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1Back to top Go down    K75 Forks on Wed Oct 23, 2013 10:08 pm

jjefferies

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In my K75C -> cafe racer restoration project I found one fork tube has rust pitting deep enough to concern me and I've been looking for a replacement tube. My search has turned up several offerings on ebay but most sellers won't return my e-mail questions. Concern is that I get the correct size. My measurement of the existing fork tube gives me 41.35mm OD. The brakes are marked as "Brembo" and are single pistons. The tube has an "S" stamped in the top plug which holds the springs in and next to the hex socket screw which you fill the tubes through.

I've searched the archives but haven't found a good description of how to identify the range of offerings in tubes for the K75 other than one comment in Showa Front Fork. Which I believe was intended for other purposes:

if your (Sachs or Brembo) fork works rough - throw it out
get a complet Showa (incl seering because of 41.0 mm instead of 41.3mm)
Which leads me to believe I have the Brembo tubes.

So can anyone educate me on the differences in fork tubes for the K75 and the K100 and their interchangeability? And BTW, is a 38 mm OD fork tube worth anything? That was my first error.
thanks
J.
P.S. Rick G has a nice chart in Chart of tubes and Oil quantity that gives me the idea that there were three basic types.

    

2Back to top Go down    Re: K75 Forks on Wed Oct 23, 2013 10:19 pm

RicK G

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I also have the dimentions chart thanks to K & R


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"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats." from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

3Back to top Go down    Re: K75 Forks on Wed Oct 23, 2013 11:24 pm

jjefferies

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Hello Rick G,
That's impressive and looks like part of what I was looking for. BUT (sorry), this bike seems to fall into some sort of hole in the chart. By the VIN as taken from MAX BMW's website and from the title: From MAX BMW website K75C(K569) Produced: 03/90 USA. I'll make a copy of the chart for future reference. But can anyone describe how to identify the various forks? And what does that "S" stand for? Sport? And if it is sport does it actually mean anything?

Thanks for the help.
J.

    

4Back to top Go down    Re: K75 Forks on Wed Oct 23, 2013 11:42 pm

RicK G

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AFAIK the S is for sport and came on the K75s and one of the K100 RS models for a short time as a special edition.
The forks have a much shorter travel, 125mm as against 187mm I think.
I don't know if the K75 and K100 S forks were the same diameter.
But the big problem we now face is that many things get changed around from model to model due to crashes and replacement or just because the owner likes them better and just general wear and tear.
My wifes K75 RT has forks that look identical to a K100RT but are 41mm and not 41.3mm as the K100 forks are.


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"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats." from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now
    

5Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 12:13 am

K75cster

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for clarities sake read the R/H side of your rear frame tube above R/H footpegs. it will say K75 something and you should also have a date there usually 08/87 etc but if it is a K75 it should have a sports fork set in it, ready to see if the forks have a bridge/brace and a two piece fender set, usually signifying a sports fork with 135mm travel. i believe you will need the numbers on the inside of the fork tube right next to the tyre, so you have to remove the wheel to read them, god bless those little bike builders


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

6Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 3:43 am

jjefferies

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@RicK G wrote:AFAIK the S is for sport and came on the K75s and one of the K100 RS models for a short time as a special edition.
The forks have a much shorter travel, 125mm as against 187mm I think.
I don't know if the K75 and K100 S forks were the same diameter.
But the big problem we now face is that many things get changed around from model to model due to crashes and replacement or just because the owner likes them better and just general wear and tear.
My wifes K75 RT has forks that look identical to a K100RT but are 41mm and not 41.3mm as the K100 forks are.
From the thread on the SHOWA forks that I cited above was the bit of information that the Showa is 41 mm as opposed to the 41.3 mm for the Brembo and Sachs. Course I have no idea if that poster knew what he was wribling about. What was curious is that the table you posted for me had no reference to K75C after '88 while my bike was built in '90 and sold in '91 as a K75C. Guess we aren't the only ones confused.

    

7Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 3:46 am

jjefferies

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@K75cster wrote:for clarities sake read the R/H side of your rear frame tube above R/H footpegs. it will say K75 something and you should also have a date there usually 08/87 etc but if it is a K75 it should have a sports fork set in it, ready to see if the forks have a bridge/brace and a two piece fender set, usually signifying a sports fork with 135mm travel. i believe you will need the numbers on the inside of the fork tube right next to the tyre, so you have to remove the wheel to read them, god bless those little bike builders
The bike does have a bridge/brace and a two piece fender set. But one of my "improvements" was to bead blast and powder coat the frame. You wouldn't believe the amount of rust. But powder coating fills in some of the stampings as well as removing the factory VIN sticker. I'll look at the fork tubes (I believe you mean the lowers) in the morning.
thanks

    

8Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 9:56 am

Ghost who rides

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I could be wrong and it wouldn't be the first time but '90 sounds too late for the C model.
Better heads than me will chime in to confirm. My K75C has 41.3mm forks no S stamp.


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1986 K 75 C 2nd owner 187,000kms showing .
1987 K100RT Police repainted, rough and unloved.
    

9Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 10:48 am

MikeP

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Most sources show the K75C ending production in 1990. From that point onwards the naked K75 is just that, listed as K75.

The easiest way to separate the two is by the rear brake (drum for K75C and disc for K75) and rear wheel. The 'C' has the drum cast into the wheel.


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1992 K1
1993 K1100R (used to be an LT)
    

10Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 12:01 pm

duck

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@MikeP wrote:Most sources show the K75C ending production in 1990. From that point onwards the naked K75 is just that, listed as K75.

The easiest way to separate the two is by the rear brake (drum for K75C and disc for K75) and rear wheel. The 'C' has the drum cast into the wheel.
The first gen of K75 standards (86-89) also had a rear drum brake. In 90 they got the rear disc.

The last K75C was built in March of 1990.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

11Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 2:07 pm

MikeP

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@duck wrote:
@MikeP wrote:Most sources show the K75C ending production in 1990. From that point onwards the naked K75 is just that, listed as K75.

The easiest way to separate the two is by the rear brake (drum for K75C and disc for K75) and rear wheel. The 'C' has the drum cast into the wheel.
The first gen of K75 standards (86-89) also had a rear drum brake. In 90 they got the rear disc.

The last K75C was built in March of 1990.

There are some sources that list K75 production from 1986 to 1996. They appear to be contradicted by BMW who list the K75C as 07/85 to 03/90 and K75 from 07/90 to 09/95.

There does not appear to be a 'K75' model designation prior to 07/90 (no matter what national importers may call them), if they were neither K75S nor K75RT, they were K75C.


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1992 K1
1993 K1100R (used to be an LT)
    

12Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 3:19 pm

jjefferies

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@MikeP wrote:Most sources show the K75C ending production in 1990. From that point onwards the naked K75 is just that, listed as K75.

The easiest way to separate the two is by the rear brake (drum for K75C and disc for K75) and rear wheel. The 'C' has the drum cast into the wheel.
Dunno Mike, maybe there was some sort of cross over period right at the end of the production run of K75C's. The bike under restoration is by all sources built in 3/90 but has a disk brake in the rear and as I mentioned, Max BMW (who may not be the final answer but who surely got their parts info from BMW) shows it by VIN to be a K75C.

    

13Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 3:37 pm

duck

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It's no longer there but the official BMW Motorad site used to have spec sheets up for the old models. The one for the K75 standard had production starting in 86 and ending in 96.

If you look at the parts at the RealOEM site, it only shows parts being available for the Gen 1 K75 available for Europe, not the US, so the Gen 1 (0561) standards may not have been exported.

And here's a listing of K75 production VINs by month: http://www.bmbikes.co.uk/chassispages/enginechassisK75.htm


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

14Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 4:36 pm

MikeP

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@jjefferies wrote:
@MikeP wrote:Most sources show the K75C ending production in 1990. From that point onwards the naked K75 is just that, listed as K75.

The easiest way to separate the two is by the rear brake (drum for K75C and disc for K75) and rear wheel. The 'C' has the drum cast into the wheel.
Dunno Mike, maybe there was some sort of cross over period right at the end of the production run of K75C's. The bike under restoration is by all sources built in 3/90 but has a disk brake in the rear and as I mentioned, Max BMW (who may not be the final answer but who surely got their parts info from BMW) shows it by VIN to be a K75C.
It could be that it has been swapped to a disc brake set-up at some stage. I personally know of one at least where that's been done using a front-end damaged K75S as a donor.


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1992 K1
1993 K1100R (used to be an LT)
    

15Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 4:52 pm

MikeP

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@duck wrote:And here's a listing of K75 production VINs by month: http://www.bmbikes.co.uk/chassispages/enginechassisK75.htm
That list highlights my point regarding accuracy; it lists K75T (US market only). That's because BMW do not recognise K75T which was a BMW(NA) parts-bin "special".

Look at the fiche that BMW dealers use (Max BMW is one). It lists the K75C and K75 giving the span of the production and they do not run concurrently.


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1992 K1
1993 K1100R (used to be an LT)
    

16Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 6:15 pm

K75cster

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To help identify your forks perhaps this thread will help
http://www.k100-forum.com/t4858-front-forks?highlight=forks


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

17Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 6:58 pm

jjefferies

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@duck wrote:And here's a listing of K75 production VINs by month: http://www.bmbikes.co.uk/chassispages/enginechassisK75.htm
Ok, the list does show the bike as a K75C on the last line of K75C/K75T. Last seven of the VIN are 0133119. And it came to me with a rear disk brake and the swing arm etc setup for disk. For whatever that matters.

    

18Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 7:44 pm

duck

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@jjefferies wrote:
@duck wrote:And here's a listing of K75 production VINs by month: http://www.bmbikes.co.uk/chassispages/enginechassisK75.htm
Ok, the list does show the bike as a K75C on the last line of K75C/K75T. Last seven of the VIN are 0133119. And it came to me with a rear disk brake and the swing arm etc setup for disk. For whatever that matters.
That's one of the last Cs made (March 90) so it may have come from the factory like that. Or a prior owner converted it from drum to disc. It's not very hard to do.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
http://www.ClassicKBikes.com
    

19Back to top Go down    Re: K75 Forks on Thu Oct 24, 2013 8:19 pm

Two Wheels Better

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Just to help with information on K75 'S' forks, I have a complete set fitted to my 1987 K100RS (triple clamps, tubes, sliders and all). The slip right in with no rake/trail number differences. The immediate difference is that they have a much shorter, firmer spring rate, use just 280cc of oil per leg, and have a small 'S' scribed into the top end of the tube underneath the black plastic cap. Mine are the two-piece mudguard (fender) version. I prefer to use 5W fork oil as they're very stiff in comparo to the various other longer travel, softer sprung K versions. The 5W helps with small ripples in the bitumen (tarmac). Combined with an nicely adjustable but stiff, Italian-made Bitubo rear shockie I 'feel' the road beneath me.


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'87 K100RS, '93 K1100RS frame with '02 K1200RS motor, brakes & wheels, aka theBig Block.

Writing is like driving at night in the fog. You can only see as far as your headlights, but you can make the whole trip that way. ~E.L. Doctorow
    

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