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taff_d

199a Front Brake

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never mind that - what are the lottery numbers!:rolleyes:.  joking apart yes i agree about the cast iron liner, however my mate did his using a brake disc/drum hub off a 4x4 that had the handbrake shoes on the inside, it may have been a Terios??  your liner suggestion is better, far less machining and as you say one liner will probably do 2 pairs of hubs.

 

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As stated above all pivots need to be 100% and the thing held on while you pinch it up. In the end its an old bultaco and as vesty said (sic) i dont worry too much about brakes.

have you seen his cutaways?

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10 hours ago, hencam said:

never mind that - what are the lottery numbers!:rolleyes:.  joking apart yes i agree about the cast iron liner, however my mate did his using a brake disc/drum hub off a 4x4 that had the handbrake shoes on the inside, it may have been a Terios??  your liner suggestion is better, far less machining and as you say one liner will probably do 2 pairs of hubs.

 

If I won 20 million in the lottery I'd spend half on coke and hookers. The other half I'd probably just waste...

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Finally got to have a look at the brake, the drum has definitely been sleeved with cast iron and measures the correct 125mm. Measuring over the shoes it reads 123mm (this is with new shoes fitted) is 1mm aside a bit excessive for clearance ? The brake arm spindle is very slack in the brake plate this will need machining and sleeving and the cam profile is worn so I'll have to do a repair on that as well.

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Hi Taff, some folks make the hole in the brake plate 'big', so when you fit the wheel you can apply the brake to centralize the plate and shoes....then tighten the spindle to lock it in the centralized position. Hope that makes sense, cheers.

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2 hours ago, bashplate said:

Hi Taff, some folks make the hole in the brake plate 'big', so when you fit the wheel you can apply the brake to centralize the plate and shoes....then tighten the spindle to lock it in the centralized position. Hope that makes sense, cheers.

I've always viewed the whole "hold-the-brakes-on-while-you-nip-up-the-axle" routine with extreme scepticism. I mean, if everything is in good condition you're going to have what, maybe 2 thou clearance between the backing plate bore and the axle - not enough to allow any significant movement. Likewise, if everything is in good condition you'll have nice square faces on the backing plate, the sleeve in the fork slider and the bearing spacers, so that when you tighten the axle everything pulls up squarely and securely with no scope at all for movement. But if things are so worn that you have to play these mickey-mouse games upon reassembly then I think some work to restore proper fits is in order. There simply shouldn't be any possibility of the backing plate being out of alignment once the axle is tightened.

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I own one Bultaco 125 mm front brake backing plate that the brake cam hole was crooked in the backing plate. I did have the hole machined square and a sleeve inserted by a qualified person but it never worked properly. It was always spongy and wore the shoes on an angle. Just check that before you go too far. It must have been either a Monday morning or a late Friday afternoon one. That`s the only explanation I can think of as to why it is crooked. Graham.

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On 04/07/2017 at 8:57 AM, scot taco said:

Oldjohn,

I have a few spare IT175 front wheels(one of my favorite bikes) and would like to use one of those on my 199a.How did you secure the backing plate to the fork? The only other thing that I have not checked out are axle sizes to see if I could get the correct bearings in it for the Sherpa axle.

Sorry about the long delay in replying but here are a couple of pics. I polished the hub and if you stand back far enough, and it's dark, and you squint a bit it doesn't look that much different from a Bul hub. The backing plate was anchored with a 3mm thick P clip or strap; I'm sure there are neater methods but I didn't want to weld anything or do anything that wasn't easily reversible. The additional arm and spring was added as a temporary measure (about 2 years ago) until I could fit a hairspring to the original arm. I still haven't done this....

The stock Yam brake worked well, but I like to experiment so modified it further. I added an anchor lug (held by the two bolts near the cam in the photo) and removed the pivot pin opposite the cam. The cam now only works against the leading shoe, and this shoe pushes against the second shoe (via a floating bobbin) which in turn bears against the anchor lug. Basically it's just a copy of the servo style drum brake layout that was commonly used in cars. It just needs a very light touch - you can easily lock it up with two fingers on concrete or one finger on dirt. Still it isn't over-touchy and is quite controllable. I'm thinking about trying the same system with a Bul hub (using an iron liner) - this might give decent brakes but still retain the original appearance.

 

 

yambrake1.jpg

yambrake2.jpg

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On 09/07/2017 at 2:20 AM, oldjohn said:

I've always viewed the whole "hold-the-brakes-on-while-you-nip-up-the-axle" routine with extreme scepticism. I mean, if everything is in good condition you're going to have what, maybe 2 thou clearance between the backing plate bore and the axle - not enough to allow any significant movement. Likewise, if everything is in good condition you'll have nice square faces on the backing plate, the sleeve in the fork slider and the bearing spacers, so that when you tighten the axle everything pulls up squarely and securely with no scope at all for movement. But if things are so worn that you have to play these mickey-mouse games upon reassembly then I think some work to restore proper fits is in order. There simply shouldn't be any possibility of the backing plate being out of alignment once the axle is tightened.

it sounds like it shouldnt matter but does make a marginal gain (sky) and thats what we're after.

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20 hours ago, oldjohn said:

Sorry about the long delay in replying but here are a couple of pics. I polished the hub and if you stand back far enough, and it's dark, and you squint a bit it doesn't look that much different from a Bul hub. The backing plate was anchored with a 3mm thick P clip or strap; I'm sure there are neater methods but I didn't want to weld anything or do anything that wasn't easily reversible. The additional arm and spring was added as a temporary measure (about 2 years ago) until I could fit a hairspring to the original arm. I still haven't done this....

The stock Yam brake worked well, but I like to experiment so modified it further. I added an anchor lug (held by the two bolts near the cam in the photo) and removed the pivot pin opposite the cam. The cam now only works against the leading shoe, and this shoe pushes against the second shoe (via a floating bobbin) which in turn bears against the anchor lug. Basically it's just a copy of the servo style drum brake layout that was commonly used in cars. It just needs a very light touch - you can easily lock it up with two fingers on concrete or one finger on dirt. Still it isn't over-touchy and is quite controllable. I'm thinking about trying the same system with a Bul hub (using an iron liner) - this might give decent brakes but still retain the original appearance.

 

 

yambrake1.jpg

 

Thats not good at all.

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On 16/10/2017 at 4:49 PM, nigel dabster said:

Thats not good at all.

If by that you mean it's ugly then I'd have to agree. But all I have to do is fit a conventional stay rod and return spring to make it look fine. 

The areas where I usually ride have lots of long, steep hills and again, the brake is not good. It's bloody brilliant!

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39 minutes ago, oldjohn said:

If by that you mean it's ugly then I'd have to agree. But all I have to do is fit a conventional stay rod and return spring to make it look fine. 

The areas where I usually ride have lots of long, steep hills and again, the brake is not good. It's bloody brilliant!

No. To have a protruding arm is against basic trials design

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Get hold of a Grimeca , ex Fantic SWM, etc.  While your on, fit it up with the drum at the correct side. For some strange reason Bulto put it at the wrong side & cable routing is rubbish. 

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On 03/07/2017 at 10:14 PM, hencam said:

Hi TrF, 

i went with the recommendation of Steve at VS, it is a brown material, very fibrous and has like a very thin brass weave in it.  he will know, I think he does a grey material which is slightly harder but still better than the hard, polished grey shiney $hit that comes on replacement shoes. I made an error in my calcs to Steve and given time constraints, I wanted them for the weekend and this was Thursday I had to machine them, it is a bugger to machine, nice sharp HSS lathe tool eventually did the trick.

I had the same trouble with my cub hubs in a Drayton C15 and my Whitton Hubs in a Drayton Bantam, even with new aftermarket brake shoes and the top quality Whitton hub the brakes could best be described as mediocre,  a quick call to Steve at VS and 2 pairs of shoes in the post arriving next day, before my exchange shoes and cheque could have got to him.  they are slightly more expensive than off the shelf ones that don't work but they transform the bike and give you a steady progressive brake that will bite if you want it to.   VS are knowledgeable and the service is 2nd to none

 

  

Yes VS do a god job, have their trials spec rear shoves on my Sherpa.

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