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-   -   Aligning a Fork. Who's done it? (https://www.bikeforums.net/showthread.php?t=1196739)

Classtime 03-27-20 06:49 PM

Aligning a Fork. Who's done it?
 
https://sheldonbrown.com/brandt/align-fork.html

My Motobecane Grand Jubile pulls to the left when riding no handed. It does this with different wheels and wheels reversed etc. The headset is fine. It passes the flop test etc. I believe my fork(s) is a good candidate for the Jobst Brandt treatment because the rim is about 3mm closer to the left fork blade. So, when I adjust each blade 3mm to the side that I need to lean (right), in order to ride straight, the wheel will be centered?
R
Have you done it? Did it work?

thanks
jeff

unterhausen 03-27-20 06:56 PM

I'm not sure what the Brandt treatment is, but I have aligned many forks with the Park fork alignment checker and the Park bending arm tool

Insidious C. 03-27-20 07:06 PM

I did one like that (Jobst Brandt) and was able to make a noticeable improvement. It took very little time and the fork stayed in the frame.

Recently I had fork that the wheel wasn't centered in but the bend was not so easy to see. That went to gugie to fix. I know my limitations.

gugie 03-27-20 07:09 PM

Man, thought I’d started enough threads on this so you didn’t have to ask this question.

The Jobst method works sometimes. Oftentimes the problem is one blade is slightly longer than the other - possibly because the rakes don't match. I made my own fork reraker and have learned how to massage them to be even, dropouts aligned, and parallel.

52telecaster 03-27-20 07:34 PM


Originally Posted by gugie (Post 21387063)
Man, thought I’d started enough threads on this so you didn’t have to ask this question.

The Jobst method works sometimes. Oftentimes the problem is one blade is slightly longer than the other - possibly because the rakes don't match. I made my own fork reraker and have learned how to massage them to be even, dropouts aligned, and parallel.

can i send you a fork?

gugie 03-27-20 07:35 PM


Originally Posted by 52telecaster (Post 21387096)
can i send you a fork?

Got plenty of dorks out here, thanks.

:bike2:

Ah, a fork you say. PM me. Seems I do a couple a month, three currently in l'Atelier. I can usually turn them around fairly quickly.

52telecaster 03-27-20 07:54 PM


Originally Posted by gugie (Post 21387099)
Got plenty of dorks out here, thanks.

:bike2:

Ah, a fork you say. PM me. Seems I do a couple a month, three currently in l'Atelier. I can usually turn them around fairly quickly.

message sent.

Classtime 03-27-20 08:48 PM


Originally Posted by gugie (Post 21387063)
Man, thought I’d started enough threads on this so you didn’t have to ask this question.

The Jobst method works sometimes.

I have the tools for sometimes. 🤞

thumpism 03-27-20 08:56 PM

Back in my shop days we did test rides after every assembly and "hands off" was one of our test modes. If the bike did not track straight we'd tweak the fork (in the bike) to fix it. Bike goes left, tug fork blades left; bike goes right, tug fork blades right. A few millimeters was usually sufficient and we always realigned the fork tips afterwards.

By "tug" I mean that, with the bike in the stand, you first measure the distance between the dropouts so you have your ground zero, then brace a knee against the fork crown and pull the nearest blade toward you; that is, you tug the right blade to move it to the bike's right. Then you tug the left blade to close up the gap you just increased. You'd work from the opposite of the bike to go in that direction. Good luck! It's not difficult.

As mentioned by others, there might also be issues with differing fork blade lengths or bends.

Classtime 03-27-20 09:01 PM

But,
Jobst Brandt wrote,
"If the fork is only bent to the side, the correction must be to the side to which the rider must lean when riding no-hands."

thumpism 03-27-20 09:09 PM


Originally Posted by Classtime (Post 21387205)
But,
Jobst Brandt wrote,
"If the fork is only bent to the side, the correction must be to the side to which the rider must lean when riding no-hands."

Was that a response to my suggestion? I suspect that Jobst Brandt would want the spacing of the fork tips to be correct, so if you move one fork blade you would also move the other.

Classtime 03-27-20 09:22 PM


Originally Posted by Classtime (Post 21387205)
But,
Jobst Brandt wrote,
"If the fork is only bent to the side, the correction must be to the side to which the rider must lean when riding no-hands."


Originally Posted by thumpism (Post 21387216)
Was that a response to my suggestion? I suspect that Jobst Brandt would want the spacing of the fork tips to be correct, so if you move one fork blade you would also move the other.

Correct. Both Blades. But, if bike steers left, I must lean right to keep straight. And I move the blades right.

thumpism 03-27-20 09:25 PM

Bike left, correct left is what worked for me.

Doug Fattic 03-27-20 09:34 PM

I'm a long time pro builder and teacher and must confess I don't read or evaluate what home shop methods might work. What I can say is that really accurate fork alignment is a bit of a process. I'm also a painter and have found the majority of frames that have come in for work were not that accurately built. Well at least not up to top American frame building standards. The blades need to put the dropouts at exactly the same rake (the up/down distance) and equidistant from the steerers centerline (the same side to side distance) . In addition the flats of the dropouts need to be parallel to each other and the blades + dropouts need to be the same length so a wheel centers. If any one of those are a bit off, it can prevent a wheel from being in the dead center.

My fork fixtures are very accurate and I have to make sure when the steerer is tightened down, the fork is not twisted. The fixture will tell me how the fork needs to be bent. I take the fork out of the fixture to bend it by holding the steerer in my bench vise with a wood block and pull whatever direction the blade needs to move. This is a back and forth process until both the up and down and sides put the dropouts right where they belong. Then I take my Campy H tools (dropout alignment tools) and tweak them until the H tools Cups match each other. Now I can use a true front wheel to see if it centers. An advantage of a 1" steerer is that sighting down the steerer it is easy to tell if the rim is a bit to one side or the other. If it is off, I file a bit out of the dropout slot until the wheel centers. I never start to file until all the other checks show perfect alignment. (By the way there is not such thing as "perfect "alignment" but on a fork I would not be satisfied if something was more out than just a couple of tenths of a mm.)

Classtime 03-28-20 06:47 AM

Thanks Doug.
I'll put this here also https://www.bikeforums.net/19566057-post16.html from Andy Stewart.
Next step will be to try these ideas and see if I can make my $50 rescued Motobecane ride as nicely as my $70 rescued Raleigh.😉

repechage 03-28-20 07:44 AM

From eBay I purchased a VAR fork alignment fixture long ago.
it is for checking the fork and as Doug wrote the fork is to be removed to manipulate.
Like Gugie, I have made my own tools for “encouraging” them straight.
long ago Park made some too.
one method that the shop owner I first worked for employed was to have a number of short straight ga spokes, they would get placed on the fork in intervals and then “sighted” it would often guide the work quickly, exposing a blade that was taking a more direct route to the dropout.
the VAR tool does require the crown race be removed and as Doug also wrote set without twist.
I would not straighten any fork without the tools.
the other item to check after- barring mfg defects- of which did happen with more frequency than one would have hoped, do check the frame for headtube/seattube twist.

i always suspect those extravagant paint mid 80’s Italian frames. Even out of the carton.
i had a reputation for sending those back.
the distributor never argued. That shop owner learned not to notify the buyer the frame had arrived until approved.

T-Mar 03-28-20 07:46 AM

Before you attempt a fork alignment, make sure that's it not the head tube that twisted relative to the seat tube or a misaligned rear triangle. Both can cause the same symptoms. All three measurements and fixes are relatively easy to perform, though the corrections involve trial and error, which is greatly facilitated by proper tools and experience.

Ferrouscious 03-28-20 02:43 PM

It really doesn't require much to do a general alignment on a bike, just basic tools and patience. Check frame alignment with the string test. Tweak with gentle persuasion with a 2x4. Check spacing with a ruler. My process for checking fork alignment is to remove it, clean it, and place it on a known flat surface facing forward/downward. Take note of the crown's position relative to the flat surface. One side might be a little lower than the other. Install a wheel without its tyre and sight down the steerer tube through the valve hole in the rim. Centered? Good. If not, realign the blades or file the dropouts, whichever is needed. Check dropout spacing on the fork. Assemble bike and properly adjust headset. Can you ride without hands? If not, re-rake one side of the fork with the appropriate tool (preferably a pro tool, but homemade works too). Have a shop align the derailleur hanger and check the dropout faces for parallelism. Done!

If at any point you feel uncomfortable with the necessary steps, take it to a shop, or better yet, a framebuilder.

unterhausen 03-28-20 03:17 PM

I have to say I wouldn't mess with a fork until I measured it.

noglider 03-28-20 03:34 PM

There are three measurements that matter. 1. If the two blades are off to one side, that's the easiest to fix, and I have done it successfully.

2. The rakes must be the same. This is the distance forward of the plane formed by the steerer tube. This is harder to get right.

3. The length of the blades must be the same. Sometimes when correcting the rake of one blade (2), you alter the length. This is why I've found fork alignment to be so tricky. When you fix (2) or (3), you worsen the other.

Classtime 03-28-20 05:38 PM

It has begun.

https://cimg1.ibsrv.net/gimg/bikefor...bedd463091.jpg

billnuke1 03-28-20 06:51 PM

Park Tool FT-4...

https://cimg0.ibsrv.net/gimg/bikefor...34582cb9f.jpeg
This works, too...

billnuke1 03-28-20 06:57 PM

You’ll need this, too...but, be careful...very effective!
https://cimg9.ibsrv.net/gimg/bikefor...1b870d2d5.jpeg
Cool tool...zombie wacker!

Kabuki12 03-28-20 07:56 PM

My daughter has a 1978 Grand Jubile and right after she bought it I took it to a bike shop to buy new tires for her run by a guy who raced and actually knew the ins and outs of these bikes when they were new. After putting new tires on her bike , he was mounting the front wheel and said the alignment of the fork was off. He showed me his gage and then he got out his tool and with some persuasion was able to align the fork. He let me watch him , I had never seen that level of work done.

Classtime 03-29-20 09:14 AM

Well....
I put it back together and it is a little better no-hands. Before the next adjustment, I'll need to fashion a workable gauge. I can't make the sight tube thing work with my current assortment of garage stuff--The steerer tube on my fork has some additional stiffener thing brazed in at the crown and my sight tube is too large.


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