It stops! But...

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I've got the new forks and disk brake on my bike. The brake is bled, the leaks are fixed, and it WORKS! Now I can stop! And with the Nissin master cylinder it doesn't have that "wooden" feel. The new forks seem to work well also, and the 40 mph headshake is gone (old forks had bent tubes and sloppy bushings).

But. The front wheel is way out of alignment. It's offset 10mm to the left. The fender doesn't fit and the bike was pulling to the left on the test ride. Hub alignment looks good, it's the rim/tire that appear off. Could the wheel have been built with the wrong offset? It's an ebay special and I don't know its history. Is there anything else I should check before getting out the spoke wrench? I don't see anything else obviously wrong but appearances can be deceiving...

Debby
 

Anonymous

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Think the rim has an offset, to allow for the disc and such, maybe it is also the case with a drum brake. My tire is very close (1/8 inch) on one side to the fender support. If it's pulling to the the side, though, have you loosened the top nuts, the nut on the bottom of the steering head and the pinchbolts on the triple trees up and bounced the front end up and down a few times to let everything find it's place and then retightened it all up? The forks can bind if the triple trees are tightened in the wrong alignment and cause strange things with the handling. Isolatics are in shape, you once said, and the only new change is the forks...there is, I assume, oil in both forks and not just one, or? Someone will correct me if I'm wrong, but the chance of there really being gross misalignment with an original rim seems slim. Who would change it, for what reason? If the rims are non-stock, though...might be. On your picture, it appears to be an original rim. See what the others say...someone will have a solution that won't involve a spoke wrench.
 
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The pics show the bike with the old drum brake. This is the new disk brake front end I'm talking about (that's why it stops now). New forks (with new stanchions) and a used wheel I bought off evil-bay.

The disk brake wheel does have a large offset to accomodate the rotor. This wheel came from a bike that ran at some time in the past. It's an original Dunlop rim but I don't know if the wheel is rebuilt or not. Still, you'd think it should be reasonably close. I hate to go messing around with the spokes unless I'm certain that's the problem. But some say the rotor-side spokes should appear "nearly vertical" due to the offset. These don't. Also, the spokes on each side have about the same tension. You normally have to tension the rotor-side spokes higher to pull the rim over. So maybe whoever built the wheel didn't get it right.

But I'd better go through the fork alignment procedures again too. I might not have that right.

Debby
 

ILLF8ED

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front disc brake wheel offset

Hi Debbie,

There is definitely an offset to the left for front wheels with disc brake. I just measured mine from the rim to the fork slider on each side.........it's 1 1/4" on both sides. This is with original Dunlop MC275 rim and Buchanan stainless spokes. Kelly Moss in San Jose built my wheels.

I checked the NOC website to see if they had offset dimensions, no luck. They just comment that when the wheel is attached to the fork the rim should be centered.
 

Anonymous

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like Alice said..."curiouser and curiouser".

Mine was always off center between the forks (disc brake, 72)., and may it sound dumb or not, but my rear wheel, when viewed from the rear of the bike, is off center by reference of the tail light and such, also to the left...but even assuming the fact of being off center, it should still drive straight, as long as the wheels are aligned with each other and the forks are straight, or? Some machines have everything off center, and still drive straight as an arrow...witness a Vespa Scooter if you will. It is unbelievably heavyer on one side than the other, due to the motor weight being all on one side, but they handle wonderful depite that fact. If debby's bike didn't have this pulling before the fork/wheel change, it should be there that the problem will be found. Unless the isolastics have gone to pot, that will cause a pull to one side too. You say the fender won't fit on now...how can that be, is the tire scrapeing on it or what? If so, it would indeed be an extreme amount of "off center" to cause that...let us know.

Just found Captain Nortons notes:

http://www.captain.norton.clara.net/cnn3.html

49.1 Wheel Offset.

Date: Mon, 11 Dec 1995 09:13:41 -0500
From: MOTOJEMS

When lacing your '74 Commando front wheel, the offset distance between the brake rotor mounting surface and the CENTERLINE of the rim should be 1 13/16" (that's one and thirteen sixteenths). The drum rear wheel should have the rim centred. If you need more advice, call Buchanan's 818-280-4003.
Lanny "Greaseberg".
 

ILLF8ED

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front disc rim offset

Hi Debby,

I just measured mine using a string taped top to bottom on each side of the rim and measuring to the center of the flange where the spokes attach. Right side (disc side) 3/4" inside of rim & left side 1/2" outside of rim. Spoke flanges on the hub are 2 1/2" side to side and the rim is 2 3/4" side to side to the outside of the rim. The distance from the outside of the rim to the mounting plane of the disc is about 3/8" no where near 1 13/16". I wonder is the 1 13/16" is for a rear disc.

As you said the disc side spokes look vertical, while the other side has a conical appearance.
 
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40 mph headshake gone?

40 mph headshake gone?
Guess what is coming back when you straighten that wheel!
And to think that all along I thought tire pressure contributed to the headshake, and it was mere correct wheel alignment.
Ahh, those sneaky Brits.
 

Anonymous

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Recommend taking the time to read the middle link, a couple of entries above. Long and drawn out, but, if you can picture what the author is trying to explain......really good info. maybe not what all of us can do or afford, but the theory of how all of the isolatics funtion together, will be enough to make you feel funny about not checking this stuff out when you have the mchine apart next time...mine will be looked at......
 
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Re: front disc rim offset

illf8ed said:
Hi Debby,

I just measured mine using a string taped top to bottom on each side of the rim and measuring to the center of the flange where the spokes attach. Right side (disc side) 3/4" inside of rim & left side 1/2" outside of rim. Spoke flanges on the hub are 2 1/2" side to side and the rim is 2 3/4" side to side to the outside of the rim. The distance from the outside of the rim to the mounting plane of the disc is about 3/8" no where near 1 13/16". I wonder is the 1 13/16" is for a rear disc.

As you said the disc side spokes look vertical, while the other side has a conical appearance.

I took the measurements tonight and indeed the wheel is built with the wrong offset. The rim needs to be pulled over another 5mm to the rotor side. That will center the rim in the forks and the rim-hub measurements will match yours also.

The spokes are tensioned pretty much the same on both sides (and not tight enough either) so maybe I can loosen the left/tighten the right and get it into correct alignment, if I'm lucky. If I'm not lucky I'll have to get new spokes of the correct length and maybe a new rim if this one is drilled incorrectly.

I do have experience building bicycle wheels and the rear wheels are built with an offset like this to provide clearance for the cogs. On a typical 8 or 9 speed rear, the drive side spokes are usually 2mm shorter than the non-drive ones and they're tensioned tighter too. It's called "dishing" the wheel. I wouldn't be surprised if these spokes are all the same length and the rim is recycled from a drum brake wheel which has a different drilling pattern I'm told. I have a feeling it's going to need a complete new build but we'll see...

Debby
 

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front wheel offset

debby,

If you have an original Dunlop rim on the front, the drum brake rim code is MB41, also same for the rear drum brake. The original rim for a disc brake front is MC275. It's stamped on the rim. If the spokes you have aren't the right ones I doubt if you have enough threads to offset the rim. Good luck!
 

Anonymous

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Thats good concrete info that I didn't know....thanks...I have to find two rims for my next project, and that will help me......
 
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spokes

Greetings,
Debby mentioned certain bicycle rims having different length spokes.
I checked my 850 parts list manual and noted that there are four different spokes listed for the disc brake wheels (IE inner and outer for the left and inner and outer for the right), no doubt of different length. When lacing and truing the wheel you should be able to tighten the spokes up evenly and the offset will be built in.
justa thought,
 

MichaelB

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Hi Debby, Glad to hear it's 5mm not 10. My Mark III was off 3/16 in the front and was able to be corrected. You might be able to, good luck.
 
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I looked at the rims before leaving for work. Both are original Dunlops. Rear is stamped MB41, front is stamped MC275. So it's the right rim. At worst I'd just need new spokes. :)

Thanks for the info David! Would probably be hard to tell the difference by inspection.

Debby
 
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