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Last summer, my A-type overdrive on my 71 tr6 would Intermittingly work. Tranny fluids appear to be topped off base on the overflow I'm getting when taking the plug out. Adjusting the solenoid by the book would not engage the overdrive. I adjusted it by pulling the tranny cover off, drove it, adusted it until it engaged. Once everthing was put together, overdrive DOESN"T ENGAGE.
1)Solenoid moves about 1/4" up and down. Is this normal or should it have more movement?
2)Do I have enough fluid in the tranny?
3)Is their an easier way of adjusting the overdrive?
4)Any suggestion?


A quarter inch sounds about right.

I assume the solenoid is not intermittently operating as that would prevent it from engaging.

Are the interlock switches (for 3rd and 4th gear) on the tranny working properly and are the connections clean? Is the OD switch in the car itself working properly?

There is a relay that allows the solenoid to engage. If it is faulty or intermittent, you will have a problem as you describe. In my 69 the relay is beside the fuse box.

Is the engagement rod and lever(the thing the solenoid contacts) well clamped? If it isn't the overdrive won't engage.

Have you tried cleaning the strainer on the bottom? May be blocked and not getting the fluid it needs. There is a screwed cap on the bottom. Remove this and inspect the strainer and clean as necessary. (requires draining tranny)

Have you changed the tranny fluid? Some tranny fluids do not work well with the overdrive I hear. I recently used a GL-3 fluid from NAPA and it seems to work OK.

That's about it from the outside I think. Anything else requires disassembly.

Good luck.
Michael S. Petryschuk

Thanks for helping me out.
Responses to your email is as follows:
1)How does one test the interlock switches?
2)I'll need to check the connections if they are clean
3)Verified that the od switch works.
4)Relay clicks so I guess the relay works. How does one test a relay?
5)Engagement rod and lever are well clamped.
6)Haven't checked the strainer on the bottom
7)Tranny fluid: Redline(I think it's 95w gear oil. I'll need to check it tonight if this might be an issue).I've had the tranny fluid in for about 2 years with about 2000 miles of use.


benjii--FYI the 'A' O/D was not designed to use gear oil as it accelerates wear due to the much higher hydraulic pressures it produces. You should be using non-detergent 30W motor oil. If you go to John Esposito's Quantum Mechanics website, there's a lengthy tech article on the subject.

Rick O.
72 TR6 ['A' O/D]
Rick Orthen

Rick Orthen (and anyone else),
I appreciate you taking time to help me with my tranny issue. Obviously, I didn't know about the faster wear with the gear oil.
I went to John Esposito's website but, couldn't find the article. Can you post the address the article is in?
Here's a few questions I have:
-What non-detergent 30W motor oil do you use?
-Michael uses GL-3 fluid from NAPA and seems to work well for him. Is this recommended?
-What is the best way to drain ALL the gear oil out of
my tranny and od?


Based on your comment of gear oil, I would suspect that this may be contributing to your problem particularly if you did have it changed recently (2000 miles is recent).

I am not familiar with Rick's suggestion. The TR6 manual actually recommends a GL4 oil which seems to have an SAE of 90 or so. I will need to research it further I guess. It was suggested to me that the GL3 was the way to go. Please note I do have an A OD unit and have also put about 2000 miles on it since I changed the tranny fluid.

To test the interlock switches, use an ohmmeter and if you get zero ohms across the 2 switch contacts when the gear is engaged and infinite ohms when the gear is not engaged the switch is working.

If the relay is clicking it probably is working. When engaged you should get 12 volts across the relay lead that goes to the solenoid and the ground.

To drain pull the bottom plug and the OD threaded darin plug and wait. This will do the job.

Michael S. Petryschuk

Greetings all,

as per the previous discussion, John at www.quantumechanics does highly recommend the 30 weight non-detergent motor oil for the trannies. It is found under the article of the month section on the left hand side of the page. Seeing as this is their business, I will be using the same.

Ken Jackson

"Last summer, my A-type overdrive on my 71 tr6 would Intermittingly work."

Are you saying that it would go in and out of OD while driving or sometimes not go into OD when you flip the switch?
The A Type OD solenoid has 2 seperate coil windings with an internal switch. The "closing" coil has a higher current draw as it is used to lift/open the valve. After the lift, the internal switch opens and the "holding" coil holds the solenoid in place.. holding the valve open..keeping the OD engaged. If the holding coil does not hold then you will have intermittent OD.
The solenoid can be removed and then disassembled. You might find you have a little rust up inside the solenoid. This should be removed and a light coat of dielectric grease applied.

Another consideration is the isolation switches on the top cover of the transmission...dirty connections or intermittent operation. There are actually 3 interlock switches on the tranny top. The one closes to front of tranny is for 3rd and 4th gear, the one that is closes to driver side is for reverse, and the one closest to passenger side is for 2nd gear. A type ODs have OD capability in 2nd,3rd, and 4th gears...J types only have OD in 3rd and 4th. (FYI). I agree with Mike, If you hear the relay clicking in and out then it is working.

Other potential areas:
First to check that the solenoid is moving the valve to proper height. On the passenger side of the OD is a "valve setting" lever. When OD is engaged the hole in this lever should line up with a hole in the OD casing. If not then the solenoid needs adjustment.

Another area if OD does not remain engaged is the valve leaking due to crap on the valve seat. I will not get into the removal of the valve until you have exhausted all above areas. There is a caution involved in the valve removal.

OD oil. The "official" Laycock-De-Normanville OD service manual says use SAE 30 oil in the OD.
The "official" BL TR6 service manual says (gearbox and overdrive) API-GL4 (hypoid 90).

I just read the article and an interesting point to make.
I put NAPA GL4 oil in this spring. My OD seams to leak more( higher pressure???). When doing a top up, the oil was full of bubbles...sludging???
This winter will be a drain and refill with SAE30 oil.

Did anyone happen to go down the page and see
the "proper way to shift in an out of OD"??

Rick C
Rick Crawford

In my gearbox with "A" type overdrive, I have used Valvoline 20W50-R (for racing) for the past 15 years more than 87,000 miles. I have always switched into overdrive with full power on the loud pedal, but I usually let up for a microsecond just after I have switched. The pressure I measured the last time I had the tunnel out was 325 psi which is normal for the "A" type O/D. I also switch out of overdrive under full power if I can. These "tricks" avoid the clunk you get if you lift off the pedal. I have never clutched to go in or out of overdrive. They were made to be used this way for rally competition when the earliest TR2's were introduced.

Don Elliott, Original Owner, 1958 TR3A, TS 27489 LO
Don Elliott

Benji--The best way to drain your O/D is also the only way: simply remove the big brass plug and the smaller NPT plug to the rear of it. But first it is good practice to relieve any hydraulic pressure from the O/D by cycling the O/D swtich/solenoid a few times witht the key on and the gearbox in a permissive gear.

Let drain overnight (or less if you have it warmed over). I bought an inexpensive adjustable spanner to get at the brass plug. Once removed, take out the magnetic dounut and screen. Note any debris there and clean it up with solvent. Put a bit of gasket sealer (Hylomar or equivalent) on both sides of the paper gasket before refitting.

To refill, remove the NPT plug that's on the driver's side of the gearbox and use a bottle pump to send in the new 30W motor oil. [I use Valvoline, the only brand of ND oil I can find locally.] Stop when the oil runs out of that hole, and replace the plug. Start your TR and cycle the O/D a few times to circulate the oil. Recheck fill level and your done for another 20,000 miles or so.

Rick O.
72 TR6
Rick Orthen

Forgot to point out that this procedure is best done on a lift (to keep the car level). If you use jackstands instead, use at all four corners and at the same height.

Rick O.
72 TR6
Rick Orthen

Rick C--I thought we schooled you that GL4 and our brassy gearboxes don't do well together? Shame on you! Get it outta there.

Rick O.
72 TR6
Rick Orthen

To all of you,
You guys are a great help!! I'll be working on the tranny this weekend. I'll give ya'll my results later. I am a little confused about which fluid I should put in????
Regards to all,
Rick Orthen,
Inexpensive adjustable spanner? You must be a British bloke.

Rick O
Yes you did set me straight long ago. That was with GL5 though not GL4. GL4 is OK and does not attack the brass/bronze...GL5 does. Even though GL4 is safe, it still gives too high a pressure in the OD and promotes "foaming" of the liquid.
Rick, "the only brand of ND oil I can find locally"...the name of the store is ???please.I am sure ND is getting harder to find.

Benji, it is simple. Wait for Rick O to respond to the store name then get thyself there.
Rick C
Rick Crawford

Rick C--I'm way old school, can you say "GL3 hypoid"? That's why I think GL4 or 5 is way too modern for our gearboxes.

The 30W ND Valvoline is available at my Advance Auto. If you can't find it, ask them (or Car Quest, or Pep Boys, or AutoZone) to order for you. You might have to get a case, but that'll only set you back $10 or so and you'll be set for life.

My spanner is part of a 3-spanner set I picked up cheap from Harbor Freight. Yes, it's catalog name was "spanner" as it "spans" the width of any conceivable bolt head or nut! Works great on that ugly O/D plug.

I'm a bloke-wanna-be who loves both the 4- and 2-wheeled (Meriden/Hinckley) Triumphs.

Have at it!!

Rick O.
72 TR6
Rick Orthen

I changed my tranny fluid last weekend with Valvoline non detergent 30w oil. Tranny shifts smoothly and overdrive works. I'm back in action!!
Thanks to all for your help.

Sounds like one of my winter projects is to drain the GL4 and get some 30ND oil. Thank you O:)
FYI, I replaced the stupid drain plugs (tranny and oil pan are same plug) with off the shelf brass water fitting plugs with the same taper thread. Fits the head of a socket.
Rick C
Rick Crawford

This thread was discussed between 10/10/2005 and 24/10/2005

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