Knocking from rear (full suss Giant Reign X1)

konadawg

Have replaced all (- all -) suspension bearings. Shock upper bush too (lower still perfect and no play).

After all the work - but may be coincidental - noticed a knocking when travelling at speed over "busy" terrain - basically bumpy rock and the like. Knock also evident if unladen bike rear is simply pulled off a step and allowed to drop.

As previous - anything that could be related has been replaced.

I am suspecting the rear shock. Is this possible? It's a DHX coil.

Apart from replacing the top DU bush I did not even remove it but upon returning from a recent bike holiday (BEFORE doing any work) I liberally applied spray oil to all linkages and bushes including the shock to tide me over until I obtained the bearings.

There is still some oil evident at the lower shock bush. It's been a couple of months now and I am suspecting that the oil I am seeing is coming from the shock and not what I applied, in fact today I wiped most of it off and will keep an eye on it.

But other than that, damping seems perfect and as far as I can tell the shock is performing perfectly. Unless of course it is responsible for the knock-per-bump. The knock, I must add, seems to be on the rebound. Seems to be... which is why I generally only notice it on, as above, "busy" terrain and not normal riding however much I use of the shock's travel.

At first I suspected an overinflated rear and deflated the tyre on the trail, which helped greatly. But re-inflating to a reasonable 40psi and the knock is there with a vengeance, so overinflation is not it even though running low pressures may mask it.

Oh and I also checked for a loose spring, in fact just to make sure I wound it down a bit so now it is definitely not loose.

To add some more - keeping a toe on the rear rim and attempting to check for any play in suspension etc by pushing and lifting the rear gives a negative result. There is nothing obviously wrong or I think I'd have discovered it.

Thinking about this as I write - I could imagine an internal rebound bumpstop having failed, but not sure whether it even exists and furthermore I have set damping to be on the slow side so this would have minimised the phenomenon.

Wonder whether anyone has any insight or experienced this sort of thing, don't want to run any expensive experiments with new rear shocks.

Thanks to any that can help.

Herdwick

try full rebound damping and compress as far to the travel you can, if it's rebound related it may show
can't think anything else as you prety much covered everything in your post, at least of what I can think.

rockmonkeysc

I had a Reign X and had all sorts of peoblems with the back end of it. Check the lower linkage around the cut out for the ISCG tab recess, they crack there very easily and then the linkage hits the ISCG tab. I broke three linkages in a year!
It eats bearings as well because they are tiny and the linkage rate means you end up with a very heavy spring or very high air pressure.

konadawg

Well shock is leaking, confirmed...

Any idea whether this is DIYable or is there HP nitrogen in the mix somewhere? It's a DHX Coil with piggyback.

rockmonkeysc

http://mtbmechanics.m.webs.com/site/mob ... network=fw

konadawg

Thanks for that, I actually found that site independently and the file is very useful. Took it apart, well where I needed to, and noticed that there is a scratch / small gouge on the shaft...

Anyway have just applied JB Weld and fitted a new o-ring (quite a bit of wear on old one) tomorrow will sand JB and re-assy.

As an aside damn thing seems to have nothing metric on it even the o-ring was a pain to source measuring up at 12.3 x 3.65 mm.

Fingers crossed.

The Rookie

That's because most stuff MTB is sized in the US!

rockmonkeysc

Americans cant understand the metric system. They are now the only developed nation still using imperial measurements. When they try to use metric it rarely goes well.

The Rookie

RockmonkeySC wrote:

They are now the only developed nation still using imperial measurements.

Have you any proof.....that they are a developed nation?

konadawg

Well as far as durability of the repair, only time will tell, but what I can say is that the knocking was definitely coming from the rear shock due to the leak of oil, because now it's completely gone.

I think the shock, possibly due to air being where it should not be i.e. replacing some oil volume, was rebounding harshly on the top out under certain conditions.

Or, the internal floating piston was impacting. Hard to tell. Did not measure lost oil volume. But the IFP seemed to be right at the bottom of the piggyback rather than appx 30mm down. Was a bit of a pig to withdraw, too, had I not had a rather particular pair of pliers that look like (and may have been!) designed for tooth extraction I might still be struggling.

But prior - to - repair testing of rebound using the ISO approved method of rapidly weighting and unweghting of the seat gave an all-OK result, so in summary, that means nothing!