1992 K75S - Front suspension

I am used to riding my 1994 K75 and I have now gotten my 92 K75S going. I rode yesterday and noticed that the front suspension seems much different on the 92 K75S than the 94 K75. The 92 K75S seems to be a bit softer and more bouncy. It does not seem bad, just different.

My question is: Should the 92 and 94 feel the same.

Is the difference that I feel likely because of the difference in age (92 and 94) or was there was a difference between the K75S and straight K75.

Or, is it something different all together that I should check into? Any thoughts?

Ed

All the S bikes came with Showa forks - but I believe that after 93 all K75's came with Showa too? Fluidblock maybe?

My bike is a 95 S with "C" bars. I think it feels somewhat "slower" in handling compared to my father's RT, but my suspension is definitely stiffer. I attribute that to a different fork size, the fluidblock in the S, the slightly different handlebar shape, and the weight difference between the two bikes. I also know that the fairing/windshield/speedometer moves around a lot more on the S, giving some illusional differences.

Sorry - i don't know if that was helpful...

drneo66 said:

All the S bikes came with Showa forks -

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This is not correct. Early K75Ss came with Fichel-Sachs forks. They were the sport suspension version which were different than the non-sport suspension version of the K75C. The sport suspension version of the F-S fork is differentiated by an S stamped next to the fill plug. The Sport version has 2" less travel, has the dampning control in only one fork, and uses less oil.

THEN in 8/91 (the start of the '92 model year) they changed all K75s to the Showa forks (which has caused alot of confusion). If you look in the front suspension section of the Clymers manual to get the amount of oil for a K75S, you will get the correct level for the F-S fork (which is HALF the amount for the later SHOWA fork). It doesn't tell you (in that section) that you must go to the post-90 appendix in the back of the manual (if you have the newer edition that covers the post-90 Ks).

Ed,

When your two bikes left the factory, they had the same identical forks.

First, are you sure the bouncyness is at the FRONT. Bouncy while riding is usually at the rear.

Dive at the front (and subsequent rebound) is noticed under braking, especially at stops

IF there IS a difference at the front, it would be caused by:

Difference in front air pressure between the two bikes.
Difference in the level of the oil in the forks (changed by a previous owner)
Difference in oil viscosity of the oil (changed by a previous owner)
Difference in spring rate (changed by a previous owner)

If none of the above, it is possible that the piston seals or damping springs are worn.

98lee said:

Ed,

First, are you sure the bouncyness is at the FRONT. Bouncy while riding is usually at the rear.

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I'm not sure what I'm feeling is in the front, but it felt to me like it was in the front. The rear has a fairly new (looks brand new and with very few miles on it) Wilbers on it. I have been searching for information about any potential adjustments on it. So far, I have not found any information about adjusting and/or whether I can make the bike lower.

So, while I think it is the front, it may not be. What I'm feeling is not in braking, but in the ride, and I really have not got enough riding time on it yet to fully analyze what I'm feeling and when. I have worked on many components on my K bikes now, but I have no experience at all with anything associated with the forks or rear shock including checking or replacing oil.

Any guidance would be appreciated.

Ed

My hunch is that the rear strut (shock) needs slightly more preload, and then slightly more rebound damping.

Agreed.

If you are noticing it at times other than braking, it is quite likely the rear is too soft or under dampened or both.

OR

Your other bike is too stiff.

Sort of depends on your definition of bouncyness. Compliance is good, bouncyness not so much.

98lee said:

Ed,

When your two bikes left the factory, they had the same identical forks.

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In all my reading I'm pretty sure that the K75S (Sport) was the only one with sport suspension so it seems to me that the above statement and even thought this discussion is a few years old it doesn't make sense to leave this alone (if it is untrue)

Did someone in this thread state that there is an S stamped near the drain screw?

jimnto said:

In all my reading I'm pretty sure that the K75S (Sport) was the only one with sport suspension so it seems to me that the above statement and even thought this discussion is a few years old it doesn't make sense to leave this alone (if it is untrue)

Did someone in this thread state that there is an S stamped near the drain screw?

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98lee's statement you quoted is true because at the start of the 1992 K75S production year BMW put Showa forks on all K75s, or should have. I have a very early production 1992 K75S which still has the older "S" sport forks. There is an "S" stamped on the top filler plug. Having had a K75 with the Showa forks I think they are better over all than the earlier sport forks.

98lee said:

This is not correct. Early K75Ss came with Fichel-Sachs forks. They were the sport suspension version which were different than the non-sport suspension version of the K75C. The sport suspension version of the F-S fork is differentiated by an S stamped next to the fill plug. The Sport version has 2" less travel, has the dampning control in only one fork, and uses less oil.

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Is this the S - it is on top of the bottom triple clamp. I ask because there is no 'S' stamped in or beside the metal of my fill plugs and both tubes look identical. I am asking because my bike is an '87 K75S and I put 330ml of fork oil in (because I didn't see this red 'S' until now) and I am finding the front forks quite stiff. Quite!

Since mine is a K75S - should I have put less fork-oil in even withstanding that there is no 'S' stamped in the metal? In other words is I am driving a K75S is it that I def have the sport forks (I think I know the answer but since there is no "S" stamped in the metal and the tubes are identical - well I probable guessed wrong).

and here is the bike for fun - I am so happy to have recently acquired it.

jimto,


ALL K75Ss prior to the Showa forks (8/91) had the F-S Sport front forks. They did not all have the S stamped on them (under the black plastic cap on the top of the fork tube). My two early Ss (1st and second day of US spec. production) do not have the stamp. All my ‘88Ss have the stamp. I would think that your bike that was several hundred bikes into the run (first several hundred were Red Metallic), would have the S, but maybe not. But they ARE Sport Forks (unless a previous owner switched them).

Put 270-290cc of oil in each fork.

Your bike appears to be a very late ‘87 (black drive train and wheels instead of silver) but it still has the typical rectangular ‘87 rear brake reservoir.

What are the last four numbers of your VIN# ?

jimto,

98lee said:

What are the last four numbers of your VIN# ?

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How fantastic - to have this confirmed. Last 4 #0630
I put 330 in and I do like something about the stiffness (When I think of my standard forks on my Suzuki DL650)

I might see if i can carefully bleed out an equal amount from each fork. If not I will drain and refill.

Thank you for any info.