[h16]

this is basic stuff I know. I've seen the excellent threads on bluto tuning, length change, rct conversion, bottomless tokens etc. I did not want to pollute any of them. I have also read most of the '15 bluto/reba service guide.

I have a '15 100m (according to label) bluto - but I'm wondering if I'm getting the full travel or not.

The fork has ~100lb air pressure and is suspended in these photos. I measure ~2.75" of possible travel from top of oil seal to bottom of fork crown.

given that fork is listed as 100mm - my max travel expectations were 3.5 inches give-or-take - based on this:

is that wrong to begin with?

here is what I get when fork/wheel is fully suspended in stand - no contact:

in reality I see about 2.75" when bike is unweighted and on the ground.

I see other photos in various places which appear to show much more of the gradient exposed - but nothing entirely reliable.

I also don't understand the sag gradient - under no circumstances have I been able to extend the fork lowers by pulling to expose below the 10% scale mark. It typically hovers at ~15%.

other contextual stuff:

Does this all sound correct ? are my expectations/thinking that I should have potential for more than 2 3/4" travel for a 100mm travel fork just wrong?

thanks for the help

 

[ishpeming]

Yea, my fork works about like yours. I've had it for almost a year and after worrying at first and doing the turnagain kit so it would work at all in low temps I am to the point of riding what I've got and not thinking about it. And I love it. I can ride summer single track and mostly keep up with any group. Could not with my old rigid fat. No sense in worrying about it too much. Good luck to you. Ride on........

 

[Jayem]

If it's 100mm and it has the internals for it, there's no reason why it shouldn't be giving 100mm. My pike gives the 160mm exactly. Sometimes the negative spring sucks the fork down a little, which requires pulling up to allow the detent in between the spring chambers to equalize, and under extreme conditions/suck down, requires pumping up to max rated psi and doing the same thing, or trying the zip-tie trick (see suspension board) or loosening the bottom bolt and knocking the shaft free to allow it to equalize.

The other issue common to the motion control type dampers is they tend to leak out over time and pour the damping fluid into the bottom of the fork, which hydro-locks the fork and eventually results in less and less travel and damping ineffectiveness.

 

[RickyB]

A good friend of mine had the same thing you showed in your pics. Said 100mm on the fork, but came set with 80 mm internals. He returned it to the shop and they fixed that for him.

 

[mtb_fun]

There is a Schrader valve on the end of the air tube. The reason you do not have full travel is because there is too much air in the negative side.

You need to remove the Allen screw from the bottom of the left fork leg and reach in with something long and skinny to release some air from that schrader.

I recently had to do this to the Reba on one of my bikes.

 

[h16]

I'm going to try this negative air bleed idea - a couple of questions:

1) will I possibly need a new crush washer since I'm removing the lower bolt?

2) is there fluid in the leg that will drain out when I remove the bolt, if so do I need to tip it somehow not to lose fluid?

3) should I leave any pressure in the negative side, or should I bleed it all out?

I don't have a crush washer on hand nor extra fluid, and I don't want to leave the thing in an unusable state - got a good ride planned for tomorrow.

Here is what I think we're talking about from the manual:

 

[mtb_fun]

I would let all the air out of the fork, flip the bike upside down, remove the 5mm socket head screw and release the air from the negative side schrader. I did not replace the crush washer when I did my REBA and it does not leak.

 

[h16]

that will be my plan - thanks for the info - really helpful - will report back later.

 

[h16]

I just did the negative air bleed - as suggested by mtb_fun.

That seems to have done the trick.

When I released the positive pressure via that air cap - the fork compressed noticeably - perhaps another indication that the negative side was holding pressure.

When I poked the negative-side schrader valve - pressure was noticeably released - I let all of the pressure out.

Here is a shot of unladen travel before bleeding the negative side:

This is unladen travel after bleeding negative side:

I believe I now understand the sag gradient scales - there appear to be multiple scales on the upper tube - one scale for 80mm- another scale for 100mm - and more (perhaps 110mm or 120mm - I cannot reveal them fully). Mine - being 100mm - is now situated close to 0% on the 10mm scale.

Here is what I get after the negative bleed with no weight on the fork:

I will now let this thing sit overnight to make sure no oil leaks out of the hex bolt and crush washer that I removed, and later re-installed. So far so good.

thanks to mtb_fun for this helpful advice.

 

[chocolatemoeze]

Why is there pressure in the negative airchamber in the first place? What attribute does it affect?


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[Harold]

There's supposed to be air in the negative chamber. Problems can occur when there's too much or too little. The solo air cartridge that the Bluto uses is supposed to automatically equalize the pressures, but there's an older dual air version where you had to manually adjust the negative air spring.

Tech Tuesday - What a Negative Spring is and Why it Makes the Coil-Spring Nearly Obsolete - Pinkbike