-
Hey Guest!
British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!**Upgrade Now**
(PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
TR2/3/3A TR3A overdrive conversion - whats needed
- Thread starter TFR
- Start date
Share this page
D
DougF
Guest
Guest
Offline
An overdrive to start. The proper dash switch, which for your car should be the big monstrosity toggle unit that fits to the left of the steering wheel near the heater switch.
Wiring harnesses, upper and lower; relay; and solenoid. I can't remember if you need different mounts.
If you are mounting an overdrive to your existing transmission, you will need a new main shaft.
Wiring harnesses, upper and lower; relay; and solenoid. I can't remember if you need different mounts.
If you are mounting an overdrive to your existing transmission, you will need a new main shaft.
Geo Hahn
Yoda
Offline
I added OD to the TR4... the package from Quantumechanics had everything included: Gearbox, OD, wiring harness (upper & lower), switch, relay & solenoid, angle drive... just add oil.
https://www.quantumechanics.com/
Oh, I see he also sells an installation kit with all the bits if you already have the OD. Lots of other stuff and tech info there too.
https://www.quantumechanics.com/categories.php?op=newindex&catid=7
https://www.quantumechanics.com/
Oh, I see he also sells an installation kit with all the bits if you already have the OD. Lots of other stuff and tech info there too.
https://www.quantumechanics.com/categories.php?op=newindex&catid=7
TR3driver
Great Pumpkin - R.I.P
Offline
You'll also need the adapter plate that goes between the OD and the gearbox; plus the isolator switches for the top of the shift cover. If your shift cover is not drilled and tapped for the switches, you'll need to do that too. (Takes an unusual metric tap, 16x2.0 as I recall.)
But the wiring is trivial to fabricate on your own, and almost any switch will work. The original 'teardrop' is nice because it puts the toggle where you can hit it without taking your hand off the steering wheel.
Mounts are the same (if you get a proper TR A-type OD), driveshaft is the same; but you'll need a different, longer speedo cable. Speedo itself does not change.
Note that installing the OD requires partial disassembly of the gearbox; might as well replace the seals, 2nd gear synchro and countershaft/bearings while you're in there.
I would suggest a few modifications (unless you're a purist)
1) Add a diode across the relay contacts to absorb the kickback from the solenoid. If you do this, you can use an ordinary 12v automotive relay.
2) Add a fuse in the power to the relay and solenoid. In addition to reducing the chances of fire if you have a short, it will protect the pull-in coil inside the solenoid, if for some reason the plunger hangs up.
3) Although the factory powered the OD solenoid from the battery side of the ammeter, I moved mine to the load side. That way, the ammeter tells me a bit about what's going on if the OD doesn't work the way I expect. I can see the needle kick for the pull-in solenoid, and just barely twitch for the holding coil.
4) If you are going to have the shift cover apart, add "backing washers" to the (new) shifter shaft seals. Eg MMC P/N 9560K53. I don't know if the original seals actually fit or not, but the seals sold today (which are just O-rings) don't fit right and leak.
I actually bought "double seal" O-rings to go on top of the washers, which seem to work very well. If they hold up on the car, I may offer kits of 3 O-rings & 3 washers (since I bought 100 of them).
But the wiring is trivial to fabricate on your own, and almost any switch will work. The original 'teardrop' is nice because it puts the toggle where you can hit it without taking your hand off the steering wheel.
Mounts are the same (if you get a proper TR A-type OD), driveshaft is the same; but you'll need a different, longer speedo cable. Speedo itself does not change.
Note that installing the OD requires partial disassembly of the gearbox; might as well replace the seals, 2nd gear synchro and countershaft/bearings while you're in there.
I would suggest a few modifications (unless you're a purist)
1) Add a diode across the relay contacts to absorb the kickback from the solenoid. If you do this, you can use an ordinary 12v automotive relay.
2) Add a fuse in the power to the relay and solenoid. In addition to reducing the chances of fire if you have a short, it will protect the pull-in coil inside the solenoid, if for some reason the plunger hangs up.
3) Although the factory powered the OD solenoid from the battery side of the ammeter, I moved mine to the load side. That way, the ammeter tells me a bit about what's going on if the OD doesn't work the way I expect. I can see the needle kick for the pull-in solenoid, and just barely twitch for the holding coil.
4) If you are going to have the shift cover apart, add "backing washers" to the (new) shifter shaft seals. Eg MMC P/N 9560K53. I don't know if the original seals actually fit or not, but the seals sold today (which are just O-rings) don't fit right and leak.
I actually bought "double seal" O-rings to go on top of the washers, which seem to work very well. If they hold up on the car, I may offer kits of 3 O-rings & 3 washers (since I bought 100 of them).
