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Triumph Repair/TR6 Overdrive


Hi Howard

Im hoping you can advise me on a problem im having with the Overdrive on my 1974 TR6. Mine is a J type (3rd and 4th gear overdrive only) with the overdrive 'switch' being a stalk on the steering column.  

The car was sold to me with this problem which is essentially that it suffers a very long delay when engaging the overdrive.  Sometimes it takes up to around 10-15 seconds to engage (and sometimes i have given up waiting!). Sometimes it will engage after a second or two.  It always disengages without delay. Oil level seems fine although i have to admit I dont know when the oil was last changed and im planning on doing this soon. Before i start changing solenoids etc what do you think is the likely cause.

Many thanks in advance


Hi Tony,

Slow engagement can be just a minor thing but to try to diagnose it first decide if the problem is more noticeable when the car is first driven and is not as much of a delay after it has been driven for an hour or so. If this is the case, change the oil and if it has gear oil in it like BLM recomended, change to engine oil. Then drive it for an hour or so and see if it engages better and check it after the oil has cooled. Don't use any of the 5w oils and never put any additives in the oil.

That usually corrected the problem of slow overdrive engagement and gear clash on shifting due to worn syncros.

At the dealerships we found this before BLM took over MG, Triumph and Jaguar. When Blm found that we all had switched to engine oil in the gearboxes they sent the dealers a memo to switch back to gear oil and within a week we had cars lined up with complaints that the syncros didn't work and overdrives were very slow to engage especially when cold. So we just didn't tell BLM and we all switched back to engine oil. We monitored the cars that we had put engine oil in the gearboxes and over a period of several years and noted no increase in gearbox ware or failures so we continued the practice of using engine oil in the gearboxes.

Let me know,


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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