more fork oil changing questions/ Getting the air out

2 replies to this topic
  • Tom

Posted May 29, 2000 - 02:15 PM


Kevin and Guys,

Thanks for your previous answers.

Now my question is a bit more specific:

The manual talks about pumping the damping rod up and down. It also says take the outer tube and extend it 7 inches a few times. Then it says fill to the top and watch the bubble come out. Then measure.

Now my question, what is the proceedure you use to remove air? Then, when do you measure; i.e., when oil is to the top of the outer tube and after you've pumped the damping rod? The second question is important to me because the damping rod holds oil that won't be part of the measurement. Therefore, the final oil level will increase during use, which could help blow a seal.

Thanks for your time.

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  • James_Dean

Posted May 29, 2000 - 03:53 PM


Following the procedures,
- fill to the top
- pump the damping rod
- refill
- pump the outer tube (extending only 7+in., not past 8in.)
- measure and adjust the level, with the damper rod BOTTOMED and the outer tube BOTTOMED. The damper rod must have the spring guide on. The damper rod and it's internal oil WILL be part of the final measurement. This seems simple enough. There will always be trapped air below the fork cap and around the spring. We are trying to remove trapped air in the damper rod and between the inner and outer tube in this procedure.

- Bleeding the air off consists of letting excess pressure out while the forks are fully extended. Thus, there is only atmospheric pressure in the fork while they are fully extended.

-Pressure rises as the forks compress. More oil makes for less trapped air and progressively stiffer forks in the last 1/3 travel. This is the alternative to stiffer springs, heavier weight oil, or cranking up the compression damping adjusters to prevent bottoming. It is only effective past 2/3 travel.

[This message has been edited by James Dean (edited 05-29-2000).]

  • Ken

Posted May 30, 2000 - 05:38 PM


James Dean, Kevin in NH:

I experienced a problem similar to Tom's with oil level. I changed my fork oil after a month or so of break-in (in '98), carefully followed the procedure in the manual and set my oil level. This spring I ended up having a fork seal go out. When I measured my oil level during disassembly for the seal change, it was 1" higher than I thought I had set it previously.

Here's my question:

When pumping the outer tube up and down, I assume this is to remove air trapped between the inner and outer tube. When complete, there should be bubble free oil in this area. What happens when, after complete assembly, the fork is fully extended? My thinking is that the oil that was between the inner and outer fork tube has to be forced back out of this area, thus raising the level. Once extended and then collapsed, air could again be trapped in the space between the inner and outer tube and give a "false" level reading. It also appeared like the holes through the inner tube (near the top) were above my oil level setting. This also leads me to believe that there could be air between the two tubes after extending.

Sorry to ramble, but does this mean that once a fork is air bled, oil level set and then extended an accurate oil level cannot be measured?



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