Side to side when braking

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NorCat said:
Many thanks for all your contents and recomentations, the bike has had this bad habit since I bough it.

I will change the steering and front weel bearings and make sure the weel axel and triple clamps are correctly tight as first step as I'm not sure of their perfect state.

Change tires goes second as the front is good and the rear has 25% wear.

The weel axel had play on the fork slider and was modified for proper fitment, i will recheck if that is well enough.

The disc brake is perfectly square, I took off the original disc and fit a floating system with a 13 mm pump conversion, it had a very poor Norvil disc with a Nissin caliper, de adaptor was not high quality either and took it off to fit a Madass 140 full kit with first class fitment to make sure that was nothing left on this department.

Weel alignment is as good as it can be, new rims and isos was the first thing done, the installation of the CNW head steady was the last thing on this department

The fork seams OK and the rear suspension is with new Hagons adjusted too max spring rate, i would like to adjust them to the middle position for better comfort but if I soften them the movement goes worst.

Regards
Antonio
Click to expand...

Hi Antonio,
If it's been like this since you bought it, did you know the previous owner, or do you know the bikes history? It's possible that it was involved in an accident and something is out of alignment. There are different yokes dependant on the year of the bike and they should not be mixed. Why was the hole in the slider larger, do you know? Also what type of handlebars do you have? If they are high it will exaggerate the problem.

Maybe it's worth starting to measure the frame for possible issues? here's a link to an earlier thread which has the frame dimensions pictured.

Is my frame bent?

My seat frame has me wondering if it has been tweaked. I am using the level as a straight edge to show the curve that when I look at other pictures of frames - does not look this way. I would not be surprised if it was - these things happen - learning to wheelie is hard! At least it can be...
www.accessnorton.com www.accessnorton.com

Cheers,

cliffa.
 
Measuring the rake is important. I bought a magnetic base protractor from an engineering supplies shop to do it. A decrease in the rake can decrease the trail and so can increasing the yoke offset. As you increase the trail the likelihood of getting a weave moves from as you brake, to as you accelerate. i.e. Decreased trail can cause a weave as you brake. If you increase the trail, the bike can self-steer positively in corners (oversteer),, but you might need a steering damper to stop the weave as you accelerate out of corners. Oversteer when racing is much better than understeer because you can be much more aggressive and know you won't run wide in corners..
 
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I'd check the frame behind the steering head to see if it looks as though it has been bent from a front end collision. That can decrease the rake.
 
The bike has had this problem since I bought it six years ago.

I don't know the bike's history, it had been waiting 25 years for someone to restore it to go back to the street.


The handlebar is the standard European for Mk3 model.
 
Keep trouble shooting sensible. Then if all the normal checks are OK, start with the more hard to check items. CHECK THE FRONT FORKS. Remove fender and check lower legs for play. You only have to search the front 1/4 of the bike.

Just last week our front load washer started leaking water. I instantly thought door seal and almost ordered one. I decided I was being a bit premature with my diagnoses and looked at supply line and drain hose. The drain hose had popped out of the drain. KISS
 
Beach said:
Keep trouble shooting sensible. Then if all the normal checks are OK, start with the more hard to check items. CHECK THE FRONT FORKS. Remove fender and check lower legs for play. You only have to search the front 1/4 of the bike.

Just last week our front load washer started leaking water. I instantly thought door seal and almost ordered one. I decided I was being a bit premature with my diagnoses and looked at supply line and drain hose. The drain hose had popped out of the drain. KISS
Click to expand...
How can verify if the fork internals are worn?
 
NorCat said:
How can verify if the fork internals are worn?
Click to expand...
Remove fender, loosen tube cap nuts, grab bottom of legs and try moving. This after you do other simple checks. The middle front fender bracket doubles as a fork brace.
 
NorCat said:
Too large hole in the slider was found, an aluminum insert was fited, as there is not much material the shaft was reduced in order to place the insert properly.
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I don't like the sound of this. Do you mean the axle has been reduced in diameter?

If so over what part? These axles are not over generous in the first place.

Not relevant here but the rear axles have a nasty habit of breaking where they screw into the stub axle. Hence the availability of single piece rear axles
 
NorCat said:
Too large hole in the slider was found, an aluminum insert was fited, as there is not much material the shaft was reduced in order to place the insert properly.
Click to expand...

Like JohnM, I don't like the sound of the above statement. The front axle must have the stepped change in diameter or it can't put the spacers and races under pressure properly, Then the pinch bolt tightening makes sure the pair of sliders are parallel. If someone turned the stepped thickness off the front axle and used a spacer in the slider instead, then you need a new axle. (and maybe a new slider if that one has been machined oversized)

The axle must have the step in it like the one pictured below

Side to side when braking
 
o0norton0o said:
Like JohnM, I don't like the sound of the above statement. The front axle must have the stepped change in diameter or it can't put the spacers and races under pressure properly, Then the pinch bolt tightening makes sure the pair of sliders are parallel. If someone turned the stepped thickness off the front axle and used a spacer in the slider instead, then you need a new axle. (and maybe a new slider if that one has been machined oversized)

The axle must have the step in it like the one pictured below

Side to side when braking
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Several of you have pointed to this same direction, I will remake de fork to weel axle assembly with a new axle and a lower fork leg, put new weel bearings, change all fork internal consumables and the directional bearings too.

Things are now clearer for me, many many thanks for your ideas, there is light at the end of the corredor now.

The other ideas have been the working line till now and valid they have been checked and corrected in previous interventions.

It will take some time to get the parts to refit all, I will revert with the end of the story in a few weeks, many many thanks all!

Regards
Antonio
 
NorCat said:
Too large hole in the slider was found, an aluminum insert was fited, as there is not much material the shaft was reduced in order to place the insert properly.
Click to expand...
Replace the fork leg would be my best advise, taking out the excess clearance between the spindle and the leg with a shim is a bodge.
The fact that ther is only one clamp as I found will not sufficiently take out the play and provide a suitable clamping force to stop the assembly twisting under braking.... I bit the bullet and replaced the fork leg.... problem solved
 
olympus said:
Replace the fork leg would be my best advise, taking out the excess clearance between the spindle and the leg with a shim is a bodge.
The fact that ther is only one clamp as I found will not sufficiently take out the play and provide a suitable clamping force to stop the assembly twisting under braking.... I bit the bullet and replaced the fork leg.... problem solved
Click to expand...
I can see a consensus on this diagnosis!
I will do it!
Les see the prices from AN, i believe is the only source, isen't it?
 
Antonio, ALL of us here are guessing what the problem might be based on your discription.

The way to repair ANY bike is to:

1)Disassemble

2) inspect the parts

3) determin if parts are good or bad

4) replace or repair any broken parts

5) reassemble

Just believing all of our guesses at the cause of the problem , and replacing random parts hoping for a fix is not a good repair method. If you took the axle apart and posted pictures of the axle and slider with the insert, maybe that would help your diagnosis, but just from reading your text here, it's really just all of us guessing at the cause of your problem.
 
Hi all: I am just getting around to restoring a 72 combat I bought in 1997 and probably blew up in 2006, I know, my bad. I am the second owner of that bike and bought it from a guy that was not particularly mechanical. I put euro bars on it when I bought it and before I ever rode it far. One oddity - when I was riding it a lot was that it would weave fairly badly when I put my feet on the passenger pegs and laid on the tank moving weight bias to the front wheel. Some of that was tuned out by adjusting the rear wheel to be aligned with the front wheel by sight and not by marks on the forks. However, this spring when I started to reassemble it I found two problems.

First the rear forks where warped so that one end was about 3/4 in higher than the other when the pivot end was laid on a flat surface. Secondly, the gearbox mainshaft had a stress fracture where it rode in the outer sleeve gear bushing. My guess is that is was ridden with one or both chains too tight and that may have warped the swingarm.

I wonder if this was causing my weave since I had the usual avons on it, all of the wheel bearings and head bearings looked good and even the swingarm bushings weren't bad. Only other wear that could be related to handling was that the brake side fork tube had the hard chrome worn off due to braking thrust, I presume.

Anyway, I believe the swingarm can be twisted this way and could be a contributing factor to the weave on braking which transfers the weight to the front wheel in a way not entirely dissimilar.

Just a thought. M
 
ilikevelos said:
Hi all: I am just getting around to restoring a 72 combat I bought in 1997 and probably blew up in 2006, I know, my bad. I am the second owner of that bike and bought it from a guy that was not particularly mechanical. I put euro bars on it when I bought it and before I ever rode it far. One oddity - when I was riding it a lot was that it would weave fairly badly when I put my feet on the passenger pegs and laid on the tank moving weight bias to the front wheel. Some of that was tuned out by adjusting the rear wheel to be aligned with the front wheel by sight and not by marks on the forks. However, this spring when I started to reassemble it I found two problems.

First the rear forks where warped so that one end was about 3/4 in higher than the other when the pivot end was laid on a flat surface. Secondly, the gearbox mainshaft had a stress fracture where it rode in the outer sleeve gear bushing. My guess is that is was ridden with one or both chains too tight and that may have warped the swingarm.

I wonder if this was causing my weave since I had the usual avons on it, all of the wheel bearings and head bearings looked good and even the swingarm bushings weren't bad. Only other wear that could be related to handling was that the brake side fork tube had the hard chrome worn off due to braking thrust, I presume.

Anyway, I believe the swingarm can be twisted this way and could be a contributing factor to the weave on braking which transfers the weight to the front wheel in a way not entirely dissimilar.

Just a thought. M
Click to expand...
It's very possible. Wheel alignment is not purely horizontal, they should be in the same vertical plane as well, otherwise the suspension travel in either direction will be having a very de-stabilizing effect.
 
Twisted swinging arms are very common. My bike had the same issue. However it caused bad tracking when taking hands of the bars rather than an issue while braking
 
I had a problem where my bike went nuts on 70 mph sweepers. [ original Avon GP ] Went through the whole bike then it also started to wobble when i took one had of the bars.

In the end, I removed the Avon and fitted a TT100. problem solved. I fitted the Avon on the back wheel and wore it out with no problems. I use TT100's front and rear, and when the front tyre starts to wear slightly on the sides, I remove it and fit it on the rear. It lets me know any way as it starts to wobble a bit at 30 mph, but is otherwise perfect at high speed.

Tyres are cheep. Even if it does not fix your problem, you wont be out of pocket.

Apply the KISS principal to everything you do before getting scientific.

Dereck
 
" How can verify if the fork internals are worn? "

Remove the DRAIN PLUGS and see what kind of effluant comes out .

If its just muddy grunge , flush with kero ( plugs in , tip kero in, pump forks , drain. repeat . UNTILL CLEAN nil residue drainings )

One throws ALL drainings in say a white two litre plastic ice cream container . plastic.
Let settle and pour off ' the top ' ,

Set down angled . Later stick your finger in the low corner . If theres metalic debri , it didnt come from ELSEWHERE . Somints WORN .

Whoever , if nice clean oil came out , when you initially drained it , we'll let you sit down and have one beer & a silly grin on your face .

Draining , can take a while , as you may imagine . Best to leave container ( and funnel ?) under it for a 1/2 hour .

Blocked , or on centertstand , both'll drain even .
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DONT OVERTIGHTEN the Axle Pinch Bolt ! Can crack the fork casting if babooned .
All them bits wanna be clean and grit free, for CORRECT ' tourqueing ' .
---------------------------------------------------------------------------------

A straight edge set along on top the frame top tube will tell you how many cars its rearended or trees etc hit . A inch or two bow will crank out no trouble .:eek:
 
kerinorton said:
I had a problem where my bike went nuts on 70 mph sweepers. [ original Avon GP ] Went through the whole bike then it also started to wobble when i took one had of the bars.

In the end, I removed the Avon and fitted a TT100. problem solved. I fitted the Avon on the back wheel and wore it out with no problems. I use TT100's front and rear, and when the front tyre starts to wear slightly on the sides, I remove it and fit it on the rear. It lets me know any way as it starts to wobble a bit at 30 mph, but is otherwise perfect at high speed.

Tyres are cheep. Even if it does not fix your problem, you wont be out of pocket.

Apply the KISS principal to everything you do before getting scientific.

Dereck
Click to expand...

The only thing I’d add Derek is that KISS first IS being scientific !!
 
There is a saying in quality management - 'DO IT RIGHT FIRST TIME' - manage the risk. Even a road bike is usually capable of doing 100 MPH - too fast to get off ?
 
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