Bowdenex Brakes

[Malcolm Parker]

I am currently overhauling a set of Bowdenex front brakes which are destined for the sprint car project.  The cables were still connected up to the back plates and operating levers and that end of the system is no problem.  The other end of each cable has a threaded rod attached and between this and the cable outer is a piece of mild steel 1" x 1/4" x 4" long  with three holes. This is presumably bolted to the chassis (front cross-member?) to locate the cable outer.  It looks as if there should be a threaded sleeve that screws onto the end of the cable to clamp it against the piece of steel bar, and take up the slack.
I am going to use a Ruby type brake cross-shaft and would like to know how the two Bowden cables are connected to the central lever of the cross-shaft. I assume there must be some form of balance arrangement. 
My project will have a floor attached to the underside of the chassis cross-members and about 4" of ground clearance so I cannot afford to have any parts of the braking system protruding below the floor.

[Steve Jones]

Malcolm's photos of the Bowdenex parts referred to above.


  Bowdenex Cables 2.JPG (Size: 41.73 KB / Downloads: 656)


  Bowdenex Cables 1.JPG (Size: 37.77 KB / Downloads: 647)

Steve

[Ian Williams]

You are correct Malcolm the flat bar bolts to the front crossmember and on the systems I have worked on there is a round bar around 4" long with two 1/4" holes passed through the the drop arm of the cross shaft for connecting the inner cable's. There is no swivel compensator as you can tension each cable independently, if you wanted to fit a compensating device the cables would need to be shortened.

[stuartu]

Malcolm, according to page 60 of your copy of my book (I am still grateful for the money, thank you) the bar is of silver steel. If you have not done so already may I recommend hanging the cables up somewhere convenient and applying (SAFE!) heat to persuade years of solidified grease to depart. I tend to replace with a lightish oil eg one's modern car's engine oil but often that is hardly necessary.

Regards,
Stuart

[John Cornforth]

Hello Malcolm

I still have the Bowdenex parts I removed from my car years ago, which I have just measured for you.  The 3 holed strips do indeed fix with 2 bolts each to the cross member and hang down.  I don't know how far apart they were mounted laterally, but for a straight-ish cable pull (see below) it would be 4 or 5 inches. There is a lower counterbored hole in the front of each strip into which the ferrule of the cable outer is located, there is no nut or other fixing for this. Even though they are made from quarter inch thick "boiler plate", I suspect that both they and the cross member probably flex back a bit when you are really using the brake pedal - a triangulated arrangement would probably be stiffer.

There is also a steel bar which is half an inch diameter and five and one sixteenth inches long.  Through this are two quarter inch holes spaced by 4 inches.  The threaded cable inner ends pass through these and are equipped with nuts and locknuts to set the cable length. The bar is a sliding fit through the two holes of the forked end of the central lever descending from the cross shaft, and takes the place of the standard yoke and swivel compensator.  The bar normally sits symmetrically in the central lever, even though there is no fixing or screw to guarantee this. Brake balance is achieved through cable length adjustment, though I suspect that additionally the bar may pivot just a fraction and the central lever may twist a fraction to give a little bit of compensation, given the high forces on them.

People seem to have mixed views on Bowdenex.  The main advantage is that it removes the "anti servo" effect of front axle twist experienced with the earlier lighter pattern front axle, and removes the effect of steering lock on braking.  The kits (From Super Accessories ?) included longer levers for the front, plus a matching set of longer levers for the rear so pedal pressure was reduced (in theory) in exchange for a longer pedal travel and more frequent need for adjustment. The disadvantages are extra weight and cable friction especially if full of old grease ( Some say that oil should be used ).  Ground clearance is no better or worse than the standard open cables.

Hope this helps

John Cornforth

[Malcolm Parker]

Malcolm, according to page 60 of your copy of my book (I am still grateful for the money, thank you) the bar is of silver steel. If you have not done so already may I recommend hanging the cables up somewhere convenient and applying (SAFE!) heat to persuade years of solidified grease to depart. I tend to replace with a lightish oil eg one's modern car's engine oil but often that is hardly necessary.

Regards,
Stuart

Thanks Ian and Stuart, that is very helpful.  The fitting instructions on p60 make complete sense.  I was thinking of a way to compensate the front brakes but now realise I don't need to.  The cables are very stiff, full of solidified grease. Heating them and refilling with oil is a job for tomorrow.  I had thought of coiling the cables up and putting them in the oven in a pyrex casserole dish but don't know how long they will take!

[Mike Costigan]

Next week's casserole may taste a bit funny ...

[Malcolm Parker]

Thanks John, that is very useful and simple enough to do.  I think the secret with Bowdenex brakes is to use thin oil in the cables to minimise friction as Stuart suggests.  My backplates are fitted with the correct long cranked Bowdenex levers.

[Ruairidh Dunford]

Be careful to make sure the correct one is correct to everything else you have.

Mixing does not work (guess how I know).

   

   

I had other examples but have given them away - no photos, sorry.

Which is which? Stuart, over to you...

[Robert Foreman]

I would not use silver steel for the anchor but instead use EN24T. Also my views are similar to Ruairidh's, maybe stronger.