Moss Motors, Ltd

So....

I have the 59 year old transmission perched in my bench vice, the larger anciliary parts have been removed. I have the top cover off and can see all the moving parts inside (very neat) and I am about to pull the insides out and find my problem.

 But...I am not really sure what I am looking for.

When the car was in one piece and drivable the transmition would not stay in third gear by itself. I could hold it in gear but if I were to let go of the shift lever it would eventually slip out of third.

Any ideas what I should be looking for? 

Thanks.

Stub 

The part number for the 5-speed conversion kit ...

Just kidding.  Assuming you haven't found a collection of broken teeth or needle bearings in the bottom of the case,  "renew" the three selector shaft springs (Moss catalog page 14, part #27).  These press a ball bearing into a detent on the selector shaft to hold the gears in position.  The selector "forks" (part #8) will show wear on both faces.  Failure to stay in either first or third gear is the classic description of a very tired TD transmission.

Horst Schach's restoration book "The Complete MG TD Restoration Manual"  has an excellent chapter on overhauling the TD transmission.  IMO, try replacing those springs first.  Also, some people will add shims to increase the spring force on the ball detent.  As you can see, the cost of the replacement parts adds up very quickly, making the 5-speed transmission cost-competitive.

Contact Motorbill66 (aka Bill Wardlow) at his LBC restoration business.  He's rebuilt a gazillion MG transmissions over the years, and can help you trouble-shoot and make decisions on best options  http://www.motorwayltd.com/.

The 5-speed completely transforms the "drivability" of the car.  Worth every penny 

Dick,

Thanks for the quick reply.

The 5 speed would indeed be a nice addition but the $4000 it would cost will go a lot further getting the car back together if I spread it around. That improvement will have to wait.

In the mean time I have ordered the book you suggested and also investigated my gear box a little further.

It turns out that the set screw (#16 pg14)  that was holding the 3rd/4th gear selector fork (#8 pg14) in the correct place had broken. Consequently the selector fork evidently was allowed to travel too far and all the spring and balls (#89, 90 pg14) that position the 3rd/4th sliding hub (#88 pg14) had fallen out. I found them falling out of the gear box case when I had to turn it upside down trying to get the broken end from the set screw out. 

So... What caused the set screw to fail? I also found one tooth from the large cog (top gear) on the cluster gear (#75 pg14) missing so maybe when that happened it caused such an uproar in the box that it kicked things about and broke the screw. Maybe.

Unless I hear different from an expert I plan on reassembling the box with the missing tooth. It seems to run smoothly while hand turning the shafts so I am hoping that it wont be missed.

Now all I have to do is get all those pin bearings back in place.