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MG MGB Technical - Throttle/Accelerator cable

My throttle cable broke today by the nut at the carb linkage end. Is replacement as straightforward as pulling the old cable out and threading in a new one from the pedal end?

(I have a 1973 B, SU carbd)

cheers
Nat

Yes. Just make sure seat the outer at each end and to leave a small amount of slack to ensure throttle can close properly, and do not over tighten the clamp nut as this can cause it to cut the new cable. Jim
jim soutar

That's assuming that you're just going to replace the inner cable, as I did last time using an inner brake cable from an old fairy cycle I'd dismantled of my daughter's.

However, if you want to replace both inner and outer that ferrule bit above the inner wing can be a fiddle. The mounting on mine had rusted out, so it was floating about.
Peter Allen

As Jim says. The copper clamp washer should have a groove from memory on my 73 (or maybe it has just warped over time), which helps reduce any cutting action at the carb end.

If you are replacing the whole cable the inner should just sit in the cable guide that sits beside the pedal box. I suspect like Peter's mine had broken so the outer was flopping about and bending the inner where it passed through the body. If yours needs replacing you will probably need to remove the pedal box cover, and slim hands help, easier than I was expecting. With the old one removed thread the screws up from inside the cabin first to check the threads are clear.

The cable should be adjusted so that when the pedal hits the toe-board stop plate the carbs are just about fully open, but not stretching the cable.

Also when at idle there should be a clearance of 12 thou between the top of the finger on the throttle interconnecting shaft and the underside of the choke interconnecting shaft. This ensure that at rest the throttles are controlled by the idle screws and are not hanging on the cable. If it hangs on the cable then you get a varying idle speed as the cable expands and contracts with heat and cold.

Both these are set by a combination of of the clamp nut at the carb end, and the pedal stop and lock-nut in the cabin.
paulh4

cheers all.

Yes, I'm only replacing the inner cable.

If there is no groove on the washer, should the cable at the carb link end be wrapped round the cylinder or be clamped against the lock nut and washer straight?

Paul, I can't quite picture what you mean about where the 12 thou clearance should be, do you have a picture?

thanks
Nat

Not normally a groove in washer, just NIP nut tight enough to hold cable, I would change the outer as well, as Peter says its a bit of a fiddle but smoother action will result.
jim soutar

The point where you need free-play is arrowed in the attached, a feeler gauge should be a loose fit in the gap. If it's a tight fit it means that the finger is starting to open the butterflies and means they could be hanging on the cable. It's not that critical as long as you do have a clearance, but if you have more clearance than you should it means the throttle pedal will have a 'dead' area where moving it does nothing, if you have a spring on the cable clamp to the bottom of the heat shield as mine originally did. I took it off as with it the throttle pedal movement was stiff and jerky, but there are still springs on each of the butterfly levers.

The cable attachment is at the bottom of the picture. The inner goes straight through a hole in the threaded stud which protrudes from a hex section. It's clamped between that hex section and a copper washer (on mine) with a nut.



paulh4

Thanks all, now sorted!
Nat

This thread was discussed between 07/01/2018 and 13/01/2018

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