# AMP Clunk



## modifier (May 11, 2007)

A while ago I built up an old FSR as a SS for my GF and used an AMP B4 fork that I had hanging around. I hadn't ridden it anywhere but the yard until I took it on some trails today. The bike works fine as a whole and the fork too for the most part considering it's simple design. Absorbs shock and is pretty stiff, but man is it noisy. I remember it making some noise and have heard others comment on it, but this is ridiculous. Every time it tops out there is a metal to metal clunk that reverberates throughout the whole bike and particularly to your hands. I can't actually figure out what is hitting what but it sounds like damage would be in order if you road it very much. If the trail is smooth it's fine but hit some rocks or roots and forget about it. 

Back in the day I did ride it a lot for a couple of years as it was my only bike at that point but I don't think I could put up with it now. Maybe I reserved myself to ignore the noise and concentrate on the performance, weight and the fact that I had a disc brake which was a big deal at that time. The "shocks" and bushings were rebuilt by Amp not that long ago in hours of use but a long time ago in years. It's pretty tight and has some bump dampening but no rebound that I can tell. 

I was wondering if anyone remembers a fix or band-aid for the noise. Maybe some rubber sleeves around the shock bodies to contact the linkage before topout? But that may put side load on the shock and damage seals. ?? Any ideas?


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## Boy named SSue (Jan 7, 2004)

There should be a rubber bottom out stop on the bottom of the crown piece. Is that missing?


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## modifier (May 11, 2007)

Boy named SSue said:


> There should be a rubber bottom out stop on the bottom of the crown piece. Is that missing?


No that is there, but bottoming is not the problem. It's topping out.


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## richieb (Oct 21, 2004)

Sounds like you damper is out of oil - rebuild it. Instructions are around the internet somewhere. It's not too hard. Also, your bushings may be worn and loose. They'd be step 2...


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## DeeEight (Jan 13, 2004)

Top out clunk is the damper cartridge needs oil. The rebuild instructions are on the Amp-Research page.

http://www.amp-research.com/company/history/amp-research-mountain-bikes/


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## modifier (May 11, 2007)

OK, thanks. Guess I need to take them apart. 

One had a little oil film after riding but the other one is dry. I know there can't be much oil in there but you would think you would see some weeping if the seals were compromised. 

But I'll check it out.


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## DeeEight (Jan 13, 2004)

thru-shaft shocks in general will lose oil around the shaft seals. The good ones are designed to be user-serviceable. The problem is many users are could never be bothered. Hell even today you see people complaining if they have to wipe dirt off their fork slider seals after riding.


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## cdn-dave (Jan 6, 2007)

I've got the same clunk and yah, the shock is out of oil (no damping). It wept aa ton of oil, as evident by the accumulation of dust...


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## modifier (May 11, 2007)

Since that bike is a hanger most of the time I wasn't in too much of a hurry to get at this but decided today was the day. Found my original manual too alone with some rebuild kits and a shock body clamping tool. 

So I disassembled the shocks. 1 probably had about half the oil left and the other had almost none. Did everything according to instructions and when I put the first one back together and compressed it oil shot out. It's coming from around the lower mounting bushing. The shaft inserts into the "cap". I guess to get that last mm of travel when the cap was machined the shock shaft bore goes all the way through to the pivot bushing bore, so the only thing sealing that area is the pressed in bushing. It seems like it would have been better if they did not intersect. The pivot/mounting bushing seems to be in pretty good shape but it must be compromised because it no longer seals.

So what next? I could try and find some kind of oil proof sealant or glue and try and clean inside the cap and fill the bottom of the bottom of the cap. Or I guess I could try and press out the tiny bushing and either find a new one or press it back in with, once again, some kind of oil proof sealant, or maybe a new bushing is all it would take.

Any ideas?

I can try AMP on Monday too if nothing pops up here.


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## cdn-dave (Jan 6, 2007)

Wow, I just looked at the instructions Dee (#5) posted, and your F4 is quite a bit more involved than my F3. At least with the F3 there's a "tetra" seal around the shaft before it goes through the cap.

I've contacted Amp as late as 2008 before moving to Europe, and had great service from them. Brion La Belle is the guy to ask for (hopefully he's still there).

cheers,
dave


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## modifier (May 11, 2007)

Ok, figured it all out.

I talked to Brion today and he explained everything in detail. I have to admit that while listening to him some of it was going over my head because I did not have the understanding at that point of how it all worked to fully get what he was describing. But after readdressing the shocks I got it down. 

I replaced all the seals, cleaned everything up and using the fill level gauges and clamping tool (that I fortunately have) put it all back together with 10 wt fork oil. It's actually pretty easy, so if I was riding the bike much changing out the fluid more often would not be hard and probably should be done due to the small volume. 

My misconception about why the oil was leaking out past the bushing was because I was reading the procedure of how to change out the oil in an older generation shock that does not have the intersecting bores I spoke of above. With the new design oil does not get to that area unless it leaks past the seals and you also no longer need the o ring seals on the caps. The printout I have says on the front that it is for The F3 and F4 forks so I just turned to the section about changing fluid not realizing that they have different shocks. The instructions I was looking at were for the F3XC shock. You have to turn a couple of pages to get to the F4BLT instructions. 

I haven't been on trails yet but just riding the bike around the yard is night and day. It works like it is supposed to once again.


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