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Help needed - fork tweak

Old 07-12-09, 11:42 AM
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markk900
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Help needed - fork tweak

A month or two back I managed to do a dumb 1mph crash in my back yard that ended up bending my front rim. I sourced replacement rims (Alex DM18), and rebuilt my front wheel. Everything went pretty well until I did a quick test ride the other day to see how things were settling in, and discovered that my bike now wants to pull fairly hard to the left.

I've spent several days now trying to see where the problem might be - my suspicion is that I tweaked the fork a bit in the crash, causing the wheel to be canted ever so slightly. However, I can't see anything obvious and when I try checking alignment with a straight edge I can't find any significant issues.

Question: how do I determine where the problem might lie? If it is the fork, is it possible to twist it back? If not the fork, what do I look for in my wheel building that might be causing this issue?

Bike is my Peugeot AO-8 - stock frame and fork....

Any advice is much appreciated....

Mark

Last edited by markk900; 07-12-09 at 11:42 AM. Reason: typo
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Old 07-12-09, 12:32 PM
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The problem could be the fork or the frame itself, possibly a twist in the head tube. The fork could have one leg offset fore/aft relative to the other and/or both could be shifted sideways relative to the steerer column.

Provided the are no actual creases in the fork blades (usually on the back and just below the crown), they can be straightened. Checks and striaighterning can be done at home, but they are tedious and require removal of the forks. Most people prefer to utilize a well equipped LBS. If you're still interested in proceeding on your own, let us know.
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Old 07-12-09, 12:37 PM
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thompsonpost
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When you bend it once, it becomes weak. Bend it again and it becomes weaker. Bending it back could end in disaster after you've ridden it and start to get too confident. You could end up breaking it in the same place next time and at a much faster speed.
 
Old 07-12-09, 12:40 PM
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Also consider a bent steerer. I have a fork where the blades are only a little off, but the steerer itself is bent ever so slightly to create a pull.
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Old 07-12-09, 12:42 PM
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Sounds like a tweaked fork. But could you have inadvertently dished the front wheel rebuilding it? Make sure your front axle isn't bent also.
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Old 07-12-09, 01:23 PM
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Thanks all so far for the thoughts - whatever is bent it is not by much - there is no visible bend, so damage to paint, no cracks, etc.....I'm mostly upset because it was such a slow speed spill and both taco'd my rim and now apparently bent something else. I am not overly concerned about bending this back if it can be done - its not out enough that bending it back will put tremendous stress on anything.

I had wondered about the dishing, but measuring from the seam at the back of each fork leg to the rim using a digital caliper the wheel is as centered as I can make it...perhaps 0.5mm out?

Hadn't checked the axle yet - thanks for the suggestion. Also, hadn't considered a side-to-side tweak - found an article on line suggesting a way to realign that. T-mar, I am interested in trying this at home first.

How would I check the steerer? I expect the reply might be take it to a good shop and let them see if they can find the misalignment, right?

I've had this bike since 1973 - it really pisses me off to have this problem after all this time! Thanks again for the suggestions.

Mark
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Old 07-12-09, 01:47 PM
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thompsonpost
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IMHO, straight up, I would buy a new fork and install it and be done with it. You're really stressing, and considering the bike is 36 years old or older, a new fork is a good start in the major maintenance department.

Otherwise, I'm sure you're going to take it all apart, try to fix it and either damage it further or discover a replacement is in order.
 
Old 07-12-09, 04:23 PM
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I spent some time with straight edges and rulers and determined that there was a little lateral displacement of the fork legs when I went down....I've mcgyvered things back into place and it seems much better now.

Thompsonpost: you are of course correct - the ultimate solution is a new (used) fork, however that will need paint and decals, so will be a longer term fix. My daily rider is the Trek I picked up early this year so the Peugeot is more for nostalgia and occasional rides.....so I can afford to fix it slowly.

However, one of the main reasons I like old stuff is to hold onto an era where things were fixed rather than replaced. I want to be able to tear something down, renew only what needs renewing, and build it back again.....so I will always look first to finding a way to retain a part rather than replace it.

In this particular situation I was taking my inspiration from Eugene Christophe, who broke his forks in 3 TdFs: in the 1913 race he carried the bike 14km to the next town, and borrowed tools and material in the blacksmith shop to fix his own forks....after hours of work he returned to the race to finish 29th. Ironically, he was also riding a Peugeot!

Mark
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Old 07-12-09, 04:36 PM
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Mark, I would also check the steerer tube, which is inside the head tube. I've bent one before and had to ditch the fork for a replacement. You'll need cone wrenches for the top nut on the headset.
 
Old 07-12-09, 04:51 PM
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Considering the relatively low speed of the crash there's a very good chance nothing needs to be replaced.

Install your front wheel and check its position, remove it and flip it around. If its in the same position your wheel is properly dished and the issues with the fork.

Forks with legs that are sweeped to the side or with 1 leg back are tough to eye up.

1. Align your front wheel with the top tube and measure the distance from the centerline of your skewer to the centerline of your BB or rear axle. A difference from left to right will tell you if a single leg is bend back in relation to the other.

2. If you know your wheel is properly dished dead on, install and check to see if its centered in the fork. While sitting on the bike if your wheel is canted left your fork need to bent to the right. Obviously if your wheel sits canted to the right your legs are bent to the left.

Hopefuly your not dealing with a combination of a side bend and a back bend.
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Old 07-12-09, 05:42 PM
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Axle, anyone?
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