The MGA With An Attitude
MGAguru.com MGAguru.com
Accelerator PEDAL POSITION, Part 2 - CB-114A

On Jan 25, 2010, David Lake in Queensland, Australia, wrote:
carburetor linkage "My accelerator cable keeps pulling out of the trunnion on the lever and then I have a slack cable and less throttle. I have a spring on the lever which I think is too heavy so the cable is slipping. I stretched the spring to hopefully fix this (maybe not overly correct). My question is how many of you have the lever (Connected to number 13 in the image), at the carb/cable connection set horizontal when relaxed and how many have it set down maybe 10-15 deg. When you pull the cable it would seem that if it was slightly set down to start with it would be still traveling through an arc at the top rather than been pulled directly upwards".

Yes, the throttle lever needs to be lower, not horizontal at rest. Correct lever angle should be at right angle to the cable in mid stroke, traveling through equal angles up and down at ends of stroke. If you do not provide this symmetrical stroke the lever will make a more acute angle with the cable at one end or the other of travel.
carburetor linkage
The throttle pedal will have more physical travel available than the lever on the carb shaft. There is supposed to be an adjustable pedal stop on the floor beneath the pedal. I do not see instructions in the Workshop Manual for adjusting the cable and pedal stop, but this is how I do it (and why).

1. Set angle of the cable lever arm on the carburetor to have symmetrical stroke and to be approximately at right angle to the cable in mid stroke.
2. Seat both ends of the cable jacket firmly in the cable anchor sockets.
3. Pull the cable wire all the way forward until the pedal hits mechanical limit at top of stroke.
4. Lift the cable stop gently upward to remove slack in the axle pin joint, and tighten the nut to secure the cable. When finished there should be only a tiny bit of slack in the cable at rest, just enough to assure the it will not bind or prevent full return to idle position.
5. Press the pedal down full stroke with one finger until the cable draws the throttle plate(s) full open, and it therefore hits end of travel at the carburetor(s).
6. Adjust the pedal stop to touch the under side of the pedal at this point, and tighten the bolt in that position.

Adjustment in this manner will assure that the cable will travel far enough to provide full opening of the throttle plate(s). Heavy foot on the pedal will not stretch the cable or damage the linkage parts. There will be no excessive slack in the cable, so the outer jacket will not be able to jump out of the cable anchor. The throttle pedal will rest at maximum height, about even with height of the brake pedal in raised position. This allows you to slide your right foot straight across left or right from one pedal to the other at top of stroke.

Some people with long legs may prefer to set the pedal lower, very close to the floor when fully depressed. Adjustment procedure is different to achieve this effect.

1. Set the pedal stop to the lower position as desired, and tighten that bolt in place.
2. Set angle of the cable lever arm on the carburetor to have symmetrical stroke and to be approximately at right angle to the cable in mid stroke.
3. Hold the pedal down against the bottom stop.
4. Hold the throttle arm all the way up for throttle plate(s) to be full open.
5. Seat both ends of the cable jacket firmly in the cable anchor sockets.
6. Pull the cable wire all the way forward until the outer jacket is tight and firmly seated in the cable stops at both ends, and tighten the trunnion nut.

When finished the throttle plate(s) should be full open at full pedal press, and the pedal stop still prevents stretching of the cable. With pedal full up there will be some available travel remaining toward top of pedal stroke. There is a small spring on the back end of the cable just aft of the firewall that pulls the pedal up to highest possible mechanical travel. This Pull-off Spring (and related bracket) was added at car no. 24594 in December 1956. Earlier production cars didn't have it but it is recommend that you retrofit these pars to earlier cars. If you adjust the pedal to travel lower at the bottom end and not so high at the top end, you would have to remove this spring to prevent it from pulling the pedal higher.

If this spring pulls the pedal higher it could allow the cable jacket to slip out of one of the end anchor cups where the cable jacket might rest on top of the cup rather than inside, and the pedal would come to rest slightly higher. Then next time the pedal is pressed full down it would stretch the cable before coming to rest on the pedal stop, possibly damaging something in the throttle linkage.

With throttle pedal adjusted low like this, if you put your toe under the throttle pedal and lift (intentionally or accidentally), it would allow the cable to go slack, possibly letting the outer jacket slip out of the cable anchor at either end, resulting in the same problem just noted.

The low pedal position is a bit more of a fiddle for adjustment, but may be worth the effort for some people with long legs (who don't mind that the pedals are not equal height at rest).

HomeBackTopNext
Thank you for your comments -- Send e-mail to <Barney Gaylord>
©2010 Barney Gaylord -- Copyright and reprint information