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Big Healey Throttle Linkage

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Lin

Lin

Jedi Knight
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Hello all,
Some may recall a few previous questions I had for the forum about the installation of a throttle cable mechanism in lieu of the original mechanical linkage. I am still inclined to go this route on my car, but before I do I want to at least understand the engineering behind why the original mechanism was designed the way it was.

I have noticed that on most healey race cars the throttle actuation is by cable. The original linkage abandoned. Jeff Johnk's car (which is very fast by the way, with the new DMD aluminum block with the DMD head) uses a direct throttle rod with ball joints from the pedal shaft to the carb throttle shaft instead of a cable.

Is the original design the way it is because of the need to connect the throttle relay for the overdrive? If the explanation isn't the overdrive, I am puzzled as to why such a complex system would be developed when the Bugeye of the same vintage used a cable process.

I hope someone can explain this to me. Thanks.

Lin Rose
1960 BT7 in restoration
1959 Bugeye
 
Hi Lin,
It's hard to guess why the factory chose the linkage over cable. Certainly in part, because of the need to operate the throttle position switch. However, a cable junction with separate cables to the throttles & to the OD switch would be easy to do. Cable is certainly easier to manufacture & cheaper.

Some racers feel that the cable operated throttles are more direct & less prone to failures. Others feel that the cable has it's own set of problems & stay with the linkage. I've had quite a bit of experience with both & a cable is certainly easier to set up from scratch. It is more easily bound up because of heat injury & contamination. Both are equally subject to failure when things break or get stuck & must be lubed occasionally. Linkage can be easily checked for pending failures. The cable has to be taken apart to determine it's condition & it can break without warning if neglected. Cable is possibly more likely to fail in a throttle open mode, linkage, in the throttle closed mode. Today's high quality, low friction cables would be my preference if I was starting over, but, my 49 year old linkage is still in top condition & operating with no signs of wear or failure.

Take your pick.
D
 
Well Lin,The throttle linkage in the big Healey has so much lost motion in it it is totally unsatisfactory for serious racing.However, the throttle switch played no part in the design shift in the race or rally car. The overdrive in these cars if used is controlled directly via a gear lever switch the accumulator sleeve is removed and the overdrive operates in what is termed the bang bang mode requiring in most cases the use of the clutch.--Fwiw---Keoke--OH! why did they do it the way they did? cus those bits were in the bin I guess.???
 
Thanks gentlemen,
While I expect that your answers are correct, in this case they do not fully satisfy my curiosity. But my wife says I have spent enough time on this. "Do it and move on!" Thanks.
Lin
 
Lin, /ubbthreads/images/graemlins/iagree.gif your mate very smart girl.---Keoke /ubbthreads/images/graemlins/laugh.gif
 
[ QUOTE ]
Thanks gentlemen,
While I expect that your answers are correct, in this case they do not fully satisfy my curiosity.
Lin

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If your curiosity were ever fully satisfied, what would be left?
Some things can never be known. Maybe someday. Just store it in the back of your mind or somewhere, & ask again in a different time & different place. It has taken me 60 plus years to find some answers & others probably never will be had. I suspect that the design details of the big Healey were done by a different group than the details for the Sprite. The initial details were certainly done at different times.

Sorry for your frustration.
D
 
Hi all,
Frustrated I am not. Curious I am! Over the years I have come across many critics and cynics who are quick to judge and almost always they give little credit to those who actually DO SOMETHING. My experience, whether in mechanics or management is that MOST people (exception: Mr. Lucas - just kidding!!) are well intended and they typically invented a process, came up with a design, or defined an approach for good reason. The good reason escapes us as time passes, conditions change, technology improves and etc. Therefore, I remain curious about the complicated throttle linkage contraption, but I am willing to give the designers the benefit of the doubt until I know more.

Then again, there are those examples of incompetence that the critics love to catch and we romantics call "character." Perhaps the mechanical throttle linkage contributes to the character of our cars as inelegant and unrefined as it might be.

Ah well, I still love my car. They got a lot more right than wrong didn't they!

Lin
1960 BT7 in restoration
1959 Bugeye
 
Lin,

All I can do is speculate. Perhaps this has something to do with the interchangability of the cars from LHD to RHD. After all by looking over the linkage the part that is interesting is the shaft that spans the entire front firewall. Also I have watched many things get designed. Depending on the designer, perhaps this was a scheme that the person responsible for the throttle linkage just reused. Does this type of linkage exist on any other cars besides the Big Healey? I hate to say laziness, I probably mean expedience in design. But it did not change for a decade.

Anyway, don't give up. Perhaps ask Jerry Coker?

I am interested to see how the conversion comes out. I am converting to a Smitty kit and will do away with all the unused electronics and overdrive throttle switch. Perhaps now is my chance to upgrade.
 
Hi Tracy. My XK140 had the same type of mechanical (Rube Goldberg)linkage. Never failed nor has my Healey. So why did I buy the extra linkage parts from you in Dixon? Hey, 5 bucks is a cheep garentee. When you carry spares those parts never go out!
 
Been there, done that with the Cape set up. Too hard to set up without the engine out. Too hard to adjust with the engine in. Works better with RHD, I am sure. Eventually the header heat stiffened it up. Very hard to get the bell crank ratio's correct for full throttle at the same time as the stock pedal contacts the floor. If you don't care, you could make another stop up from the floor to suit where full throttle ends up after all the finagling under the hood.
 
I have also suspected that the linkage was the result of the orginal RHD design. Probably figured more strength was needed to transfer the throttle movement to the other side of the car and then to the carbs, throttle switch and overdrive. When LHD cars were made it was probably more convenient to stick with the same basic layout, though it may not have been needed, given the short distance to the carb throttle shaft from the pedal.

All conjecture! Don't really have a clue and I am no engineer.
Lin
 
Yep BH, most of the early Jaguars,Volvos and Daimlers have a similar cross shaft The linkage from the cross shaft to the carbs on the Daimler V8 Saloons is very Interesting because the carbs set on different sides of the engine. That was good speculation on your part.I never gave the LH/RH drive bit a thought.---Keoke--- /ubbthreads/images/graemlins/laugh.gif
 
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I have also suspected that the linkage was the result of the orginal RHD design.
Lin

[/ QUOTE ]

Lin

BUT...were these cars really designed as RHD?

90% of the production went to the USA and export was always the principal goal. At this time in the UK, priority was given to supplies that were required for export products.
Photos of the 1952 show car show DMH sitting in the LHD seat
 
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BUT...were these cars really designed as RHD?

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Hi Derek,
I think the cars were designed to go either way. My car (LHD) has holes blanked off on the right side for the steering column thru firewall, accelerator pedal thru pedal box and both master cylinders. The steering box and idler arm mounts are the same also.
 
Hi Gregg

Thats correct... however there may have been some items that favoured one side or the other... for instance the position of the handbrake. To me that favours LHD.
 
[ QUOTE ]
for instance the position of the handbrake. To me that favours LHD.

[/ QUOTE ]
I have to agree with you there Derek. It's not as much fun touching your OWN thigh when "parking" /ubbthreads/images/graemlins/devilgrin.gif
 
I do have some pictures of the Cape cable installation on a LHD BJ8 if someone is interested.
Ken
 
Hi Ken,
I would love to see your cable installation photos. I still have not decided what I want to do for sure. Thanks.
Lin
 
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