knocking sound front fork

Never really paid as much attention to this as today. Was on a road were the expansion joints were really bad and the front end/ fork seemed to knock loudly like it bottomed out. Did it about 5 times today. Seems as if it is pulled out to the stop, not on compression. Any fix or is it normal. Knocked like it hit a mechanical stop??

Are you sure its not the gas tank moving on its rubber bumpers?

Well pretty sure. Pretty loud klunk. The rubbers seem tight and I have Corbin seat that rests against the tank.

1976 R75/6. Yes I know the valve cover is on the wrong side. Has already been swapped just not in this photo.

OHScot said:

1976 R75/6. Yes I know the valve cover is on the wrong side. Has already been swapped just not in this photo.

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Beautiful bike. Very nice fairing. What kind of fairing is it? It looks like you have the standard bars on it. No clearance issues?

I know my questions aren't solving your problem. Just looked too nice to resist. Thanks.

Slight clearance issue at full turn. Hannigan faring very nice in cooler weather.

20774 said:

http://hanniganmotorcyclefairings.com/main.html

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Thanks Kurt and OHScot, as always, for the good info. Had a lengthy conversation with Jerry at Hannigan. Loads of info and something new to save pennies for.

Stem bearings feel good and play is correct no wobble at any speed. The sound seems to be the fork hitting an internal stop?? Just one quick pop /clunk. Guess I will have to start pulling and beating on stuff to see if any play or looseness is in the front end frame area.

sumran said:

Thanks Kurt and OHScot, as always, for the good info. Had a lengthy conversation with Jerry at Hannigan. Loads of info and something new to save pennies for.

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I bought mine used on the IBMWR board. Was manufactured in 1977 and had no unusual wear or stress cracks. Just a quick refinish and was good to ride. Great storage and comfortable wind protection. Not car like but it makes all weather riding comfortable. Every once in a while on hot days I stand or put my helmet to the side to get more wind flow. Jerry was a real resource providing a few of the bits and parts needed and a complete manual at reasonable pricing. like the Airhead itself I believe these things are made to go the long haul.

OHScot said:

I bought mine used on the IBMWR board. Was manufactured in 1977 and had no unusual wear or stress cracks. Just a quick refinish and was good to ride. Great storage and comfortable wind protection. Not car like but it makes all weather riding comfortable. Every once in a while on hot days I stand or put my helmet to the side to get more wind flow. Jerry was a real resource providing a few of the bits and parts needed and a complete manual at reasonable pricing. like the Airhead itself I believe these things are made to go the long haul.

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Is yours an SS or an ST

I believe it is a ST the larger of the two. I started looking for a Pichler because I always liked the look, found Hannigan. Would have mounted a RT fairing if I could have figured it out. Not sure what you would gain if you already have an RT??

OHScot said:

I believe it is a ST the larger of the two. I started looking for a Pichler because I always liked the look, found Hannigan. Would have mounted a RT fairing if I could have figured it out. Not sure what you would gain if you already have an RT??

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The RT fairing was removed by the previous owner and I don't want someting that big. I have a Parabellum Scout which is smaller, fork-mounted unit. It works well, but is not as stable as a frame mounted unit. It is a little warm in Florida for an RT fairing. The ST would probably be a bit much as well. But the shape and lines of the fairing are sharp.

your vintage bike has two rubber like bumpers inside each fork leg unit, age and fork oil often reduce these to mush. if the forks have not been overhauled recently it woud be good to do so. also looks into fork tube alignment. best to do all at once...

yes but no

The rubber bumpers sit at the very bottom of the slider to cushion the fork tubes from a severe bottoming-out. I believe what is happening here is a bang at full extension; am I right?
Makes me think the forks were not set up properly the last time. More on that later...

I have no doubt that if those rubber donuts are original they are in fact mush, causing the fluid to be contaminated possibly plugging holes.
I would suggest draining the fluid, droping the slider caps and checking/replacing those donuts ($8?). They are the only thing that REALLY need to be replaced at a 'rebiuld'; everything else can be cleaned and replaced barring damage or corrosion (you do replace the fork oil regularly?).
I have come across many of these rubber things that you can shape like putty once old.

If you replace the fluid, replace the fill caps and take the bike off the center stand. THEN remove the fill caps to equalize the air pressure in the system. With the front brake on and the fill caps out, compress the front by pushing down a few times to bleed trapped air. CAREFUL here, if the fork fluid you just put in hasn't entered the lowers from a clog or otherwise, you will get a BLAST of 7wt oil on you. Its best to have a buddy/wife hold the machine when equalizing the pressure to get it right on and then replace the fill caps. i.e. Don't sit on the machine when replacing the fill caps or the opposite will happen as if you left the machine with the forks extended when you replaced the fill caps.

If the machine acts choppy when you accel/decell you may have an air bubble in the fluid. Try bleeding and re-equalizing the air pressure again.

For OHScot: after you have reset the air pressure per the above method, does the bike seam to sit about 1/2-2" lower in the front. Replacing the fill plugs while the bike is on the center stand will totally upset your bike on bumps and blow oil out of the fork seals. Are your sliders oily? I bought an R100 that made the same "clunk" and had a leaking fork seal. I checked the suspension out just like I described and replaced the fill plugs on the center stand like I advised against. Same "clunk" over rough roads. Then it occurred to me what I did, removed the fill plugs while holding it upright under its own weight and they sprayed air out. No wonder!
I'm willing to put a money back guarantee on this free info as the solution to your clunk.

It has been 3 years since I have changed the fork fluid. I have always filled it and left the caps loose on top and worked the suspension to work out any air. Will have to tear into the forks and try to see what has happened. They work well normal riding and seem to compress and release as they should. Used 2.5 wt oil at the last change. As far as I know they have never been apart. The rubber outer boots are about due. Guess I have my first rainy day project. Thank you all for the sugestions so far. Was kinda of hoping some one would say oh this is it tighten this bolt.

Weight?

2.5wt seems extreamly light.
For what reason are you using such a light weight? I've never even seen a bottle of 2.5.
I would think a 7-10wt oil would be more appropriate. I would also suggest a yearly fork fluid change when you change your brake fluid. You do that too right?

Anyone have opinions on fork oil weight for specific models they have found to be perfect combos?
I know everyone has an opinion on motor/gear oil, just curious about the interest here.

-dan

Have to check the fork oil weight. Seemed wrong when I typed it, but I remember hunting all over for it. Might be 7.5. Bounced the fork on the ground on the center stand and it thunks when fully extended, like it hits a stop. Also when bouncing the front end on the ground with the brake on the caliper pops. Guess I should order seals and boots and whatever is the hard stop bumper and tear it apart. Hope it is safe to ride as the weather is getting nice. Will have to wait for rain or snow.