Potential to overcome broken throttle cables

[oldbutnotslow]

Having suffered yet another throttle cable failure whilst at Spa last week I have set about looking at the likely cause and a possible solution. On every occasion the failure of the cable has been at the throttle pedal end.

The standard arrangement on my car has the inner cable soldered nipple passing through a slot to fit inside the top of tubular throttle pedal. See pic 1 here

This arrangement bends the inner cable just at the point that it exits causing stress on cable when the throttle is closed and again with near or full throttle opening. The constant bending of the cable would appear to cause fatigue of the metal strands leading to eventual snapping of the strands and subsequent failure of the whole inner cable. This problem is compounded by the pedal arrangement not having a maximum travel restriction and by my having a heavy right foot!

 

I wanted the solution to

A) Be simple

B) Be easy to make and

C) Provide as far as possible provide a linear pull on the cable. (difficult given the arc motion described by the pedal)

My solution was to utilise a similar arrangement to that used on the clutch cable. See pic 2 here

The throttle pedal was drilled and a U shaped bracket formed which has been attached to the throttle pedal by a small bolt and 2 lock nuts which provide free movement up and down of the bracket. The new arrangement has the throttle cable passing through a hole drilled at the front (bottom of the U bracket) with the inner cable being secured by a solderless nipple.

This would appear to give a fairly linear pull and to overcome the fatigue problem caused by the constant bending.

I propose welding a bar on the rear of the throttle pedal which would be threaded and a bolt and lock nut arrangement similar to the at rest pedal height adjuster fitted to provide maximum travel restriction.

Only time will tell if this is just a load of hokum or if it will work but it cant be worse than the standard arrangement!

 

 

Grant Taylor - Oldbutnotslow

OBNS Motorsport

 

[Grubbster]

Fit a pedal stop (or long bolt) as well, takes minutes and removes all the unnecessary load from the cable.

[Geoff Wilcx]

Second for a pedal stop - its the the quickest and most reliable fix...nothing more to it that that.

 

My Winter '08 Upgrade was to a screaming DVA K05.

 

www.geoffwilcoxphotography.co.uk

[Bricol]

Indeed - pedal stop sorts it. 8yrs and cable shows no sign of damage.

 

Bri

[Jason Plato]

the metal of the pedal looks like it would eat through the cable as it passes through in front of the throttle pedal.

 

All you have to do is file a slot *down* the length of the pedal so that when the pedal is depressed the cable doesn't come into contact with the metal of the pedal.

 

second safeguard is to fit a throttle stop to prevent stretch as mentioned above.

 

 

here is my Duratec R .... C7 TOP

Taffia AO

[Paul Deslandes]

I used a clevis arrangement along similar lines to yours and it works very well. I combined it with Bob Simon's pedal box lead in roller/pulley arrangement which solves the problem of the throttle cable being bent through a sharp angle just before it enters the pedal box, but you really only need this if you have a large sausage air filter which forces the cable downwards. A pedal stop is essential and should be on all three pedals, including the clutch if hydraulic.

 

 

[shn7]

Pedal Stop every time. All three of my Sevens had had both clutch and throttle pedal stops fitted and I've never suffer a cable failure.

 

Steve.

Sussex (West) AR

Not forgetting Percy the Polar Bear who recommends

Puddle Pet Care

[John Vine]

all three pedals

Clutch and throttle, yes, but the one in the middle 🤔.

 

JV

[Paul Deslandes]

Yes, fair comment!

 

 

[susser]

I've thought about a similar arrangement to yours Grant. The current design is very poor and looks like a prototype. This looks much more workmanlike.

[millsn]

I made a yoke by welding another parallel arm to my throttle arm and mounting an aluminium pivot between the two. The throttle cable is (was) then held by a grubscrew through the aluminium pivot block (it was roughly 10mm square and 1" long) and the whole aluminium block pivotted with the movement of the throttle cable as the arm went though its travel. Pdeal operation was much smoother, no subsequent failures. I no longer need the same setup so it got junked years ago or I'd post some pics.

[susser]

Another good way would be to use an arc shaped top of the pedal so the cable only bends at a good sized radius. (No moving parts)

 

Edited by - susser on 17 Oct 2009 22:46:47

[Alaskossie]

Another solution, used by bsimon in USA, is to machine a small ball-bearing guide pulley that mounts in the throttle-cable hole in the pedal box.

 

Of course, access to a machine shop and a handiness with tools helps considerably.

 

Alaskossie

[Bricol]

All seem rather over-complicated.

 

Ensure the cable is positioned in the pedal box so it acts as it's own bushing and the inner doesn't drag on any metal part of the pedal box.

 

Bend the pedal, lengthen the slot in the top, so that at your desired foot pedal position, the cable end is suitably positioned so it starts off slightly lower than the cable, swings over to be slightly higher, then ends up on the stop slightly lower again - minimising the amount of drag the inner has on the outer.

 

Fit a pedal stop so the end of the slot in the pedal isn't being used as a guillotine on the cable everytime it's brought to a stop by the throttle stops on the carb/throttle bodies.

 

However, I do understand the urge to create interesting, complex, over the top solutions to simple problems 😬 - I watch my collegues at work do it everyday - whereas my reputation of "scrap-iron Brian" makes it simple, cheap and easy.

 

Bri

[anthony1956]

odd. my throttle cable to pedal arrangement is nothing like that - it's a round thing (like a small circle of lead) on the end of the cable and pivots in place where yours has a screw nailing it in place so it can't move.

 

Very interesting - now I see why these are seen as breakables and mine hasn't, not once in many years.

 

 

 

Anthony

[Stationary M25 Traveller]

.... ping !!!! 😬

 

 

[anthony1956]

I take it that's my DeDion Tube.. ?

 

Anthony