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.

Original Post

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 .

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.

It is a very real thing.
In the railroad industry we deal with welded rails that are literally miles long. We do an operation called thermal adjustment. By heating the rails to around 125 degrees, about what they will see in direct sunshine on a hot day, and then pinching it down to the tie plates and ties with special clips, the rails are left in tension on all but the hottest days. This controls the build up of compressive forces in the rails called sun kinks that cause serious local misalignments and derailments.
We usually work with 1,600’ long rail strings and thermite weld the butt ends together as we go.

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

Add Reply

Likes (0)
Post
×
×
×
×