MG TD/TF Gearbox

by Bob Grunau


The TD/TF gearbox is weaker than the TC gearbox and requires rebuilding more often. I've heard of many TD gearbox troubles in the past year so I thought it would be of interest to jot down some notes or tips for the potential rebuilder.

Removal and disassembly of the gearbox is covered in the TD/TF Workshop Manual, Section F. The disassembly is not difficult, but a systematic removal of parts and laying them out on a bench in sequence of removal will greatly assist the reassembly. The parts required will of course depend on the overall condition of the gearbox, however, the following should be carefully inspected.

  1. Layshaft - Check for wear at each end where the needle bearings run. If you can see local wear at either end of the shaft, it should be replaced along with the required needle bearings.
  2. Layshaft Bronze Thrust Washers - These have oil rings machined into them and must be replaced if end float of the laygear exceeds approx. 0.010". I think 0.006" (6 thou.) is the correct end float. (Can anyone confirm this?)
  3. Laygear - Check all gears that no teeth are missing. Particularly inspect the 1st gear teeth, if these are already chipped, the gearbox will be very noisy in 1st gear.
  4. First gear - Probably marked the same as the laygear 1st, therefore, replace these gears in pairs. Slight wear or marks on these gears will not harm as long as you can tolerate a slightly noisy first gear (also reverse).
  5. Ball Bearings - The front bearing is removed from the front motion shaft by removing the nut in front of it. The nut is a left-hand thread so removal is opposite to what you might expect. This is not mentioned in the manual. Check the front, centre, and rear bearings by "feel". Some experience is required here, but excessive play or roughness is not acceptable.
  6. Shifter Forks - Thickness of the forks is approx. 0.300", anything less than 0.250" (1/4") indicates excessive wear and replacement or repair is required, otherwise gears will not be engaged fully.
  7. Synchromesh Units - These are integral with the 2nd, 3rd, and 4th gears. Careful inspection may indicate these to be loose or very worn. - wear would be indicated by a "smooth" appearance on the brass synchromesh units. When new or in good condition, the synchromesh units have cuts in the brass every 1/8".
  8. Gear needle bearings - Probably OK. unless they indicate any deterioration.
  9. Remote Control Gear Lever - To remove for rechroming, one of the locating pins on either side of the lever must be drilled out. Excess wear of the remote control shaft in the housing may result in gear lever rattle at speed.
  10. Gearbox Mounting Rubbers - Replace if spongy or visual deterioration.
I hope the above is of some help to you. If the gearbox has a known defect, then it is wise to purchase the required new parts before laying the car up. On a routine rebuild I would have the following parts on hand:

Gearbox gasket set

Front & rear oil seals

Front, centre & rear ball bearings

Layshaft

Layshaft thrust bearings

Cost of the above are nominal, approx. $50 total and if you collect them before disassembly, the whole job should go faster. In addition, it may be wise to locate a lay gear and first gear so you can purchase then if required.

One additional point, removal of the top cover of the gearbox will indicate 3 small springs at the rear of the cover with 3 small steel balls under the springs and bearing on the shifter shafts. Removal of the shifter shaft will indicate 2 additional steel balls between the shifter shafts. In total, 5 steel balls are used to locate the shifter shafts.