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[stinkwheel]

This is on my iron barrel 350 trials bike.

In short, apply brake. Excessive braking force applied, rear brake locks, wheel skids, brake plate rotates in swingarm, mayhem ensues.

First time I put it down to me having the brake rod too tightly adjusted and it locking as the suspension compressed. The pivot pin actually sheared and ripped itself out of the swingarm.



I replaced it, made a new brake rod reassembled and went for a test ride. First application of the brake it did the same again. This time it also broke the pivot pin end of the brake shoe and buckled the end plate of the swingarm so badly, I felt it was safest to replace the swingarm.

This time, new swingarm. New brake plate because the other one was buckled, new pivot pin, new brake shoes. Attached the cam bush "finger tight", placed it in the drum, applied the brake firmly, removed the brake place carefully and nipped up the cam bush retaining bolts with a thin spanner, appled the locknuts. I then put the assembly in the bike, loosely fastened the hub spindle and pivot pin nuts, mounted the wheel then applied the brake and nipped up the hub spindle nut, pivot pin nut and wheel nut before releasing the brake and adjusting the brake so it had free play even on full suspension compression.

Went out for a ride today. Covered about 30 miles with the rear brake being fairly poor (as expected with new shoes). Towards the end of the ride I had a wee "incident" (both me and a car approaching a narrow bridge, both of us going too fast). Emergency stop and the rear locked. After this, I noticed the brake was grabbing with minimal application so I rode home carefully without using it.

On inspection, yet another pivot pin is now bent (this is number 3, a fourth one never made it to a road test because the threads stripped as I was tightening the nut). Another set of shoes fractured at the pivot pin end.

Couple of other points.

It's done it with two different drums.

My brake setup has a homemade shorty brake lever which operates from the standard fulcrum. The back part of it where the brake rod attaches is the same length as the original. The pedal section is about 1/4 the length of the original for the trials footpeg positioning so I should be applying significantly less pressure than a standard one.






I do notice (and always have noticed) a degree of sideways flex on the brake plate when the lever is applied.

Thoughts so far as to what might be going on here:
Is the flex in the brake plate causing the shoes to misalign when applied?
Perhaps the floating bush moved when I panic braked?
The grip of the trials tyre when it locks is such that the brake assembly can't cope with the force?
The pivot pins are sub-standard and are bending when a powerful braking force is applied?

This is getting expensive. It's cost me two sets of shoes, a swingarm, four pivot pins and a brake plate so far!

For one thing I'm going to ask my local engineering guy to make me a new pivot pin out of EN8 or better.

I'm considering looking at some way of preventing flex on the brake plate:
1) Welding ribs to the original,
2) Fabricating a new one out of steel plate that's "full thickness" all the way round instead of just reinforced in a strip along the middle.
3) Fitting a Reddich made alloy brake plate, but I'm not sure if they'll fit?
4) Springing for a Somner rear brake plate. I'm not sure my German is good enough to order one though.

Interested in other thoughts...

[Duke of Wybourne.]

Is there a possibility that when you are applying the brake that the application is causing a " servo effect" on the shoes, i.e. That they are pulling themselves further on once they come in contact with the drum ? I've seen it happen, but never on an Enfield.

[Wheaters]

Is it possible that something is coming into contact with the brake pull rod? It looks very close to the underside of the footrest. If the footrest came down onto it as you were braking, or hit a bump, it could multiply the force applied to the brake assembly.

It must be taking a huge amount of force to lock the rear brake like that; looks like a geometric locking force.

[stinkwheel]

Is there a possibility that when you are applying the brake that the application is causing a " servo effect" on the shoes, i.e. That they are pulling themselves further on once they come in contact with the drum ? I've seen it happen, but never on an Enfield.

That's what it feels like, like the brake was "camming on" although it wasn't doing it this time until after I did an emergency stop on tarmac and locked the wheel. I locked the rear a few times deliberately during the rest of the ride to see where the bite point was but that was on a loose surface, braking performance was mediocre -as expected- and locking the rear took firm pressure.

After that initial lock up, the slightest application of the brake causes the same effect. I'm assuming the pivot pin and brake shoe had failed by this point. it was like something "let go" during the emergency stop.

Is it possible that something is coming into contact with the brake pull rod? It looks very close to the underside of the footrest. If the footrest came down onto it as you were braking, or hit a bump, it could multiply the force applied to the brake assembly.

It must be taking a huge amount of force to lock the rear brake like that; looks like a geometric locking force.

I thought the rod tightening as the suspension compressed is what happened the first time but I can't see anywhere it's happening. I was careful to make sure the brake wasn't coming on even at the extreme end of its range of movement.

It's not as close to the footpeg as it looks in that picture. If anything, the rod is further away from anything it could foul now because I've got extra long shocks fitted. I checked for anything fouling when I first got the rear end assembled by moving the swingarm up and down beyond its normal range of movement with no shocks attached.

A couple of better pictures:


You can't see in this view but the rod is well clear of the pivot pin laterally.


Brake shoe damage, suggesting a torsional force? Although in fairness, this may have happened as a result of the pivot pin twisting:


What's getting me is the damage this is doing. I'd expect even if the brake were camming on and totally locking up, surely the wheel should slide before the pivot bends?

I'm going to pull the hub apart tomorrow and look for other issues.

Couple more thoughts:
There is slight (as in a barely visible rocking) sideways play of the brake cam in the bushing.
Could the whole wheel have moved in the swingarm fork-ends causing it to toe-out? And would that cause the brake to over-apply? The spindle was done up tight although I didn't check the position of the snail cams when I undid it all to see what the damage was.

[windmill john]

Not a hijack, but a rant of sorts...

I’m new to RE, over a year or so. But, I’ve had many bikes, a fault possibly, but have performed most maintenance tasks on my bikes, I try to do everything; though the novelty of tyre changing is wearing off!

But.... I have never seen anything like the rear brake adjustment on my cast iron!!! It is one of the hardest jobs I’ve ever done and that includes timing chain on Airheads; easier I say!

Maybe I’m doing it wrong, but I cannot believe the tightening of the axle nut keeps the bike straight, how crazy! So I loosen all three nuts as per the manual. I really need to loosen the big nut a lot as the snails are hard to adjust if I don’t. So chain adjusted, big nut tightened. Brake on, brake nut tightened.

Okay, so we have right hand side of axle miles away from the snail. I have to pull the wheel towards me, clamp it with my foot whilst I tighten the axle nut.

I cannot comprehend having a wheel held straight by the tightness of the nut! Thanks god it’s castellated and has a cotter pin.
Any other bike I’ve had, if the nut came loose then the chain might slacken, but you wouldn’t end up going round in a bend.

The brake works well, but I’m surprised more have not sheared due to strain.

[Nitrowing]

After the 2nd failure I'd be looking for a rear disc conversion!
Normally, a rear wheel will lock up long before mechanical failure so I'd think there's something seriously wrong with the hub that's causing this. Is it cracked?

[Wheaters]

A useful "mod" I've found is a pair of snail adjusters with a 1/4" square hole cut through them for a (socket set) ratchet driver. Levering the cam adjusters round using the socket handle makes it a much easier job.

Alternatively, you could buy a pair of Mr H's adjusters which slip on over the ends of the swing arm "legs"(?). These work like other adjusters. I think you need to ensure that both ends of the axle plate are parallel, otherwise they wouldn't sit vertical. On my 350 I'd need to grind the lower part of the plate back about 6mm.

https://accessories.hitchcocksmotorcycl ... 0adjusters

[stinkwheel]

After the 2nd failure I'd be looking for a rear disc conversion!
Normally, a rear wheel will lock up long before mechanical failure so I'd think there's something seriously wrong with the hub that's causing this. Is it cracked?

Might be now?

I'll be having a very good look at everything when I reassemble although it has done this with two different drums. I'm going to check the various spacers for damage and paralellness (is that a word?) too.

[p]

I'm looking at the picture of the cracked brake shoe; when I last replaced shoes on my 350 yr 2000 I had to file out those ridges in the "half Holes"ends as my pins didn't have grooves for them, don't know if it is of any relevance?
I can imagine lugs being forced apart otherwise, which would result in fracture just where yours is.....

[Nitrowing]

A useful "mod" I've found is a pair of snail adjusters with a 1/4" square hole cut through them for a (socket set) ratchet driver. Levering the cam adjusters round using the socket handle makes it a much easier job.

I fitted stainless ones I found on ebay (because they're prettier ) and they're a definite improvement.