Installed Progressive front springs on a 1980 450S? How big of a spacer did you need?

[seinwave]

I'll be ordering a pair of Progressive front fork springs (item number 11-1109) for my bike soon. The documentation I can find says you'll need to cut some PVC or similar to length to act as spacers inside the tube. I'd like to have that done before they arrive so I can make the process as fast as possible.

My starting point will to get the new (unloaded) spring + new spacer length to equal the old (unloaded) spring length (there doesn't seem to be a proper stock spacer). It's pretty easy to find the length of the new springs (19.75"), but all I can find is the service length limit of the stock springs (19.5"). I'm guessing this the stock springs, when not worn, are somewhere pretty close to that, in which case I won't need a spacer (and will just have a little "extra" preload over stock from the 0.25" difference).

Has anyone installed these springs on these bikes? Did you need to manufacture a spacer of any kind, and how did it go?

Another question: the Progressive instructions specifically mention that if your forks have a damper rod with a small spring on it, you shouldn't use it with the new springs. The 450 does appear to have a small spring on the damper rod, but so does the 850G referenced in the seminal tract by BikeCliff (https://gsarchive.bwringer.com/storagecliff1/images/Install_Progressive_Fork_Springs.pdf) and there's no mention of the damper rod at all. I think the Progressive instructions must be referring to an extra spring between the damper and the main springs; is this right, or do I need to fully remove the damper?

 

[Nessism]

The spacer length depends on your weight, and the amount of "sag" while you're sitting on the bike. As a starting point, I'd make the spacers so that they are flush with the top of the fork tubes when the fork is fully extended. The cap will provide about 1" of compression when unladen.

 

[seinwave]

That's exactly what I'm going for to start with; on the videos I can find it seems that the stock springs are either at or just above the top of the fork tubes (i.e., where I want the new springs to be) after the caps come off. That's why I want to know the actual (unworn, unloaded) length of the stock springs, so I can prefab some spacers to make the new springs match that length. Seems likely that like the new springs are longer and will be above the fork without any spacer, so probably won't need any spacer at all (until I start tweaking for sag).

 

[bwringer]

...
Another question: the Progressive instructions specifically mention that if your forks have a damper rod with a small spring on it, you shouldn't use it with the new springs. The 450 does appear to have a small spring on the damper rod, but so does the 850G referenced in the seminal tract by BikeCliff (https://gsarchive.bwringer.com/storagecliff1/images/Install_Progressive_Fork_Springs.pdf) and there's no mention of the damper rod at all. I think the Progressive instructions must be referring to an extra spring between the damper and the main springs; is this right, or do I need to fully remove the damper?

Yes, you cut spacers to suit once you have them in hand. Nessism's advice is a good place to start. Adjust to taste.

The springs will come with a hunk of appropriate PVC. You won't know how long to cut them until you have everything apart, so there's no point in cutting the spacers beforehand. A tubing cutter, like you'd use for water pipe, does a very nice job of cutting PVC.

Something like this guy:
https://www.homedepot.com/p/Husky-1-1-8-in-Quick-Release-Mini-Tube-Cutter-80-784-111/303666106


As to the instructions, Progressive is talking about setups where there are two springs on top of the damper rod instead of one long one. They're telling you that the new Progressive spring replaces both springs.

As far as I can tell, your bike only had one long spring. Remember, one Progressive part number fits a skrillion different bikes, so the instructions cover a lot of possible situations.


What you might be talking about is a small spring, maybe an inch or so long, that is the top-out spring. Do NOT remove the top-out spring. This is the smallish spring that goes around the damping rod and underneath the head of the rod.

Part #12 here:
https://www.onlinecycleparts.com/oemparts/a/suz/50d3f0aef8700230d8b4b94b/front-fork-model-t

 

[seinwave]

That's what I assumed re: the damping rod, thanks for confirming. I figured the Progressive instructions are referring to a small section of spring some bikes have above the damper, not the one on the damper itself.

I understand I might need to finetune spacer length once the springs arrive. I am asking for the stock spring length so I can at least have a first-guess when they arrive. Do you have any information on that?

 

[bwringer]

The Clymer shop manual (found here: https://gsarchive.bwringer.com/ ) gives the following service limits for the stock fork springs:

So they're toast at 496mm, but that doesn't tell you how long they were from the factory, and a few other things you'd need to know to guesstimate a spacer length.

I haven't worked on a 450 in a long time, and we didn't keep any records of the spacer length. Maybe someone somewhere with a 450 who happens to weigh about the same as you happened to wrIte this down...?

 

[RichDesmond]

Keep in mind that you will most likely want to have the new total spring/spacer length a touch shorter than the stock setup.
The stock springs are very soft, and Suzuki compensated for that (sort of) by using a lot of preload. With the new, better, springs you'll need less preload, which means less total length.

Ed's advice about starting flush with the top of the fork tube is usually about right for bikes with plain non-adjustable fork caps. Hopefully the new springs are short enough that they don't stick up above the top. At 19.75" I'm guessing that they will be close to the top but a little below.

I'm not too far from you (Prince William County) so if you have more questions or need a hand let me know.