Subject: 3-4 shift rod detents, why it pops out of 3rd gear, and what to do about it.

At 11:08 PM 1/20/02 -0800, Malcolm Cox wrote:
>"On rebuilding my gearbox .... I noticed that the detent depth in the gear selector rods do not conform to the latest (lemme see, thats about 40 years ago!) factory recomendations. The rods have clearly been replaced at some time and show little wear, so they predate 40 years ago."

Got any use for some more rods? I have a few sets of them left over, as they never seem to wear out. The 40 year old parts usually do look nearly new.

>"I have been vintage racing the same gearbox for about 5 years ( perhaps 6,000 track miles) and have never had it "automatically" jump out of gear, except due to occasional driver incompetance. So before I spend hard loot on new selector rods, or ponder myself into a hole in the ground, I wondered what has been your opinion on the deep detent contoversy!"

I have personally put nearly 200,000 miles on MGA 1500s, with lots of autocross time and a little open track time, and never had one jump out of 3rd gear. Then 18 months ago [that would be June 2001] I had the good fortune to discover the circumstances under which the thing would pop out of 3rd gear. I had run my MGA for several hot laps around Blackhawk Farms track with no problem. Then I switched places with a friend so he could get some seat time. The first time he came bearing down on the last turn it popped out of 3rd gear, even though it had never happened to me. And it continued to do so consistently for him.

It was closely related to his driving technique (not so great). As he was approaching a turn at high engine speed in 3rd gear (~6000 rpm) he would depress the clutch and release the throttle while applying the brakes. With the engine vibration and zero torque on the gearbox internal parts, the 3/4 shift rod would vibrate out of position and end up in neutral as the engine was slowing down. If you just took your foot off the throttle without depressing the clutch it wouldn't do that, as the reverse torque in the gearbox would keep enough friction on the 3-4 sliding hub so it wouldn't slide. Now that I know when it will do it and when it won't I have quit worrying about it and have never bothered to do the suggested modification to the detent. It has still never popped out of gear for me.

If you want to do this modification, you do not need to buy a new shift rod, just grind the detent notch a little deeper in the original one. Complete instructions for the modification are in the MG Series MGA Workshop Manual.

$.02,

Barney