Bowdenex REAR levers

[John Mims]

I've been working on the brakes on an RN that one of my sons has bought. This had an original Bowdenex front brake conversion, which we decided to leave.

Having sorted the front hubs, brakes and cables, I turned my attention to the rear brakes, starting on the O/S. The shoes were completely dry and had very little wear. 

However, the levers are are 3/16" longer, centre to centre, than the cranked front ones (I think this means that the front brakes have been coming on sooner). The rear lever is the type with an eye and a tiny split pin hole drilled through it to anchor a headless clevis pin. The lever has 1A7197 stamped on it, which appears to be from a 1936 Ruby (interestingly, this is the number for the N/S lever, not the O/S).

I did consider fitting new long ball-end levers, as a set of new ball-end cables came with the car, but these are also 3/16" too long, and I would really prefer to have front and rear levers of the same length. I tried fitting a spare Bowdenex cranked front lever of the same length, but it either reaches too far forward or too far backwards.

I would be interested to know what rear levers other people have fitted to accompany a Bowdenex front conversion. Were matching levers supplied with the kit? Does the extra 3/16" in length matter? Will I have to fabricate them?

Thanks in advance

John

PS. I've lost my link to Dave Armstrong's Speedex site and can't find it again. I seem to remember that brake levers were dealt with there.

[Ian Williams]

I am a fan of CORRECTLY assembled and set up Bowdenex conversions, in good condition they work well and solve the problem of rotating front axles reducing brake efficiency, in a this case if may be easier to simply revert to an open cable. Regular readers here will know that an unworn and properly set up std braking system is considered by many of us to be fit for purpose and completely adequate for normal use. If your actuation system is compensated perhaps the 3/16" will not matter, there is also a school of thought that shorter front levers helps with bringing on the fronts harder than the rears, remember in a perfect world we want the fronts to do more work than the rear. Leverage ratios in the complete system should be considered and I am assuming you have a std uncompensated cross shaft with standard leverage ratios? With all non standard set ups there is an element of trial and error when trying to make it work, for every action we take there is usually a trade off of some kind.

[Bob Culver]

The Bowdenex was suited to specials with lowered axles and extended radius rods which are even less rigid than normal.
3/16 seems hardly here or there. The leverage varies considerably anyway depending on the degree of cam rotation.
What is total length of arms? I have asked before but no responses, but can long levers be fitted to rear pre Ruby axles (without inverting) I suspect the Ruby axle has the cams further forward enabling long levers. Has car got original diff?

[Speedex750]

Hi John,

The SPEEDEX site is under reconstruction, kindly to be hosted by the A7CA (note to self; must get my finger out with it).

The rear levers you describe are for the short lived 1936 models to go with the oval backplates and shoes (some are cast iron, some aluminium) with the offset pivot. The rears should be 2 1/4" between centres and matched, on a standard set up, with front levers 2 3/8" between centres. The 1936 fronts look like Girling type ball ended levers but without the recess for the felt washer. As you point out the rear levers are handed, the eye is twisted slightly to match the approach angle of the cable, they should be installed leaning in towards the backplate.

Usually Bowden front levers are cranked (and handed) with 2", 2 1/4" or 2 3/8" between centres and came with equal length straight rear levers. I'm not sure how much science went into the design of these but some extra leverage, at a cost of pedal movement, is probably not a bad thing.

These standard rear levers are probably better than the short Bowden ones, equivalent to the mid sized ones and only slightly shorter than the 2 3/8" ones. They should work fine on a Bowden set up in my opinion.

Hope of use, Dave

[John Mims]

I am a fan of CORRECTLY assembled and set up Bowdenex conversions ...... and I am assuming you have a std uncompensated cross shaft with standard leverage ratios? With all non standard set ups there is an element of trial and error when trying to make it work, for every action we take there is usually a trade off of some kind.

Thanks for such comprehensive and helpful advice, Ian. Yes, the RN has an uncompensated cross shaft, although not quite standard as it is solid bar rather than tube, but fitted with standard length levers. It seems a previous owner put some effort into the braking system as all the cross shaft bushes have been replaced and have no play in them. In fact, after being unused for a few years, they had seized to the cross-shaft.

......What is total length of arms?
I have asked before but no responses, but can long levers be fitted to rear pre Ruby axles (without inverting) I suspect the Ruby axle has the cams further forward enabling long levers. Has car got original diff?

Bob. For length of the rear arms, please see below. As for whether they fit on pre-Ruby axles, they seem fine on the RN, without being inverted. If anything, they could sit a little further back.

Hi John,

The SPEEDEX site is under reconstruction, kindly to be hosted by the A7CA (note to self; must get my finger out with it).

The rear levers you describe are for the short lived 1936 models to go with the oval backplates and shoes (some are cast iron, some aluminium) with the offset pivot. The rears should be 2 1/4" between centres and matched, on a standard set up, with front levers 2 3/8" between centres. The 1936 fronts look like Girling type ball ended levers but without the recess for the felt washer. As you point out the rear levers are handed, the eye is twisted slightly to match the approach angle of the cable, they should be installed leaning in towards the backplate.

Usually Bowden front levers are cranked (and handed) with 2", 2 1/4" or 2 3/8" between centres and came with equal length straight rear levers. I'm not sure how much science went into the design of these but some extra leverage, at a cost of pedal movement, is probably not a bad thing.

These standard rear levers are probably better than the short Bowden ones, equivalent to the mid sized ones and only slightly shorter than the 2 3/8" ones. They should work fine on a Bowden set up in my opinion.

Hope of use, Dave

As ever, Dave, thanks also for your extensive info on brakes. As a result, I've been re-measuring the levers I've got. The rears are 2 1/4", as you said, not 2 5/16" as I first thought. Of the Bowden fronts that I've got, one is 2 1/4", the other three are nearer 2 1/8", so I'm down to approximately 1/8" difference in length, front to rear. Having drawn arcs of 2 1/8" and 2 1/4" in my notebook, I can see that the difference in movement along a tangent is very small. So will probably just refit the rears, but properly handed. Look forward to the Speedex site re-emerging.

Thanks to all three of you for your help

John