Big Jeff Posted May 20, 2003 Share Posted May 20, 2003 My forks seem to be topping out when I go over a large bump. It's mainly when I'm going kinda slow and going over a speed bump or something similar. I hear a "whack" sound of the forks topping out. I have racetech springs, rebound and dampening. Any Ideas ? Big Jeff Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 20, 2003 Share Posted May 20, 2003 Topping? Not bottoming? Who did your RaceTech install? What's your weight? Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 20, 2003 Author Share Posted May 20, 2003 Yes topping out. 230lbs Me and some buddies did the install. Big Jeff Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 20, 2003 Share Posted May 20, 2003 I've got $50 says it was done wrong. Sorry to be blunt and rude, but... I weigh a little less than you now (but recently weighed more), and have NEVER topped or bottomed the forks since the RaceTech job. I ride over stuff pretty hard, and have done quite a few miles on dirt roads, no problem. My guess is going to be that you didn't do the rebound shim stack properly or maybe screwed up on the bleed hole? I'm not an expert on the fork jobs, but those are the first obvious things that come to mind. You should call RaceTech. What oil did you use? How much preload? What level is the oil at? Quote Link to comment Share on other sites More sharing options...
Mithrandir Posted May 20, 2003 Share Posted May 20, 2003 Did you do the rebound damping rod back up under each cap? Sounds like you didn't. If you get a big clunk as the wheel drops away from the bike then that's almost guaranteed to be the problem. Quote Link to comment Share on other sites More sharing options...
Northman Posted May 20, 2003 Share Posted May 20, 2003 Michael (CaBeR) had the same issue after having forks/valves installed for him by a competent shop(? :roll: ). If I remember right, one of the valves was installed wrong, or the valves were installed backwards. Either way, it sounds like something was botched. If the damper rod was not installed, you would have known it long ago, but it's easy enough to check, even on the bike. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 21, 2003 Share Posted May 21, 2003 Did you do the rebound damping rod back up under each cap? The damper rod controls BOTH rebound and compression damping. Once compressed on the first bump, it would stay there and the bike would just be a pogo stick in both directions. Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 I do get a clunk as the the wheel drops away from the bike. otherwise it rides ok, a little soft. Nice and responsive over multiple small bumps. Big Jeff Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 21, 2003 Share Posted May 21, 2003 What oil did you use? How much preload? What level is the oil at? I've still got my 50 on an install error. Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 10 w oil 22mm of preload oil level i'm not sure, we used some paper guage. could have gone a little strong on the oil but not by much Big Jeff Quote Link to comment Share on other sites More sharing options...
Redbird Posted May 21, 2003 Share Posted May 21, 2003 22mm of preload? I've got almost 120mm in mine with the racetech springs (no valves, but I cant' see that making a difference on preload). Also, I believe racetech recommends 5w for use with their valves. Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 I think it may be compressed by 22mm. I need to look at my paperwork Big Jeff Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 21, 2003 Share Posted May 21, 2003 :shock: Ok well, I guess we can fix you right up. Change the oil to 5w. Your 10w is FOUR TIMES stiffer than what they recommend (due to fluid dynamics, double weight = four times less flow). Also note that the recommended RaceTech brand oil is actually a 2.5-5w, lighter than a true 5w. Set the oil height to 160mm. This is important. I'm going to guess you might have too much oil. Do you remember how much you used? You should have 20mm preload. Your 22mm is close enough. Now while you have all this apart, go through the instructions regarding the shim stacks again, and double check everything. Double check the hole you drilled in the damper rod (you did drill that, right?). Make sure the rebound valve kit is not upside down. Have you measured your static sag? Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 On the sheet from Racetech the recommended fork spring preload was 20mm. I ended up with 22mm because I had to add a washer. Big Jeff Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 I tried for 160 mm using that paper guage they give you. I'm sure I got the hole right. I had Racetech explain it to me. Do you think the oil weight could cause the topping out ? Big Jeff Quote Link to comment Share on other sites More sharing options...
Northman Posted May 21, 2003 Share Posted May 21, 2003 I've got almost 120mm in mine with the racetech springs That's the spacer length you have there, Tim. I have just over 120mm in spacer length, with the same 22mm preload that Big Jeff has, and mine works fine. Static sag was 32mm on mine at 225lbs, and works fine. Carlos is absolutely correct on the fluid change, and I'd do it as soon as you can. The heavier fluid will give you a much harsher ride, by really stiffening up the damping. Also be very careful when measuring fluid height, as high levels will cause a harsher ride, also. Quote Link to comment Share on other sites More sharing options...
Mithrandir Posted May 21, 2003 Share Posted May 21, 2003 It might not be topping out. If you're saying the bike feels a little soft, I still think its a damper rod problem. Why? Because you say it works fine over small bumps, but only on the bigger ones do you notice anything. On small bumps, with no damper rod, you won't feel anything. It's mainly spring and the oil won't have any effect. That is, your weight will more than cancel out the lack of damping. But, when you hit the big bumps, you don't feel anything as the fork compresses, but you get a big bang as the weight comes of the front and you get a double action of the spring pushing both the wheel towards the ground and the bars in the direction they were already travelling (ie towards you). If the oil is too thick, you won't normally get a big bang coming through the front. What it means is that the damping can't work effectively because it cannot move fast enough. If the oil was too thick (which it is anyway) then you'd be feeling the suspension as quite harsh even on the small bumps. Having the rebound shimstack around the wrong way is an interesting idea. Thinking aloud here, I don't think that would cause the feeling you're getting. If the stack was the wrong way around, you would effectively have two compression stacks and no rebound. That means any compression action would feel really harsh, but the rebound would try to lengthen your forks as quickly as possible. (Note that it is possible to put rebound valves in the wrong way around, but the difference is only a couple of mm in the fitting and would have no effect on the actual damping performance, because the valves are 2-way, not a 1-way). Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 21, 2003 Share Posted May 21, 2003 I don't think it would, but I'm not a real expert on the subject. I think you made a mistake in the rebound valving, and with the extra-stiff compression due to the heavy oil, it's pumping up. Check your sag, to see if the effective spring rate/preload is correct. It should sag a little over an inch. Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 21, 2003 Share Posted May 21, 2003 Also be very careful when measuring fluid height, as high levels will cause a harsher ride, also. Hmm, just thought of something. Did you measure the height with the forks compressed, or extended...? Do you remember how much total oil you used? Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 The ride is deffinately not harsh, It's real similar to stock. Just more responsive. We added the oil while the fork was extended. I was not the one pouring I was holding the fork tube. I don't remember how much we used. :sad: Big Jeff Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 "but the rebound would try to lengthen your forks as quickly as possible" That's exactly what happens. When I go over a big bump or drop off. Clack !! Like 2 stilletto switch blades Big Jeff Quote Link to comment Share on other sites More sharing options...
SwampNut Posted May 21, 2003 Share Posted May 21, 2003 We added the oil while the fork was extended. AHA! Well, you're supposed to adjust it with the fork COMPRESSED. You've got a shitload of oil in there that shouldn't be there. So the oil is acting as a spring and making the forks top out. Damn, if you think that rides good, you're gonna jizz when you feel them with the right oil at the right level! Remove ALL the oil. You can do this by removing the forks and inverting/pumping, or by removing the bottom bolts with an air impact (will need it for replacement also). Refill with the right oil, pump the forks up and down 10 times and the damper rod 15-20 times. Then measure the height with the forks compressed and the spring OUT. The capacity of both forks is just under a liter, just over a quart. When you buy oil look for a liter jug--if it's a quart it won't be enough. Quote Link to comment Share on other sites More sharing options...
Big Jeff Posted May 21, 2003 Author Share Posted May 21, 2003 Ok, sounds good, thanks. "Refill with the right oil, pump the forks up and down 10 times and the damper rod 15-20 times. Then measure the height with the forks compressed and the spring OUT. " Can this be done on the bike ? Is there a set volume of oil for our froks ? I ordered 2 quarts of Racetech oil last night. "Damn, if you think that rides good, you're gonna jizz when you feel them with the right oil at the right level! " Kick ass ! Big Jeff Quote Link to comment Share on other sites More sharing options...
tvking Posted May 22, 2003 Share Posted May 22, 2003 Sorry Jeff but you're gonna have to remove the forks. :sad: I suppose it's possible to do on the bike but it would be a hassle and I'd want to be sure it was done right. Quote Link to comment Share on other sites More sharing options...
Mithrandir Posted May 22, 2003 Share Posted May 22, 2003 Easy enough to do on the bike. Just pull the axle/wheel/brakes/guard, undo the damping rod bolt on the bottom of the fork and then pump the fork bottom up and down a number of times to get rid of the old oil. Put the bolt back in, then fill up. Quote Link to comment Share on other sites More sharing options...
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