Replaced throttle cable after finding knots tied in it by previous master mechanic.
The design of this system does not appear to me to be the best design . Plus the cable return spring tension seems awful high and that bend the cable makes before the engine bracket is way too tight. Not too satisfied.
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I used a Lokar 96" universal throttle cable. Cut it to length and had no problems.
I found my cable rubbing on the kick panel, which was causing friction in the cable operation. I slotted the panel slightly which made it operate much smoother.
Good lead Larry. Thanks .
My take away is:
1. When replacing the cable you must feed it from the engine side into the cabin to avoid damaging the carb end tube. Any decent mechanic would note that.
2. The bends the cable makes at the fire wall are well within the minimum allowable bend radius for a 1/16 in. cable. Not an issue.
3. The tube on the carb attach end is there to support the return spring when compressed. If you choose to remove the return spring support (tube) then ditch the spring because it's gonna get funky when compressed. Note, as posted in the previous thread the spring design does remove excessive wear from the carb throttle shaft and bushings. It's ( spring) selected for correct throttle peddle feel.
4. The return spring is opposing the cable so at full throttle (compressed spring) is the tension more than the cable design load ? Not sure but I doubt it. That's basic engineering if you have the required info. Do keep in mind that the cable core want's to straighten out ( go linear ) when under tension so there is wear taking place between the core and housing. Machines love lubrication so lube it. And remember that nothing last forever.
5. The weak link in the design is the cable attach at the engine. The cable must not only be properly aligned with the throttle attach at the carb it must be firmly attached to the cable bracket. Ours are not. And the bracket is attached to the engine with only one bolt. Not good should the bolt loosen allowing the bracket to move. Bottom line is the bracket sucks.
6. Last, to properly rig the throttle control you must adjust the secondary stops at the pedal. Must ! The primary full and idle stops are at the carb linkage. But if you don't have the pedal stops properly adjusted then bad things can happen. This is a somewhat educated guess on my part. I've spent a long time adjusting cables on aircraft so I think I somewhat ( for sure maybe ) understand them. My guess is to adjust the pedal stops to a clearance of .030 to .050 after the carb linkage stops have made contact. Maybe more but leaning to the safe side. The cable will stretch allowing the full throttlle stop at the pedal to be contacted. I noted knots tied in my throttle cable to shorten it and that someone had removed the full throttle stop (bolt) for the pedal. It's amazing the the cable never broke or the carb linkage was not damaged. Most likely saved by a light footed driver.
I did note that the cable was moving at the engine bracket causing a bind so I'm thinking about a better bracket. Thinking ... Ha Ha.
My 5 cents on Pantera throttle controls. Fire away guys .
Here's a topic authored by John Taphorn in 2014 on the subject of improving the throttle cable, at the intake manifold end.
He's got the right idea, almost. The cable attach point has to securely hold the cable in place (clamped) at the right angle so the cable can follow the arch the carb attach point travels with throttle shaft rotation. That's complicated by the return spring guide and lack of a pivot point at the end of the cable housing. Lucky for us the throttle shaft attach arch is small. It's a function of the distance of the throttle shaft center to the cable attach. The greater that distance the harder it is for the cable to follow. It can also reach a point where it will go over center and act like a ski boot binding. That's bad.
A housed cable like we use will over time find it's happy place so only clamp it where it is necessary. Like people cables can have problems when others try forcing them where they don't want to go. There also has to be enough slack so the cable can move with the engine. Car structure fixed and engine moving.
Last cables under constant tension will stretch at first. Specially stainless steel so you need to keep an eye on them and adjust after a replacement.
Since I'm blabbering think on this. Airplanes go from sitting on the 150 degree Vegas ramp to 80 below zero at 30,000 feet. Airplane is aluminum and the cable is steel with very long runs front to rear. Aluminum's expansion coefficient is about four time that of steel so at 30,000 feet for hours the plane shrinks and it's goodbye cable tension. On a large aircraft you can be talking inches. Nowadays it's all fly by wire so no more cables. But an A10 warthog has a manual reversion system. After your wires have been shot to pieces the pilot can go to manual reversion which is good old cables to the rescue. The old stuff just works.
The thread George linked from JT is the one that gave me the ideas on my throttle bracket.
Thanks, John T.!!!
Rocky
rocky posted:Thanks, John T.!!!
humbly agree
72panterasteve posted:I used a Lokar 96" universal throttle cable. Cut it to length and had no problems.
someone recommended this to me as well and it was a fairly simple swap/fix.
Look at any large bridge and you'll see the expansion joints.
larryw posted:In the railroad industry we …
Larry my father was a section foreman for the Southern Pacific during the depression era. His crew maintained the track in the Tehachapi Pass which included a helical section known as the Tehachapi Loop.
The stock throttle cable bracket on the left cylinder head is soft mild steel- about like coat-hanger steel, so stockers are often bent and can be straightened with your fingers. And with the single nut attachment, they are almost never tight. All this changes any fine adjustment. My cable jacket has popped out of the bracket recess a couple of times, holding engine idle speed at 2000 rpms
Exactly what mine is doing.
What Did they think would hold the cable in place ?
At best it's poorly done.
Gonna make a new bracket because I don't trust it.
George, That's a long train.People never appreciate how much steel changed the world.
Panteras and trains, I'm in.
Punky, I made a 7075-aluminum bracket and pinned it to my aluminum head so the bracket couldn't rotate on the stud, then safety-wired the cable jacket end to the bracket so it didn't pop loose any more. Not attractive looking but its working so far.
I tried the safety wire thing and wasn't happy.
The pin is a good idea.
Great minds think alike.
Happy April fools days.
