Product Description
Triumph TR2-5 Overdrive
An overdrive conversion is among the most useful The ‘A’ Type overdrive unit that was fitted as an option as a rule operates in 2nd, 3rd and 4th gears. The only exception to the rule is for the overdrive unit originally fitted to TR2s up to TS5979, which operates in 4th gear only. Overdrive provides a 22% reduction ratio to the engine speed for a given road speed when engaged. The reduction ratio is signified by the serial number prefix of the Laycock unit. In the case of the TR 'A' type this is 22/. Other cars used a different ratio unit, notably the Standard Vanguard at 28%, whose serial number begins 28/.... Overdrive gives useful additional gear ratios, for use under all driving conditions. Creeping about in town, the use of 2nd overdrive and 2nd gear saves on the continual 2nd to 3rd to 2nd gear changes. It nicely bridges that 2nd to 3rd speed ratio gap. The 4th gear overdrive provides effortless high speed long distance touring economy. The 3rd gear gives that little extra help for high speed overtaking when an upward gear change could best be ignored.
Notes: Depending upon availability the type of annulus fitted to reconditioned exchange overdrives may differ from original, necessitating recalibration of the speedometer.
After initialisation, it is important to set up the actuation valve lever accurately to ensure correct operation. Ensure gearbox is clean internally before fitting overdrive - avoid cross-contamination from dirty oil.
OVERDRIVE HINTS
The correct operating pressure (o.p.) range is 380-400PSI. On an otherwise good overdrive our new springs should increase this by 20PSI (i.e. 400-420PSI). The overdrive ceases to be of any use below 360PSI. Padding the spring will increase the operating pressure. Never add more than 0.040", which may produce an extra 20-40PSI, though the engagement will be fiercer. Packing a worn spring will make no difference. The pressure should be measured using a suitable gauge reading up to at least 500PSI, screwed in place of illustration no 68 in the operating valve port.
Fault Diagnosis:
1) Most work requires removal of the gearbox from the car and the overdrive from the gearbox.
2) Jumping out of overdrive when warm/under load is usually due to worn accumulator piston rings and often the bore.
3) A stuck pump piston may be accessed from the underneath by removing illustration no 84/85, the illustration no 76 and pushing upwards on the revealed base of the plunger (illustration no 70). If it sticks again, you're wasting your time, go back to '1'.
4) A sudden cessation is often caused by the circlip (illustration no 126) breaking - go back to '1'.
5) Intermittent working may be cured by dumping gearbox and overdrive oil and cleaning the filter (illustration no 77) and the magnetic collectors (illustration no 78). Refill with 20/50 multigrade oil, run for an hour or so (up to 50 miles) and dump the oil again. Refill this time with hypoid oil (XPG041L).
6) Air trapped in the system can often be bled out by removal of plug illustration no 68. Place a catch tank under the car below the valve. With the back wheels jacked off the ground, start the engine, engage 4th gear and allow air to pump out of the port for 1 to 2 minutes. Replace the plug and top up to correct the oil level.
7) If the overdrive does not disengage, don't even think about using reverse gear. Again, remove plug illustration no 68, then illustration nos 67 to 63. Inspect valve illustration no 63 and you'll see a tiny hole about midway from either end. Scrupulously clean the whole valve and check the hole by sucking or blowing through it, then carefully replace illustration nos 63 to 68. Don't forget to reseat ball illustration no 64 into the casing. Check the engagement again. Sometimes the clutch linings (illustration no 129) stick to the brake ring. A sharp tap or two with an iron hammer often releases the bond. Failure of these two suggestions to cure the lack of disengagement usually requires a return to no 1 above.
8) That clutch slip feeling under load or while engaging overdrive is probably due to a worn illustration no 129, especially if the overdrive feels hot and the oil smells. Replacement of no 129 is the only answer (via no 1).
9) The above hints assume there is no other problem associated with electrics (wiring/switches), which should of course be checked first if the overdrive fails to operate correctly.