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Bob uk
Unregistered guest
Posted From: 94.197.122.74
Posted on Wednesday, 24 September, 2014 - 07:58 am:   Edit PostDelete PostView Post/Check IP

In my misspent youth as a motor bicyclist. Going fast on feeble brakes was the norm. Because brakes were feeble correct adjustment was important to maximise stopping power.

When the brake is fully applied the angle between the cable and the brake lever on the drum should be 85 deg approximately so that further application causes the lever to get nearer to 90 deg which is maximum leverage. After 90 deg the further application will lower maximum leverage.

On hand brake systems the same is true whether rod or cable. Some linkages such as Hispano squeezy on RR cars has a complex series of rods that must be set to the angles in the book to work properly. And often an angle is over 90 when off and less than 90 when fully on.

Modern drum brake such as my jeep the cable enters the drum via the back plate and pulls a lever pivoted to the rear shoe. The angle of the cable and lever MUST always be less than 90 deg for the handbrake to be at its best.
Some cars have more than handbrake cable adjustor and it is often possible to get the adjustment out of wack and the handbrake lever feels ok but the relay lever angle is wrong and the handbrake is s##t.

If doing a shadow h/b it is worth reading end of chapter G to get the brake the best it can be which is not very good.

(Message approved by david_gore)
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Bob Reynolds
Prolific User
Username: bobreynolds

Post Number: 161
Registered: 8-2012
Posted on Wednesday, 24 September, 2014 - 07:52 pm:   Edit PostDelete PostView Post/Check IP

Does anybody know why the Shadow has such a complicated system of levers and linkages to operate the throttle, instead of a simple bowden cable?
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 1056
Registered: 6-2009
Posted on Thursday, 25 September, 2014 - 01:20 pm:   Edit PostDelete PostView Post/Check IP

Serendipitous coincidence, the following quotation from Hemmings Sports & Exotic Car, regarding a Bentley of a particular vintage and the violation of the KISS principle of engineering:

"it all appears to have been an effort by highly educated engineers with too little to do engaged in solving a nonexistent problem"
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Bob uk
Unregistered guest
Posted From: 94.197.122.73
Posted on Thursday, 25 September, 2014 - 09:20 am:   Edit PostDelete PostView Post/Check IP

A well balanced and designed rod linkage will give a nicer pedal action and fine control.


But the simplicity of a Bowden cable is attractive.

I noticed that many older cars favoured a rod linkage, about 1960 the Bowden cable which has been around longer than the car started to be used for throttle hand brake and clutch.

Also rod brakes on push bikes were replaced with cables.

The only reason I can think of for the tardy use of cables is a sudden method of making them cheaper and or some design break through.

In all the cars I have designed and built I have always used a throttle cable without a second thought. It's sort of an obvious thing to do, and every home built car I have seen uses a throttle cable.

Having a rod throttle is part of the RR flavour and looks very smart.

Bob UK because my real name is Robert and I come from the United Kingdom.



(Message approved by david_gore)
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 3087
Registered: 4-2003
Posted on Thursday, 25 September, 2014 - 11:59 pm:   Edit PostDelete PostView Post/Check IP

That throttle linkage is a gem. You can drive any old SY banger with all its engine mounts broken yet the accelerator pedal gives no hint of anything amiss. It's just a pity when everything else from the radiator to the propshaft goes guts-up. Lucky that throttle linkage is so simple and lasts forever, long after the bonnet release cable has frayed and snapped and your Vincent Black Shadow has lost its front brakes for the same reason.

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