Triumph Repair: TR5 Reverse Gear engagement, bentley manuals, manual haynes

Question
QUESTION: Hi Howard

I have a TR5 which is in excellent condition however it does spend most of its time in my garage and I haven't driven it for a few months. The last time I jumped in to go for a quick drive to blow the cobwebs off, I engaged reverse gear to back out of the drive. All was well until half way out of the drive, the reverse gear seems to stop or slip but the gear seemed to still be engaged but it wasn't going anywhere. I drove forward in 1st gear it all seemed OK, but each time I go into reverse I get a slipping engagement or no engagement followed by a locking/ meshing of the back axle/wheels which rocks the car to a stop. I can then re-engage 1st gear it drives forward OK without any clutch slip. Can you let me know what you think as getting the car to my mechanic is quite a distance and bit of drama if it turnout I can sort it out myself.

Thanks Robert
PS thanks for your help in the past

ANSWER: Hi Robert,
When you were in reverse and it locked up the drive, the transmission had shifted into two gears at the same time. This can totally destroy the transmission. So I advise you not drive the car at all until it is repaired. It can be just in the upper shift tower where there are two ball bearings and a plunger that prevent two shift rails from moving at the same time. So the problem can be in there. It is also possible that a shift fork had come loose from a shift rail.

Either one can be repaired by removing the transmission tunnel and removing the shift tower.

I have never been into a TR-5 but I am guessing that it is the same box as a TR-6 and I have rebuilt many of them. All gearboxes have a lock-out device to prevent two gears from being engaged at the same time.

If you want to do it yourself you should purchase a service manual. Haynes manuals are available at many auto parts stores and Bentley manuals are available at most Triumph parts companies on line. Read the procedure and follow it and if you run into trouble contact me through this program and I will try to help. Don't attempt it without the manual.

Howard

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

QUESTION: Thanks Howard...not what I wanted to hear really...so I called my mechanic to discuss with him who did rebuild the TR's overdrive recently. He seems to think it is more likely the overdrive being left on when in reverse which can cause the symptoms I have have described as well, and hopefully if I flick the overdrive off and engage 1st and then back to reverse it should sort it out, if not give a call back further investigation...I appreciate the difficulty in making a diagnosis over the web, but just wondered what your thoughts might be on this theory?

PS I think the TR5 box is the same as the TR6 as you suggest, only the overdrive got upgraded from A to J type on the later TR6's

Answer
That is also a possibility if you have an overdrive on the car. A sprag bearing in the OD will only go in one direction and if you try to force it backwards it can explode the OD unit. If someone didn't wire up the lock out switch correctly you will be able to engage the OD in reverse and in 1st and 2nd also.

Howard