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Sttering lock up under heavy braking

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I am a new convert to classic biking and have a 1960 Dominator 99. All appeared great until, on a ride out, I found it necessary to brake hard (my bike has a TLS front brake) when the steering tightened up to the point where I found it very hard to balance let alone steer to avoid an object in the road.  Any ideas where to start looking?

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Sounds like the head bearings need adjusting or in worst case need changing.

regards

Tony

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Sounds like something amiss in the steering head department! Put the bike on the centre stand and move the bars full lock from left to right, is the movement smooth and frictionless, are cables of anything getting in the way? If you get on the bike and roll it a few feet forward and apply the front brake you might be able to feel the free play in the steering head.

Then secondly,  put the bike on the centre stand, raising the front wheel offf the ground, place yourself in front of the bike and slacken off the steering damper if one fitted, (you probably do not have one fitted), whilst keeping the bars still with the left hand, push and pull the front wheel with your right hand and feel for  free play in the bearing adjustment. If the steering is notchy you may get away with adjustment, but if adjustment cannot correct any free play or tightness, it is new bearings I am afraid.

Check your wheel alignment, are the wheels aligned properly, long straight pieces of wood help here and a mate.

Check front and rear suspension function, works properly.

Has the bike got an MOT? Or when was it last done? Unlikely to be this but is your frame straight?

Is there play in your wheel bearings, spin the front wheel, it should turn freely and quietly, do the same with the rear wheel, make sure the rear chain has no tight spots.

Is there play, in the front brake TLS unit, slacken the Front brake off then re-adjust, turning the wheel to check for the bite point, when the brake is applied, make sure the brake shoes free, when the front brake lever is released. Then report back!

 

John

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I had some alarming things happen on one of my bikes. On heavy braking the front brake cable snagged and when the suspension unloaded  the brake  fully locked up and the bike would not move an inch . Thinking it a fluke I forgot about it . Bad mistake!!.Later the steering damper fell apart and dropped into the wheel locking the steering to one side at 50 mph. .Never realised I had grass track skills. 

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This locking-up of the steering, under heavy braking, is generally the result of the mudguard wedging between the two downtubes. Though worn head races may also add to the problem.

Not saying that your problem isn't steering bearing related, but from your description the brakes could also be a suspect.  Did this occur shortly after you started out? Some brake linings absorb moisture, particularly in humid weather, and can be very grabby until you cook the moisture out with gentle application at very slow speeds. Different linings can cure this. Linings that are contaminated with oil or gas can be grabby. (I don't think you can clean contaminated linings - I think they have to be replaced.) Sometimes disassembling the brake plate and cleaning and sparingly lubricating every bearing surface with high temperature grease can cure grabby brakes.

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As it is the steering that locks up it is almost certainly to do with the bearings, not the brakes, even though they trigger the fault.

By all means check the most easily accessible items like play or noise from the wheel bearings, but it would have to be seriously bad to lock the steering!

The head bearings may be so badly worn that the ball races are locking into a heavily worn outer and/or inner race or the bearings/races may have broken up.  This would give the same result whether they were ball races or taper rollers.  As Tony says, you might need to adjust or change them.

With the bike on the centre stand and weight off the front wheels, turn the handlebars fully left and right several times, listening or feeling any grating or crunching - then do the same with the weight on the front wheel.  Even if you can't detect anything you would need to dismantle the forks and get at the bearings.

I think some of the answers here are assuming you have wheel lock-up rather than steering.

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There is very little clearance between the frame tubes and the mudguard on featherbed Nortons. What can happen, especially if the mudguard stays are a bit long, is that under heavy braking the forks compress fully and the mudguard hits and wedges between the downtubes. This is particularly noticable with improved braking from TLS brakes. Check the mudguard for witness marks from frame contact. 

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A shunt in the past can slightly bend the front downtubes  and shorten the wheelbase making contact with the mudguard possible.  Apart from the braking contact the handling may not be adversely affected, in fact it may feel better, !. It depends on what you are used to.

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I had the mudguard / frame tube interface problem on a Norton / Enfield hybrid many years ago when descending Hard Knott two up. The guard caught between the frame tube and exhaust on hard brake application causing total lack of steering. How we laughed......

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This gets worse by the minute, the front mudguard jamming into the front frame tubes, under heavy braking, either too much movement in the Roadholders or a badly designed plot, you couldn't make this up!

Not sure the Norton brake jamming situation front mudguard jammed in the frame rails is one I would look forward to, in a tight situation, stiffer progressive fork spring of thicker oil in the forks maybe!

 

 

Is this what they meant with the "Unapproachable Norton" epitaph on the rider's gravestone!

 

 

John

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Look elsewhere as John says, with forks on full compression on any motorcycle the mudguard should not engage with the frame.

Check the build of the front end, mudguard and frame to see what is in the wrong place. 

Using the mudguard / frame combination as a fork stop is not a good idea nor was it designed that way. 

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Hear, hear, Ashly...there is no way the mudguard can reach the frame unless the bike has had a front end shunt. I have however seen several over the years that have suffered exactly that.

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... a pattern mudguard or stays bringing it closer to the frame. Or as in my case mismatched frame, forks and yokes.

The Enfield / Norton (Enfield frame, Norton ES2 engine and gearbox) was actually a real horror but I needed a bike in a hurry and it was available cheap.

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At least it wanted to go straight on. Mine landed at high speed after a flight from a humpback bridge,the wheel turned 90 degrees ,the bike went end over end a few times ,one of its landings was a soft one. me. I thought it was totalled. and me too. But a few days in Hospital ,I patched it up and rode it back to London from Cumberland.  As you did back then.

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The Featherbed frames were built on jigs but often tensions built into the headstock by the welding process for the tubing resulted in front end steering angles which did not match those of the plans.

The fact is (& several postings above confirm this) the front mudguard will jam up against the downtubes under heavy braking. This should not happen....but it does and quite a number of riders who have come a cropper as a result of this unwanted wedging will confirm this phenomena.

On my 1965 Atlas it did so and this was confirmed by the marks on my freshly stove-enambled frame done by the correctly fitted  Dominator front mudguard. The steps I took as a solution were to renew and preload the internal springs, renew the damper pistons and use straight SAE 30 oil in the forks.

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Phil and others who have experienced the Norton "Mudguard frame" clash! I know you are all men of integrity and it seems like most of you survived fairly unscathed, except for Robert, I believe it was cited that Norton Road Holders had a 5 1'2 to 6 inch possible  fork movement, did/does the Covenant conversion help negate the clash also do Matchless Teledraulic's, on which Road Holders were copied from avoid this error of bottoming out, or is it just an unfortunate approximation of mudguard to frame down tube positioning on certain machines?

I used to have a  "Test circuit" event in Ramsgate very early in the morning whilst trying to tune the front forks of my BMW K75, this involved a few straights, a 90 degree bend a chichane  pass the waterfall e..t.c. not quite the IOM but good enough to predict front fork behaviour and I found after some R& D the cheap 20/50 motor oil in the forks gave me the best experience, even over expensive Fork oil and gave better Lap times on my phones Stopwatch!

 

Incidentally, my new front forks from RGM have the oil holes moved so that the bottoming out issue doesn't happen under a full braking event.

 

 

John

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Gentlemen,

 

Many thanks for all your helpful suggestions.  I thought I would start with the easiest to determine and the one that best fitted the symptoms - the mudguard/frame interface!.  There it was on the front of the frame clear evidence that it had been in contact with the mudguard.  The original mudguards had been replaced with stainless steel items, the front one attached to the bottoms of the forks by a stout round stainless bar bracket which passes round the outside of the guard, this also bore evidence of contact with the frame.  Problem solved once a replacement mudguard can be found which sits closer to the tyre.

Again many thanks

Mike

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There is no problem with forks bottom out under braking, the problem is how they get there. The hydraulic conical throttle valve system is very good providing it is right will give a soft stop. I have seen the same system on periscope mast elevation systems, it works well. 

Mudguard fitment is usually the cause. Pattern mudguards or even correct mudguard not fitted where it is supposed to go. Then you have the different sliders, bridge pieces various etc, so worth checking the whole set up. Just like the Domi centre stands recently sold online not by a UK vendor I may add, gives the bike a nice swing accessory that does little else. 

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I suspect  that  the main issue you have is the stay is too long. Wanting a slim mudguard (mine is for an 18"wheel), I shortened the stays to keep the mudguard close to the tyre - with a new tyre, the moulding spikes very gently brush the bridge in the forks.

Even with my Laverda front brake used hard I have no dings in frame or the mudguard.

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Might be worth checking the wheelbase to another slimline. One possibility a sidecar yoke got in there?.Still looks too close. 

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I always thought that sidecar yolks extended the wheel base, this mudguard hitting is a shortening issue. As soon as I read the first post I though aha we have been there and got the T shirt. I had the dent in the mudguard to prove it. I don't think that forks bottoming out would/should cause this but a wrong fitted mud-gaurd!! The first time I experianced this was nipping round Hyde Park corner in the half dark with the option of black ice lurking.-we rode home very carefuly after this!!

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Have to admit I know zilch about sidecars , I was put off when with a mate we decided to do the Dragon Rally with a Panther and  SC .Then the girlfriend wanted to come. On the test run the sidecar and bike went different ways.I think she thought it was deliberate,  Its possible.

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My advice is don't mess about with this - do the steering freedom checks advised by other members and if in any doubt, just renew the two stem bearings - it's simple, quick and cheap and then you know all is good there. Just done this - coincidentally - on my 1960 Dommie 99, so now have complete faith it will be fine on the road.

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Robert:

Did you double up in the sidecar with your girlfriend?

That must have been fun!!!!

Mike

 

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