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Hi, I'm new to this rear suspension business, I have a couple of questions. I have a specialized pitch.
My shock pivot bolt appears slightly slack in the bush. Lifting up my seat, i get the tell tale sign of a loose bush, but it has been recently replaced along with the spacers. Removed the shock from the bike, there is no play between the bush and shock or spacers and bush, I did notice quite a bit of slack between the pivot bolt and spacers. IMO, this is what is causing the slight bit of play in the rear.
Is this normal or acceptable? A off the shelf bolts diameter is not going to be made to a tolerance that allows a nice snug, slip fit. Is the bolt that comes stock on the frame more than a off the shelf bolt, a custom bolt? Is it normal for it to wear during use and need replacing?
During turns which you're really nailing and pumping hard, is it reasonable for the suspension to compress around 75%? In my head a lot of force is going down from your body, through the bike, to the ground, then a reaction force from the ground to the bike, it's reasonable right?
Former...I tighten the bolts and try to ignore it 😎
Later - no idea, but it sounds reasonable. In theory you should "just" bottom out your suspension once per ride.
The thing is with air springs, you can't actually bottom out an air shock due to the spring rate rising pretty steeply at the end of its travel.
No I wouldn't expect there to be a loose movement on a rear sus setup. If theres a slight bit of a clonk when you lift the back end up and put it down, then somethings loose somewhere that shoudln't be.
Knowing Specialized, one or more of the other pivot bearings has wear/play in them.
^Can people not read?
I have located exactly where the play is coming from and the reason why. It's the upper shock pivot bolt.
I'm dubious whether replacing it will cure it because bolts aren't generally made to have a precision fit, just a location fit.
So is it likely for the bolt that is in there to be a custom bolt? I've located off the shelf replacements for a fraction of the price from specialized, it's just whether an off the shelf bolt will do the job, which I doubt.
Then just asking if it's deemed "acceptable". To me it's not acceptable, but i'm a mechanical engineer and very pedantic, and just checking if i'm being overly so.
the bolt is there to clamp across the upper shock mounts. if the mount kit is loose on the bolt then you need to tighten the bolt up - the mount kit should be clamped firmly by the frame.
the mounts turn on the replaceable bushings in the eyelet of the shock not at the frame.
Same problem with my 08 pitch pro but I've never bothered to look for the problem until now and there is play in that area.
It's not worsened over time for me although I don't ride it that much.
And I don't notice it when riding.
Edit, just had it apart and the bolt is the wrong size on mine by quite a bit. You could contact specialized to see if they have a bolt to fix this?
Tighten the bolt up properly. If it's already tight then you've misdiagnosed the problem.
75% is about right you'll have used 3" travel from your normal sagged position leaving an inch and a half travel for big hits.
You can bottom out air shocks but you don't feel a clunk due to the bump stop fitted to stop you damaging the shock. Shocks with a large volume air sleeve like the DHX air and rp23BV's are more prone to bottoming if you havnt had them tuned/modded the aircan.
The clamping force of the bolt will only tighten side to side play, the play is up and down.
The play is 100% where I say it is.
Diagnosed through disassembly and measuring, also by simply having my thumb between the rocker and shck and feeling the up and down play.
No, as you tighten the bolt, it should also pull the parts together, preventing vertical movement as well.
Either its worn the clamping surfaces (because its free to move) so you have a wider gap to fill or you're not doing it up tight enough.
Isn't that a worn shock bush?
It's not a snug enough fit between the bolt and the bushings, you can do it up tight but there is enough leverage in that area to cause play.
^Bingo.
As per Van Halen. With a shock and pivot bolt out of the frame there is often play, its there to clamp, rather than act as a sliding fit rotating shaft. With the shock in the frame, fully bolted up, you should be able to feel the play with your fingers between the mating parts. (i.e. fingers against between shock bush and frame mount....or fingers against/between main pivot swingarm and frame) Play should be checked with the bike built up, not part stripped down.
I replaced the shock bush on a frame a while back, convinced it would cure the problem. It didn't, and it turned out the main pivot bearing was totally worn out. Replacing that cured the problem.
And by the way, I'm a Chartered Mech Eng - don't get quite so offended when people suggest other ideas 😉
Mounting bush should not move relative to the mounting bolt when correctly assembled and tightened up.
My FSR has movement relative to the bushing / bolt when loosely fitted, but when tigtened up correctly there is no movement.
The bolt dia relative to the mounting bush is largely irrelevant, its about how tight the bolt is to hold it all in place.
Don't be so defensive either.
Do up tighter and use threadlock. Mine was coming undone all the time on my Stumpy - enough in the end to smooth out the bolt head so i could not tighten it enough anyway - a new bolt kit cost £40 from Specialized.
Also, as noted above, check main pivot for play sideways and vertically.
Classic worn shock bush. And piss poor assumption by mfrs that a stock bolt will be of decent roundness & diametrical tolerance.
I'm sure DTSwiss use a spherical bearings in theirs. That, in theory, sounds loads better.
I've always thought it a poor bit of design.
I was once told to just tighten till all play dissapears!!!
Second question, yes, of course it is normal. Its doing what its supposed to do, but play with comp & rebound, dont just leave at halfway. Spend an hour on a short-mixed trail & try different settings. "Bottoming" the suspension wont hurt it.
Thanks for any help.
Maybe it is as simple as getting out my torque wrench and having a check, i'll give it a go.
Just tighten it progressively until it doesn't do it anymore. The worst that could happen is you'll strip / snap a stock bolt.
As others have said (I think), generally the reducers/top hats (i.e the bits that the bolt goes through and sit inside the eyelet bush) are kept in place by being clamped together quite tightly.
There's no way the tolerance between reducers and bolt will be low enough to avoid movement if it's not all clamped up real tight.
As for the final question, I think that's fine. 25% sag (or more) is considered normal, so you've only got to generate 2g (ish) through a berm to get 75% travel.
Engineers eh? I don't think amny engineers are involved in spec'ing bolts.
glenh - 3g Shirley?)
You've already got 1g at standstill, hence the 25% sag.
and so 2g would take you to 50% 3g to 75%. And it's be at an angle to the vertical anyway?
Bolt.. hmm.. on my bikes it's a pin that's bolted in place, and hence a proper machined fit with a hard material. The shock bushing needs replacing periodically, and the pin does but less frequently. Once ayear or so for bushes depending on the frame.
Call TFTuned, they are ace and will know all about your bike and its tendencies to wear suspension bits and sell you an appropriate shock mounting kit.
Suspension will compress in tight berms yes. You can use this to your advantage cos it can extend and rocket you out of the berm.