I have a 2007 Specialized Stumpjumper FSR with a Brain, and the rear suspension feels 'notchy' on the compression stroke. The bearing bolts are all tight and I can't find any play. The shock has just been serviced and received a clean bill of health. The air pressure and damping are as suggested in the manuals and the rubber O-ring tells me I'm not bottoming out. The handling otherwise feels fine and predictable, yet I'm feeling a gentle 'clunk' mid travel.

Am I feeling the Brain activating on the bumps? Or is something else not quite right? Ideas to investigate welcome.

Can you turn the brain 'off'. That'll confirm it, wouldn't it?

rusty notchy bearings?

The shock has just been serviced and received a clean bill of health.

Can't really be anything other than the shock really.

Assume you've removed the shock from the frame and checked that the bearings run through the full range of movement with no friction?

I'd go for manked up / rusted bearings personally.
as retro83 says would confirm this.

Are you getting any 'squelching' from the shock in either the compression or rebound stroke?

Definitely new bearings needed.

The horst link one especially don't move much and you are probably feeling them just "let go" mid stroke. Just changed the bearings on mine. A bearing kit for the whole lot is £40 from Spesh, and (contrary to popular opinion) you don't need any special tools. A vice makes things easier, but you can do it with a hammer, a large flat bladed screwdriver, a collection of sockets and a g-clamp. Took me about an hour.

HTH

Did you put new shock bushings on the serviced shock??

I demo'd a 2010 Stumpjumper FSR Expert and you could feel a clonk through the frame everytime (I assume) the brain activated. It didn't seem to affect the performance but was quite annoying. It was the same feeling as when you whack the rear rim on a root if your tyre pressure's too low.

Thanks guys – very useful suggestions. Some further info to aid the diagnostics:

@Spock/BuigYinn: Shock bearings not rusty (I checked them when I took the shock out), but will disconnect shock again and check there's nothing else in there.

@NickC: There is no 'off' function for the Brain, only degrees of firmness/softness. I'll try running it super soft and see if it feels different.

@LoCo: No squelching. It used to, and that's why I had it serviced.

@BorisElbrus: Could be Horst bearing. Will check.

@Stumpy01: that describes the symptom perfectly. Maybe that's just the way it is. Any other Brain users recognise this?

My '07 Pro with brain doesn't do the notchy thing at all – well not since I changed the bearings anyway. On the Stumpy's the brain doesn't lock out the suspension just stiffens it up when the trail is smooth. So you shouldn't get a jolt mid stroke, as a bump big enough to take it to mid stroke would already have opened the brain, if that makes sense?

Hard to say what is causing this without the bike in front of me, I have known the brass mass inside the inertia valve in the brain to stick causing strange behaviour.

@boriselbrus: Agree with your logic. I'll explore some more. Re: replacing bearings. I get sockets + G-clamp/vice (I assume to push old bearings out/new ones in), but what are the screwdriver and hammer for? I generally try to avoid uncontrolled bashing 🙂

@LoCo: Brain functionality was checked at service too; all OK. Maybe a quick call to TF Tuned.

TF don't do brains. So you've got a non adjustable brain ? You've just had it serviced ?

marting – Member

@Spock/BuigYinn: Shock bearings not rusty (I checked them when I took the shock out), but will disconnect shock again and check there's nothing else in there.

I mean the frame / rear triangle bearings, not the bushes that hold the shock in place.
Take the shock out completely and then try and move the rear end through its range of movement up and down by hand. Does it move smoothly or is it indexed? (Best to take the wheel out first)
If its smooth, then look to your shock for the problem. If its notchy BINGO! Problem found.

OK…
Took the shock out, moved rear frame end to end; super smooth, so not the bearings.

Played with the brain: if I slack it off completely, I don't notice the 'notch' and if I firm it up, the 'notch' comes back -> it's brain/shock/firmness related somehow.

It might be also be simply that the wheel rim is bottoming out with firmer settings (will experiment with tyre pressure to see)

Sounds like the Brain activating to me.Higher the setting the more notchy it will feel as it takes more to get the shock moving