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feetupfun

Sherpa T Brake Shoe Pivot Arrangement

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The offset pivot arrangement for the brake shoes in both wheels of my M198 had me wondering if there were brake shoes from a different bike that would fit and not have the offset pivots. I'm trying to maximise the performance of the brakes by avoiding the eccentric loading against the drum that the standard bultaco pivot arrangement creates.

I have looked in the EBC catalogue and there were a few alternatives that looked like possibilities. Fantic 240 shoes appeared the closest in the catalogue. They are for the same diameter drum and are the same width shoe and use a standard pivot arrangement.

I know I can have the existing shoes modified by welding and machining then relined but it would be a lot easier if some other shoes fitted.

Has anyone tried something like this?

Thanks

David

Photos added

Edited by feetupfun

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Bultaco brakes like most ts drums are not that good but don't see how a differentmake will help.

Road bikes of the same era had twin leading shoes that would be better.

The thing that makes them work better is to make sure all the componantry is 100% and yours could be 50 % of the trouble.

Rod back gives the best results, I have bushed the pivot points as well before now which helped.

Long arm s on both as well.

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Yip, don't see the point of going non standard, fit Newfren shoes and linings (available from Bultaco UK)

Rod back brake (not cable); well lubricated pivot points: centralise the brake by pulling the lever on fully when tightening the wheels spindles and as Dabster says long brake arms, all help.

One of the best set ups I have ever ridden was Snr. Greeves' 199A model, the back brake was fantastic, no grab and progressive action to slow the plot down most effective.

I learned about centralising the brakes from Vic Allan back in 1974. He watched me refit my back wheel and intervened saying "Are you not going to centralise that brake then?" He demonstrated the technique and that's how I learned!

Big John

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Hi Feetupfun,I don't know if you've had steel liners put in the hubs yet but when you do it might be an idea to find someone(a local machinist perhaps)who will machine the liners such that you end up with the absolute minimum clearance between lining and liner.This will help to increase the contact area and also reduce the amount of lever movement.I did this to mine and the results were really good.Cheers,ALT.

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I usually get the shoes fitted with oversize linings and then machine the linings to fit the diamater of the drum. Same principle just prefer to machine the shoes which are cheaper and easier to replace. One other thing prefer cast iron liners if poss.

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If you have a thicker liner and minimal clearance,you can use standard shoes-no need to machine shoes every time they are replaced.Just my opinion.Incidentally why iron in preference to steel? Cheers,ALT.

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I'm not a qualified engineer, but does an iron lining not disipate heat better than steel? Hence iron barrels with steel liners?

I might be wrong...

Big John

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Coefficient of friction + better feel with cast iron IMHO plus i can choose the material that i have the shoes relined with :thumbup:

Edited by Old trials fanatic

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Thanks guys. I agree with your suggestions. I think I gave the impression of being a bit of a yokel with those photos. They are "before"photos of a bike which came in boxes and had been sitting around for about 20-25 years, judging by the age of the tyres (Japanese trials universal Dunlop on front as fitted to TY twinshocks when new, and Pirelli MT13 on rear).

I've attached a photo of the front wheel in the process of being restored as a reference for the standard of the restoration I'm aiming for.

By the time I get to ride this bike it will:

Have had high friction linings fitted to the Bultaco shoes, and machined back to exactly fit the drum, while in position on the backing plate.

Have had both drums lined with steel (front drum already lined when I got it and has just been machined to remove slight grooving and rust) (cast iron liners not available where I am getting the rear drum lined).

Be using a rod and left brake pedal.

Have the backing plate centralised when tightening the axle nut.

Have a lubricated cam and bush and brake pedal pivot.

Have a high tech, low friction front brake cable.

Be using the original AMAL brake lever.

Have a lengthened brake arm on the front.

Bushing the pivots as suggested by Nigel Dabster will get rid of 99% of my issue with the design so I'll probably go that way.

Thanks

David

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I too like the polished brake hub exterior. always thought the el-cheapo black paint was just a way for a financially stuffed Bultaco to save money from 1978 on

I too seek a more eficient front brake. Have performed most of the fixes herein mentioned-still not that flash, as many a marking observer at the end pegs will attest. Recently got a set of Newfren shoes from Bultaco UK - will fit shortly

However, my research reveals an Italian Enduro bike called a Accossato ( 80cc & 125cc) from the late 80s or early 90`s ( last drum bike before the disc ) had a TLS brake hub at 125mm X 25mm, the Sherpa size. The shoes are still in the EBC catalogue, but I can`t find an EBC dealer who has them, here or in UK

If I could get a set of those shoes I would have a TLS backing plate machined up to fit the Sherpa T. front drum

There is apparently one downside to a TLS front brake on a Trials bike-they are not very efficient going backwards.

I know, you are not supposed to go backwards, but occasionly ambition ( or is it ego ) exceeds ability and I find myself stranded up a bank on a loose surface with a (slowly ) backwards sliding bike. A little retardation in that situation would go a long way.

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I too like the polished brake hub exterior. always thought the el-cheapo black paint was just a way for a financially stuffed Bultaco to save money from 1978 on

I too seek a more eficient front brake. Have performed most of the fixes herein mentioned-still not that flash, as many a marking observer at the end pegs will attest. Recently got a set of Newfren shoes from Bultaco UK - will fit shortly

However, my research reveals an Italian Enduro bike called a Accossato ( 80cc & 125cc) from the late 80s or early 90`s ( last drum bike before the disc ) had a TLS brake hub at 125mm X 25mm, the Sherpa size. The shoes are still in the EBC catalogue, but I can`t find an EBC dealer who has them, here or in UK

If I could get a set of those shoes I would have a TLS backing plate machined up to fit the Sherpa T. front drum

There is apparently one downside to a TLS front brake on a Trials bike-they are not very efficient going backwards.

I know, you are not supposed to go backwards, but occasionly ambition ( or is it ego ) exceeds ability and I find myself stranded up a bank on a loose surface with a (slowly ) backwards sliding bike. A little retardation in that situation would go a long way.

Theyre also illegal over here.

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Being picky the hub came black?

Nigel Dabster

You've got a good memory and eyes like a hawk. Yes the black painted bit on the ribbed section and spoke flange has to wait till next weekend. The conical polished bit is standard though.

That reminds me of something. The brochure shots of my M198 look quite drab with the black motor and black fork sliders compared with the preceeding shiny models. I do like to maximise shiny bits but am keen to have it look like it did from the Bultaco factory.

OTF what's that about no TLS front brakes on twinshocks? It's OK here in OZ with rules only specifying "drum brakes" for twinshock class. Don't see too many TLS brakes though. Maybe it's the travelling backwards fright factor?

DabDab the linings for the M198 are relinings of the original shoes by an automotive brake company using a very high friction coefficient material. I've recently fitted a set to my KT250 (after machining hub and shoes) and it is a revelation. I'm in the process of fitting a set to my 250 Majesty too and expect to be assembling the wheel this weekend. Will post results.

Edited by feetupfun

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