To my other TR6 Pages

October 30, 2016

Accelerator Shaft

[Click the pics for a better view]

For left hand drive (LHD) TR6 cars, which is the vast majority of them, the accelerator pedal on the left side of the car has to operate the carburettor throttle plates on the right side of the engine.  This is accomplished by a metal shaft running cross-wise directly behind the engine.  On the port end of the shaft is the accelerator pedal, attached such that pushing the pedal rotates the shaft.  The shaft passes through the firewall in the driver's kickspace, across the engine compartment where its starboard end is supported by a hole into the passenger's footwell.  Just before it leaves the engine compartment, the shaft has a lever arm clamped to it.  This is where the corburettors' throttle linkage connects.

The shaft and pedal were rusty and dirty, but in servicable condition. The lever arm had an ovaled hole where the linkage attaches.  The picture doesn't show how bad the elongation was.  The path from the accelerator pedal to the carb throttles in a TR6 is a complex one with an unreasonable number of joints and pivots, each contributing its share of slop to the total, so to tighten the system up, every intersection has to be made as good as it can be.  For the lever arm, I welded up the hole and redrilled it.

The other thing about these shafts is the bushings that it rides in.  They are reportedly hard rubber or plastic, prone to wear, and a bear to replace.  I wouldn't know what they look like, because they were not present in this car--probably wore through and fell out during the Reagan administration.

This is an area that begs for improvement, and there are many good solutions.  For this car, I made two of these little bushings out of nylon.  They are a sliding fit on the shaft and a firm fit in the tub holes.  Nylon is a reasonable choice due to its natural lubricity.

There is also a spring that pulls the lever arm down, which rotates the pedal up.  The spring was pretty rusted, so I got a close-ish hardware spring and modified to to be a close match.

So here are all the parts that will go into the new and improved accelerator shaft assembly.  The shaft is painted, the lever powder coated, and the clamp screw replated.

There is a difference of opinion on which way the lever arm goes on the shaft.  Most, if not all of the catalogs show the long arm on the outboard side, while Bently shows it the other way.  I assume Bently is right, but since my new bushing moved the lever arm towards the center of the car a little, putting the arm to the outside put it in better alignment with the body tab that the extension spring connects to.  

At the other bushing, a keeper pin goes in a drilled hole.  The lever arm is positioned such that putting the pin in the hole slightly compresses the Thackery spring washer on the shaft next to the arm.  This takes up any back and forth play in the shaft so it can't rattle.

Accelerator action is now tight and smooth.

This was a fun little project.  It took a few hours, but the cost was almost nothing.

Comments to Ed at:

To my other TR6 Pages