Accelerator Cable Discussion


Subtopics covered in this article -


The accelerator cable is routed from the accelerator pedal through the floor pan, then into a flexible guide tube near the transaxle, and finally through a tube in the fan housing to the carburetor, where it attaches to a lever arm that in turn attaches to the throttle valve inside the carburetor. In the top of the lever arm there is a screw that rests on a stepped cam. This cam is attached to the upper butterfly valve in the carburetor, the choke, which we will discuss later.


Experience: Accelerator Cable Replacement

Dave found that one of the reasons his car was not idling as is should was that the accelerator cable connection under the accelerator pedal was not attached correctly. "A very poor design," he thought at first. He bent the metal piece of the end of the cable around so that it could not come loose or get twisted around improperly. Then he was able to adjust the cable properly at the carburetor end.

Some time later Dave's accelerator broke while he was driving home from work, right behind the metal fitting that he had previously bent around to make it fit properly. Dave then examined the fitting on the new cable properly and had a learning experience! :-) The proper attachment of the fitting on the forward end of the accelerator cable is shown in the following picture -


Correct Attachment of the Accelerator Cable


While poking around behind the fan shroud from the left side, Dave found the copper guide tube coming through the fan shroud but NOT going through the hole in the firewall. So he jockeyed it into position and I had his son hold it in place while he pulled the old cable out from the front. Dave discovered that was was frayed down to two strands about two inches from the front end.

While his son held the copper guide tube in place, Dave started snaking the new cable towards the back, greasing it as he went. It got right to the hole in the firewall and hung up. So Dave crawled under the car and jerked the flexible tube out (he wasn't going to replace it, but when he found the fitting on the rear end missing he changed his mind). Getting the cable into the tube and the tube in place was fiddly, Dave found but not so much so as guiding the end of the cable out of the flexible tube, through the hole in the firewall, and into the copper tube that goes through the fan shroud.

During this process Dave found that something was interfering with the accelerator tube just forward of the firewall. He crammed a piece of stiff wire through while his son was watching from underneath -- he found the interference to be the new tranny rubber he had installed. So Dave cut a little notch in the rubber to accommodate the cable and reinstalled the cable with no problems.

Then came adjustment time. First Dave adjusted the cable exactly according to the specification -- accelerator pedal all the way to the floor, throttle lever wide open, 1mm clearance between the lever and the carburetor body. No problem -- except adjusted that way the throttle lever wouldn't return all the way to the cam and the throttle valve inside the carburetor was open too much -- thus high idle, just like before when the throttle valve was sticking. Dave decided that wouldn't do and readjusted the accelerator cable as Rob suggested -- throttle lever against the cam, cable pulled back as tightly as possible (finger tight). With it adjusted that way Dave was able to proceed with the fine tuning.

Dave expressed concern about the interface point between the rear end of the flexible tube and the copper guide tube as it pokes forward through the firewall. The fitting on the end of the flexible tube is flared, and the two just rest together, or so it would appear. Manipulating that interface is all by greasy feel, with your arm bent around at a very awkward angle. It's almost impossible to see it -- it's right on top of the tranny a couple of inches above and toward the center from the clutch adjustment nut. The copper guide tube wiggles around in the fan shroud and comes out of the hole in the firewall very easily. The rubber screw-in grommet type thing on the rear as it comes out of the fan shroud is deteriorated and not doing much to hold the tube in place.

Rob responded - So which way did the cable move when you tried it my 'quick' way? Did it project further to the rear of the car, or less? If too much further to the rear of the car (more cable through the fixing nut on the accelerator arm) it might result in overstretch of the cable on full throttle, and would be pulling hard on the accelerator arm. If less cable now pokes through the fixing nut, it means that at full pedal movement you'll have a 'not quite' vertical throttle butterfly maybe lose a few revs at the top end.

Dave's response to Rob - The accelerator cable was further "in" when adjusted your way. The other way it was further "out" and the idle screw (which I knew to be set correctly) would not return to the lowest step on the cam. So setting it your way works much better. Haven't noticed the loss of a few rev's at the top end.

If you see in any of your catalogs one of those screwy little rubber grommets that goes on the rear end of the copper guide tube, between it and the fan shroud, please let me know. That would hold the tube properly in the hole in the firewall.


Experience: Accelerator Cable Adjustment

Dave posed the following question to the RAMVA Newsgroup - My car is a '73 Super Beetle. My question has to do with the accelerator pedal and cable. If the throttle lever is adjusted per spec, the cable sticks out way further (towards the back) than it should (the hold down bolt is actually on the cable). The accelerator pedal has very little travel, and when I pull it back I find that the arm with the wheel on it (accelerator cable attached) wiggles about an inch back and forth (front to back). Intuition tells me that this arm (Bentley calls it a "connecting lever") should be held completely back (no pressure on the pedal) by a spring or something and should only move forward when the pedal is depressed. I guess the throttle lever return spring should do this, but in mine there is about an inch of free play.

The bottom line is I can't adjust the cable properly, the throttle lever will not return completely to the cam, and thus I can't adjust the throttle screw or the idle. And the car runs like, well, dog do do.

Responses -

  • Check and see if you have the correct cable installed first. Or, the cable may be old and possibly.
  • Couple of thoughts -- Look under the pedal pedal for dirt/fluff etc. which might be catching the cable or pedal at that end. Sometimes some dirt gets caught under the bottom end ('floor' end) of the rubber cover on the accelerator pedal, which rubs on the floor (on mine anyway). Dirt under here tends to push the accelerator on. A squirt of WD40 etc on the shaft/bushing and little roller (I presume you have one) under the pedal helps to keep it loose too. Have you made sure the cable is not pulled too tight? I set mine by loosening the lock nut on the carby end, and while holding the throttle arm against the lowest step on the cam, just tugging the cable rearwards with fingers only (not pliers/multigrips) until it's snug -- but not tight through the throttle arm connector. This means there should be little on no play in the accelerator pedal, but not so tight that the throttle is held open on idle.

  • The cable end at the carburetor should fasten on the steel end piece, not on the cable itself. Could it be stretched, or even frayed cable (inside the cable tube)? Could it be hooked on wrong at the pedal end?

Dave's experience - This afternoon I took my 8mm box end wrench out to the car, parked at the curb in front of the house. I opened the engine lid and applied the wrench to the bolt that holds the accelerator cable into the throttle lever assembly. Then I loosened it up, held the throttle lever against the lowest part of the cam, and gave a pull on the accelerator cable. I found a problem -- the metal thing on the end of the cable pulled about 1/4-inch past the hold down bolt. I think we've got a stretched cable -- next on the shopping list. I tightened the bolt down on the wire -- not the best thing to do, but it will HAVE to do until I can get the cable replaced. I understand that's quite a chore.

Anyway, I went in and washed my hands and then fired her up. There is lots more pedal, and a MARKED improvement in the way it runs. Still hesitates a little on acceleration, but orders of magnitude better than the way is was running this morning. Now I need to check to see if the throttle lever is returning properly.

Question - My concern is that there is very little "travel" in the accelerator pedal -- the distance between no applied pressure and floor-boarded is very short. I think I need to get a buddy to help me with this, and I need to get in there under the steering wheel and take a look at what's going on. Something is definitely not as it should be. I like to be able to "feel" the accelerator pedal.

Rob responded - Hmmm... Sounds a little odd. When you floor the accelerator pedal lever does the throttle arm move all the way? (Put a brick on the accelerator pedal to hold it down if you haven't got a second person to look). You might need to remove the throttle spring if you can't find a big enough brick to hold the throttle down.

Maybe the cable has become partially unhooked or somesuch. It definitely sounds out of whack.

Dave's experience - I pulled the cable back pretty hard with my channel locks before tightening the bolt that holds it in place -- I've probably snugged it up too tight. You said to just pull it back finger tight, as I recall.

Rob responded - It certainly shouldn't need a hard tug -- it should slip both ways through the cable channel quite easily.

Experience continued - The only hard thing about taking the carburetor off is getting that blasted accelerator cable adjusted properly. I'm never sure that I've got it right. Your method (hold it finger tight and tighten it down) seems to work best, but there's still no gap between the arm and the stop as there is supposed to be.

Rob responded - Then if you floor it hard, you'd be putting strain on the throttle arm. I guess you'll just have to loosen it a bit until you get a bit of free play.

Experience continued - I can't loosen it too much -- there's only about 1/8th inch of the end of the cable sticking out beyond the connection on the bottom of the throttle arm. I am going to loosen it just a tad more, though.

Rob responded - That seems a little odd too -- mine pokes through the clamp about 1/2 way, so there's plenty of adjustment either way.


Experience: Fan Housing Guide Tube

Dave's experience - Regarding the tube that passes through the fan housing -- this tube just sits loose in the fan housing at a slight downwards angle (rear up, front down), and has a flange on the rear side which stops it falling into the shroud. This tube allows a degree of engine rotation under acceleration, etc. without kinking/pulling the cable. The hole in the FRONT of the fan shroud is a bit enlarged to allow this movement.

It would be a devil of a job to thread the cable through the shroud without this metal sleeve, and it could then bind on the shroud edges too.

Question - Somebody told me a while back that I would have to get the guide tube welded back in place. How about if I position it properly and then put a bead of JB Weld around it to hold it firmly to the fan housing? I fear that our accelerator cable is going through the fan shroud bare and that it's rubbing against the metal edge and wearing, thus the lengthening that we seem to be experiencing.

Experience continued - Earlier I asked about the accelerator cable tube and thought maybe I should "JB Weld" it to the fan housing. With the carburetor off I had a better look, and of course you're right -- the hole it comes through is enlarged specifically so the tube can move. Ours has a rubber spiral type plug that surrounds the tube and is supposed to screw into the hole, except our plug is old and in very poor shape. I've never seen either the tube or the plug for sale anywhere -- have you? The tube is so loose that it's sticking out of the fan housing towards the back! Could it be that it's just pulled back part way out of the fan housing and maybe can be slipped back into place fairly easily?

Rob responded - The sheath has a close fitting hole in the rear of the shroud, and a slightly elongated hole in the front of the shroud. It should be possible to just 'fiddle' it into the front hole, so it slides forward and sits flush against the rear (carby side) of the shroud. The front hole is elongated slightly to allow the cable itself to align the sheath when it's pulled (the throttle is worked). With the sheath too far to the rear, the cable could be rubbing on the front side of the shroud edge, especially as it now has the weight of the sheath (the bit inside the shroud) pulling it down.

If you welded (JB or metal) it in, it would lose it's capacity to self-align, which is happening all the time as the engine flexes (rotates) on it's mounts. So welding is not a good idea -- it would create a real rubbing area at the front edge of the sheath.

VW's ingenious design again.

I'm not sure if your sheath is different to mine, you have the doghouse cooler on the front of the shroud. But I suspect it's the same -- that the spot on the shroud where the cable comes through is probably 'flush', just to the right of the doghouse 'bulge'. If there is a difference, maybe you need a longer sheath? But I doubt it.

Experience continued - I was out fussing around the engine this afternoon, tightening bolts in the tin and just generally cleaning. I noticed something interesting -- the bell shaped fitting on the rear end of the accelerator cable tube isn't sticking through the front of that piece on the engine that sticks up (whaddya call it!?). It's just resting on the other side, dropped down a little by gravity. I tried to pull it through, but its too big around. This fitting must come off so you can slip it through the hole from the rear and then reattached it to the tube. If so, I've never seen a procedure that makes this clear. Can you help me with this?

Rob responded - I have a single tube-shaped piece with an expanded (your bell shaped?) end which slides through the shroud from the rear of the engine, and pokes through the front of the shroud. The hole in the front of the shroud is slightly elongated so when the cable is under tension, the tube can align itself straight along the cable. It's only the expanded end which prevents it falling through/into the shroud.

Experience continued - I'm a bit baffled by the accelerator cable guide tube. The cable is running through okay, but there is a definite mismatch at the firewall. And its so awkward trying to work back there. I'm going to reach in with my long channel locks and see if I can get a good grip on the guide tube and push it into the hole and mate it with the cable tube on the other side. It's hard because the guide tube moves so freely through the fan shroud. I think there's supposed to be a rubber grommet or something on the rear end of it that holds it in place; our's is missing (of course) and I've never seen anything like that in any of the catalogs.

Rob response - There's no grommet (and never was) on mine. The hole on the front side of the fan shroud is (on mine) slightly elongated so the cable can line up straight from gearbox end to carby end, with the tube being "supported" at that point (front of fan shroud) by the cable. Makes for a small waste of cooling air I guess, but there is definitely no grommet.

Experience continued - The guide tube goes through the fan shroud and then through the firewall, protruding about half an inch forward of the firewall. The bell-shaped end of the accelerator cable tube is supposed to slip over the protruding end of the guide tube, but I'm having a devil of a time getting it to do so without pushing the guide tube back through the firewall. I think I need an assistant to hold the guide tube firmly in place against the rear of the fan shroud whilst I reach up over the tranny and slip the bell-shaped end of the flexible tube over the other end of the guide tube (if that makes any sense at all! :-)

I'm going to detach the accelerator cable and pull it forward through the firewall, then I'm going to wrap several layers of black plastic electrical tape around the rear end of the guide tube and "screw" it into the hole in the fan shroud as tightly as I can.

Rob responded - That might work. Certainly worth a try, and easily reversible if it doesn't help.


Experience: Barrel Clamp

In January 2005 Dave replaced his Bocar 34PICT/3 carburetor with a Pierburg model. Just on accounta 'cuz, Dave also replaced the barrel clamp at the base of the accelerator throttle arm, the clamp that connects the accelerator cable to the throttle arm. Dave found that the fit was a little tight, so Dave got out his "persuader" and gently tapped the barrel clamp into the throttle lever. Mistake! The barrel clamp must turn freely in the throttle lever, otherwise it will kink the accelerator cable and cause the engine to run at very high rpm. Dave prized the barrel clamp out of the throttle lever and reverted to the old one, which is slightly smaller in diameter and turns freely. Dave made sure with a healthy squirt of WD40! :-)


Barrel Clamp

Also used to connect the heater cables
to the heater box lever arms.

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