Mechanical throttle linkage for 33

[RoadRacer]

My throttle cable snapped tonight so it’s time to move to a mechanical linkage. I’ve seen Forte’s but don’t know yet if it easily fits the 33. Also told there was one from kootenai but their website is down so I sent PM and will wait.

But I’ve seen a few others build their own (sread for example) so hoping for some pics and recommendations for parts. I have 3 weeks before the next race but this is my daily so really hoping to get parts ordered this weekend.

And pics of designs and parts much appreciated!!

[sread]

Hey James - here is a few pics of my set up. The thing is , there is no one size fits all because of the unlimited variation in engine placement, manifold height, carb, throttle body position, etc. but the principle is all the same. You will have a link (rod) connected to the skinny pedal that goes forward thru the firewall and connects to a bell crank or small arm - which then rotates a shaft with another arm on the other end. That arm is connected thru another link (rod) to the throttle body. It's a very simple system but the problem is going to installing the pieces on an assembled car...the point where the rod from the pedal passes thru the firewall is dictated by pedal placement. Next , you will need to locate the shaft which rotates on 2 rod end bearings on the firewall. This is where it gets tricky because this will typically be behind the engine or head in the space between it and the firewall. Installing the rod end bearings on the firewall could be tough because of lack of access and other stuff (probably wire bundles or a/c) in the way. And depending on the space between the engine and firewall there may or may not be enough room for the bell crank arms to swing in the arc needed.IMG_20220305_090059871.jpg

Sorry, I can't get anymore pics to load and I have zero patience for screwing around with stuff like this trying to figure it out...on top of the fact that it randomly rotates the orientation. I can just text you the pics I was able to get so you can get an idea of what the set up looks like.

[sread]

Speedway motors has a good selection of all the various parts to put something together. Here is some of the stuff I used. https://www.speedwaymotors.com/QA1-A...re,265189.html
https://www.speedwaymotors.com/Steel...tud,34302.html
https://www.speedwaymotors.com/Quick...-RH,27511.html
https://www.speedwaymotors.com/Alumi...Arms,1911.html

[FF33rod]

Cable snapped? Wow, there must have been a fair bit of binding and chafing for that to happen! I would have thought an end fitting would loosen and fall off before the cable itself failed....
Good luck with the mechanical setup

Steve

[RoadRacer]

Cable snapped? Wow, there must have been a fair bit of binding and chafing for that to happen! I would have thought an end fitting would loosen and fall off before the cable itself failed....
Good luck with the mechanical setup

Steve

Totally my fault. It was hard to see when under the dash but the pedal&cable was slightly misaligned with the hole in the firewall.. and that made it rub against the brass firewall fitting.. thousands of miles later that added up! An easy fix..went up a hole on the pedal and cut the brass fitting shorter and no more rubbing.. but I still want to replace with mechanical cos everyone seems to love it

[J R Jones]

Cable throttles are the "SOP" in automotive, motorcycle and marine industries, although drive-by-wire has become popular. As you have addressed, the cable should not side load, or have friction points,
Tensile load must be limited as well. The pedal and throttle body sector must be synchronized with a throttle pedal stop so that you can not put infinite stress on the cable when the throttle plate is at WOT.

A potential downside to mechanical rod-linkage drove development or cable controls. If an engine mount fails and the engine rotates on the remaining mounts, the rod-throttle can open unintentionally. So you would accelerate, displace the engine, and not be able to return to idle.
jim

[NAZ]

James, I see little advantage in mechanical linkage -- it's old tech and as JR said, has some safety issues to be aware of. They're more difficult to install and they still need a positive stop for the pedal. A correctly installed cable will last for years.

[RoadRacer]

Interesting, thanks. Until now everyone has said that they are much better - less drag, more precise, etc.

Sure, harder to setup correctly but I was willing to take that time.

[sread]

The main advantage to a mechanical linkage is the ability to adjust the the feel / speed of the pedal to throttle blade movement. By varying the attach point at each linkage connection you can pretty much dial in whatever throttle feel you desire. The mechanical system also tends to have less friction which also enhances the "feel" of the throttle. A well designed and installed cable system can also have a very nice, direct feel with the key being "proper design and installation"...which in practice seems harder to come by. The main issue being a cable of the correct length along with a minimum of friction inducing bends. There is also some degree of ratio adjustability available with a cable system by altering the attach points at either end of the mechanism.
As far as safety concerns, I have zero concern with the possibility of breaking an engine mount and pulling the throttle open - ain't gonna happen....but even if it did, relief is just a push of the clutch or gear lever away and turning the key. And yes, I am aware that there have been instances of just such a thing occurring - back in the 70's when production cars used soft rubber engine mounts with no safety catch. I am not worried about it...I would guess there is a greater risk to a stuck throttle from a frayed or stiff cable than a rod/bell crank system.
Now, drive by wire? no thanks - you can keep it. I despise the feel of a drive by wire throttle - just feels totally disconnected and artificial. And I am definitely afraid of the possibility of a software glitch, ecu hiccup, servomotor failure, hacking intrusion, charging system fault, or? (just take your pick) causing an un-commanded throttle position or movement.
And if all that ain't enough - I just think the mechanical system looks cool!

[NAZ]

I've used both mechanical throttle linkage and cable -- both work great if properly set-up and either can be a problem if not installed correctly. Mechanical linkage is more difficult to design and set-up than cable and there is little advantage in using mechanical as cable can perform the same functions, including manual return in case of loss of a return spring. But if I purchased a car with mechanical linkage that worked well, it's not likely I'd replace it. However, I would ensure I used motor mounts that limited engine rotation should a motor mount failure occur. Not all motor mounts have this feature and the ones I'm using on my Hot Rod don't.

I'm old enough to have lived through the broken engine mounts and safety issues that led to cable restraints and eventually, clam shell style motor mounts that limited engine rotation. Motor mounts fail and in my experience, mounts that use an elastomer vibration isolator fail more frequently than solid mounts. Some car builders use solid motor mounts for just this reason but they also improve reaction time which is why drag racers like them. Solid mounts typically have no anti-rotation restraint should a failure occur. So if you didn't build the car, be sure of what your using if you elect to use mechanical linkage. Don't just assume as this is a safety concern when using mechanical linkage.