o/d tranny question

[mgbmedic]

I recently purchased a 72 TR6 with an o/d tranny that the PO had installed half #%*ed. There is a plate that says Laycock de Normanville with a serial number that ends in "A". would this denote the A-type overdrive? Also, missing is the solenoid. It looks to me as if the solenoid would have been mounted horizontal on the drivers side of the unit. Anyone have pictures of what i need to complete the installation? There is no o/d switch on the steering column either. any help would be greatly appreciated.

 

[DougF]

The Roadster Factory used to have a book on over drives. It might not hurt to inquire about it.
There is a horizontal hooped bracket that the solenoid mounts into vertically. At the base of this bracket is a nutted stop for the solenoid piston rod. The rod mounts to an arm that mounts to the shaft to the pump.
You need the column mounted switch, upper and lower wiring harnesses (upper is available, but I'm not certain about the lower)and of course the solenoid.
The A-Type is original to the '72. As far as your question about the A designation, I can't say. The A unit is larger than the J model.

 

[Alan_Myers]

Hi,

Sounds like your previous owner got stuck and didn't know how to proceed either... at least the difficult parts are done: writing the check to buy the O/D, setting up the gearbox internals and installing the gearbox & O/D in the car!
I'm not sure about the suffix letter on the serial number, but the first two digits might give a clue. If they are 22xxxx that is usually an A-type, set up to give 22% reductuction ratio. If it's 25xxxx that is usually a J-type set up for a 25% reduction. (Both these assume no one has rebuilt the O/D to a different reduction ratio, which is rare because it's expensive, but is possible and does happen).

If the missing solenoid is, in fact, horizontally mounted as you describe, then it is a J-type overdrive. The A-type's solinoid is vertically mounted. At least this is true on TRs. Both A-type and J-type were used on other cars with varioius external arrangement of solenoids, mounting brackets, etc. Sometimes an O/D or even an O/D & gearbox combo from another car ends up in a TR. (My TR4 has a 2000 gearbox and a TR3 A-type O/D!)

Also, the linkage operated by the solenoid is external on an A-type, internal on a J-type.

I don't have pictures of what you need, but can describe it:

It sounds as if the O/D is already installed in the car, so we can skip over the special mainshaft for the gearbox and the adapter plate at the rear of the gearbox in place of the tailpiece extension. (Note: adapter plate should be safety wired, but that's internal and might be hard to check).

You need the external parts, which include:
- the steering column lever switch,
- the plinth on the steering column that accomodates the O/D switch (different on different TR models & years, metal on my TR4, but plastic on later cars and shared with headlight controls on still later cars).
- I think also a relay (assuming J-type use one, A-type does) that mounts under the dash,
- an "isolator" switch that screws into the top of the gearbox that allows O/D to be actuated only on 3rd & 4th gears, a hole needs to be drilled and tapped in the right place for this.
- a wiring harness, easy to make if you know how it is set up, but not expensive to buy ready-made from one of the big vendors.
- maybe a different speedometer cable, I'm not sure if needed with a J-type... it is with an A-type.
- recalibrated speedometer?
- in addition, I used a few rubber-lined clamps to clean up and support the wiring harness when installing mine, and some rubber grommets where the wires pass through the gearbox cover.

There is a guy selling Laycock O/D service manuals on eBay, but frankly that is likely far more than you need or want. It's mostly to do with disassembling and rebuilding (not for the faint-hearted... mine is going to John Esposito at Quantum Mechanics when it's time for a rebuild).

The factory service manual (Brooklands or Bentley, depending upon the year.) has all the detail info you need to install an O/D properly, better illustrated than possible here. I highly recommend the service manual for many reasons, not just installing an O/D.

I wasn't aware of the TRF book on O/Ds, but John Swauger at TRF Level II Service can likely help you a lot. He probably can identify the O/D for certain from the serial number, and no doubt has all the details you'll need. He's often the one who answers emails, too.

In addition, John at QM may be able to answer some questions. He is probably the most knowledgeable person in the U.S., when it comes to TR gearboxes O/Ds. Website is www.quantumechanics.com

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[mgbmedic]

wow, thanks doug and alan...I definitely need the workshop manual. The isolator switch is present. Just want to make sure I'm buying the right solenoid as it's a very expensive item. Just can't get a visual on the solenoid set up, but the manual is a good start.

 

[Dave Russell]

Attached is a pic of the type J OD & the type A OD.
D