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TR6 Refurbishing gearbox with A type overdrive


Luke Skywalker
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I bought all the basic innards to replace and realized that there was only 39k on this tranny so it probably wasn't going to need all that. So I decided to just open it up take a look inside and hopefully top off the gear lube then run it on my adapter to see if the OD works. Well after opening it it was kinda black in side.

First thoughts was it got hot and cooked the lube but this car sat outside for 35+ years (parts car) so it probably got some moisture in it and algae set in. The lube was a little gritty at first and when you rolled it in your fingers it smoothed out. So I took a can of brake cleaner and started spraying and turning the shafts. Then I opened the drain plug and started spraying again while turning the shaft and letting everything go out the bottom hole. Then used my air gun to blow out as much as possible and again rinsed it with brake cleaner.

Then opened the brass plug on the overdrive and let whatever drain out. Although it was dark too really clean and nothing in the screens. There was however a little goo on the bottom kinda like what you would see on the bottom of a automatic transmission when you do a service. It was as high as the 3 rubber washers on the bottom.

So here is my question. I need to test it but ether before or during can I or should I use a additive or a detergent lube to help clean out this unit? I'm thinking like Marvel Mystery Oil or a high detergent motor oil. Then replace it with the permanent stuff like Red Line.

The smear on the paper is from the overdrive brass cap.


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Marvin Gruber

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I'm old school. I just did that on an overdrive, I pulled big brass plug and washed with gas until it ran clean. Did pull side plate under solenoid, stood it up on end over night to let dry. Plan to run cheap 30w in it for little bit and then put in MT90


Obi Wan
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Mine was just like yours: http://tr4a.nonlintec.com/transmission/

I don't know what specifically causes that black deposit, but it's easy to clean off, at least. I suspect that changing the oil regularly will prevent it. Even in a gearbox, oil breaks down eventually. Cleaning it out as you have will take care of the transmission, but the OD is more complicated. The stuff is inside the pistons, pump, accumulator, and especially the valve. Also, if the OD has not been rebuilt for decades, the piston o-rings and other rubber parts have probably hardened.

You might want to slosh it with some kind of cleaner, maybe gasoline as Marv suggests, drain it well, and then hope for the best. As a minimum, I'd remove the OD actuating valve and make sure it is clear, especially its tiny orifice. I'd also measure the clearances between the transmission synchros and their respective gears--I think the spec is 30 mils. If the clearances are too small, you probably should pull it apart and replace them.

If it were me, I'd pull it apart, clean everything, and check things like the bronze bushings in the transmission that you can't see otherwise, and replace the seals and o-rings in the OD. But this is a big job, and I understand the reluctance to dive into it.


Jedi Knight
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The gears look good TR trans are bullet proof. How are the brass shifting forks some people are known to keep hand on shift knob causing fork to rub. As you have the A type some adjusting may be needed to arm done while running for complete shift into gear. I use WD 40 to flush gears and case or kerosene, gas can be another matter keep a fire EX close. Filling with 90 W nondetergent oil. Add some grease to shifting rods before replacing cover. and watch closely the shifting lever for REV on bottom of case. When adding oil it takes a bit to get into OD case so check level twice FYI.
As for the OD plug normal that is why they use nondetergent oil . Madflyer


Luke Skywalker
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Low mileage, I would test it first like you planned. But I will tell you I just finished a A type with 56000 on it and the thrust washer in the planetary gears was gone! I have seen that washer gone on 3 overdrives now.

By the way, I hooked up a motor and pulley system to check mine and it took quite a while to get the air bubbles out of the system. I hooked up the speedometer also and was hitting 30 to 40 mph . Still had to run about 10 min and then the pressure started coming up.
good luck with your project.



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I would just run it, but plan to change the fluid again after a few thousand miles, or a couple months if you don't drive much.


Luke Skywalker
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Bought a new solenoid for it. Hook up my electric motor and pully system. Filled the case with 30w motor oil and Marvel Mistry oil. Ran it for 5 minutes then tried to kick in the OD with a lawn tractor battery. Would not engage. Took the solenoid out and used my finger to raise the lever and the OD kicked in. Went through #2,3 and 4th gears no problem. It's been running for about an hour now in OD. Got catch pans catching oil coming out of the seals. I'll change the seals and because I don't have time to mess with it I'll take it to my Triumph tech. He is good at setting up the engaging lever plus I'll have him replace the orings.


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