Front suspension Bottom Out

[anson45]

No one has recommended Progressive Suspension fork springs. They made a big improvement in my 1983 Venture. How would they compare against the Race Tech straight rate springs if that was all a guy changed? Has anyone tried both? I'm not using my FJ for track days or even hard riding, mostly just touring.
Thanks,
Anson

[Pat Conlon]

The front end path I've traveled in my years with my FJ was:

1) Bought my '84 new...played around with heavier fork oils, different anti dive settings.
Result: Marginal improvement

2) Installed progressive springs in 1986. Result: A little better, but initial fork dive was still there.

3) In '89 I removed the progressive springs and installed straight rate springs and Race Tech cartridge emulators. Result: Much better than the progressive springs. Fork dive was almost eliminated with the 1.0kg straight rate springs and the emulators softened things up to be acceptable.

Fast forward 14 years...

4) In 2004 I removed the Race Tech emulators and installed Honda CBR600 F3 cartridges. The real stuff, Race Tech gold valve compression cartridges and rebound cartridges. Jon Cain made special adaptor hats to fit the Honda cartridges in the FJ lower slider.
Result: Holy Shit....cartridge forks ROCK...I am sold on cartridge forks. A different Galaxy than damper rod forks, even with emulators. Firm, yet soft. It took a couple of try's with the shim stacks but once dialed in cartridge forks were a huge improvement....huge.

5) in 2007 I installed some 1992 FZR1000 up side down (cartridge) forks....and, yea baby, the chicks are back.

That's where I stand today...

My point is....if you want to go backwards in time, fine, install progressive springs or emulators. However we are in the 21st century and you have much, much better options available to you...

If the RPM IAT fork valves had been available in 2004 when I converted to cartridge forks, things would have been different.

Hope this helps...

[movenon]

I went with .95 straight rate springs and they work good.  I wouldn't go back to progressives.
George

[FJmonkey]

RPM fork valves, .85 straight rate springs, and I am very happy with the front end.... 

[chefmatt]

So today I did the fork overhaul....Loosened the bolts holding the clutch and brake cylinders to get access to the top caps of the forks. lifted the front end using a hoist. The caps came off quite easily using a large bolt as an allen wrench. Drained the fork oil - it was as black as crude oil. Left fork drained 10.2 oz, right almost 12 oz. Probably this had alot to do with problems in the first place. After letting oil drain, used 15w fork oil - 12.2 oz per fork......also instead of replacing springs, we put in Harley Davidson spacer springs. they fit perfectly . The Harley springs are approx 1.5 inch stacks, and the same diameter as my fj springs. We were originally were going to use pvc pipe as spacer, but the pipe diameter was about .25 to large. Didnt replace seals or wipers, this was supposed to be a quickie job. Ha! Nothing goes as planned. The damper rod was hell getting back in all the way - it would slide in to within an inch or so, but we couldnt get it down close enough to screw the fork caps back in. after about two hours or trying to figure it out, lots of turning the fork cap trying to align the damper rod, I finally used a large screwdriver inserted into the preload adjustment slot, and gently tapped the damper rod down. Worked fine. Screwed the the caps back on, re-assembeled everything, and took it for a ride. The ride is much stiffer than before, I can really feel the road though the bars. small bumps no longer bottom it front end out, feels much more stable. Job would have taken an hour max if we didnt get stuck with the damper rods.....thanks for the help fellas!

[FJ_Hooligan]

The damper rod was hell getting back in all the way - it would slide in to within an inch or so, but we couldnt get it down close enough to screw the fork caps back in. after about two hours or trying to figure it out, lots of turning the fork cap trying to align the damper rod, I finally used a large screwdriver inserted into the preload adjustment slot, and gently tapped the damper rod down. Worked fine. Screwed the the caps back on, re-assembeled everything, and took it for a ride. The ride is much stiffer than before, I can really feel the road though the bars. small bumps no longer bottom it front end out, feels much more stable. Job would have taken an hour max if we didnt get stuck with the damper rods.....thanks for the help fellas!

Bad news.  You have a problem.  You still missed the damper rod hole.  The reason it's no longer bottoming out is that it's now binding on the damper adjuster rod.  Once you get the rod properly aligned, it will drop into place (or at least drop on top of the spring/spacer).

Another thing to consider is spring mathematics.  I'm not sure what Harley "spacer springs" are, but if they are springs then you may need to reconsider and get the proper diameter PVC and use it for an actual solid spacer.  

When you stack 2 springs together like you did, the combined spring rate is less than the rate of the weaker spring.  So, "in theory" you may have actually reduced the effective spring rate and once you get the damper adjuster rod properly installed the bike may actually be less sprung than before.  The new oil will definitely help, but the spring rate may not be what you really want/need.

[chefmatt]

Thanks for the info..I hope you are wrong tho..yikes.  No
Matter how I tried to guide the damper rod that last inch to meet up with the threads in the fork cap, couldn't get it. Until I tapped it down...very gently mind you, didn't take much at all. Any tips on alignment of the rod? Thanks

[racerrad8]

Thanks for the info..I hope you are wrong tho..yikes.  No
Matter how I tried to guide the damper rod that last inch to meet up with the threads in the fork cap, couldn't get it. Until I tapped it down...very gently mind you, didn't take much at all. Any tips on alignment of the rod? Thanks

He's not...

You have gotten the adjusting "D" shaped rod wedged into one of the outer oil flow holes.


You have to center the rod when inserting and make sure it is clocked with the "D" shaped hole in the center and it will slide right in.

Randy - RPM

[fj1289]

Another thing to consider is spring mathematics.  I'm not sure what Harley "spacer springs" are, but if they are springs then you may need to reconsider and get the proper diameter PVC and use it for an actual solid spacer.  

When you stack 2 springs together like you did, the combined spring rate is less than the rate of the weaker spring.  So, "in theory" you may have actually reduced the effective spring rate and once you get the damper adjuster rod properly installed the bike may actually be less sprung than before.  The new oil will definitely help, but the spring rate may not be what you really want/need.

OK - I am having a problem getting my head around this one.  Can you explain it further?

Is the effective spring rate lower, but you've effectively added preload?  I thought this was how they originally did "progressive" springs -- two different springs stacked on top of each other?  

Thanks!

[FJ_Hooligan]

Springs in series act like resistors in parallel.  If you put 2 springs in series (stacked together) with each spring having a 2 pound/inch rate, the effective rate of the combination will be 1 pound/inch.

I'll bet the Harley spring spacer is a short spring with a fairly low spring rate.  Adding this would give a nice cushy initial rate.  After a bit of movement, the spacer spring will coil bind (and start acting like a solid spacer) and the rate would then go back to the main spring rate.

It adds preload, but then you would have done that anyway with a solid spacer.  The FJR used this stacked spring trick on it's rear shock.  In comfort mode, two springs were stacked up to give a softer ride.    In sport mode, the two springs were isolated from each other and the shock only used the stiff spring.

A progressive spring is essentially a bunch of different rate springs stacked up on each other.  Initially the spring is nice and soft.  As the spring compresses, the lower rate coils bind up and the higher rate coils begin to stiffen up the ride.

Clear as mud?

[chefmatt]

Are there more than one of those slots for the damper rod? I felt that it went through that slot easily...

[racerrad8]

Are there more than one of those slots for the damper rod? I felt that it went through that slot easily...

Yes, look at the picture I posted earlier.

The issue with this statement;

I felt that it went through that slot easily...

is this statement...

The damper rod was hell getting back in all the way - it would slide in to within an inch or so, but we couldnt get it down close enough to screw the fork caps back in. after about two hours or trying to figure it out, lots of turning the fork cap trying to align the damper rod, I finally used a large screwdriver inserted into the preload adjustment slot, and gently tapped the damper rod down.

That last inch is the range the "D" shaped rod contacts the damper rod at the bottom and you used a hammer to install it.

It will slide right in without any force when properly installed.

Randy - RPM

[andyb]

Let's confuse things further!  Swap to a set of forks with topout springs (or whatever the hell they're called) from something newish!  First used I think on the YZF-R1, screwed with people setting traditional sag until they were more widely understood....