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[Richard230]

Recently, I have noticed that my front suspension makes a "thunking" noise when going over sharp bumps in the pavement. It also makes this noise when holding the front brake lever and pumping the forks up and down.  It does not make this noise when passing over more gradual bumps and when pumping the forks up and down without using the front brake.

The first thing that came to mind is loose steering bearings. So I raised up the front end and tried to move the forks back and forth, but no movement was noticed. The forks turned back and forth easily, and they did seem to have a slight amount of drag.  Also, on other bikes, when I have had a loose steering head bearing, I have heard a higher pitched "click" when braking to a stop.

So I am not sure if this noise is something that is the result of the design of the front forks (the upside-down Showa forks on the BMW F800GS make a similar noise due to a plastic part inside the forks bouncing around) or is due to loose steering bearings.  I had planned to visit my shop's service department and have them check it out, but it looks like it is going to be raining for the next week and this issue is no rush, so I will wait until it dries out before checking with them.  In the meantime, I wonder if anyone here has any ideas or comments.

I could adjust the steering bearing myself, but I lack the necessary special socket wrench to loosen the steering bearing nut and do not have the torque values for the lower triple clamp bolts or the adjusting or locking nuts, so I hesitate to mess with things unless I know there is a problem.

[Biff]

Could the noise with the front brake being on be related to floating rotor?

[skadamo]

Hmm. My sv650 used to make a noise like that when the suspension topped out. Maybe spring contacting something? Looking fwd to finding out what it is.

[Richard230]

It does sound like the forks topping out, but it happens when the forks are compressed, not when they extend.  I also thought that it might be the sound of the floating disc rattling, and the Zero does appear to have a floater, but the sound seems too deep for a disc rattle noise. 

I asked the Zero employee that I spoke with this Sunday about the noise (I didn't have my bike with me at the time). He thought it might be the noise of the sliding fork seal breaking loose when its "striction" was overcome.  His forks made somewhat of a noise like that, but not as loud as on my bike. Maybe the seals just need to break in more.   

Since I can duplicate the noise at a standstill, I think the use of a mechanic's stethoscope should be able to narrow down the source. All I need is someone to listen while I pump the forks up and down. I tried to do that by myself but it didn't work out too well. At times I wish I was an octopus. 

I think the shop should be able to narrow down the source of the sound quickly.  All of the bolts necessary to adjust the steering bearings (if that is the problem) are out in the open and easy to reach, so any preload adjustment should be easy and quick. When I find out more, I will report back.

[Richard230]

After getting 7 inches of rain over the past few days, the wet finally stopped this morning (more is expected later today) and the roads dried out, so I jumped on the Zero and shuffled off to my dealer to have them check out the "thunking".  One of their mechanics looked the bike over and proclaimed that the noise was coming from the suspension and not from the steering bearings. I verified that by listening for the location of the noise as he pushed the forks up and down with the front brake on.  The noise seems to originate from the area of the fork seals, where the lower sliding tube enters the stationary tube of the fork sliders. So I guess the Zero guy's comments were right. It appears that the seals are kind of tight and when they break loose quickly they make a noise. At least that is my conclusion at the moment.

[dkw12002]

My 2011 thunks too, but I've had other thunkers, so I never gave it a thought. Nice to know where it's coming from though.

[Richard230]

Speaking of suspension components, I found an on-line post detailing how to service the Fast Ace Technical Products forks on our Zeros.  Here it is:

http://www.miniriders.com/tech-talk/9093-how-service-fast-ace-inverted-forks-part-1-a.html

Unfortunately, the photos illustrating the steps for dissembling the forks have been removed. They would have helped a lot when following the instructions.  Of course, these may not be the exact same forks, but photos that I saw of a set of Fast Ace forks that were being sold sure looked like the forks on the Zero.  These Fast Ace suspension components appear to be designed for mini-motocross motorcycles - which is why I had never heard of the company.

Here's hoping that some day Zero will offer a chassis service manual for sale to the public.

[protomech]

I think I'm hearing the same sound when riding over some especially broken pavement (cobblestones would have been smoother). Not too worried about it, seems fine when the terrain is less terrible.

[dkw12002]

My thunking sound became more pronounced so I read my manual. There is a suspension adjustment area above each section of the fork consisting of a bleeding screw which  is a 3 mm hex for bleeding the air from the fork AFTER EACH RIDE and a second flathead screw for adjusting the damping Well I had never adjusted either so I did first bleed each side but nothing seemed to happen and the thunking noise was just as loud, so I adjusted both flathead screws by 2 notches clockwise...problem solved. No more thunking. I will take it for a longer ride today and if it isn't smooth, I can go back to where I started and try adjusting the fork one side at a time and only one notch instead of two, but the short ride I took felt good. The thunking noise, using the language of the manual, would have been due to rebound damping speed set too high. By turning the screws clockwise  you slow the rebound speed.

[CliC]

I'm not bleeding mine after each ride. I think that's a rather ludicrous request, personally. I figured I'd do it every week or so.

The screws are the rebound damper adjustment I believe. I haven't had the thunking on my DS, but I dialed it in midway when I got it. Haven't touched the back suspension yet.

[dkw12002]

There are supposed to be 18 positions, but there is no clicking as you turn the screw either left or right, plus the screw is a brass screw that has no markings on it so you can't tell which side of the screw you should be looking at. Thirdly, the screw does not stop when moved it a full circle. What I had to do is tighten the screws all the way down first to have a place to begin. Then I backed off 9 markings to the middle. I used a Sharpie to mark one end of the screw and also mark when I began on the dial. Otherwise I would not have known where I was to begin with. Anyway, I am 2 positions clockwise from where I started and that is 6 positions counter clockwise from the screw being fully tight. The bike rides fine now. 

[CliC]

I was able to hear the clicks, and used them as an indexing mechanism. I first looked into this because the screws on both forks weren't in the same positions. Once I started playing with them, I also noticed that they were multi-turn ("Oh sh*t!" ), so I did as you and screwed them all the way to one extreme. I then counted 9 clicks back the other direction on both (the book says there are 18 clicks total range, but I didn't verify that). After I was done with both sides, the screws still weren't in the same positions, but maybe this is normal. Never had a bike with adjustable rebound damping, so I don't know.

[dkw12002]

My thunking sound returned. I tried unscrewing the bleeding screws, bounced on the front a couple times then re-tightened the screws. It stopped the thunking noise when going over bumps.