Front Suspension Noise k75s

[Kchop]

Hey Group,

K75s 1993

First off, thank you to everyone for the past advice, just finished roughly 1400mi in 5 days. (did most of the work myself)

When going around 70mph+ and hitting dips and uneven road, etc it sounds like noise from front suspension would be best described as crunching plastic. It seems to have gotten worse as ride went on.

In order of severity and likelihood what should I be checking?

Fork oil? Fork springs? Steering Head Bearings? Main Fairing bracket?

[daveson]

I had a problem that sounds identical to your description, I like your description, I'm not too good at verbs or English as you will see, because, prior to today, I described it as plastic farts. The bikes I've had in the past that had gaiters on the forks, had small tubes for air to escape when the forks were compressed. One bike had gaiters that didn't have that feature. They were clamped to the forks with plastic zip ties which did the job, but after a while they loosened up. Still good enough for small bumps, the gaiters just expanded, but on bigger bumps the air escaped against the resistance of the zip ties.

The way I discovered the problem was with the front brakes applied to the stationary bike and pushing down on the handlebar. I solved the problem by poking a small hole at the rear of the gaiters.

You could get lucky having a helper with good ears, this might help to pinpoint the location of the noise. Probably not good to ask a helper who looks something like this:


17929880294686237526605967156083.jpg (16.45 kB . 460x276 - viewed 65 times)

[Kchop]

lol, thanks for your reply.   testing that out today.. wondering if that's a safety problem riding like that??

btw.. is that chopper???

[Laitch]

From reading your posts, it doesn't seem like you've drained and replaced the fork fluid. Accurate?

[Kchop]

That is correct, sir... I'm guessing you are suggesting to start there??

[Laitch]

Starting there would help narrow the investigation. Is your Brick equipped with a Sport fork or a Showa? The amount of fluid depends on the fork. Yours should be a Showa but a lot of parts
swapping happens to Bricks.

Showa—note the solid face slider axle mount area indicated by the arrow.

410cc for a simple oil change. Use automatic transmission fluid or 10W fork oil.

Sport—note the bladed axle mount area.

280cc ATM fluid or10W fork oil.

Follow fluid replacement instructions in the BMW workshop manual downloadable from this site—pages 00-42 to 0043. Take the Brick for a ride to heat up the fluid then change it according to instructions. A full oil replacement can get more complicated. This method should be enough to help diagnosis. The drain screws for this operation are located on the rear side of the slider. Be sure to soak them in penetrating oil like Liquid Wrench, tap them lightly with a hammer, and wail 15minutes before loosening. Those screws can seize; they should come off easily sometimes accompanied by a cracking noise. Don't try to loosen them with a dying strain; that can be followed by rounding the wrench seat or snapping the screw. If they're stubborn, heat the screw, apply the penetrating oil, wait and try later.

[daveson]

Yep, it's Chopper. Some people say that Eric Banna looks more like Chopper than Chopper himself.

It's not a safety issue if the gaiters fart to let air out. I like to think that a good fart is actually healthy.

[Kchop]

@Laitch. Seems to be a Showa. Catching up today and reading the manual. Just one question: A full oil replacement can get more complicated. The procedure that you're advising and outlining is not considered a full oil replacement??