Slugish Shock

[bootsandall]

Having trouble with a used Rockshox Bar 2.1
So building up a old Giant MCM D990, its just a fun project and if i like the feel of riding a dualie will look at upgrading but for now this will do. The frame was given to me so between all my old parts and some slowly sourced cheap parts i'm almost there.

It went for its maiden ride the other day and noticed the rear shock was taking forever to return. The rebound is set to the quickest setting, but it is slugish to return to full stroke. Every now and then it does move quicker but most of the time its slow. So it will fit in the frame as it is not standard equipment, i have had to invert it to how it normally is in most frames. Has this effected the shock, or does it just need a service as it is second hand and not sure of its history.
I also suspect that it just might be DOA and it wasn't till install and use that it was apparent.
I have attached pics so any help would be much appreciated.

 

[cluster]

No idea about most of the internals of shocks, but when you set the rebound to the quickest setting are you turning towards the minus sign? just something that can sometimes confuse people, they want it faster so they give it more speed by going plus... but in fact they need to go minus, ie. so the shock will take less time to rebound.
other than that, i've no idea sorry.

EDIT: oh, and if that is an air valve i can see in the second photo (the silver valve-cap), have you pumped it up using a shock-pump?

 

[bootsandall]

This type of shock doesn't have '+ or -' just rabbit and turtle.
I have tried it at the middle and both ends of the adjustment and still no joy. when completely to turtle it just stays in for what seems like a long time before slowly return if at all.
As for the air it is set to about 80psi which is about norm for me seeing as i'm 75kg.

 

[hiredassassin]

As for the air it is set to about 80psi which is about norm for me seeing as i'm 75kg.

that sounds pretty low... i may be heavy (90ish) but my shocks have always been set to about 160+ (current shock on my 575 is at 220).

Are you checking sag to set pressure or you just going off numbers?

 

[maxwolfie]

This type of shock doesn't have '+ or -' just rabbit and turtle.
I have tried it at the middle and both ends of the adjustment and still no joy. when completely to turtle it just stays in for what seems like a long time before slowly return if at all.
As for the air it is set to about 80psi which is about norm for me seeing as i'm 75kg.

80psi??? Upon a quick Google search, you should be around the 160psi mark (for 175lbs). For a proper setting, set the pressure based on sag (i.e. 25% or there abouts)

 

[bootsandall]

Checked the air, pumped it to 100psi and just get under 20% of travel ( 50mm of travel, 100psi gets 9mm of sag). the shock set at both ends and the middle if lent on to compress shock a few times would return at different rates each time and when set to the turtle end of the rebound some times it would compress and stay compressed. It not so sluggish as sticky with it sometimes after compression it would sit then bang extend quickly compress again and slow return, compress again and stick then slow return. Really all over shop in the way it is behaving, I can pump it higher but then it sag will be like 10% if that!
Does anyone know if the rebound value, assuming it is just a throttle valve to meter the return of air from the one chamber to the other is effected by being inverted. Does the oil in the shock interfer with the flow of air between the two chambers.

 

[maxwolfie]

Checked the air, pumped it to 100psi and just get under 20% of travel ( 50mm of travel, 100psi gets 9mm of sag). the shock set at both ends and the middle if lent on to compress shock a few times would return at different rates each time and when set to the turtle end of the rebound some times it would compress and stay compressed. It not so sluggish as sticky with it sometimes after compression it would sit then bang extend quickly compress again and slow return, compress again and stick then slow return. Really all over shop in the way it is behaving, I can pump it higher but then it sag will be like 10% if that!
Does anyone know if the rebound value, assuming it is just a throttle valve to meter the return of air from the one chamber to the other is effected by being inverted. Does the oil in the shock interfer with the flow of air between the two chambers.

How heavy are you?

 

[bootsandall]

I'm 69kg in jeans, t-shirt and hoodie. So say 74ish when all ready for ride with 2Lt of water on board. But even if the shock was under pressure for riders weight it should still behave properly just compress further under the given force. Has anyone had any experence with flipping a shock on the mounts, and has it displayed the same performace charteristics in both oritentations. So taking the cylinder body when it is normally at the top and then changing it so the cylinder body is at the bottom?

 

[3viltoast3r]

Are you using a shock pump? Also did you try turning the rebound to the middle, bouncing on it, then turning it back (If required)? May just need a service..

 

[Landon]

Old School

First off, that's a serious retro Giant you have there. It looks to be in great nick too. Nice work

How free moving are the pivot bushes when the shock is removed. There might be something going on here.

If everything moves freely enough, the shock probably just wants a service. Make sure you get a quote first. It might be worth looking around for a good deal on a new shock. You don't really want to throw $150 at that shock. Flipping the shock won't have any effect on rebound speed. That's provided the damper oil is free of air.

 

[bootsandall]

Thanks Landon, its sure is a classic, good line’s on the frame. It’s 3.3 kg with that shock with about 110mm of rear, not cutting edge but a real different bike. Still need to machine up the rear disc brake adaptor mount.
The young guy who gave it to me hadn't ridden it much before he found he liked the downhill part of the ride more than the rest of the ride, so stripped it of parts and stuck it in the folk’s garage. Parents move and suddenly his stuff has to fit at his house, was looking to unload it I think. One happy new owner here but the partner is keeping an eye on the bike count.
Before I put the shock in I could move the swing arm but it wasn't what I’d call free in its movement. Might get it apart and add a little lube to the pivot points any suggestions on what would be best, lithium grease or something thinner.
As for the shock it might be retired to the spares draw and get replaced by a new one, ever a Manitou or X-Fusion unit from the bay, they seem to be fitting the budget.

 

[Ridenparadise]

If all the pivot bearings are OK and nothing on the frame/BB is bent, that almost sounds like the shaft in the shock itself is bent. That is one cool bike. Dumbest shock position ever and that makes it even cooler. Hope it gets riding.

 

[Newton]

same shock , same problem, the shock is stuffed, if it's under warranty take it back, if not it will need a service. Mine was taking 10-15 seconds to come back.

 

[AngoXC]

The air can isn't fouling the frame near the lower shock mount, is it?

Gorgeous bike my friend.

 

[bootsandall]

Thanks for the input and the calls been made, the money been spent. Replacing with a new old stock shock of ebay, should have done that at the start. Got an X-Fusion 02 RLA that was built for Specialized's 2006 FSR-XC, they are the same length as the old shock that came stock with these frames back in the day. Hope I have more luck with this one and I should be able to mount it with the air chamber at the top this time, the Bar shock would be hitting the frame when fully extended if in the other way round. Just need to get a cover over it to save the muck from making havoc on the shock.
Thanks for all the feedback on the build, pretty cool old frame. Full carbon wrap monocoque front triangle (if you can call that a triangle!) and internal cabling with aluminium swing arm. Pretty spec for 1999 found a few threads out there on these bikes but not to many around, they only made them for one year. Well might have to move this to the rides threads soon as a build diary. Most of its done now but a few tricker parts to fabricate on the cards.