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Fork service - Oil Weight

diydiy Posts: 6,473
edited November 2010 in MTB workshop & tech
According to the SRAM Service guide I need to use different weight suspension oil left (15w) and right leg (5w). do people actually do this or will 5wt be sufficient for both.

I've also heard that standard synthetic motor oil is fine for the job.

I was thinking of using either 5wt fork oil for both or 5wt fork oil and 15 wt synthetic. Its such a small amount needed of the 15w (5 top 15 bottom on the left), I wondered how much of a compromise this is?

or am I undoing the good work of a service, with this compromise?


  • BOYDIEBOYDIE Posts: 528
    The 5wt oil is for your damper,the 15wt oil is for lubing your lower bushings,I would use 15wt in the lowers I know its 15ml/20ml only but you need to use the thicker oil so it sticks and does not break down,you also have to soak the foam rings under your wiper seals in 15wt.
    5wt is too light IMHO to lube bushings and foam rings effectively.Use the right stuff and you wont go wrong.
  • diydiy Posts: 6,473
    Thanks - Any experience of using synthetic motor oil? I have lots of
    Mobil 1 5w20 Synthetic Motor oil which I read elsewhere is equiv spec to 15w fork oil and just as good for the lubing bits.

    I have ordered rock oil fork oil in the 5w for the dampers. I have ordered new seals.
  • nicklousenicklouse Posts: 50,675 Lives Here
    engine oil grades and suspension oil grages are measured at differnt temps. and are designed to work at different temps.

    Fork oil viscosity tends to be at 40C and engine at 100C

    as a lube engin oil could be used but i would not like to think too much about the seals.

    some infos

    I know what i would do.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • diydiy Posts: 6,473
    thanks for the table, so my mobile 1 gear oil is going to be closer to 10w than 15w. Its fully synthetic, so wont swell the seals. I will give it a go with the old seals first.

    I'm not entirely convinced that a service is going to fix the problems.
  • BOYDIEBOYDIE Posts: 528
    As a quick fix I have used castrol GTX for bushing lube, it worked fine but the first chance I got I changed it for 15wt fork oil.
  • diydiy Posts: 6,473
    Did the service last night.. Kind of made the debate about oils academic given the Sh**e that I drained out of the forx. Looked like the caps had worked loose over time and allowed water/muck to contaminate the oil, as it was a grey colour.

    Quick question.. I followed the SRAM guide, but I needed to use grips (pliers/mole grips) on the -ive valve when tightening the retaining nut on the left lower leg, to stop the valve and shaft from rotating. Is this normal? It wasn't mentioned in the guide?

    Looking at the burring on the valve it looks like I was not the first person to do this and it was this that made the nut tight when re-threading, so I was wondering if its a catch 22.
  • BOYDIEBOYDIE Posts: 528
    I have used them as well,there might be a proper tool but i bet it costs a bomb.use some insulating tape to keep marking to a minimum.
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