Help For Forking Sake

[petrolheed]

Hi Folks,

new to trials and new to site... need some advice pls. I have a 2002 280 pro and all seems good apart from the front forks, they bottom out when dropping off an obstical or when dropping the front wheel. I had a go on my friends 05 gasser pro and the front end felt great. SO, the question is - how much fork oil do i use in each leg and what weight oil ?, i'm a big lad at 15 stone so would 5w or 10w be best for the job ? ... also the blue and red 'knobs' on the top of the forks, what should they be set at when chainging fork oil (what do they do ?).

Thanks for any advise guys.

P.s. fork seals seem good

[motojojo]

I think the 05' has bigger 40mm forks and yes they are pretty good, but your are good also . First you need to change the oil 5w or atf( its about 7w) and it needs to be filled to the exact specks(I don't know them off hand)if the oil level is to low they will be spongy. The adjustment knobs should be in the middle after an oil change, then start from there.

Pertol try this link.http://www.gasgas.com/Pages/Technical/trials-suspension-tips.html

[jse]

"I have a 2002 280 pro and all seems good apart from the front forks, they bottom out when dropping off an obstical or when dropping the front wheel. I had a go on my friends 05 gasser pro and the front end felt great. SO, the question is - how much fork oil do i use in each leg and what weight oil ?, i'm a big lad at 15 stone so would 5w or 10w be best for the job ? ... also the blue and red 'knobs' on the top of the forks, what should they be set at when chainging fork oil (what do they do ?).

"

Hi,

I think I can help a little. Each leg takes 300cc's of 5 weight fork oil after fully draining them. You might try 300cc's of Dexron III ATF, which is about 7.5 weight and has the correct additives and lubricity. The fork oil level (air pocket at the top of the upper tube) affects the last third of fork travel, so a slightly smaller air chamber will reduce bottoming. At 15 stone (a "stone" is what, about 14 pounds on the other side of the pond here?) you are a little heavier than me (I have an 02' 280 Pro also) so you might want to add some preload to the springs, say about 8mm to start with. The preload spacers are the grey plastic PVC tubes, usually installed above the spring. Use schedule 40 PVC to make some longer than the stock ones.

A couple of tricks you may already know when working on suspension is to first: loosen the upper tripleclamp bolts before trying to take off the top cap on the tubes. It should only be installed snug when re-assembling as the o-ring will seal oil in and the upper clamp will keep the cap tight. When putting the top cap back on, screw the damping screw in till it lightly bottoms then spin the cap on the damper rod till it also lightly bottoms out, snug the jam nut against the top cap and then back the adjustment screw out and tighten the jam nut. This way you won't damage the damping needle by jaming it into it's seat in the cartridge.

When tightening up the front end loosen all the clamping bolts except the top tripleclamp ones, tighten the top tripleclamp bolts (18 ft. lbs) and push in the front end to "center" the forks. Then tighten the lower clamp bolts (also 18 ft. lbs and use anti-seize on all bolts and screw threads), center the front end again by pushing on it. The axle clamp screws are next (don't tighten the axle much in as it will exert too much of a sideload on the bearings) and go to about 9-10 ft. lbs max. The fork brace is always last. If the holes don't line up exactly, use a rat tailed file to elongate them so the small bolts drop in. Tightening the front end this way will reduce stiction and binding of the forks during travel and they will be smooth.

The knobs at the top of the forks are fine tune adjustments for fork damping characteristics (which is handled by the "shim stack" on the piston inside the cartridge). The right one (red, "right=red=rebound") is for rebound and the left one (usually black) is for compression. I've found the Gas-Gas forks work well with the compression full out and the rebound full in (LIGHTLY bottomed out so not to damage the needle/seat assembly) but it's a personal matter as to how they are set.

Hope this helps.

Cheers.

Jon