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Discussion Starter · #1 ·
I've got a Fox Vanilla R coil shock on the back of my 1997 Marin Mount Vision. Over the past year or so I seem to have been winding more and more preload on to the shock to keep the amount of sag the same.

I haven't put on any weight.:)

Do the springs wear out and become less strong over time?

If so how long are they supposed to last before being replaced?

Thanks in advance.:)
 

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I dont think you should worry

The spring could not be taken out of a spring with mtb use. I would suspect it would take millions of cycles and extreme heat to wear out a spring.
 

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Yes they do

WR304 said:
I've got a Fox Vanilla R coil shock on the back of my 1997 Marin Mount Vision. Over the past year or so I seem to have been winding more and more preload on to the shock to keep the amount of sag the same.

I haven't put on any weight.:)

Do the springs wear out and become less strong over time?

If so how long are they supposed to last before being replaced?

Thanks in advance.:)
Springs loose tension over time and start to get shorter once that starts to happen its time to replace it. This would sound like a Material failure because the Springs on a MTB are not that stressed, and should last a long time.
 

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www.derbyrims.com
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Yes coil springs sag over time

Festusjrf said:
Springs loose tension over time and start to get shorter once that starts to happen its time to replace it. This would sound like a Material failure because the Springs on a MTB are not that stressed, and should last a long time.
But it's not a huge amount. I've felt that change in my old Vanilla-R too. I've added a turn or two of pre-load over a two year period to raise sag to the point that the spring was apparently coil binding and it broke the removable spring plate. I had to change to a 50# heavier spring, which isn't as plush, but it doesn't risk coil bind. I raised the coil spring rate in the fork to match the firmer rear spring.

It may be that the compression damping piston action is wearing down over time too. The suggestion for a nitrogen recharge above is a good one, because the high pressure reservoir charge increases compression damping very slightly (that reservoir pressure is how the 5th Element and Manitou Swinger works in tuning their platform valved compression). My shock needs that service too and I'll try my softer spring again after the service to see if I need less preload than I eventually used. I'll be sending mine to Push Industries with an instruction to not add any platform effect since my Tracer rides excellent without firm low speed compression. Maybe they can valve it to have no platform but a more rising rate of high speed compression damping so I can safely use a softer spring without bottom out problems.

Since you are a Mt. Vision rider you might be more interested than others in test riding the Jon Whyte Terra Quad designed Marin Wolf Ridge. It's pretty amazing, pedals excellent with 4 - 6 inch travel without a ride quality compromising platform shock. I wasn't very impressed with the XC Quad Mt. Vision ride and prefer your monopivot ride better, but the Terra Quad design is very advanced.

- ray
 

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skywaybuzz said:
Your possible low on NO2 pressure, time for a service. I just put a shraeder valve on my Van. R to recharge the psi cause it was bottoming easier than when it was new.
Hey skybuzz, where did you get a shraeder valve for your vanilla? I've been considering making one (but haven't got around to it) but taps in shraeder size aren't common (although M5 is close).

It's a myth that springs soften. But it is true that a badly made spring can yield, getting a little shorter every time it hits max compression until it's running below the yield point of the material.
But if you increase the preload you keep putting the spring back into the yield point.
The material doesn't soften, the spring rate remains the same but the ride height will decrease.
Measuring the spring (when it's off the shock) is the only way to know for sure.

A well made and specced spring won't have this problem. Car springs are a good example, older cars had sagging problems with age but thesedays the materials are better controlled and it's not a problem.

The spring on my old vanilla (6.75/1.75) was running at 1000Mpa stress at full compression. Fox has some pretty good metal.
 

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Festusjrf said:
Springs loose tension over time and start to get shorter once that starts to happen its time to replace it. This would sound like a Material failure because the Springs on a MTB are not that stressed, and should last a long time.
No way does a coil spring get shorter with use. Any used coil will increase its unloaded over all length. Same with valve springs for engines, if free length is longer than manufactures' spec the spring is toast. I agree that most bike shocks will never be close to the end of the life cycle. The cycle time is very low, even if its riden 7 days every week. Consider your cars valve train, it goes through full travel 60 times per second @ 3600 rpm all day long, for 100 thousand miles.
Most likley the valving or charge has been depleted.

Maybe you are now a better rider and now you have noticed ya need a change.
 

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just along for the ride
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Yes they sag over time especially if your frame is working against your spring. I jumped yup 100# on the recommended rate and now have no problems, I toasted my last shock being overworked, flex in the frame cooked it, good luck!
 

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Ridethebike said:
No way does a coil spring get shorter with use. Any used coil will increase its unloaded over all length. Same with valve springs for engines, if free length is longer than manufactures' spec the spring is toast. I agree that most bike shocks will never be close to the end of the life cycle. The cycle time is very low, even if its riden 7 days every week. Consider your cars valve train, it goes through full travel 60 times per second @ 3600 rpm all day long, for 100 thousand miles.
Most likley the valving or charge has been depleted.

Maybe you are now a better rider and now you have noticed ya need a change.
Have you never seen an old car with a sagging rear?

Springs only get shorter if the material isn't strong enough for that particular spring. Basicly the wire gets twisted too far and gets bent. It's new length is a little shorter.
A good example is to bend up a spring from a paper-clip and push it a few tims. Because the material is soo weak it'll get shorter pretty easily.

I'm not sure why your valve springs are getting longer. I haven't had to take mine out to measure. I have seen fractured ones though.
 

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Dougal said:
Have you never seen an old car with a sagging rear?

I sure have. Been wrenching for 28 years on almost every make/model vehicle you can name.
Any time a sagged/worn coil spring was checked next to its replacement (of same rate/ride height) the old was longer than its replacement. Same with valve springs, the old one is always longer. another misconception is a taller spring will have a higher rate or stiffer.
I'm not try to start an argument, only set the facts straight.
 

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Ridethebike said:
Dougal said:
Have you never seen an old car with a sagging rear?

I sure have. Been wrenching for 28 years on almost every make/model vehicle you can name.
Any time a sagged/worn coil spring was checked next to its replacement (of same rate/ride height) the old was longer than its replacement. Same with valve springs, the old one is always longer. another misconception is a taller spring will have a higher rate or stiffer.
I'm not try to start an argument, only set the facts straight.
Hmm interesting.
If only I had some to compare. (my current car springs are still good after 160,000km) I don't doubt you're right on the car springs, I'm just looking for an explanation of why.
My only guess would be microcracks or defects which somehow stress relieve the spring on extension.
 

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Fox Vanilla R

Dougal your looking for a Highway truck stem valve, I just got lucky and found one at a good small auto parts shop.Also try a truck tire repair shop. You'll need to cut it to lenght and thread it 5/16 x 24 National Fine Pitch (NFT) to match the threads in the shock. The shorter actual little valves in pic are from Michelin airstop tubes, these allow for a shorter stem sticking out the end in case the stem won't hit your seatstay at full compression like on my Tracer did. Use plumbers tape or JB Weld , (not too much or it goes inside and prevents valve from opening) to seal any air leaks(tested under water) I put in 250psi air from shock pump.http://forums.mtbr.com/attachment.php?attachmentid=24962&stc=1 http://forums.mtbr.com/attachment.php?attachmentid=24963&stc=1
 

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Discussion Starter · #13 ·
I have to admit the rear shock has never been serviced so it could easily be losing compression damping pressure.

The service is something I've been trying to put off as it still feels very smooth and plush in use.

I had the bushings in the lower shock mount replaced a few years ago as they were worn out but the upper mount had seized into the shock and I didn't unseize it whilst it was off the bike. :rolleyes: Brain fade.

Very slack as it involved bending the aluminium frame shock mounting to get it on and off. Something I really don't want to repeat in a hurry.:(

Looks like I'll have to build myself up to it.:)

Thanks for the replies.:)
 

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YES…YES…YES…

I had a turner burner from 1996 and in 2001 I wore the spring right out. I was bottoming more and cranking more preload over time. I replaced it with the same weigh new spring and it was like new. The same happened in my Marz' Z1. I wore out the springs and was bottoming all the time, new springs and the bottoming stopped and the ride got much better. Marz' offered that springs should be replaced every 2-3 years and Foxx was every 4 years.

Figure that on an old marin you have cycled that shock so many times, that you have definitely fatigued the metal.

The nitro charging could be suspect but that would result in poor shock performance that had nothing to do with the preload. If you are cranking in more rebound or the shock is weeping then get it rebuilt but if you are just feeling a little undersprung order a new spring and be very happy.
 

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Dougal said:
Hmm interesting.

I agree its odd, suspension coils are subject to the elements so surface rust could possibly explain the fatigue. Engine valve springs deal with heat and loads of cycle time, yet both are always longer after use.
Our shop has a dead small block chevy, If your interested i could yank some springs and take a pic.
 

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Cheers.

I was going to do the truck tube valve stem like you have, but I mistakenly measured the shock threads as M8 fine (8x1mm, no I wasn't using a thread gauge). Good thing I hadn't started.

I was hoping you had found a hydraulic or air conditioning fitting that wound right in, but that's okay. I'll be using a loctite thread sealant stick, wonderful things to keep in the toolbox.

I've previously been using a modified hypodermic needle/ball needle combo. But they really are a pain the rear. Fox recommends 200psi, but I also run 250 in my rebuilds.
 

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Ridethebike said:
Dougal said:
Hmm interesting.

I agree its odd, suspension coils are subject to the elements so surface rust could possibly explain the fatigue. Engine valve springs deal with heat and loads of cycle time, yet both are always longer after use.
Our shop has a dead small block chevy, If your interested i could yank some springs and take a pic.
Nah, it's okay. But thanks for the offer.
There's a cylinder head reconditioner just 1 block down the road from me.
 

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Sorry to relive this one but it got me hooked....

Skywaybuzz... How did you depressurized the shock??

I have a Giant HV shock that I'm thinking about retiring and once retired, play a little bit with it. On my shock there's a threaded cap (3mm socket I think) capped with some kind of rubber where I think it's where the shock was injected air by.

One of my ideas was to get a remote reservoir with a Schraeder to be able to play with nitro/air pressure and obviously put more oil in the shock and get the IFP on the reservoir. Maybe revalving a little or if possible machine a new piston with a PTFE glyde bushing instead of an o'ring piston to improve smoothness.

Now I see your thread I can make it some easier but the inlet port on the Giant HV looks a bit smaller. Anyway, Now I can see you can have machined a coupling with the thread of the shock hean on one side...
 
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