1980 GS750E progressvie fork springs

[azr]

Hey all. Trevor and I put new progressive fork springs in last night. We followed the instructions from Progressive which said to put in the manufacturers amount of fork oil, which is less than their max oil height. The instructions also said his bike does not need a spacer "or might need a spacer", lol. We first did it without the spacer and the forks nearly compressed all the way. We then cut a 3" spacer which brought the spacer to the top of the threads for the fork cap, it's better with less travel but still VERY soft. We didn't have PVC pipe so we just used the old spring to cut a spacer. So...our thoughts are, if we use PVC instead of the spring that will make things 'stiffer' and if we make the spacer come 'above' the threads by maybe 3/4" making the whole spacer 3 3/4 inches long that should also make things stiffen up. I just want to make sure we're on the right track here as we were both really shocked how much the forks compressed at first, I really thought it would have been way stiffer even though there was no spacer. Of course I didn't measure the length of the original two springs compared to the progressive as that probably would have helped to have a starting point with the spacer. But if I have things straight in my head, doesn't the spring control the fork travel and the spacer controls the sag?? Any and all suggestions always appreciated.

[Nessism]

You used a chunk of spring instead of a spacer? If so, then you lowered the spring rate, which may explain the problem you are experiencing.

With Progressive springs, you typically want the spacer equal with the top of the fork tube. When installing the cap you will then be compressing the spring about 3/4" due to the cap depth.

[almarconi]

You want to use a piece of heavy wall pvc pipe, I think its schedule 80, grey in color for the spacer. I cut various lengths and used a zip tie on the fork tube to measure the sag. The amount of sag you want will depend on your weight and riding style. If memory serves me, I've got about 1.25" of sag. The front end is stiff but the it handles much better than stock.

[azr]

We only used a section of spring because we didn't have the right size PVC pipe at the time. Ed, the difference with Trevor's bike is his thread for the fork cap is a fair bit lower than normal. The thread is probably 1 1/2 - 2 inches below the top of the fork, so we were just measuring to the top of the thread inside the fork to get our spacer length. We'll swap out the spring for PVC and maybe add 1/2 inch above the thread and see what we get. Thanks for the help guys.

[81ZUKI75]

Progressive Fork Springs

I've been running Progressive springs since 2009 in my 1981 GS750E. A quick look at the Progressive site shows me the same part number for the '80 and '81 models. If you just look at the gallery pics you'll see that the forks are different. Even though they are both "leading axle", the '80 model's forks extend further below the axle than on the '81. That and the fact that sag in based on rider load is why their spacer recommendation in pretty iffy.

From my notes, when I installed mine: Progressive Springs OAL = 20.75 (OEM OAL = 21.375), 1" Spacer, 15W oil, Cleaned damper assembly

In order to get the sag right, I would guess yours would need more spacer length.

[azr]

So, today Trevor cut a 3 1/2 inch PVC spacer, which brought the spacer height to 1/2" above the start of the fork cap threads (remembering that the start of his fork cap thread is actually down inside the fork by approx. 2" or so). He sat on the bike and again the forks are wayyy to soft, the sag alone is close to 5". We can increase the PVC spacer but at some point we will not be able to get the fork cap on, but really I don't think the forks should be this soft. So as of now we have new progressive springs with a 3 1/2" PVC spacer and we filled the fork oil to the OEM recommendation of 227 mm from the top of the fork and the forks are waayyyy too soft. Progressive recomends going with the OEM oil height unless it goes higher than their max of 140mm..so..we stuck with the 227mm but should we maybe go to the 140mm?? we can easily try 'probably' increasing the PVC spacer another 3/4" or so and still be able to get the cap on but I doubt that will do much as it didn't improve things much at all switching from a 3" SPRING spacer to a 3 1/2" PVC spacer. Hey 81ZUKI75 I'm not sure if you remember the oil height on your 81 750 or not??

[81ZUKI75]

Hey 81ZUKI75 I'm not sure if you remember the oil height on your 81 750 or not??

The 227mm (8.94") is the same as speced for the '81 (per my notes). I used 15W fork oil and balanced the level in the forks to 8.8" down from the top and have run that way for about 5000 mi. Remember: more oil = higher level = lower number = stiffer suspension...and the opposite is true. For some reason, which I have long forgotten, I put the level at 7" down from the top originally and it was very harsh Learn from my mistake

I don't think the oil level is going to effect the sag (until the level is so high it hydrolocks ) so keep working on that problem. Let us know what you find. Was the overall length of the Progressive springs as I posted earlier?