How To: Bleed the hydraulic preload adjustor on an Ohlins

[jasonbw]

Had some trouble with my Ohlins preload adjustor, it would only give three turns worth of preload where they should be nearing 20 full turns... meaning I was getting about 1mm preload maximum, which was nowhere near what I needed!

Turned out it had air in the system (obviously)... I looked around on how to bleed it but no forum or google search showed anything on it, so I did it myself tonight and heres how.
Note though, this is not a known thing, it *should* be left to the experts, but I did it myself since I'm way low on cash and will periodically check to see if its leaked/sagged (plus I like doing this stuff). Figured its a similar concept to bleeding brakes, and I still dont know what fluid they use so I've used brake fluid.

On the remote preload adjustor you'll see a small (3mm?) hex/allen key screw, if you unscrew this it let air escape/in depending on where the preload is turned! So be careful.

With the shock left on the bike I unbolted the remote hydraulic preload and held it high so the hose goes down to the shock *this will let the air come UP - away from the shock when you open the bleed screw.

I wound the preload in till there was just a very slight force, meaning it's just starting to work, opened the screw and it bubbled and hissed out air, waited till it stopped and the fluid settled into the chamber which is what the screw was hiding.

Slowly back the preload off - like 1/4 turn and watch as the fluid drops down as its pulling the fluid into the line, using a plastic syringe drip a few drops into the chamer till its full and again - wind the preload a little bit and drop more in... repeat... (for about 10 minutes in my case) till your all the way back out on the preload stop (zero preload). Secure the screw (which has a rubber seal) and wind the preload in all the way and measure the amount of preload the hydraulic adjustor has given you... I believe it should be around 10mm.

Now keep in mind I have no idea of what fluid is normally used, I do NOT know for sure if this removes all the air or even if this is the correct procedure... but I know its worked for me now in a pinch and I can get the sag spot on! Woo hoo.

Hope this helps
JasonBW


EDIT: The fluid to use is Ohlins (or similar) 5wt fork oil.

[Johnny]

Full credit for even working out how to do it, I wouldnt have a clue and not be tempted to try it.
But, you say it worked for you, and thats all that matters. Glad you soughted it out and now have proper adjustments.
Thanx for the write up, if anything it has given us more stupider ones, ie me, somemore knowledge.

[zenodamper]

You basically want a fluid of around 15-19cSt or so - like Ohlins 1305-01 is approximately 16cSt... but here is the clue, what is the fluid doing...? So does it matter too much if it slightly askew with the centistrokes rating, or even the VI amount? Cos at the end of the day it is not doing much work at all!! What is important is the quality of the oil - like, one doesn't want to pop or damage seals from using the wrong fluid type/quality/grade...
This method would work... but it is always better to bleed these things when off the bike - makes less mess!! And besides, once you have it off, then you can attach a fluid supply and make a nicer/faster job of things... (to be sure to be sure!)

But "A" for effort there :clap:

[jasonbw]

Ahh cool, words from a master, thank you.
15-19cSt for around a 40 degC rating as its a remote reservoir, which is great because I used a 50/50 mix of Silkolene Pro RSF 2.5 and 5wt.

Peter Verdone is one of your pals? He's doen a lot of hard work into viscosities: http://www.peterverdonedesigns.com/lowspeed.htm

copy/paste from Peters site:

On a lovely Sunday morning, the ambient temperature may be 21C (70F). Motorcycle forks will run in the 26C (78F) temp range, rear shocks will run in the 65C (150F) range and rear reservoirs will be around 43C (110F). While motorcycle rear shocks require very high VIs (over 300) to function well over such a huge temperature range, motorcycle forks and bicycles do not. Anything over 100VI will be serviceable for them.

I have no doubt if Zeno had done this work it would have been a better job, functionally and everything, but it helped me in that pinch.

[zenodamper]

Hmm... OK...

He publishes on a site (his) findings gathered from all over the place - indeed, some of those figures were supplied by Graham, GixxerG, and myself - it is fun to have knowledge bases; but it always pays to consider where or whom stuff came from, and in future days it can become difficult to see the whats and hows of the coming about! - EG: Newton and Liebniz with calculus...

In fact, he loves to get straight to the speaking out on his theories; and quite a few I can see as flawed - not just my opinion either, they have been proven by years of practicals... Yet we live in a world where it is not in our best interests to always go around correcting people!!! For there are a few people out there with a lot of money whom can even make a fairly large part of our demographic believe in their bollox - of course, having lots of advertising and marketing money really really helps there; problem with knowing the truths (which are cross-reference-able and demonstrable too - of course, if I were free to do so...) in these matters is that one can do nothing about it - each time someone buys their Ohlins parts from these particular "car salesmen" o/s they only assist their business-empire's growth! But snake-oil is snake-oil at the end of the day, and killing customer service is damaging to whom??

Ha ha - not a rant in any regard; just a wee glimpse into the world we occupy here from a different perspective...

[Johnny]

Zeno...If you can see flaws in theories, then not pointing them out is also a flaw in itself, true ??

I understand what you mean though in not, but, surely there must be a way to "point out' correct methods ?

[NotTim]

This reminds me of the old joke about the guy getting an itemised bill from his mechanic with 2 items on it, being $1 for tightening a bolt, and $99 for knowing which bolt to tighten.