Triumph Repair: 1979 triumph spitfire transmission, overdrive units, spline drive

Question
QUESTION: I have a 1979 Triumph Spitfire which has a transmission which kicks it out of reverse when you try to engage that gear. I'm looking to replace/rebuild the trans but can only find a trans with OD. Will it fit?
Thx,
Tom

ANSWER: Hi Tom,

The overdrive transmission is a highly prized unit as it makes the car useable on the expressways.

Be careful that you don't misdiagnose the problem as a transmission problem and not a clutch release problem. The easiest way to find out is to put the car in reverse on level ground with the brake off and push the clutch all the way to the floor and start the engine and just set there without the parking brake nor the foot brake on and note when the engine is idling if the car tries to "Creep" backwards. If it does you need to correct the the clutch release system first before blaming the transmission. It does not mean that there is not a problem with the transmission too but the clutch release system needs to be corrected first to know.

Howard

---------- FOLLOW-UP ----------

QUESTION: Howard--
We know we have a faulty transmission not a clutch problem.  The question is whether a transmission with Overdrive will fit in the space where a regular manual 4 speed gearbox/transmission use to be.
Thx,
Tom

Answer
Hi Tom,

Yes, the space is ok for either one except the rear transmission mount so be sure to get the OD rear mount. Also be aware of the two different overdrive units on Spitfires. The "D" type (early Spitfires) and "J" type on the late Spitfires like yours. The "D" type had the operating solenoid on the lower right side and the "J" had it on the lower left side.

As for the drive shaft, if you have the sliding spline drive shaft, it fits all applications but I don't remember if the others are interchangeable.

Howard