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1980 GS850G Fork Upgrad Recommendations??

  • Thread starter Thread starter Darin Jordan
  • Start date Start date
D

Darin Jordan

Guest
I'm just finishing up some rebuild and hop-up work on a 1980 GS850 and would like to do something with the front end. I put 15lbs of air in the front forks, but they still feel pretty soft and bouncy and it looks like the fork seals need to be replaced as well.

I've never had this type of fork apart before, but should be able to handle it (any special tools needed??).

What I'm looking for is some straight forward advice on oil weight to use, some recommendations on replacement springs, and preload heights.

I'm not going to be racing this, but would like it to perform well.

Any advice to help this "newbie" would be greatly appreciated. I've been searching the forum here, but am not really finding the info I'm looking for. Will search some more, but if you could respond here, that would be great.

Thanks!

Darin Jordan
Renton, WA
 
Sonic or Progressive fork springs are pretty standard, along with fresh fork oil while you're at it, and fork seals if you need 'em.

With the proper springs in place, you won't need to rely on air pressure.

Once the forks are working properly, a Tarozzi fork brace helps keep things in line, but it's certainly not necessary.

Upgrade the brakes while you're at it as well -- with good modern brake pads and stainless lines, GS brakes work surprisingly well.

There's plenty of info, including info on forks, on Basscliff's site:
http://members.dslextreme.com/users/bikecliff/

Calibration (which springs to get, and how much to preload them) depends on your weight and riding style. We can assume your riding style is "sporty", but what's your approximate mass?
 
bwringer said:
Sonic or Progressive fork springs are pretty standard, along with fresh fork oil while you're at it, and fork seals if you need 'em.

With the proper springs in place, you won't need to rely on air pressure.

Once the forks are working properly, a Tarozzi fork brace helps keep things in line, but it's certainly not necessary.

Upgrade the brakes while you're at it as well -- with good modern brake pads and stainless lines, GS brakes work surprisingly well.

There's plenty of info, including info on forks, on Basscliff's site:
http://members.dslextreme.com/users/bikecliff/

Calibration (which springs to get, and how much to preload them) depends on your weight and riding style. We can assume your riding style is "sporty", but what's your approximate mass?
Click to expand...


While I was searching around, I found some Progressive springs for my bike and have them on the way. Just need to figure out which seals to get and what weight oil.

I weigh 216lbs and am 6'3". You are correct... I'm just a spirited sport rider. I like performance, but just want to have fun.
 
Got the Progressive Springs and new seals. I know the recommendation for the "average rider" is 15wt oil.... I'm about 220lbs dressed and 6'3", and ride "spirited" from time to time... Should I go with 20wt oil???
 
I'd try 15W and change it if necessary. Weight would have more effect on your pre-load; aim for about 25% sag, or 1.5".
 
I agree with the start at 15w for the new springs.

I am running stock springs on my GSes (so far) and have switched to 10w.

On my Wing, the previous owner installed Progressive springs and 15w oil, I had to switch to 10w because my wrists were getting jarred at every little irregularity in the road and would hurt after about two hours of riding. Simply switching to 10w cured that and I am now able to go all day. Some days have involved 14 hours and over 700 miles. :eek:

.
 
BassCliff said:
Hi,

From my little website:

Install Progressive Fork Springs

Fork Seal Replacement

Fork Seal Replacement: Includes complete disassembly (by Mr. Matchless)

At first I used 15wt fork oil with my Progressive springs. I also went back to 10wt, with no air.


Thank you for your indulgence,

BassCliff
Click to expand...


BassCliff... Already had those .pdfs in the garage! They're all covered with dirt, grease, and fork oil now! ;) VERY helpful!!

Got the job done. Everything back together, and even installed the freshly painted fender.

Now just to wait for the carb parts to get here!.... :-k
 
Hi,

Lookin' schweeet!

attachment.php



Thank you for your indulgence,

BassCliff
 
If one just wants to change the fork oil, on a set of forks, like mine, that were just disassembled and cleaned, CAN it be done while still mounted on the bike? In other words, is there an acceptable process for utilizing the drain holes and can this be done accurately??

Just mentally preparing myself for what I'll need to do when I hear the "I told you so's" in my head and decide that I should swap out the fork oil for a lighter weight... ;) Would love not to have to completely remove these again.
 
There is a small phillips head drain screw on the bottom of each fork slider. No need to pull the forks to change the oil.
 
Nessism said:
There is a small phillips head drain screw on the bottom of each fork slider. No need to pull the forks to change the oil.
Click to expand...

Oil will shoot thirty feet out of the side if you compress the forks with the screw out!
 
Put the plugs back in, remove the upper caps. fill will oil (the proper amount, of course).

Not sure if you have air caps on there. If you do, you can unscrew the air fitting and fill through that.
If not, you have to unscrew the entire cap, which will release spring pressure, so be ready for that.
Unless you hold up the front of the bike with some kind of brace, you only want to do one fork leg at a time. :o

There is a 'trick' to putting the caps back on, let us know when you are ready for that.

If you have to remove the caps, this is also the perfect time to adjust your preload.
How much does your suspension 'sag' when you are sitting on the bike?

.
 
Last edited:
razooki said:
Just curious after the oil shoots out all over the garage how does one fill them up with oil?
Click to expand...

Hi,

I had my forks off and measured the proper fork oil level. Lots of pictures in these guides (PDF files):

Fork Seal Replacement

It really doesn't take that long to drop the wheel, loosen the triple tree clamps, and slide the forks out. Then you can get a more accurate measurement using fork oil level rather than volume.


Thank you for your indulgence,

BassCliff

 
Last edited:
I have yet to hear a good argument, geometrically speaking, as to why the forks must be absolutely upright to get a good measure of the oil height. It seems to me if you take out the springs you could leave the forks on the bike, pump them a few times to get the air out of the lowers, compress them (in which case they'll be closer to upright), and measure at the center of the forks front-to-back and still get an accurate height measure. The level will be higher in the back and lower in the front, but should still be dead-on on the sides.

In any case, dead-on accuracy of the oil height is not as necessary as ensuring that you're close and the two sides are even. You're putting in different springs so your assembled oil level will likely be different anyway.

Just my thinkin'
 
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