Brakes make forks twist.

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johnny Lagdon

johnny Lagdon

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For as long as I can remember, well around 5 years anyway, my upgraded disc setup causes the forks to twist. It is visible just pushing forward and putting front brake on. The mudguard squirms to the side of the disc, and I am forever replacing rivets on the bridge. There is a definite clonk somewhere...
I have new bushes, seals, for oil, disc, Landsdowne dampers...
Am I missing something?
 
Engineering 101, upgrade one component, and those around it are suddenly overwhelmed.
Everything is properly set up at the axle? Pinch bolt, etc.?
That mudguard bracket IS a fork brace, the four mounting bolts good & tight?
 
Tops of the stanchions need to be fully mated to the top yoke, and the meter cups and top nuts must be positively TIGHT. Of course the lower yoke pinch boles must be fully TIGHT, as should the fender bracket. Lower fork pinch bolt very tight, then try again.

I'm guessing the top yoke is your issue; please report back...
 
grandpaul said:
Tops of the stanchions need to be fully mated to the top yoke, and the meter cups and top nuts must be positively TIGHT. Of course the lower yoke pinch boles must be fully TIGHT, as should the fender bracket. Lower fork pinch bolt very tight, then try again.

I'm guessing the top yoke is your issue; please report back...
Click to expand...

How could that be the issue, when the slider is free to spin on the fork tubes if the axle bolt is removed??

I would check the axle bolt, pinch bolt, and your wheel spacers. The whole lower assembly is kept at the proper distance apart and aligned by the axle assembly. If something is causing the lower slider to twist, I would bet your axle assembly or your actual slider is to blame.

I have a fiberglass fender held on my hose clamps, which lends zero support to the sliders and I have no twist when I brake hard.

Perhaps you have not used the correct proceedure to "set" your front wheel spacing correctly. You tighten the axle bolt to spec, THEN you pump the sliders a few times before you tighten the pinch bolt. This allows your fork tubes to set your slider spacing to insure alignment before you lock that alignment in with the pinch bolt...
 
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I have one of these ,seems to help


https://www.ebay.com/itm/NORTON-COM...D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

Brakes make forks twist.
 
johnny Lagdon said:
For as long as I can remember, well around 5 years anyway, my upgraded disc setup causes the forks to twist. It is visible just pushing forward and putting front brake on. The mudguard squirms to the side of the disc, and I am forever replacing rivets on the bridge. There is a definite clonk somewhere...
I have new bushes, seals, for oil, disc, Landsdowne dampers...
Am I missing something?
Click to expand...

Are you using a torque wrench on the front wheel spindle ? it requires the full 60 ftlbs to take the wiggle out of the mudguard then pump the forks before you tighten the pinch bolt.

Best Regards
 
It sounds like you rotor and caliper are not parallel to each other when at rest. When you apply you brakes it is causing your slider to rotate into the “correct” position
Another possibility is if you recently had you pads out and put them on the wrong side when you re assembled them. Sometimes they wear with a taper and need to be returned to the same side them came out of.
I never checked the Norton manual but my Honda shop manual explains the whole procedure on setting up the front end and brakes. One thing it does touch on is checking the gap between the rotor and caliper with a feeler gauge to make sure they are parallel to each other
Pete
 
Thank you all for your replies.
I have discovered a new truth: Double check before you enquire/post.
retightened everything and twist gone-ish. Took for decent ride and will recheck....
old dogs etc!
 
How were the top nuts?

Also, I seem to recall the best method was to start tightening from the BOTTOM, and work your way up? (pumping the forks between steps)
 
pantah_good said:
On the /6 or /7 BMW airheads it was top-down.
Click to expand...
May be, but an important aspect would be to carefully eyeball the alignment at each step as well.

Bottom-to-top seemed to make more sense to me, because the axle seems to be the ultimate point to begin the alignment with the wheel itself...

I've always done bottom-to-top, and have caught discrepancies every time that way. Usually a slightly bent stanchion, or tweaked yoke. This assumes I've checked the new bushing for size BEFORE and AFTER installing them; saves time as it turns out, no need to tear everything apart again!
 
I don't think there is much need to over tighten the pinch bolt. It doesn't have to do much apart from nipping up the spindle. The auto jumbles have plenty of broken ones
 
I always tighten from the top downwards ,the pinch bolt on the spindle last , would you really want to tighten your bottom yoke pinch bolts fully then pull the stanchions upwards with the top nuts while the taper in the top yoke fully pulls up and settles?
 
No, I use my stanchion installation tool (can be done with a long section of 3/8" allthread, some washers, and some sacrificial old top nuts) to ensure the stanchions are fully up in the top yoke, then snug (not tighten) the caps to hold them at the top.
Then bottom-to-top tightening. Axle, fender mounts, bottom yoke, top nuts.

...and dont forget the bloody o-rings above and below the headlight ears!
 
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grandpaul said:
...Then, top-to-bottom tightening...
Click to expand...

G.P., don't you mean "bottom-to-top" there?

I wasn't lobbying for one tightening direction or the other, I was just referring back to a verbose, lengthy, and very German-like write up on the care and "proper setup" of those 1970-1980 airhead BMW's written by Kieth Patchett of Kieth's Touring Specialties back in the '80's. 44 pages of closely spaced typed maintenance instructions that I must have sent a check off in the mail for. Did I say very German-like? "You vill do exactly as I say!!" I have to say that I did/do follow his lengthy methods of setting the valve clearance & rockers as well as tightening up the forks with what I believe are good results. For all I know the Norton forks may lend themselves better to bottom up tightening and the BMW's better to top down. When I get that far with my Norton, I will think it all thru again, but I suspect I will lean toward the top down direction. The idea of tightening the axle pinch bolt first just doesn't compute for me.
 
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pantah_good said:
The idea of tightening the axle pinch bolt first just doesn't compute for me.
Click to expand...

Yeah, and what happens when you pull the front wheel to do any repairs, do you have to loosen everything up and re-torque?

Top-down makes sense. Was how I did it as I felt that I had to draw the forks up and in before tightening the pinch bolts.

Besides, the manual says:

All Commando models
6. Offer both fork legs through the lower and upper yoke and pull the main tube tapers into the upper yoke using the instrument cases and large chrome top bolts.
7. With the fork legs secured by the top bolts, snug the socket headed pinch screws.
8. Now tighten the fork securing points shown in Fig G8/9 in this sequence: Chrome top bolts, main fork stem nut, lower yoke pinch screws. Note that the stem nut must not be over-tightened. On 1970 models this would damage the steering head bearings, which must adjust until the forks are free to turn with no perceptible play.​
 
Each to their own method if it works for you then it must be right, when I assemble commando forks I would slide in the stanchions lightly tighten the fork top nuts plunge the forks a couple of times,then fully tighten the top nuts,check the stanchions alignment by sight or with a plate, tighten fully the steering stem nut , tighten the bottom yoke pinch bolts,plunge the forks again sometimes you may see the fork slider move very slightly on the spindle on the pinch bolt side,then plunge the forks again making sure everything works, then tighten the spindle pinch bolt,once you have done that fit the mudguard and stays making sure the mudguard fits perfectly, tweaking it if it doesn't fit ,the mudguard should be seen as a separate item to the forks , although the mudguard mount does act as a brace so should only be tightened once the forks are working properly, every bike with telescopic forks I have used this method and it always works, cheers
 
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