In an attempt to keep the fillings in my teeth and eyeballs in my head as I ride the alleged "highways" of New York State I am looking at doing some upgrades to the forks on my '94 K75RT.

I've purchased a set of Race Tech Gold Valve emulators and plan to install them before the spring riding gets into full swing.

My questions for the inmates are: Have any of you installed these devices? If so, did you use the OEM springs or go with the recommended Race Tech springs? How did the springs you used work?

Any tips on doing the job? Are there any issues in removing the damper rod? It sounds like it's screw is locked with the dreaded red Loctite.

This is interesting - I've looked at those emulators before and they seem a great idea. I'm sure you'll have lots of fun setting them up, but once you do.....

As for the dampers: undo the bottom bolts before you remove the fork tops - the spring pressure will stop the dampers turning as you loosen the bolts. 'Pologies if you already knew that (I found out the hard way, many years ago).

Springs? Don't fall for the he-man 'rock hard' myth. You need compliant springs and good quality damping. The emulators will give you high and low speed compression damping which should be the thing that delivers good handling - especially on bad roads. The emulators were conceived for off road biking, which is where the provision of high speed damping really came into its own.

I bought a set of those when I worked for a motorbike parts distributor a coupla years back. I never used them. I was looking through the company's street catalogue and spotted them, paid salesman price, which was cheap as chips. It was an impulse. Then I sent them back before I quit the job a year later. Shame, really. They might have been fun to play with.

A local suspension company, KFG Racing in Auburn, Washington, buy them all the time. They think they're the stink.

Chris, the instructions mention loosening the screw prior to removing the cap. Since they seem to be generic it's good to have you confirm that.

Yes, the idea of high speed compression damping sounds very attractive. There is an 8 mile stretch of road that I travel to and from work that is over 55 years old and hasn't seen a lot of maintenance in the 30 years I've been traveling it. At 65mph, even a half inch difference between the slabs jars the forks.

As I understand it, the stock springs are progressive wound and have a final rate of .74kg/mm. Race Tech in their super secret setup instructions recommend a .85kg/mm single rate spring. I am going to use the original springs at first. I'm hoping they will give a nice plush ride. However, I suspect that the higher rate spring will be needed to reduce the front end brake dive. That dive has resulted in some pretty scary situations that I would like to avoid in the future.

I will probably be installing them in a couple weeks, the weather is too nice right now to lay up the bike and there are still a few items I need to get to do the job. If there's any interest, I'll try to document the job.

      Put emulators in my 94 K75S two years ago, this was my second set and I was impressed both times.  The install was straight forward after sorting out the exact fork ordering and having to return the first set for the correct one.  These bikes have many different forks installed over the years and models and RaceTech needed the I.D. dimension of my fork to get the right one, they where good to work with.  Here is my thread with good help from some inmates here on getting the correct fork for my bike.
Improving a K75S front end (k100-forum.com)
   As far as the springs I would get a new set,  RaceTech says the stock spring on your RT is 74 Kg/mm and recommends 84lb/mm for my 200 lb.  When I bought the bike the front end easily bottomed out, not anymore, it also wobbled through a curve and would not hold a line, not anymore.
  Above is the Set Up Sheet for my install.   Lots of info here, note that there was an   adaptor required (about $16) and a note saying not good with the stock spring or a progressive spring. 
   To get the bolts out of the bottom you need an allen socket 3” long and an impact gun, cleaning the old lock tite out of the female threads needs a stubby pick. I used blue lock ite .

TTR, thanks! Your setup sheet is the same as mine for the Showa forks. I have the FEGV S3801 kit as well. One thing that is nagging my brain is that I think the RT has something like 2.5" more fork travel than the other K75 models. It has me wondering what surprises I will find when I do this. I probably need to spend some time with the MaxBMW fiche this evening checking fork p/n's.

Will head over to the local NAPA to get the Allen wrench for my impact wrench. Did you have to heat the screw to loosen the red Loctite?

The instructions mention making 15mm adapters by cutting off pieces of 3/4" PVC pipe which I have done. The emulators are about 1mm smaller in diameter than the pipe, and I've heard of others using 3/4" PVC pipe for spring spacers. I guess I'll find out if they'll work when I get the forks apart.

Did you try the stock springs with the emulators? I was going to give them a try before dropping the cash for the Race Tech units. I was going to see if I could adjust the spacer for the desired static sag and see how the bike handled.

How was the brake dive after you did the install? That will probably be the reason I have to get the RT springs.

I'd certainly start off with the stock 'soft' springs you've got. If a spring is too firm, then there's nothing you'll ever be able to do to get the required static sag (v. important for safety) or responsiveness, whereas if its too soft it is possible within limits to work around this by upping the preload (for static sag) and compression damping (to reduce dive)

You can easily calculate the spring rate of your stock springs, the formula is on the web. Progressive wound springs can be calculated too. Each single coil in the spring compresses the same amount per kilogramme of load. If the spring is compressed by 100mm (from its free length) then, say its got 20 coils, all the coils with 5mm or less spacing will have closed up. Once the closer-wound coils have closed up they stop working and so the spring, in effect, loses coils and becomes shorter. All you do is recalculate the spring rate for this new shorter spring, ignoring the coil bound coils completely. It can seem counter-intuitive to some folk, but if you cut coils off a spring it becomes 'harder'. Bath towels is the answer: imagine how nice and soft twenty bath towels layered on the bathroom floor would be for your tender bod to lie on. Now imagine taking them away one by one, it'll stop being so comfy! The reason why it seems counter-intuitive? because unlike bath towels we think of springs as providing resistance, rather than compliance.

Chris, this is my first foray into suspension modification beyond installing different shocks so I've been doing a lot of research, and now I'm trying to make sense of it all.  Your explanation of how the progressive spring works is helping a lot.  

From what I've seen and read, actual travel is a good way to determine spring rate, ie. a lower rate gives more travel, so if I have bottoming that's when I need to increase the rate.  Also, aggressive riders need higher rate springs.  Since I've been slowing down the past couple years, I would expect that I don't really need the higher rate that Race Tech recommends.  

I'm thinking my plan of attack now is to install the emulators with the original springs and tune for the recommended 35mm of static sag with spacer length to start.  Then use the old "cable tie on the tube" method to see how much travel is used when I ride the bike.

Race Tech specs an oil level of 140mm from the top of the fork without the spring or spacers installed.  Since the spring and spacers occupy and displace the air above the oil and I'm not using their spring it looks like I need to come up with a start point and a way of determining the best oil level in the fork.  I'm thinking here that I can start with the original oil volume minus the displacement of the emulators and an adjustment for the change in spacer length. Then I need a way to figure out how much oil to add when I do an oil change.

I'm thinking that since I use cheap ATF, it wouldn't be too hard to tune by using a calibrated tube I can slip in the filler plug at the top to reduce the oil to a desired level with a vacuum pump after the fork is assembled.  Once it feels good I can drain the fork and measure the amount of oil that comes out so I can make that the new oil refill volume.

Funny you should mention this.  

There is a chap I know who works about five minutes away and he imports them.  I was there very recently and he showed me around.  They also have an in house model which would appear to be a modified version.  I forget which brand of spring they use but I intend to visit in the coming months and upgrade the 75S.  

A YSS shock was recommended for the rear.  

GB777 will know who I mean.  In fact I was having a beer with him a few weeks ago.

TTR, I probably should have started this project earlier in the winter. The RT is my "winter bike" because it has better weather protection than my RS's so I like to leave it ready to run in the event I get a day when I can take it out. I'm hoping that if we get a couple days of bad weather next week I can get the job done.

The bike has 98k on it, but it's always been well maintained. I change the fork oil every year and the forks have gaiters to protect the tubes. The rear end has a Works Performance shock that they rebuilt and setup for me just before they closed. Works pretty nice. It's the front end that has needed attention for at least the last 5 years. The bike is not as much fun as I would like when I take it out west to the mountains.

I'm glad that you have some experience with these things, I might have some questions when I start.

The adapters are for the flat top Showa damper rods. According to the addendum they sent, the emulator needs 5mm of space between it and the top of the damper to allow for the valve to open. Apparently, a lot of the BMW models use flat top damper rods that need a spacer to create the clearance. They say you can make the adapter from PVC pipe as long as you cut the pipe perfectly square. I cut mine on a radial arm saw and they're perfect. At least one job is done.

I want to get this job done. I've been planning a trip to Fairbanks for a couple years and hope I can do it this August. On the way back I'd like to ride down the Canadian Rockies so it would be really nice to have the handling sorted. It sucks when you're getting passed by logging trucks on the downhills.

"I'm thinking my plan of attack now is to install the emulators with the original springs and tune for the recommended 35mm of static sag with spacer length to start.  Then use the old "cable tie on the tube" method to see how much travel is used when I ride the bike."

Perfect!

Don't sweat abut the oil level. What you're mainly avoiding is too much oil which will hydraulically lock the forks on compression. A tip/double check: fill the forks to the specified level (or sometimes it's the amount that specified) then, with all the internals in place except the springs, compress the forks to their maximum. Then add the springs. You should still have an air gap above the fluid - and don't forget that the volume of the spring sticking out of the top of the forks has to be deducted from that air gap too. The ratio of 'compressed' air gap to 'extended' air gap is what makes the air above the oil act like an additional spring  So if you add more oil, you increase the ratio/'spring rate'.....you get it! 


(The reason you add the springs after compressing the forks is to avoid oil dripping everywhere)

I'm beginning to feel pretty good about this project. I think I've got a good plan of attack, all I need to do now is get all the stuff together this week.

I have a wheel chock coming so I can stand the bike up without needing someone to hold it. First job now is to double check the setup on the Works(Worx) shock on the rear for sag and damping. Finally have some good weather this week to get out and do some riding on the old suspension so I will be able to tell if I'm doing any good.

Really looking forward to this, I think I'll make an effort to document this here for anyone else who might want to try it.

When the forks springs are removed, it's a good idea to double-check for stiction  (horrible word) Start with just the fork legs - no wheel spindle, and slacken the yoke pinch bolts. The fork legs should travel freely. Install the spindle and progressively tighten all the yoke & spindle pinch bolts, working the forks at every stage and checking to see if anything starts binding things up. The last thing to install and check is the wheel itself, as the action of the spindle draw bolt can sometimes pull things out of line.
If you're super-anal (or if you're trying to pin down a problem) you can try assembling just the fork tubes into the yokes and sighting them for skew, or use a flat plate (a mirror works well) held against them, to check for skew.
What you're aiming for is, with the bike fully assembled, you should be able to bounce the forks and let them return to their own, consistent height. Measure the static sag (with or without rider, it doesn't matter) and it should always be within 10mm or so, no matter how hard or which way you bounce them. Any more variance than this and the fundamental 'stiction' (yeuch) of the fork will be enough to start affecting the damping/responsiveness.

Of course this may seem super-unnecessary on a straight bike, but when you're scratching your head later down the line, twiddling the damping settings this way and that, it'll be one thing you can be confident is right.

The OTHER THING to be aware of is fork oil weight. Amazingly, it seems possible that one manufacturer's 5wt oil might be quite different from another manufacturer's. This is according to some sensible-sounding research that I read about some time back - I'll try and dig it out and post it. All it means is that you should be quite prepared, even enthusiastic, to 'tune' the fork oil - using different weights from the same manufacturer. I see that the emulator guys recommend a particular weight, but if it doesn't work for you, then just try something else.

And above all...keep notes of your settings and ride impressions!

The above is just drawn from my own experience. I'm no expert but I've made plenty of mistakes that you don't need to.

That is good advice about tightening everything one at a time. Part of my interest in the front end is that back in December I replaced the steering head bearings. When I put the forks back together I followed a procedure that sounded a lot like yours, tighten one screw, bounce, tighten another, and so on working from the top down. When finished, the test was to see how easily the axle slid in and out of the wheel. Another is with the wheel up against a wall and no front brake, I can easily bounce the front end at least 2-3 inches.

Viscosity is something I played with for a while, trying different weights in different bikes, mixing and matching. To be honest, I didn't feel that much of an impact from different weight fork oil. Different viscosities seemed to have little effect on the harshness and the brake dive. For the past 4-5 years I have reverted back to the days when my Hondas all used ATF, it didn't matter which brand, in both the forks and the shocks.

I like ATF because it is pretty consistant from brand to brand as long as you get the stuff made to the same spec. I recall reading somewhere that ATF works out to about a viscosity of SAE 7.5. It also has some nice things like seal softener, anti-foaming agents, and is fairly stable as far as viscosity over a wide temperature range.

I don't know if it lubricates the moving parts as well as fork oil, but I figure if I change it every year the level won't drop to where the forks are running dry, and I can minimize how dirty it gets.

Fork oil wt is what determines your rebound damping with the emulators, you adjust the compression damping with the valving but there must be little restriction for the rebound flow.  I have never played with oil weight or height so could not say how much difference it makes.
 
  On your way to Alaska try following the Columbia River Valley through Washington up through BC to the Headwaters at Revelstoke. This part of BC is called the Kootenay's, lots of great riding, day long loops centered around the town of Nelson.

TTR, thanks for the tip! As I get a little closer can I use you as a planning resource?

Right now, the general plan is to Iron Butt to Whitehorse/Skagway so I can ride the White Pass R.R., then to Fairbanks for a day or two, and then back to Whitehorse and then down to B.C. and the Rockies. I want to get over to Banff/Lake Louise and then down to Glacier Park. Nelson sounds like a nice place and will probably be one of my waypoints. I only have 3 weeks, and want to spend as much as possible in Alaska, B.C., and western Alberta. Fingers crossed on the border opening up by August.

   Sounds like lots of travel time, take the sweet roads and you'll have her dialed in to perfection by the time you get home.

Did this getting on for 2 years ago now, and wrote up my experience on my blog - you might find this an interesting read!

Skimming through this thread, I'm pretty sure you won't need an adapter to make the valves fit - it's the original Sachs design that has the flat topped damper rods, not the Showas. Racetech themselves seem pretty confused between the different fork types.

As for which springs to use, this is also difficult. I bought a couple of springs from an unknown Harley (which also have 41mm Showas) but these are mega hard for my 68kg self, I think I'd need to weigh at least another 50kg before they became useful. On the other hand it is not recommended to use progressive springs with emulators, for some reason.

I also wish I'd replaced the bushes in my forks, I've never seen ones so bare, but I didn't have any replacements so they went back in..

Snod, I can understand the confusion at Race Tech, the reason I haven't done anything beyond changing fork oil on my bikes until now is that the sections on front suspension in the shop manuals give me a headache.  

I have the adapters, and they cost me nothing to make, so it won't be a big deal if I find they aren't needed when I get the damper rod out, I just won't use them.  Having them will just save me a little time if I it turns out that I do need them.

From what I have read, the only real issue with progressive rate springs is that they can make designing the compression damping more complicated and allow more brake dive than fixed rate.  The theory is that the progressive rate is a band-aid for the lack of high speed compression damping over small bumps.  With high speed damping, there is less fluid resistance to high speed fork movement so a higher spring rate can be used to prevent brake dive.

I understand what I'm losing with the progressive rate springs, but I'll wait to see how things work with them.  If it turns out that the brake dive is still bad, it isn't too much work to replace them with a fixed rate spring.  Even if they don't work as they came out of the old forks, I still have a few ideas that might work to make them usable.  The big thing right now is that I'd rather not put too much more money into an $1800 bike with almost 100,000 miles on it if I don't absolutely have to.

I'm a fan of the single rate Racetech springs.  As you say its very much about reducing dive/bottoming.

On a previous bike (VTR1000) the front forks were too squishy 100mm travel with 50mm sag meant 50mm of travel left and bottoming out on speedbumps in carparks.  Springs of an appropriate rate to give less sag gave me more travel and eliminated bottoming without being too harsh.  They transformed the bike.  I fitted gold valves some time later and they didnt really make a huge difference, not compared to fitting the springs.

I have Racetech springs in my RT now, they improved the bike hugely by removing the front and back yaw from the overly soft suspension.  Still very compliant.  Its also fitted with a YSS rear shock. No more marshmallow handling.

Al

AL-58, That's really good information! It's beginning to sound like the Race Tech springs are lurking in my future. Thanks!

I wonder how much they'll sell me the returned emulators for? All this talk has me 'xcited for improvement up the front.

Years ago I put 'S' forks from a K75s on my RS. I told myself I liked it because it was less squashy, saggy long travel, but man o' manishevitz was it harsh! I grew used to it, used 5W oil, that helped a smidge, then didn't care anymore 'cause it was tight and handled well enough, didn't dive too much when the four pot Brembos and larger diametre discs were tugged into action rapidly. 

In the end a measure of control is made better, improved by more adjustable, less stiction, more supple suspension action of things like emulators.

Glad to hear you are considering going with the RaceTech springs, the bike may feel a little tight but the control and feel on your rough NY roads should make up for it. Good Luck.

Okay, emulators are installed along with new Race Tech fork springs(i was able to get them on ebay for a good price).  I decided to go with new springs because I didn't want to have to go back in again once the riding season started..

Installation was pretty straightforward.  The damper rods came out easily with my impact wrench, no need for heat or special incantations.  Put two additional 6mm holes in each damper.  The top of the damper worked with the emulator without needing the spacer.  So far, everything is a piece of cake.

Next was to fill the fork leg with fluid.  They recommend overfilling a little and using a syringe to pull the excess out.  I wanted a good number for the amount to put in so I added a little at a time until I got to the specified level.  For some reason each leg took a slightly different amount, so I averaged it at 12 1/2 ounces for empty legs, and about 12 ounces for a drain and refill.

Last step was to install the spring and the spacer to get a 15mm preload.  After spending about an hour measuring and remeasuring, it turned out that all I had to do was put all the original parts back in with the new spring replacing the old one.

I had made a spring compressor, but didn't use it for reassembly.  It was easier to just push the plug down into the leg with a Phillips screwdriver and hold it while  put the ring in with the other hand.

Took the bike out for a 10 mile ride today.  Initial impression is that going down the road it feels pretty much like it did before.  What I did notice was that backing off the throttle going into a turn did not make the front end dive, same with braking.  Also, there is no popping up of the front end when throttle is applied.  Eliminating the pitching when the speed changes certainly makes the bike feel a lot better in turns.  It seems easier to make it hold a line through the turn now.

Total cost was just under $300 for the emulators, springs, ATF fork oil, and a couple of tools I had to buy.  It's kind of a lot for a 30 year old bike, but, so far. it does seem to make the bike more pleasant to ride.

Good to hear.  Give us another update in a while.

With any luck I'll be able to put some miles on the bike next week. Right now the ignition switch has gone wonky on me and needs to be cleaned. The darn thing cut off the power three times today while I was riding.

Sounds like you've got the low speed damping under control 

How about the teeth and fillings?

The real test will be next week when I ride the Niagara Scenic Parkway. There's also another road that has a lot of "speed bumps" where I need to do a test run.