01-03-2019, 09:54 PM
Hi all, I realise I am opening myself up to ridicule and abuse here again but I had a bit of a Eureka moment this morning at the unearthly hour of 4 o’clock regarding the set up of the brake lever arms attached to the Cross Tube on my Ruby, following previous comments
Despite edging nearer to my 3 score years and ten than I would like, I suddenly thought back to my applied mathematics and mechanics from my old school days.
As a result I am pretty sure that to apply the most force into the system the two outer levers on the cross tube must be as near to top dead centre of the Cross Tube as possible, in such a manner that the prior to application of the foot brake the leavers lean towards the rear and on full application of the foot brake they should be then leaning towards the front i.e. the total arc length of Cross Tube rotation during application of the foot brake must be split equi-distant about top dead centre. I realise that some may say that the pull should stop at 0 deg but the further away from top dead centre the bigger the loss in pulling power due to an angular pull on the cable
Similar to what we all try to achieve with the brake cam levers on all four wheels only at the brake levers we want finish at 90 deg.
Similarly the lower central lever should be set using the same principles.
I attach a pdf of my scribbling which as I say are from a long time ago but I do not believe the maths or laws of physics have changed in that time, altho’ my maths may need checking!
Having stripped the system several times during the past weeks, the basic set up on Ruby has changed very little, and not surprisingly neither has the performance of the brakes, which may denote the onset of madness, keep doing the same thing expecting a different result.
So I have a couple of other thoughts, how do we know just how suitable the brake cables we buy from our normal suppliers are? This is no criticism of anyone, but how do we know if the steel used is of the correct grade, one assumes the steel would be such as to limit extension under load if it doesn’t an awful lot of force could be lost in cable extension.
Some may have seen a post on this thread by my brother who built an amazing Ruby based special in which he asked a similar question. He had no problems with his brake system until he replaced the cables and now the brakes are not as good as they were previously, he posed the question about cables relaxing under load.
Normally all steel has an elastic limit and only when this is exceeded does the steel become plastic and eventually fail.
The other question is the suitability of the brake lining materials how do we know they are correct.
All comments gratefully received.
Best regards to all
Denis S
Despite edging nearer to my 3 score years and ten than I would like, I suddenly thought back to my applied mathematics and mechanics from my old school days.
As a result I am pretty sure that to apply the most force into the system the two outer levers on the cross tube must be as near to top dead centre of the Cross Tube as possible, in such a manner that the prior to application of the foot brake the leavers lean towards the rear and on full application of the foot brake they should be then leaning towards the front i.e. the total arc length of Cross Tube rotation during application of the foot brake must be split equi-distant about top dead centre. I realise that some may say that the pull should stop at 0 deg but the further away from top dead centre the bigger the loss in pulling power due to an angular pull on the cable
Similar to what we all try to achieve with the brake cam levers on all four wheels only at the brake levers we want finish at 90 deg.
Similarly the lower central lever should be set using the same principles.
I attach a pdf of my scribbling which as I say are from a long time ago but I do not believe the maths or laws of physics have changed in that time, altho’ my maths may need checking!
Having stripped the system several times during the past weeks, the basic set up on Ruby has changed very little, and not surprisingly neither has the performance of the brakes, which may denote the onset of madness, keep doing the same thing expecting a different result.
So I have a couple of other thoughts, how do we know just how suitable the brake cables we buy from our normal suppliers are? This is no criticism of anyone, but how do we know if the steel used is of the correct grade, one assumes the steel would be such as to limit extension under load if it doesn’t an awful lot of force could be lost in cable extension.
Some may have seen a post on this thread by my brother who built an amazing Ruby based special in which he asked a similar question. He had no problems with his brake system until he replaced the cables and now the brakes are not as good as they were previously, he posed the question about cables relaxing under load.
Normally all steel has an elastic limit and only when this is exceeded does the steel become plastic and eventually fail.
The other question is the suitability of the brake lining materials how do we know they are correct.
All comments gratefully received.
Best regards to all
Denis S