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Author Topic: "clunk" from the front end?  (Read 3338 times)

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Offline SOHC4ever

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"clunk" from the front end?
« on: July 28, 2009, 10:24:53 AM »
bike is a 76 750 f.

Every time I go over a bump, something up front gives me this ANNOYING clunk clunk.

It sounds like it's coming from the instrument cluster, but I've tightened everything up and can't imagine where it might be rattling. Could it be my front end? If I stand on the bike and give 'er sh*t, I can't make it clunk, but short, sharp bumps bring it out every time.

Any suggestions?
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Offline mcpuffett

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Re: "clunk" from the front end?
« Reply #1 on: July 28, 2009, 10:44:17 AM »
It could be your steering head bearings with to much play in them? or it could be your front caliper pivoting arm with to much play on the arm? have you checked either of these?
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Offline Johnie

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Re: "clunk" from the front end?
« Reply #2 on: July 28, 2009, 10:50:55 AM »
Quote from: mcpuffett on July 28, 2009, 10:44:17 AM
It could be your steering head bearings with to much play in them? or it could be your front caliper pivoting arm with to much play on the arm? have you checked either of these?

I vote for the front caliper pivot arm.  Grab hold of it and shake it up and down and see if you get some movement.  If you do not have that spring tension set right it will rattle on the bumps.  Been there...
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Offline IAmCitizenMe

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Re: "clunk" from the front end?
« Reply #3 on: July 28, 2009, 11:03:42 AM »
Obviously it's not a motorcycle, but my Camry used to make a clunking noise when i hit a bump but I couldn't tell where it was coming from. So I put the car in neutral and rolled down a hill with the engine off. I could hear the clunking much clearer and I was able to find the source of the problem.
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Offline honda750k

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Re: "clunk" from the front end?
« Reply #4 on: July 28, 2009, 11:20:17 AM »
Get the front end off the ground and see if the forks move forward/backward and if the steering feels smooth with no weight on it. worn/loose steering head bearings are totally possible.
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Offline Flying J

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Re: "clunk" from the front end?
« Reply #5 on: July 28, 2009, 12:06:55 PM »
To check the steering head i roll my bike up to a wall and push forward. If its loose you can feel the bike move forward as the tire stays still.
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Offline nippon

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Re: "clunk" from the front end?
« Reply #6 on: July 28, 2009, 12:39:22 PM »
If you think it is the pivot arm of the brake caliper, try the following:
Move the pivot arm up and down with your hands. If you can move it
a long distance, then your pivot arm should be responsible for the clunk.
Too much play.
I replaced mine with a stainless bolt and a bronze bushing (made on a lathe) in the pivot.
Now, I'm able drive over bumps w/o a 'clunk'.

nippon.
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Offline GammaFlat

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Re: "clunk" from the front end?
« Reply #7 on: July 28, 2009, 04:43:43 PM »
I was really really sure I tightened the top triple tree bolts.....

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Offline Steve F

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Re: "clunk" from the front end?
« Reply #8 on: July 28, 2009, 06:50:17 PM »
Quote from: Johnie on July 28, 2009, 10:50:55 AM
Quote from: mcpuffett on July 28, 2009, 10:44:17 AM
It could be your steering head bearings with to much play in them? or it could be your front caliper pivoting arm with to much play on the arm? have you checked either of these?

I vote for the front caliper pivot arm.  Grab hold of it and shake it up and down and see if you get some movement.  If you do not have that spring tension set right it will rattle on the bumps.  Been there...
+1  I agree....mine does the same thing, and this coming winter, I'll be making bronze bushings for the caliper mounts to take care of it.
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Offline gane

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Re: "clunk" from the front end?
« Reply #9 on: July 28, 2009, 09:50:10 PM »
silly thoughts , but clunks are usually caused by large amounts of unchecked travel. possible culprets, stem bearings, fork bushings, absent fork oil, wheel bearings,worn caliper carrior arms. easy check, takes at least 1 person who can hear, and the abiltiy to reproduce noise. try 1st. dead bike, w/front brake applied rocking front & back. 2nd bike on center stand, same. 3rd, change fork oil. yes, the dampers on old fours were sprung, but with crappy/low oil they will clunk when "topping out". old springs sack out. even if they measure to spec. add spacers til you must compress 'em @ 1 inch to fit fork caps. era forks used 5w ATF step up to a 10 w, fork oil. w/ stock amount.  the only wearing piece if fork damper is the sealing ring at lower damper,  try these, I think you'll be impressed.G
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Offline Really?

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Re: "clunk" from the front end?
« Reply #10 on: July 28, 2009, 10:24:26 PM »
I never really rode the bike much before I tore the front end down but I noticed the front end clunk when I was sliding the forks down the tubes,  it was either on and off the center stand or pivoting back and forth on the center stand.  My springs were too short.
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Offline tlbranth

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Re: "clunk" from the front end?
« Reply #11 on: July 29, 2009, 08:04:51 AM »
Lots of good suggestions here. You might also check your upper triple clamp for breakage.
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Offline SOHC4ever

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Re: "clunk" from the front end?
« Reply #12 on: September 01, 2009, 12:33:10 PM »
Quote from: gane on July 28, 2009, 09:50:10 PM
silly thoughts , but clunks are usually caused by large amounts of unchecked travel. possible culprets, stem bearings, fork bushings, absent fork oil, wheel bearings,worn caliper carrior arms. easy check, takes at least 1 person who can hear, and the abiltiy to reproduce noise. try 1st. dead bike, w/front brake applied rocking front & back. 2nd bike on center stand, same. 3rd, change fork oil. yes, the dampers on old fours were sprung, but with crappy/low oil they will clunk when "topping out". old springs sack out. even if they measure to spec. add spacers til you must compress 'em @ 1 inch to fit fork caps. era forks used 5w ATF step up to a 10 w, fork oil. w/ stock amount.  the only wearing piece if fork damper is the sealing ring at lower damper,  try these, I think you'll be impressed.G

Alright - I wan't able to reproduce the noise by compressing the shocks on a still bike. I'm a big boy, and I gave 'er sh*t, but no noise. SO: I changed the fork oil. Drained the old (STANKY!) oil from the drain plugs in the bottom, opened up the big nut on top and put the stock amount of ATF in each fork. After no small amount of hassle (and new oil spots in the parking garage, sorry Mr. Landlord) I got it all back together, and the clunk is WORSE! Now I can produce a clunking noise with the still bike.

Questions -

how do I know that I have the right springs in there? They're under compression at rest, which is why I had a tough time getting them back together.
Is there anything else that should be in there besides those big springs? spacer, etc.?
Could I be missing anything? Repeated inspection yielded nothing out of place on the front end, but I have nothing to compare it to, so I might not know.

Any and all help is appreciated - this is starting to drive me nuts.

Oh yeah - front caliper adjustment is solid. It's not that.
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Offline voxonda

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Re: "clunk" from the front end?
« Reply #13 on: September 01, 2009, 12:43:33 PM »
Did you put the small springs in, on the damperrod. Does your 'clunk' appears on the compression stroke or on the rebound? Have seen fronts that missed the small reboundsprings on the damperrods.

Rob
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Offline mystic_1

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Re: "clunk" from the front end?
« Reply #14 on: September 01, 2009, 12:52:08 PM »
Don't know if you've already seen this:

http://data.sohc4.net/SB750/750_34.pdf


Written for K0 and K1 750s but might apply to you as well.

mystic_1
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Offline SOHC4ever

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Re: "clunk" from the front end?
« Reply #15 on: September 01, 2009, 01:19:01 PM »
Quote from: voxonda on September 01, 2009, 12:43:33 PM
Did you put the small springs in, on the damperrod. Does your 'clunk' appears on the compression stroke or on the rebound? Have seen fronts that missed the small reboundsprings on the damperrods.

Rob

The clunk is on the compression stroke. I only took the top springs out of top of the tubes - I suppose that I have to have the forks off of the bike to properly assess the damper rod / spring assembly?
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Offline SOHC4ever

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Re: "clunk" from the front end?
« Reply #16 on: September 01, 2009, 01:19:54 PM »
Quote from: mystic_1 on September 01, 2009, 12:52:08 PM
Don't know if you've already seen this:

http://data.sohc4.net/SB750/750_34.pdf


Written for K0 and K1 750s but might apply to you as well.

mystic_1

I hadn't seen that. Thanks. I suppose putting a couple of washers in there can't hurt.
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Offline Raul CB750K1

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Re: "clunk" from the front end?
« Reply #17 on: September 01, 2009, 01:42:27 PM »
Quote from: mystic_1 on September 01, 2009, 12:52:08 PM
Don't know if you've already seen this:

http://data.sohc4.net/SB750/750_34.pdf


Written for K0 and K1 750s but might apply to you as well.

mystic_1

I located the clunk long time ago. With the bike parked, just hold the caliper with the hand and move it up and down, and it will make a familiar sound.

I bought the shim washers long ago but I'm waiting until it is time to replace the pads to overhaul everything.
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