking like a 2nd hand unit off ebay, considering you got the bike for 20quid, I'd say another shock is still value for money.

 

[ChrisEyles]

Yeah, that's what I was thinking too @Crackle.

I'm afraid I know precisely nothing about rear shocks, other than that I rather like having one now I've tried it What should I be looking for? Obviously the distance between the holes where the shock mounts to the frame has to be good, but what other variables are there to think about?

A quick ebay has revealed this:

http://www.ebay.co.uk/itm/Bicycle-M...hash=item20f4969e60:m:mhn9rXppgRXbHuKi7QHqG2w

It's so cheap it's ridiculous. Am I right in thinking it probably won't survive a back wheel heavy landing over an 18" drop-off? TBH I'm not too fussed about performance as long as it smooths out the bumps a bit and has at least some degree of damping, but it'd be nice to get something that'll last a little while.

 

[Crackle]

I've never had any bike with a rear shock, so I'll have to defer to greater knowledge, which hopefully will be along soon. I'd be tempted to pay a bit more than 6 quid I think, I doubt that'll be any better than your current broken one.

 

[ChrisEyles]

Yep, that's definitely my immediate assumption too. On the other hand, I have bought a few extremely cheap bits and bobs from China (chains, cassettes, and a wheelset) which have performed, as far as I can see, about as well as other options costing several times as much. Quality control seems to be more of an issue than general low quality judging from reviews. Definitely happy to learn from those on the forum who have more of a clue than I do though!

 

[Jody]

Check the eye to eye length measurements and get the right spring weight which on your's looks to be 550-700. The problem you might encounter would be how much travel the shock has vs the new one. You might have to alter the pre load to stop it bottoming out under heavy load. You're not really able to change the shock characteristics your price point and type of shock, so I would stick a cheapy on and get some more miles out of your bike.

 

[ChrisEyles]

Thanks @Jody, that sounds like it should be enough info to get a near enough match - I wasn't sure if there were any other important variables in the equation.

AFAIK the travel on my bike is 100mm on the rear, but I don't know what the stroke length of the current shock is. I'll guesstimate and hopefully like you say upping the preload will be enough if the shock bottoms out. At least at that price, it doesn't matter too much if it all goes horribly wrong!

 

[Cubist]

I'm with @Jody on this one. If you can see any oil on the shock you have, then the chances are it is blown, and nothing serviceable. If you love the bike enough to want to upgrade the suspension, then there will be something out there that will upgrade it, but then the back end will be better than the front, and the merry go round of chasing perfection starts! For a fiver I'd stick one of those cheapies on. Travel is likely to be anywhere between 50 and 100 mm, and you can't expect much more than taking the sting out of the bumps anyway. That then means that the only question is eye to eye measurement. Play with the preloads as you have already suggested and work on a compromise between topping out and bottoming out.

Otherwise, if your budget allows, how about one of these?
http://www.tftuned.com/mobile/push-industries/c364

 

[lpretro1]

Yeah, that's what I was thinking too @Crackle.

I'm afraid I know precisely nothing about rear shocks, other than that I rather like having one now I've tried it What should I be looking for? Obviously the distance between the holes where the shock mounts to the frame has to be good, but what other variables are there to think about?

A quick ebay has revealed this:

http://www.ebay.co.uk/itm/Bicycle-M...hash=item20f4969e60:m:mhn9rXppgRXbHuKi7QHqG2w

It's so cheap it's ridiculous. Am I right in thinking it probably won't survive a back wheel heavy landing over an 18" drop-off? TBH I'm not too fussed about performance as long as it smooths out the bumps a bit and has at least some degree of damping, but it'd be nice to get something that'll last a little while.

Please please do not try and fit ones of these - it will be destroyed within a ride and may damage yuor frame and your goodself - these are the things fitted to 'look-alike' full susp bikes by catalogues/supermarkets - absolutely dreadful.
You will not be able to get parts for that shock given it's age - time for a replacement

 

[Jody]

Please please do not try and fit ones of these - it will be destroyed within a ride and may damage yuor frame and your goodself - these are the things fitted to 'look-alike' full susp bikes by catalogues/supermarkets - absolutely dreadful.
You will not be able to get parts for that shock given it's age - time for a replacement

It's OK saying don't get that but what would you suggest. With the greatest respect to Chris it's a 20 quid bike that was low in the range when new and he is having a good time on it. The shock quoted won't damage his bike unless it bottoms out and the frame makes contact hence suggesting that it will need a good deal of pre load. Personally I would stick a cheap shock on it, have some more fun on it and save his pennies for something higher spec if he is still enjoying it.

 

[ChrisEyles]

@Jody's got it right - it's not a bike worth spending any money on, and if/when it gives up and dies I'll look for a better second hand bike. I'm not expecting miracles, and I've had plenty of fun on the low-end shock so far.

@Cubist I emptied my pockets by shaking my trousers upside down but didn't quite come up with enough to get one of those you linked

 

[ChrisEyles]

Was just about to take the plunge and order one of the cheapies, but turns out they are all 150mm eye-to-eye, whereas my current shock is 185mm. It looks like this is going to be a pretty big difference and the back wheel could clip the seat tube - urk!

So unless anyone tells me otherwise I think I'll carry on riding as is for a little while and keep a lookout for a similar (but maybe a little nicer) bike in the mean time. Fortunately there are a couple of nice upgrades on the bike (the wheels in particular are actually pretty good and the brakes are Deore LX) that I'd be able to swap over if/when I find another one!