Problem with sticking throttle cable

[turbo]

I really need some help here. The original throttle cable lasted 13 years. It then developed a problem where it would bind up at idle. I replaced it with the same cable, a A-750 acs. It lasted a month and ended up doing the same thing. I installed another one yesterday and it bound up at idle on the first run-up. Any thoughts on this problem. Thanks

[gasman]

Originally Posted by turbo

I really need some help here. The original throttle cable lasted 13 years. It then developed a problem where it would bind up at idle. I replaced it with the same cable, a A-750 acs. It lasted a month and ended up doing the same thing. I installed another one yesterday and it bound up at idle on the first run-up. Any thoughts on this problem. Thanks

Are you sure the problem is the cable? I would look elsewhere.......

[Bob Axsom]

In December I went to Fort Bragg, CA and worked with Red Hamilton to rebuild my engine. While the engine was removed I decided to replace the vernier cable that I installed when my wife and I built our RV-6A with a friction lock cable to satisfy the formation and Reno requirements. I flew home to Northwest Arkansas and all was well. I changed the plane to race configuration and was going to fuel up for the first high performance speed test but after I started the engine it was running too fast and I pulled back aggressively on the throttle to slow it down. It bound so hard that I could not free it from the cockpit even by pounding on it.

Red bought the cable through Wicks but it was an ACS cable. I returned it directly to Wicks priority mail with the tracking number 9505510617543051509906 on 2/22/13 and requested failure analysis that I would pay for with no strings attached. I posted my experience on the YAHOO Group - SARL site and perhaps through that stimulation I got an e-mail from a Wicks employee asking about the return because he said they couldn't find it. I gave him the tracking number and shipping date, etc. and never heard from them again even though I followed up with another email later. That cable had a slot on the end of the outer sleeve for the remote sleeve termination instead of the double nut and lock washer method and threaded sleeve of the original cable. I ordered a replacement through Van's which has the threaded sleeve and nut termination configuration of the original vernier cable and I have had no problem. I have just written it off and moved on but you are not alone in your experience. If you go to the YAHOO Group SARL site you will find several messages on that failure with inputs from others that are familiar with the problem.

Bob Axsom

P.S. I have the original letter in Word form with photographs that I can send you if you like via e-mail. The letter is 12 pages long and includes photographs. It exceeds the VAF size limit even without the photographs.

BA

[Pat Hatch]

Turbo, as I mentioned at SNF, I would check your carb linkage--you mentioned that you had--but I'm wondering if something isn't loose inside your carb or servo, forget which you have. Intermittent sticking butterfly? Pretty obvious it isn't the cable at this point, wouldn't you agree?

[Bob Axsom]

I am kind of familiar with failure analysis and destroying the evidence so when I had my failure I removed the cowl, removed the AN3 bolt hardware attaching it to the throttle lever without disturbing any piece of the failed system. With the control cable connected to nothing it was still stuck. Then by grabbing the end of the cable and pulling on it I was able to overcome the bound condition with force applied in tension.

Believe me when this happens to you it gets your attention.

Bob Axsom

[zilik]

Turbo,

Have you done a post mortem on the cables and found the culprit. Check your engine to battery and airframe grounds. Years ago the shift cable in my 72 Trans Am kept failing; sticking in park. Turned out the ground to the engine was bad and cable took over the duties of grounding the engine. The cable would slowly weld itself to the sheath.

[Pat Hatch]

Gary brings up a real good point. Bob, too. I guess if you release your cable linkage at the throttle arm and it's still sticking, it has to be the cable. I had the braided engine ground come off on my RV-4 years ago, and when it happened, it melted the sheath on all 3 cables, pretty dramatic. (The braid just fell out of the crimp on the engine ground.) Now I run two engine grounds for that reason. If for any reason you're getting high resistance at your engine ground (e.g., corroded connection) your ground will find another path, which unfortunately is often the control cables. I wonder if your replacement control cable is somehow being fried by a faulty ground somewhere. Worth a look. You asked for ideas!

[turbo]

here is the final scoop on the throttle issue. the cable was mounted to close to the motor mount and got bent. it now has 1/2 inch clearance. thanks for all the input.

[Mike S]

Turbo, thanks for closing the loop on this one.

[Bob Axsom]

Could you provide a few details on cause, effect and failure mode? I have written mine off as an undiagnosed failure (since I sent it back to the seller and no longer have it to analyze myself) but I would still like to know the details of the failures.

Bob Axsom