Mono shock lost rebound?

Smash101 · Jun 7, 2015

Hi all,

I was riding my 2010 fx450 on the single trails with my brother yesterday in the Wombat State forest here in Victoria. Between trails we sometimes have ride down gravel roads that may also include a bit of a drag race.

Yesterday's drag race saw me going a little too fast for the corner ahead, I tried everything to pull the bike up but knew I was not going to make it, so I picked a line between two trees and hoped for the best.

The road was slightly off camber and I didn't see the huge rock just over the 2 meter embankment until it was too late, according to the GPS I hit it at 58.4 kph, I flew arse over tit down this two meter embankment landed on my head with the bike following shortly after and landing on top of me.

I was a little sore, still am, can't believe I rode away from that. Anyway it ripped the seat and rear guard/side plate assembly off, the usual twisted forks, and may of over extended the swing arm as I found the mono shock protector on top of the tyre and not in front of it where it should be?

The bike felt fine at first but after about another ten minutes of riding the rear shock lost all rebound, it's like a pogo stick.

I'm not very experienced with suspension work apart from the odd fork seal.
Has anyone heard of this happening and any ideas on the solution? And don't say ride slower

Thanks in advance.

Mark.

bushmechanic · Jun 7, 2015

happens sometimes after a big hit

the pressure has probably leaked out either from the reservoir or out around the shaft
seal .. there will be oil there in this case and the seal will be stuffed

if you remove the shock and shock spring then measure the shaft force at mid stroke with bathroom scales it should be in the region of 20kgs

any less and the rebound won't work properly

Smash101 · Jun 7, 2015

Thanks,
but the strange thing was I didn't see any oil, I thought the same thing?

Maybe the piston has separated from the shaft? It does make a bit of chunking sound when fully unloaded.

Smash101 · Jun 7, 2015

Also there is no rebound at all.

bushmechanic · Jun 7, 2015

no way to tell really what happened unless you open it up

if the rod force is too low that indicates a loss of pressure

if the rod force is ok then yes something is likely to be broken or loose

have you tried winding the rebound adjuster all the way in ?

Smash101 · Jun 7, 2015

Thanks Bushie,

I believe there may be some internal damage due to the clanking noise it was making.
I don't have tools to remove the spring, nor any nitrogen.
I think I will just take it down to the bike shop tomorrow, I will update when I get the prognosis.
Thanks again.

bushmechanic · Jun 8, 2015

FWIW you don't need any special tools to remove the spring

unwind the upper preload collar as far as you can then push the outer part of the lower spring seat up away from the inner part then remove the wire retaining ring, the whole lot then slides down over the bottom clevis

also FWIW you don't need nitrogen .. i don't use it. I replace the WP reservoir bolt with a shcrader valve and use compressed air. if you must have nitrogen you can take the bike and shock to be refilled at some stage after you get it working with air.

the difficult bit is refilling the shock with new oil and bleeding out all the entrapped air bubbles from the oil. that the main reason taking it to a shop will be easier.

Smash101 · Jun 8, 2015

I'm worried about damaging the lock nut holding the tension in the spring, do you have any back yard solutions. I tried a spanner that fit perfectly into the notches in the ring but it eventually slipped, I don't want to damage anything?

bushmechanic · Jun 8, 2015

small locking bolt is undone right ?

make sure the shock and threads are as clean as a whistle with a pressure cleaner

then reductuer H72 spray, some heat and an alumnium drift should start it moving

you are right to be careful though as the aluminium threads can gall pretty easy

try tightening it a bit if thats easier then clean the exposed threads.. or just give it to the teenage shop apprentice

Smash101 · Jun 8, 2015

This is the type of nut holding the spring tension, I loosened the lock bolt but still struggled to move it

bushmechanic · Jun 8, 2015

you could try taking the locking bolt right out and gently levering the big collar open, then squirt a bit of oil in there

they are hard to move sometimes because of the alloy body/alloy nut heat generally always works unless the main issue is dirt stuck in the threads

there is another way with a press

you can compress the shock 50mm or so then put 6 big cable ties on it to hold the spring together remove from the press then take the bottom spring seat off.

if you don't have a press you can jack up a vehicle and squash the shock under it between 2 blocks of wood.

Smash101 · Jun 12, 2015

Just received a call from the bike shop, apparently I snapped the piston off and scored the cylinder so the shock is a write off.

I was quoted $3,500 for a new one but I'm not sure if I can justify spending that amount of money to replace it.

I think I will look for second hand.

Smash101 · Jun 12, 2015

Anyone know of an alternative manufacturer or solution? Also what mono shocks from other bikes will fit?

Kt88 · Jun 12, 2015

Sweet lord, just find one on eBay. That's as much as I paid for my whole bike.

Taffy · Jun 13, 2015

I had the nut come off the end of the shock shaft on one of mine? I have a spare shock here but it is as a result of the above. no real damage but obviously the thread on the end of the SS isn't like new.

I had been re-valving and re-valving it and the shock was getting better and better. but the more shims I added, the nearer the shock shaft nut got to the end.

in the end one day i let it overhang the end by1mm and thought it would be OK.....

yup.....!!!! you got it.

regards

Taffy

Smash101 · Jun 13, 2015

Kt88 said:
Sweet lord, just find one on eBay. That's as much as I paid for my whole bike.

That's right, it's half of what I paid for the bike

Smash101 · Jun 13, 2015

Taffy said:
I had the nut come off the end of the shock shaft on one of mine? I have a spare shock here but it is as a result of the above. no real damage but obviously the thread on the end of the SS isn't like new.

I had been re-valving and re-valving it and the shock was getting better and better. but the more shims I added, the nearer the shock shaft nut got to the end.

in the end one day i let it overhang the end by1mm and thought it would be OK.....

yup.....!!!! you got it.

regards

Taffy

Like I said I've never pulled apart a mono shock before and thank God I didn't, i would hate to mess something up so valuable that I didn't know much about and like you i don't mind a bit of a tinker to try and make things better.

But one stupid riding mistake has cost me $3500 for the shock, a broken rear guard, maybe a bent fork as that is now leaking, bent bars and whip lash.

I will be way more cautious on gravel roads from now on.

bushmechanic · Jun 13, 2015

you could price an ohlins TTX from david at fastbike industries

otherwise yes just get one off ebay, ask on DBW and ktmtalk to find out which shocks from ktm models will fit.

Smash101 · Jun 13, 2015

Cheers mate, i could get an Ohlins for $!375, I'm happy to pay that but they don't have great reviews? Are they really that bad?

Smash101 · Jun 13, 2015

Could someone tell me if the fx fe 08-10 have the same shock?

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