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Slipping Throttle Linkage, What Part To Replace?


Grover
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After initally thinking it was the throttle cable that was slipping (I don't have the stock rod as I'm not running carbs any more) I confirmed that it's actually the lever which is spinning on the splined nub protruding from the side of the pedal box. Even with the bolt on the lever fully tightened, there's still enough slop that the lever can slip under pressure.

 

So, which part needs replacing (assuming it can't safetly be fixed with the existing parts)? There are still some subtle splines on the nub of the pedal rod, but I can't see any splines for it to mate to on the inner circumference of the lever itself. Are there supposed to be splines on there or is it purely a friction fit?

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I've taken the pinch bolt out of the lever... Use a grinder cut off wheel to open up the pinch slot so the bolt can clamp tighter. No new parts needed.

Other times I've replaced both the lever and shaft to repair a slipping joint. I usually try making it fit tighter first.

Oh, well maybe a new lock nut and some loctite on the pinch bolt too.

HTH

Edited by tjones02
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Thanks guys. Yeah, I figured I could force it to close tighter by using your method Tom, but wasn't sure if there were supposed to be splines on that lever that have just been rounded off. Can you confirm this one way or the other? And thanks for the photo Andrew but I'm going to try to avoid welding it if possible. Curious to know if that is the "correct" resting angle for the lever, all the way up at the top like that.

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. Full rest is not against the body. Fully down/floored is usually somewhere near or just below horizontal.

 

Yep, as Tom mentioned "usually" plays a factor.  The upright position will be dictated by where your "fully-down" position is (and this will vary depending on on your linkage setup [DCOE cables, stock, etc.]).  You don't want fully down to be much below horizontal.

 

This is about where full throttle should end up....

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  • 1 month later...

If you've not already done so, it's not a bad idea to fab an adjustable 'stop' on the floor beneath the pedal. Right foot weight increases during acceleration (particularly with the sound of DCOEs), and you end up pushing the pedal past the point of the carb's wide open throttle position. The weak point in the design when using a cable becomes this connection at the pedal box. One of the thru bolts into the pedal box attaching it to the body is exactly beneath the pedal stop on the back side of the pedal. You can take a longer bolt through the carpet, with a nut holding it in place at the proper length of the WOT position. Pretty it up with a rubber stopper and Bob's your uncle, as they say.

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Andrew, thanks.  That's the worst possible, but most useful answer.  I have a spare arm (actually I'll need several as after four hours under the car last night mine are falling off) so maybe I'll drill several holes and experiment.

 

Is there a favorite bike cable used for these hookups? The one on the car now is so long I have it ziptied to the upper radiator hose...

 

Stacey, that's a great idea for fine-tuning the setup - right now I go from closed to full open in about an inch of pedal travel, so I need to do something about the leverage issue.

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Part of the problem seems to be that, based on Andrew's comments above, the actual length isn't something known.  (And apparently the Weber kit includes a Shimano brake cable anyway...)

 

After hours of struggling with the lever and the PO's mechanic's bodged clevis, I'm wondering if the right answer isn't a better cable length adjuster; something like VT 26-0508:

https://www.masclassics.com/vtwin/0994.php

 

Or this one: http://www.eurojamb.com/brake-cable-end-clamp-norton-triumph-bsa-250-350-441-650-750-p-1620.html

 

Andrew, how would you attach that cable to the Weber linkage (the one I linked above)? The clevis setup looks neat (though the offset load on the pedal lever would be a bit interesting), but the other end looks like it assumes a flat lever of some sort.

 

Or is Marshall's point that the cable inner is replaceable, and that's the solution here?

 

Thanks for all the good ideas - and the 2' length number (though in my case the linkage is on the rear carb with the cable exit facing forward... so who knows what will work for me...).

Edited by mikesmith
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I finally got around to shooting a couple pics of this.  I have been rebuilding my webers and installing a rod-style linkage system and finally finished last weekend.  For years I was running an alfa style center pull using a mountain bike cable, which worked ok, and I always knew I could repair it anywhere if it failed (which it never did).  I went to a Jegs cable, which is the same as the Lokar noted above, but had to modify the pull arm where the cable attaches to the linkage.  In short, to answer your question on pedal travel, getting the appropriate pedal length to match your linkage actuation using a cable requires a little bit of geometry, but by using the full length of the arm on the pedal box, and a long arm on the linkage makes for a very smooth and light pedal feel due to the achieved leverage.  I probably would have gone with the top mount spring linkage but prefer the look of the vintage rod style.  Time will tell If I made the right choice.

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Thanks. Maximum leverage vs. cable drag is actually achieved with the shortest possible arm on the pedal; I managed to put something together with the cable I had on hand after picking up one of the Lokar cables which was a complete waste of time - no way to adapt it to work with the top-mount linkage.

 

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This is the linkage and arrangement currently in the car. I've seen most folks flip it around, but the pieces I have to hand won't work like that - the coupler between carbs won't work with the actuator arm, so I'll need to do some more shopping at some point.

 

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Please no chiding about the arm between the cable guides, or the stupid fuel line setup; this is all the PO's legacy and as soon as I get some other things sorted, it's going in the trash.

Edited by mikesmith
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