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MG MGB Technical - Tranny Swap Summary

I've been driving my '67 GT for almost a week since replacing the 3-sync transmission with a 4-sync gearbox. The results are mostly positive. Best of all, the new starter is amazing. It sounds so much better than the old one, which often disengaged before the engine started, resulting in a "waaaoooow" sound that raised eyebrows in the parking lot. The new starter never disengages before I release the key, and I doubt it will ever get stuck in the flywheel like the old one did. I was told that this was a result of the ring gear being chewed up, but the ring gear was fine. I think the inertia starter was just too antique for me.

The next best thing is synchro first gear. All you diehards can claim to double-clutch your way into your non-synchro first gear, but I could never master that move well enough to pull it off when anyone was watching. So rather than be embarrassed by the crunch of gears grinding, I usually chose to be embarrassed by the sound of the engine trying to smooth a low-speed start in second gear. Synchro first makes it so much better! Also, I thought I would have difficulty remembering that I no longer need to stop the lay gear before shifting into first while stopped. But it is already feeling natural to shift directly into first without nudging second. And so far the car has not refused to go into first gear at a stop, which it used to do just often enough to catch me unawares. Yes, I know you can double-clutch your way out of that one, too, but it was always quicker to just throw it in second and let the clutch suffer the consequences.

I do miss the short-throw shift of the old transmission, which had a more precise feel. I still have to give the shifter a little slap to get into reverse gear, but I'm used to that. I covered the enlarged hole in the transmission tunnel with duct tape for the time being, and am looking forward to cobbling up a lengthened tunnel cover. Right now I can't tell whether the "new" transmission is noisier than the old one or if it's just the lack of a good tunnel cover.

My left leg sometimes got sore from depressing the clutch pedal, and I'm in pretty good physical condition. I guessed that the clutch must be a high pressure type, so I purchased a normal Borg & Beck replacement kit, rather than the heavy-duty model. I'm glad I did. The pedal effort is much less than before. I don't drive the MG hard, and the clutch seems strong enough to handle my driving.
Glenn G

If you have replaced the inertia starter with a pre-engaged then it *won't* ever disengage before you release the key, and it *won't* jam with the flywheel (unless it goes faulty). Those are both features of the inertia starter - the first documented by the designer, the 2nd undocumented :o)
PaulH Solihull

Yes, the new starter is the late-model pre-engaged type. And I believe both "features" of the earlier starter are documented, as it says in the workshop manual that the starter pinion may become "meshed permanently with the geared ring on the flywheel." I remember being dumbfounded by that statement the first time I experienced the inertia starter locking with the ring gear. Also, the workshop manual advises that the starter must be removed if this happens. I complained about that in this forum and was given much better advice: simply turn the squared end of the starter shaft until it disengages. That's better, but it's a poor alternative to a starter that does not get stuck! -G.
Glenn G

I was able to release a stuck inertial with a push in 4th gear. Later the somewhat chewed ring gear was replaced. Interesting things one learns with an old car.

I had an early RWD Corolla many years ago. The shift boot was split and there was a lot of terrible transmission noise. I thought the gear box was going out. After I replaced the boot things quieted down nicely.

I hope you find an easy fix like that.

Oh yes, thanks for the update.

Bob
Robert McCoy

Glenn,
You may want to get one of these
http://clarkandclarkinc.com/1200_transcover.htm
I hope to be fitting my own in the next few weeks............finally!
Eric Martin

I did this swap, to my '67, some 25 years ago. It was an incredible improvement over the 3 synchro trans. The first 4 synchro trans, that I installed, was a huge improvement over stock. I later switched over to a '72 Black label 4 synchro/OD trans. This has been in the car for almost 25 years and totally transforms the driving experience. I, too, went with the later pre-engaged starter, from a '68 GT parts car. It's still going strong after all these years. RAY
rjm RAY

Just a couple of things to add. I was cleaning up the garage over the weekend and took a close look at the old flywheel for the inertia starter. It is pretty chewed up in two places on opposite sides of the ring gear. So it is possible that a new ring gear might have cured the starter from getting jammed. Still, since it is mentioned in the workshop manual, maybe not!

The other thing -- the new starter doesn't jingle like the old one did when driving normally. I spent a lot of time locating the source of that jingle and never got rid of it until now. -G.
Glenn G

All the wear does take place in two positions as generally an engine will always stop in those positions. Unless original ring gears came with chewing-up built-in, then a new one will eventually go the same way :o) Except that pre-engaged are a bit gentler, I think.
PaulH Solihull

Just now got around to reworking the transmission tunnel cover. This was not an easy task, and I would recommend it only if you have some experience welding and hammering sheet metal. I cut off the rear part of the cover while fitting the transmission, so the first job was to weld it back together. Then I cut it in two just ahead of the gearshift hole and welded in a patch to add 2-1/4" to the length of the cover. At this point I had eight hours of work in the cover, and I put in another five hours reshaping the edges to make a tight fit between the rear end of the cover and the tunnel. I used the original captive nuts where possible and one large sheet metal screw on the rear edge. I put silicone sealer all around before the final fitting. It was two days of welding, grinding, hammering and some swearing, but I am satisfied with the result. The metal cover adds structural strength, rigidity and good sound control. However, it seems this job will never end. The hole in the carpet doesn't line up with the new placement of the gearshift, so new tunnel carpet will be next. -G.

Glenn G

This thread was discussed between 14/04/2012 and 29/04/2012

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