Rear shock gone?

[MD77]

Hi all, I'm new to the forum so please be gentle 

I bought my 08 GS500F in Oct 2016 as my first bike..... I'm loving it so far, gives me everything I need for my first bike.

I was due a MOT today and the guy at the garage failed it as the rear shock needs replaced, the bike's only done 15k miles though and I know the rear shocks on the GSs are notoriously soft, is there any way I can tell the rear shock's gone before I need to fork out for a replacement​

Thanks in advance, Mark

[pliskin]

A blown shock would likely be wet with oil. Or, it would spring back up with a hard clunk after being compressed.

[MD77]

Thanks pliskin,. No oil and clunk......just a bouncy rear end

[sledge]

Yes.......it failed the MOT!

Do you know better than the tester, someone who spends every working day examining shocks and various other motorcycles and their component parts?

If something has failed internally the shock will go soft without leaking any oil

Even if you take the bike elsewhere for an MOT the failure is recorded against the reg no and they will be all over it like a rash.

If you are on a budget buy a used replacement, clean it thoroughly so it stands out, fit it then take the bike back for a retest. If they can see you have made an effort they are more likely to give you a pass.

[MD77]

I know it failed sledge, I'm not arguing the point.    It's my first bike, so far I've managed to do some maintenance myself and I've learned a lot about the bike in the few months I've had it but I'm not sure how "I" can tell the shock has gone. As I said, I know the rear shock is notoriously soft, having never ridden anything else before I have nothing compare to, which is why I asked the question.

When the back end is pushed down how much "bounce" should there be......is there a measurement that's used or is it a best guess that's used?

  Pliskin's already said that there should be some oil and a clunk, which there isn't any of either, which is why I'm looking for clarity

Cheers

[The Buddha]

No oil outside the shock = its not blown a seal.
Of course a GS shock is dead when it leaves the factory.
Usually they don't clunk. The shock will pogo but it would need to have a spring stiff enough to pogo. Else it wont. I think a GS shock is pretty soft and likely wont anyway.
I blew a GSXR shock once and that did pogo discernibly.
Cool.
Buddha.

[mr72]

Well the only real way to tell is to put it on a shock dyno.

Hey first just a touch of theory/terminology here. The "shock" on the rear of your GS500 is comprised of a coil spring that is integrated with the damper ("shock absorber") in a coil-over fashion. Presumably the thing the inspector says is "gone" is the damper portion, not the spring.

The job of the damper is to prevent oscillations of the suspension. When it is compressed, it will rebound and the weight of the motorcycle on the spring is like a giant pendulum that will cause the thing to go up, down, up, down for a long time (oscillate). The damper is there to prevent it from cycling through this oscillation, so if you compress it, it will rebound back to something like the original position and stay there.

If you pulled it all the way off the bike and remove the spring (which is not trivial), then you could "hand check" the shock to be sure there is at least SOME damping but you will never be able to apply the forces and rates of force that it gets on the road this way.

The normal test is if it bounces up and down when you compress and release it, then the shock is shot. If it rebounds and comes to rest on its own without oscillating, the damper is at least doing SOMETHING.

It's the spring rate that's "notoriously soft", not really the damper. The damper is matched to the spring from the factory. A heavier spring will exert more force on rebound so it requires more damping to control it. A soft spring doesn't require as much damping.

I think if the shock were truly shot, you'd know it by riding it. The rear end would be obviously very uncontrolled and traction would be a serious problem. If you went over any kind of bump especially in a turn you'd be in for quite a thrill ride. I don't know for sure because I've never experienced it, but I can assume.

My suspicion is the inspector saw oil on the shaft of the shock and assumed it meant it as defective.

[sledge]

No........there doesn't HAVE to be an external leak or a clunk for a shocker to be faulty. There are internal seals that can fail.

What does the report say? Oil leak or inadequate action? They are two different failures.


I suggest you ask the tester, its all at his discretion 

[sledge]

Give us the reg of your bike, I can check the failure result on line and comment from that

[MD77]

The MOT fail reads "rear shock absorber has inadequate damping​ effect"

[sledge]

If it was leaking the failure would read something like " evidence of  leakage from shock absorber"

The tester has used his judgement and discretion to decide the shock has failed or is worn, he doesn't have to be specific but if it was visibly leaking it would say so in the documentation.

Its 9 years old, they don't last forever 

[sledge]

Take look at this.....


http://www.motuk.com/bike/2-4.asp#Menu_Top

[MD77]

Thanks sledge.  I guess the experience the tester has gives his the knowledge of what's good vs bad.    Looking at the link and the MOT fail reason (2.4.A.3b ) it coincides with inadequate damping effect.

I might go for a straight swap from a gsx600f........ is it a case of get the bike on the centre stand, undo the 2 bolts on the shock and replace..... or does the rear wheel need to come off?

[mr72]

That's a "Katana" over there right? If so you don't have to remove the wheel at all. You do have to remove the seat, tank and air box. The shock comes in and out through the opening where the air box sits. It won't fit going through the bottom. But besides that, yeah it's remove two bolts and Bob is your uncle.

[MD77]

Mr72, yeah, it's a Katana in the UK.   I've already had the seat, tank and air box off before so shouldn't be too difficult to do a swap for the shock by the sounds of it.

Thanks for everyone's help

[The Buddha]

No........there doesn't HAVE to be an external leak or a clunk for a shocker to be faulty. There are internal seals that can fail.

What does the report say? Oil leak or inadequate action? They are two different failures.


I suggest you ask the tester, its all at his discretion 

No the way a GS shock is built, this can not happen. Fluid is passed through metal orifices in he damping rod and big plungers with holes etc, there is no sealing in it from chamber to chamber. The shock has to lose most of its oil for this to fail.
Think of it ad moving your hand through a trough of water. In fact a trough of water will make a batter shock than the original GS one, but you get the idea. the trough has to be lower in water level to get the "damping" action to stop.
Cool.
Buddha.

[The Buddha]

The MOT fail reads "rear shock absorber has inadequate damping​ effect"

OK the new shock is that way, now how was yours bad then
Cool.
Buddha.

[Bluesmudge]

If its your first bike you may not realize how bad the shock actually is. You have nothing to compare it to. I bought my GS500 with 14,000 miles and didn't realize for a few months that the bike already had a blown shock. I think it was blown when I bought it.
If you try to ride the bike hard in the twisties you will realize how dangerous it actually is. Turned out I wasn't dragging my center stand because I was a really good rider. It was because of the shock.
If you ride the motorcycle at highway speeds on a concrete road (not asphalt) with expansion joints you may pick up an oscillation in the rear end from the small bump at each expansion joint. When my shock was really blown my bike would pogo stick down the highway. That was when I knew I had to get a new shock. I replaced it with a Katana (GSXF600) shock. If you weigh under 190 lbs (86 kg) the Katana shock will be too stiff for you. Get an R6 shock instead.

If you replace the rear shock with something stiffer make sure you get new springs and oil in the forks as well. A soft front end with a stiff back end is a bad idea.

[Endopotential]

I'd vote for the R6 shock as well.  Perhaps the best mod I've done on my bike.  It's great having the adjustable compression and rebound damping, which the stock shock does not have.

Replacing shocks is not exactly a plug and play.  It does take some fiddling to get the bike lifted properly, and a bit of pounding to persuade all the linkage holes to line up.

There's a lot of threads on shock upgrades on this forum.  Also some more info and pics on my build thread in my signature below.

[MD77]

The bike definitely does bounce a bit, but you're​right, I've nothing to compare it to.

I'm only 70kg so sounds like the R6 would be best.    Had a look at a vid on YouTube, looks like the guy needed to do some grinding.......I know it might be a tight squeeze but does the R6 need that type of work to fit