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Front Suspension

D

Diver

Forum Apprentice
Past Site Supporter
Hi all.

What is the correct air pressure in psi for the front forks on my gs850g. Also, can I replace the oil in the forks without removing them with 251ml of oil. I can't seem to get a clear indication from the manual.

Regards

Chris
 
cannot provide a certified psi number for you, but I seem to remember that mine was in the single digits for the 1100. not much.

with regard to your fork oil swap, there is a small Phillips screw and copper washer on the bottom of your fork legs that is a drain plug for fork oil. you can drain oil from there, then replace from the top caps while installed in the bike. it will not be a complete drain-out of old fork oil, so if you do this, drain the fork oil into a measuring container and then replace the same volume of fresh fork oil into the fork after you drain. it will likely not be the full 251ml. this assumes that the proper volume of fork oil is in there to begin with!
 
Diver said:
.......What is the correct air pressure in psi for the front forks on my gs850g......
Click to expand...

The correct pressure is 8.5 psi to 17 psi. Use a hand pump to pump air in, and not a compressor, because not a lot of air is needed and the high pressure from a compressor will blow the fork seals.
 
Air pressure forks were a fad during the GS era. As the years went on, and bikes continued to advance, manufacturers quickly ditched the air.

In the USA, there are various companies making fork springs, which eliminate the need for air pressure. Sonic Springs, Progressive Suspension, Race Tech, to name a few. You may want to check around in your market for something similar. It's money well spent.
 
When I got the GS1000 air forks working on my 850, it worked well at 14psi. However, it was a pain in the asset keeping the air in, and it had to be checked every day.
I ditched the idea and fitted Wilbers springs from Germany, and made up some pre-set adjusters for the fork tops. Barely had to look at them since and it rides pretty well.
A tip: most Euro GS850s were sold with non-air forks, using a pre-set factory adjuster, if you can lay hands on a set of orignal Euro forks, you save yourself a great deal of trouble. The only reason I didn't re-use my originals was that they were just totally worn out.
 
The only reason to run air in the forks is to make it 100% original. New (straight rate) springs will make a world of difference. Tip: take into account, when you select the spring rate, possible weight gain on your account. Particularly if you're of a certain age. :rolleyes:
 
Like Grimly, mine had no air. There was a ramp type adjuster inside the top of the shock.
A good starting point for preload is to have 25-30% of the suspension travel used up with the rider on the bike.
The 850 has 160mm travel so that means 40-50mm of sag.
Put a zip tie on the shock and sit on the bike with as little load on your boots as possible.
Snug the zip tie down at the fork seal.
Get off and with the front wheel off the ground measure between the tie and the seal.
As said by others drain the oil from below. It's amazing the junk that collects down there. It took me three 'flushes' to get it looking anyway clean.
Be wary of using volume to get the level. It's a ball park measure. Check the level with a tape or rod.
 
What's the best way to check the oil level in the front forks without removing them.
 
Manual says remove forks and use special tool etc etc.
I do it with the springs removed, forks still on the bike, and use a measuring tape or a rod or stick with the forks fully compressed.
Is it the best?
Never had any issues doing it that way.
 
How far down :)
Spring out, forks fully compressed the oil level is 140mm (5.5 inch) from the top of the inner tube.
Mark your rod and use it like a dipstick.
I have used a metal measuring tape.
 
What oil are you using?
One member here swore by 5W.
I use a moonshine mix of ATF and 10W40 engine oil.
 
Hi Brendan.
Haven't purchased any yet.
I have both of the oils you mentioned above.
When you say forķs fully compressed, do I need to put a load on the front suspension.
 
Diver said:
Hi Brendan.
Haven't purchased any yet.
I have both of the oils you mentioned above.
When you say forķs fully compressed, do I need to put a load on the front suspension.
Click to expand...

If you do that, you'll never get it back up on your own.
Bike on centrestand, and the stand tied forward (or braced from the rear) so the bike can't roll off.
Fork caps off, remove the springs, hoist the forks upwards with a ratchet strap tied to the roof or an engine crane or the yokes.
Measure oil level.
 
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