Sticky throttle cable

Hi folks, '77 GT4, throttle cable snapped so got another from Superformance. Fitted up pretty easy but now find it is very sticky coming off idle, impossible to moderate and drive.
I removed and refitted it a couple of times and it is no better. The pedal end mechanism is freely moving as is the linkage at the carb end, and the cable runs free in itself when not connected so all the components are fine. Strangely when I manipulate the sheathed part of cable at the carb end - the part in the rubber tube between the firewall and adjuster, it frees up. On a drive it gets progressively more sticky to the point of being undriveable after 10 minutes. Same when I manipulate the cable under the car between the down tube and the tube to the pedal it frees up for a bit too. By manipulating I mean hooping it a different way or moving it to a different angle in relation to the fixed ends. Very puzzling. Somehow the cable is getting snagged up in the sheath and I can only attribute it to too tight a radius in the sheath at certain points (coming up out of the down tube and into the fixture on the manifold) or the free part under the car.
An observation; to thread the end into the pedal assembly requires the cable to turn clockwise, and it spins in the sheath whilst turning. All good. To thread the end into the carb linkage end it needs to be turned of course therefore twisting the cable as the pedal end is now fixed and can't spin. Could this be the problem or is there another way to fit to prevent twisting up the cable? What I did was twist the carb end anti clockwise so when threaded into the carb end receiver it unwound itself whilst threading in so I don't think there is a lot of twist in the cable.
Any help here would be appreciated.
Thanks.


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Thanks for the ideas.
Did the cable with no twist. Still a problem. I'm really at a loss to figure this out as all of the individual components work well on their own but when hooked up, it is a very stiff throttle pedal action coming off rest and more strangely it gets worse over 10 minutes of driving so something is moving around to a non ideal position.
Will have another go, this time looking at the pedal end as th engine end has no clues.

 

Hi, thanks for that. I think you will be right, I've checked everything and all is good and free moving except when the load comes on the cable then it gets sticky. The Superformance cable must be low grade to need lubrication but I will do this now and hope for the best.
I haven't driven the car but every night I go to the garage to exercise the cable and it is slowly getting better - must be finding its groove and the lubrication will surely help.
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Thank you for your ideas. The pedal is good and free moving so I'll get some cable lube. I think this is the problem because all the individual parts check out OK. Pedal is free, throttle linkages are good and cable runs nice with no load on it, only when loaded is it sticky.

 

Update!

Checked cable for kinks and damage and all good.

Cable lubricated; not much difference.......not as sticky but still way too firm. It's getting hung up somewhere.

I investigated cable ferrule angle in relation to its housing at each end as a possible cause of some friction if the cable was coming out of the ferrule at an angle and rubbing on the inside bore of the ferrule.
Quite happy with the underfloor tube as it houses the ferrule well and square on so the cable has to come out of the ferrule straight.

Engine end a bit different as the curve that the cable outer has to assume to find its way to the chassis down tube upsets the angle of the outer coming into the back of the adjuster - even though the design of the ferrule at that end should prevent oblique angles. I 3D printed a support to keep the cable square to the adjuster bolt. Image Unavailable, Please Login Image Unavailable, Please Login

Just a question, since my original cable was broken I had no reference if the bare part of the cable that hooks up to the carb end goes above the arm or below. I have it above.



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Just to note, the family are away so I haven't had the opportunity to inspect all areas whilst the pedal is operated. I'll do that when I can get someone in the car and look at both ends for hang ups.


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Next step; genuine Ferrari part. Where would I find a good source?


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Update....sorry for the updates but I'm finding this is a good place to write down my steps so I can eliminate things and not go back. (Old forgetful mind!).
And also fact check with you guys who are very helpful.

I suspect the graunching and stiff jerky pedal action is all down to the grey sheathed part of the cable and the hollow adjuster bolt arrangement at the engine end.
I believed originally that it was either the sharp turns in the sheath as it has to line up to the adjuster bolt squarely at the engine end or the cable running out the end of the ferrule at the bolt end and through the bolt itself. Remember I was saying that if I manipulated the cable it got better or worse.
Saabguy and Martin are onto this when spotting the kinks in the cable which occur at precisely this point. So the cable is under a lot of pressure there and is rubbing on an inner edge or surface that I can't see that causes the kinks and of course the rubbing which feels stiff and graunching at the pedal end.

Process of elimination;

Cable;
Yes it has had a lot of twisting when I was incorrectly trying to fit both ends. The cable is still in very good order despite a few kinks at the carb end that I describe above. No damage evident due to twisting. I got my old one and twisted it plenty to see what happens and it comes back fine.
I' Ve done a loaded cable test out of the car with weights and tight bends in the grey outer sheath. Works smooth but you can hear the braided cable working on the insides of the sheath, which I think would be the surface of the bare metal spring type windings normal to the insides of all cables. So not unexpected. Maybe confirms the lack of teflon inner sheath in the reproduction Superformance cable? Not silky smooth.
The out-of-the-car car loaded cable test eliminates the sharp bends in sheath theory. I also re routed the cable down the firewall on the outside of the chassis tube to avoid the really sharp adjuster bolt entry angle and there was a small improvement but still sticky.
I Lubricated down the cable well with motorcycle cable lube.

Pedal.
Inspected the actuating arms under the car through the floorpan hatch (right hand drive car) and all free to move with no snags.
I Hooked up the cable to the pedal end and ran the cable through front chassis tube and straight out the back of the car underneath. Got my wife to operate the pedal while I applied simulated carb return spring load by hand and pedal is silky smooth. Even at a lot more load when she can hardly press the pedal down, still very smooth. So Pedal assembly is good. Cable was dead straight.

Front horizontal chassis tube; always unlikely to be a problem as the cable feeds through very well each time from the back of the car with no snags. Sheath Ferrule seats well into recess at back of tube. Cable Comes out the rubber grommet at the front easily and is not hung up on it. So The chassis tube Also passed the test above - the straight cable pedal test.

Chassis tube that goes up the firewall;
No obstructions as the sheathed cable slides in from engine side really easily each time and out the bottom. Takes a nice curve to the horizontal tube entry.

Rubber tube over cable sheath in engine bay;
Doesn't seem to be an issue. Originally thought its length being a little long makes the cable take a very sharp turn to line up with the adjuster bolt but this is debunked by the out-of-the-car cable sheath bend and load test.

Tight turn of sheath as it comes up out of chassis tube and lines up to the adjuster bolt assembly on the rear cam cover;
Cable and sheath passed the out-of-car load test and sheath tight turn test.

Carbs;
very smooth action on the linkages when hand operated.

This leaves only one area;
Where the sheath and its special end ferrule meets the adjuster bolt and how the cable travels through the bolt.
So the problem is either that it doesn't line up square and the cable is rubbing and graunching on an inner edge that I can't see or a cumulative effect of a braided cable in an unlined sheath and the oblique angle of entry into the adjuster arrangement rubbing. I'm struggling here because the cable can be lined up by hand so it is absolutely straight on, and when my wife operates the pedal it is still sticky and graunching but to varying degrees depending on how I manipulate the cable. Now this manual realignment all resets itself when driving as the cable is pulled back out of alignment by the pedal action and forces. In an earlier post I showed a 3D printed ABS cable support but with heat, it softened and did not do a total job of holding straight but I thought it might help.

So my prognosis is that the cable is of inferior quality. The special end ferrule and recess in the adjuster bolt head that accepts the special ferrule has too much play and allow the sheath to take on an oblique angle to the adjuster bolt centerbore hole and so the inner steel cable is catching edges. Evidenced by the kinks in the last photos. There is no access to the centerbore to drill out or arris the entry points because the cable can't be taken out of the bolt.

I'll try as a last thing to grease the bolt's bore and if that improves then all is confirmed. Even if it works, I'm not so happy with the cable taking that crooked path and rubbing.

All I've read so far is that this is where the cable snaps most frequently and this is exactly where mine snapped due to fraying.

Interesting!!!
But still not 100% there yet.

 

Thanks JCR.
That was my next call after trying to source a genuine cable....

But, I've just sorted it.

I Tried stringing up cable ties in the engine bay to guarantee a straight angle of attack into the adjuster, and lots of grease inside the bolt.

No luck.

Out of complete frustration and after inspecting all areas with a magnifying glass to look for hook ups and rough edges, I pulled the ferrule off the end of the cable as the last resort because this was the only uninspected or tested part left.

Bingo. The inner metal part when cut to length during manufacture was turning into the cable bore and constricting the cable. I was able to nip the burr off to gain back clearance.
I can only but think that the early days manipulation of the cable improving the situation sometimes placed the burr in a better or worse position and was behaving or otherwise therefore changing the feel.

The photo is after nipping the burr off and showing a clear bore.

Thanks people for your help. Many many hours of frustration but very smooth now.

I'm a shade tree mechanic and do OK with simple jobs. Just really glad I didn't take it in to the pro's for them to chase their tails and send me the bill! Image Unavailable, Please Login




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