Throttle Cable Design Modification

In the mid-2000s I did a fair amount of research regarding the conversion of the original mechanical throttle control linkage used on Big Healeys to a cable system similar to what DMH used on the Sprites. I was restoring my BT7 at the time. The results of that research and a description of what I ultimately chose to do is documented in an earlier post on my website: http://valvechatter.us/?p=6497.

However, I have never been completely satisfied with what I chose to do. It is now 2020 and I have continued to visualize the approach to a throttle cable system as implemented on John Trifari’s AH 100. I saw John’s car at the 2005 Conclave in Winston-Salem, NC, so I have been carrying that idea in my head for fifteen years! I thought I remembered that John, who has since passed away, had the pedal modification done by British Car Specialists. I sent David Nock, at BCS, an email with a photo of John’s pedal assembly and he recalled doing the work. He suggested that they had used a pedal assembly from a later Triumph Spitfire, perhaps MKIV or 1500.

So, I went on an internet search for the right pedal assembly and after not too long I was able to purchase a couple of the pedals. Why this particular pedal assembly you ask? Well, what I like about it is that the cable attaches directly to the end of the pedal – no levers are used. It also has a pedal stop built in for the “at rest” position as well as an adjustable pedal stop for “full-throttle” application. This prevents stretching and possibly breaking a cable and doesn’t stress any throttle levers at the carbs either. Using some photos I took of John’s car in 2005, I was able to determine where the pedal assembly mounting bracket should be placed and approximately where a hole needed to be drilled in the bulkhead to route the cable to the engine compartment. The 3000 is a little different than the 100 but the guidance was still valuable. 

With that background the following provides a photo and narrative description of what I did for the Bloody Beast! First, here are the images I worked from taken of John’s car:

John Trifari Pedal Install

Trafari throttle MG Component

The following image shows the original Healey pedal installed in my car. As one can see, the original pedal exits out the side of the footbox. On the end of the pedal rod I had installed a custom fabricated lever to which the throttle cable was attached.

Original Healey Accelerator Pedal

I suppose that one can begin the project in the engine compartment or in the interior. I chose to begin with the pedal fitting in the interior. This is one of the pedals I purchased. I cleaned it up a bit and put a coat of black paint on it just to do the fitting work. I will powder coat it later.

Spitfire pedal

This is a part diagram from the Rimmer Bros. on-line catalog. While one cannot order a new pedal, I was able to order parts #1,3,4,5,6,7.

Spitfire Accelerator Pedal Parts Diagram

The image below shows a comparison of the Spitfire pedal to the pedal as used in John’s car. As you can see the pedal is perfectly straight. To use it in the Healey, the pedal needs to be bent. So I put it in the vice, heated it with a torch and bent it to try to approximately match what John’s looked like. I think I came pretty close!

Pedal Comparison

Triumph Spitfire Accelerator Pedal for Healey

Then it is really just a matter of trial and error to properly mount the assembly to the end of the footbox. It required cutting out a small section of carpet and after removing the white hardboard insulation from the engine compartment side of the footbox, I drilled two 1/4″ holes for the 1/4″ x 28 – 5/8″ hex head bolts that mount the pedal swivel bracket to the footbox wall. While I was at it, I marked the hardboard insulation to drill two holes for clearance of the bolt heads and washers.

I installed a new pedal swivel bush and tube from Rimmer Bros part #s AHH5301 and AHH6504 and greased the new swivel bolt when attached to the footbox bracket.

New Pedal Swivel Bush and Tube Installed

Trial Fitting the New Pedal Assembly

Spitfire Pedal Swivel Bracket Mounting Bolts

Insulation with Holes for Pedal Bracket

After installing the Pedal Swivel Bracket to the footbox wall, the next step is to drill the hole in the top of the footbox for the cable to pass into the engine compartment. Two smaller holes also need to be drilled for the MGB “top hat” accelerator pedal guide. This takes a little care as the “top hat” needs to be properly aligned for the cable from the pedal but also to avoid fouling against the steering shaft.

MGB Accelerator Cable Guide part #372-060 from Moss

Accelerator Cable Guide Installed

With the pedal assembly in place, I then turned to making a bracket to hold the cable between the two SU carb float bowls. I made a pattern out of cardboard first and then cut the bracket out of a piece of steel sheet. After drilling the holes for mounting to the carbs, for the carb breather holes, and for the cable guide I bent the bracket to get the proper alignment to the throttle lever at the carbs.

Throttle Cable Carb Bracket

Powder Coated Carb Throttle Cable Bracket

Unfortunately, I do not have part numbers or even the source for the components I used to guide the throttle cable and to secure it to the lever on the car throttle shaft. I had the parts in my collection of odds and ends.

Throttle Cable Fittings

I acquired the accelerator cable from Sports and Classics, TKC3915 for Spitfire 1500 1978-80, Item #CBL75. The cable was a new old stock item and the outer sheath of the cable fit perfectly for the Healey application. Unfortunately, the inner cable was too short. However, I was able to find a cable of sufficient length with a small ball on the end of the cable that would fit the spitfire pedal. I purchased it from Moss Motors , Part #734-300. I just cut the end off the cable and then inserted it into my cable fastener. I ordered a few extras just in case of a break! The Moss Motors inner cable is 45 1/2″ long. I cut off 11 1/2″ ending up with a final cable length of 34.”

Of course, one could just use the Moss Motors cable (inner and outer) and not bother with the cable sheath from Sports and Classics, but the outer cable would be much longer than required.

Spitfire throttle cable Moss 734-300

The end of the cable at the pedal is secured to the pedal with a little metal spring clip. I was able to purchase the clips from British Parts Northwest. Part #153041. The lead ball on the end of the cable fits nicely in the indentation of the clip when it pops in place.

Accelerator Pedal Cable Clip part# 153041

The image below shows the pedal installed with the cable and clip in place. Note the fit of the cable end ball in the clip.

Throttle Cable, Securing Clip, and Pedal in Place

After installing the pedal and trying the assembly I wasn’t happy with the strength of the pedal return spring. I did find another spring at Lowes that improves the pedal return though I may still try to find something a little stronger yet.

Pedal Return Spring

This final image shows everything installed. While I am very pleased with this approach to installing a throttle cable in the Healey, I will pursue finding somewhat stronger throttle return springs to make the engine just as responsive to coming off the pedal as it is to depressing the pedal. I am particularly pleased with how easy it is to adjust full throttle application with the threaded (5/16″ hex head bolt) pedal stop.

Final Installation of Triumph Spitfire 1500 accelerator pedal in the Bloody Beast

One more ten-year renewal project behind me and on to the next!

 

 

 

 

 

Leave a Reply