My forks suck. I think they have been rebuilt, but I am not sure. They do not leak any fluid, but they stick in the compressed position when coming to a abrupt stop from time to time, they bounce like hell until about 30mph, and generally piss me off. Here they are: I took the cap off last night, and removed the top screw that the spring rides against: Under that was a small spacer. It's only maybe 1.5" and I do not think that it was making much of a difference. I removed the spacers on both of the front forks and went for a ride. The bike seems to have more sag, and the front may be a little softer, but it just aint gonna cut it. I know there have been a few threads about front fork upgrades in the past. But... Tonight I plan to change the fluid, and see if that makes any difference, but the fluid looked fairly new on the bits I removed. There are only 3 upgrades I have read about for these forks: 1. Progressive Springs I think a set of progressive springs will run around $90 shipped. Is this gonna make a $90 difference? What should the overall length of the stock spring be? Do they compress over time to a point that will make them choppy? 2. Emulators(sp?) I am totally in the dark about these, but I am guessing they are installed at the top of the forks to regulate internal pressure? Is there machining needed to install these? 3. Frork Brace. These are also roughly $90. Whats the best place to start? Can a later better set of forks be fitted without much modification? Are there any other options?
I'd first change the fluid (you were there already.) Maybe use a different weight oil? Then get the legs aligned. Someone else should tell you how, it's difficult for me to clarify in Dutch, let alone English It makes the forks work with a lot smoother, could cure both the sticking as the pogo (or are they sticking in there as well, could both be.) Getting them aligned isn't difficult, explaining how to is... Heavy duty / progressive wound springs could make a difference. On my 60/6 I had them in the stock forks (drum brake.) I was impressed by the huge difference they made compared to stock. But now I have a dual Brembo fork in the /6 and when changing from stock springs to the same progressive wound ones I couldn't really tell that much a difference. It's all in how worn out your springs have gotten over the years I guess, so start with checking that (length would be the thing to measure, see a manual for reference.) The stock /6 on mine were a bit short, so worn out. No idea on the springs that were in my current forks. Putting a spacer in there doesn't make any difference on the way the spring acts, it only puts a bit more pressure on the springs causing a bit less sag when mounting the bike, as you have discovered. Now, let's hear the real experts, for I only tell you what I've experienced and heard from others
My suggestions: 1. Change the fork oil. Experiment a bit with viscosity and amount. 2. Check your fork springs - don't assume you have stock springs in there. Riding w/o the spacers will only make it worse (and dangerous). T.
1. Re Progressive springs: most think that these are worthwhile. Do you know what you have? (incidentally, the springs should stick out a couple of inches when you take off the caps, which are being forced up while you unscrew them.... am I not seeing that in your photo?) 2. Re emulators: cannot fit them to these forks. 3. Fork brace: might make some difference if you ride hard. 4. Other front ends: yes, there are a number of things that can be done, starting with a later generation of BMW front ends on into other bikes' front ends. The later/better BMW doesn't transfer easily with spoke wheels, though. First thing you should do is get yours up to snuff... what you describe is not right, at any rate. Start with the easy stuff, including fluid replacement and fork alignment. Your forks sticking "down" is not normal, for sure. There is an excellent article for how to align the forks, but it so incredibly anal about everything that it makes it more than a bit scary. Read this and weep Not being particularly obsessive, this is what I did, and it worked just fine. I don't race and I don't obsess: Remove the handlebars and all the stuff in the way. Remove the fork caps. You can leave the springs and fluid in there. Remove the center nut holding the triple tree. Be sure not to torque against the steering stops, as described in the article, either during dis- or assembly. You should now be able to lift off the top triple, which is just a flat plate. This is a good time to check for steering head bearing for notchiness and tightness. You want the steering to turn easily, without any notchiness or tendency to stick in any one place. Too loose or too tight is not good. You will have the stem head nut exposed, so it can easily be loosened/checked/tightened at this time. Next, undo the pinch bolts at the bottom of the triple tree, the big aluminium jobbies that clamp onto the tubes. These will be very tight, and you may have very gently pry the clamp apart: I did this by pulling the bolts completely out, and tapping a big screwdriver into the slot from the side. You will find that the forks will now slide up and down. You don't want the clamps to be too loose, just enough to be able to move the fork tubes. Now you go the axle, and make it ready to pull out. What you are looking for here is for the axle to slide easily back and forth: if one side or the other is twisted, or not in the same plane, the axle will bind and make it hard to move. So gently move, twist, each of the fork ends to get the axle to the point where you can slide it in and out without undue difficulty. If the axle has not been removed in some time, go ahead and pull hard to get it out, clean it up and lightly grease it, and put it back. You are using the axle as the alignment tool and alignment checkpoint. It will never be so easy as to just slide out ever-so-easy, you are not looking for that, but it should be easily pullable with the tommy bar. You can do this with the wheel in place, which makes it a little more difficult, or you can pull the wheel and set it aside. With the axle in place, put the top triple back on. The two forks-plus-axle may have to be slid up or down a touch so that they meet with but do not deflect the top triple. Note that they are machined to fit into the top plate. The top plate should lay flat, not be bowed up or down, when you push the axle/wheel/fork assembly up to it. Once the assembly is up to, and inserted in, the top plate, firmly snug up the big aluminum lower triple: these are what hold the assembly from going up and down. Snug the top of each leg to the top triple plate. Go back to the axle, see that it still pulls out pretty easily. Lower the bike onto the ground, bounce and compress the front end. Recheck axle, then firmly tighten the axle, then the lower triple, then go the top and torque it up. Be sure to not torque against the steering stops, as they can twist the assembly. Drain/change fluid, take it out for a test. I like to hand roll the bike and slam on the brakes as I push down, to get a feel for how easily it compresses. I have added a little more fluid to make the front end less squishy. Lots has been written about it.
As said allign your forks, but yes, buying progressive springs will be the best thing you could have possibly done (besides good tires/brakes) to keep yourself alive in a panic situation.
Thanks Bob! I will try that tonight. I dont know jack about forks, but the choppy ride and sticking certainly seems that it could be caused due to binding/misalignment. That doesn't cost anything, and seems like the right place to start. Thanks for taking the time to explain the process.
Please confirm that the spring WERE being held in by the cap? Am unsure, and the photo makes it look like the spring top is 'way down in there.....
Drain the fluid and look for chunks- the bumper at the bottom of the forks has a habit of turning into goo over the years and plugging up everything inside. The new replacements from BMW are an updated formula so the problem shouldn't reoccur. Throw some progressive springs in there and experiment w/ 5-7.5 weight oil. I've found straight 10w too heavy. Good luck
That spring had very minimal pressure on the top nut that holds downward pressure on the spring, even with the spacer, as in I could thread it on with 1 hand and little effort. The bike however was on the center stand and that puts the front tire about an inch off of the ground. If there should be more pressure than that with the fork completely extended, my springs may very well be wore out. I will try to find the correct expanded spring length and measure it when I do the alignment. I ain't even asking about fork oil.
Sounds like your springs are toast. Go with any brand fork oil you can get at your local shop or parts place. As mentioned before 10w is pretty heavy. If you are a light guy, try 5w; if you are a heavy guy like me, mix 5 & 10w 50/50 to get 7.5w. You are prolly gonna be amazed at the dirty smeg that comes out of your forks.
First off, I'd recommend stock BMW springs. They're better quality, plus cheaper. Also, there are maybe three different strengths (or more) to choose from. That's the way to go! The stiffest ones came on the RT. The spacer is for pre-load - pretty much the same thing as adjusting the rear shocks for extra load. Ideally, the front end will sag 1/4 or so, of the total travel. Check total length unladen, then sit on it and the distance should be 1/4 to 1/3 of the total travel distance less. Add the spacer if it sags more than that, remove some if less. Very important - align the fork tubes! Emulators - these are actually more sophisticated dampers than the Brembo front end, and it's difficult getting emulators to fit in there properly. I've heard of it being done, but haven't ever gotten feedback that it was worth the trouble. Fork braces are nice, but may not be needed; depends on how you ride, your weight, skill level, etc. I like 5wt fork oil, but when using stiffer springs, stiffer oil is needed to damp the extra forces. Experiment till it turns out right.
According to Clymer a R100S front spring free length should be 22.32in, or 567mm. Mine measure 20 5/8". I believe that these may be from another bike or front end. I think the bike had front end damage at some point, and the front is pieced together. It has 2 different types of fork parts (uppers and lowers). I drained the oil. Can AW 32 hydraulic/jack oil be used? The guys at the parts store, of course, had none of those listed in the manual, and suggested that. Monday I am going to order progressive springs. The set Huckys has is 555mm. Thats 12mm shorter than what is specified, but I can put a spacer in to adjust the overall length to compensate. I hope. Planning a ride to Barber next week...
I second the comment above that the bottom doughnut could be smegtoast... this is what I found when I pulled mine apart: The spacers (what they should look like, as opposed to the disintegrated smeg above....) are the white donuts on the left: Re fork fluid: have heard of folks being quite happy using the red ATF!
nice post. im in the same situation with my r100rt-- i just did a little 100 mile ride and i thought my hands were gonna fall off.
Depending on what you're used to, you can get the forks decently compliant by the proper fork oil, and alignment. Like everyone else has said, time to strip em down and rebuild them. While they are apart you need to make sure one or both of your fork tubes isn't bent. Fresh oil, and spend some time aligning them when you assemble the front end. They'll never be as compliant as modern forks, but with some work you can get them to an acceptable level.
give me a shout if you need a hand. it's been a few years since i've done a set of forks from that era but i can at least add to your confusion if nothing else.
AW 32 is approximately a 10W oil....I'm going to try some in my /6. I work for an oil company and we sell 32 in bulk so it won't cost me anything.
Modern fork engineering has adopted the theory that progressive springs are not working as was originally believed. The idea was to create a very plush ride at the first few cm's of fork travel but as the progressive winds of the spring becomes coil bound the rest of the fork travel is firmed up to prevent the forks from bottoming. The problem with this Cadilac type of ride is that the static sag is excessive and the nose dive under heavy braking is nerve-wrecking, and not to mention the wallowing feeling when going fast into a bend with a bump or two. Manufacturers have been installing linear springs for the last 15 or so years. This type of spring behaves better under braking, feels firmer in the bends although it might also give more feedback from the road surface making the ride slightly less comfy but so much safer. If you need to replace the springs rather fit linear springs that is firmer than the stock springs. The over all length is not important as long as the springs won't become coil-bound before bottoming. You can always fit a spacer of the appropriate length. Pre-loading of the springs is normally around 15 mm.
Blake, I am planning on rebuilding the forks next week, after my trip to Barber. I will pick your brain if I get stumped. I have ordered the progressive springs from Huckys they are about 2" longer than the ones I removed. I will prob install a small spacer and increase it in small increments to suit my riding style. I drained the fork oil and inspected it. The oil was in good condition with no rubber pieces or chunks to speak of, however it was pretty dark. I have put about 6k miles on the bike since I have had it, and prob. should have changed it by now anyway. If I get the springs by Thurs. I will put them in, refill the oil and try it out on the way to B'ham and back. If not I will throw the old springs back in, and go anyway. One thing I have learned about old bikes that I have owned, is that if I wait until everything is right to ride it, it never gets ridden. If I had to ride 500 miles on a bike with no issues I wouldn't know what to do with myself.
