Front Fork Phobia - 1980 GS550L

[ddaum]

Hello again everyone.
Here's the deal:

1980 GS550L, 26K mi., nearly all stock. Only had the bike about a month. I just replaced the 25 year old stock rear shocks with some progressives, and they were a GREAT improvement. While out testing/riding today the stiffer rear suspension really opened my eyes to how horribly spongy the front forks are. The scary thing is that while braking, (with both brakes, or just rear) the bike DIVES to the point that I have to brace myself with my arms and hands on the handle bars. Keep in mind that this is not heavy braking. Now, I'm a good mechanic, but this being my very first experience with motorcycles is making it a bit tricky for me. I referred to my Clymer, but don't want to do a complete rebuild of the forks if I don't have to. (I live in an apartment with no garage.) The fork seals do not appear to be leaking, but this may be because of low oil levels in the forks. I've searched the forum and read threads about forks, but they were mainly newer or bigger models, so no real help there.

1. Is there an air pressure requirement for these particular forks? There are no shreader valves up top, only what looks like a large chrome bolthead at the top of the forks. If so, how do I add air?

2. Is there a way to check the oil level in the forks and fill them while on the bike? Like I said, the seals look good, but I can't be certain without making sure there is oil in the forks to begin with.

3. If someone can help me with a way to do this, What oil should I use? I'm a heavy guy (6'2" - 255lbs) and I heard that heavier oil should be used for heavier guys.

I really want to stiffen the front up to match the rear now, and get rid of this diving action when I'm braking. (Believe me, I'm braking correctly.) It's really spongy and uncomfortable to ride while stopping. Any help is greatly appreciated!

[duaneage]

If there is no air valve you don't have air shocks. I do and I like them although most people convert to progressive rate springs and forget about air.

You may need to replace the seals. Are there any leaks?

The fluid is measured (typically) with the forks off, straight up in the air, springs out, and tube compressed. My 650 has 7 oz of fluid which tanslated to about 6.25 inches from the top of the open fork tube to the fluid. Both forks must be within 1 mm of each other so it is important to do this right.
Some people drain out what is in there into a measuring cup, flush out the forks with solvents, then pour the same amount plus a tiny bit more into each fork and call it a day. I measured mine and it seems to work OK.

Try 15 w fork oil and see how it goes. you may be heavy but the bike is not really, total weight on the forks and the oil is not as great as a 1100. Some people are going to tell you to use trans fluid to save money but I think that 7 bucks for a quart of fork oil (and you'll have enough to do this twice) is not gonna break the bank.

[Hotblack]

It's very possible that just changing your fork oil and cleaning the forks out will help your front end out, you never know if previous owners ever touched it or not. I agree that spending 7 bucks on a bottle of fork oil is probably worth it, and you know exactly what weight you're putting in. I run 15w in my 550 and it's fine. I'm 6'2 220 lbs. Actually when I put the 15w in I weighed almost 240 and it was fine then too. Keep in mind these are basically the same forks used on the big bikes, so a lighter oil is logical for a bike weighing 100 lbs or more less.

[SqDancerLynn1]

Good chance the forks are leaking Should have 8.5 ? ozs of oil in the forks. Be carefull taking the top plug off it will have some spring preload depending on condition of the springs. If their is very little preload ?? You can use some PVC pipe to make a small spacer. 3/4-1" to start

[Nerobro]

My money is that your forks are eitehr low, or empty of oil.

People reccomend NOT running any air in the forks. I'm apt to agree with that.

Fix the fork oil problem. And set your front sag properly. While you don't have a preload adjuster, what you can do is add pvc spacers on top of the fork springs to set the proper sag. I will be doing this myself soon ;-) I'm sorry, but 3" of static sag is a little to much for my tastes. It's not like I bottom out my forks much, but it would be nice to have that travel to work with when heeled over into a corner.

[ddaum]

So, should I remove the forks to do the maintenence?


Thanks for all the replys. I guess I'll tear into her again this weekend. If
anyone else has something to add, please do, especially if you have experience on my particular year and model.
Thanks again!

[Nerobro]

I'd do them in place. NO reason to mess up what is most likley good alignement :-) Also the tripple trees do an awesome job at holding the forks steady for you.

[jimcor]

The 80 550L is not an air pressurized fork.

Do not bother trying to check the fork oil level. Change it. Don't fool with the seals till you know they are leaking. Fork must be disassembled and sliders (lower legs) will need to come off for seal replacement.

Otherwise, forks can remain on the bike to change oil or springs. You'll need to prop up the bike under the engine while it is on the centerstand once the plugs and springs are removed. or else it will dive forward. I use wd-40 to clean out the sliders.

According to the Clymer manual the forks on the 550L take 217cc or 7.3oz of SAE 15 oil. I don't spend $7 a bottle on fork oil. I just use 15w50 motor oil.

You can make a preload spacer, as noted, from PVC pipe. I would try this before going to Progressive Springs. The 550L is always going to be a diver under braking.

Using Progressive Springs on the '80 550L will require you to either make a spacer to replace the smaller of the two fork springs per leg. Or going contrary to Progressive's instructions to remove it and running without a spacer and leaving it in. This is what I did. The front end is stiffer this way, and to somewhat compensate for the harsher ride a lighter oil and somewhat less oil capacity could be used.

Other tips: Make sure you have the proper size socket to fit the the cap nuts before you start this job. A big adjutable is not appropriate. You'll want to do this while bike is on centerstand and engine is propped up, and forks are fully extended. You'll be pushing against spring pressure when you go to put the caps on. Care must be taken so the fork legs or cap threads are not cross threaded.

Unbolt handlebars, move back to tank. Use rags and bungee cords to hold so your tank is not damaged.

This should have been the first 'other tip'. Do the pumping with the bike on its wheels. Drain oil one leg at a time before you remove cap nuts. This way you can pump the remaining oil out after it quits draining. Careful it's a messy job. Use a plastic bag over fork drain to prevent oil spray from going everywhere. Use duct tape to hold it if you're doing the job by yourself.

[ddaum]

Jim,
Thank you for all the great information. I think I can tackle this one, but i do have a couple more questions:

You can make a preload spacer, as noted, from PVC pipe. I would try this before going to Progressive Springs.

1. Can you tell me exactly what you did?
2. Can you remember the diameter and length of the PVC, and tell me where to insert it?
3. Do I remove the smaller spring when istalling a preload spacer or leave it in?
4. Where do babies come from?

Thanks!

[jimcor]

What I did was go to the Progressive Springs and still used the smaller spring with the new springs.

Progressive says to not use the smaller spring. But the thing is the springs are made for the 550 line and it turns out the L forks are longer than the E. So you either must make a spacer or you have lots of sag or keep the small spring and have stiffer forks. I wish I would have saved the money and just added the spacer.

You want to keep that smaller spring even with a spacer using the original springs.

Buy a couple of washers that are wide enough to fit in your fork tubes without interference, this will fit on the top of your springs and support the spacer you make. Select PVC pipe that will fit in the fork and the caps. Before you change fork oil, with bike on centerstand and forks fully extended use a marker and note where forks enter the slider. Take bike off center stand and mark where bike sits on forks now. Measure the distance between marks. This is where I would start with the length of my spacer. This is just the way I would do it. Don't really know if there is an 'official' way to preload springs. Couple, three inches maybe. But that should make a big difference in ride.

[ddaum]

Thanks for the explanation, that's probably where I'll start.
So, should the spacer go between the large spring and the small spring, or between the small spring and the cap?

[jimcor]

put it on top of both sprigs.