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Thread: Over drive

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    Over drive

    Hi im new to the forum , iv recently purchased a tr3 smallmouth TS20934-LO.matching numbers car in need of full restoration
    While reading up on the manual and looking at the gearbox , i noticed there seems to be one or more isolator switches missing / plugged off these plugs seem to have been there long term . a lot of the wiring with the car and to the overdrive is also missing , i take it theise switches are needed . can any one help me with this

    Regards
    TRo8son1
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    Great Pumpkin TR3driver's Avatar
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    Re: Over drive

    The switches are quite important with the overdrive. Sounds like someone may have switched some components without really understanding what they were doing.

    The good news is that you have the plugs, so adding the switches is fairly easy. There is an adjustment procedure though, you may need multiple gaskets under either switch to get proper engagement. See page 26 in the gearbox section of the workshop manual.

    The OD wiring is fairly simple, easy to fabricate yourself if you can solder. Should be a relay on the back of the battery box (near the heater). Two wires from it to the OD. One wire to the ammeter, another to the operating switch on the dash. Last wire from operating switch to starter switch.
    (Some sources say to pick up power at the fuse block and control box which will also work fine. But what I outlined is what I found on TS39781LO and it appeared to be original.)

    I do recommend two modifications to the OD wiring. A diode from the relay output to ground will make the relay live longer, and an in-line fuse in the wire from the ammeter will help protect the solenoid if it gets jammed, in addition to the wiring.

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    Re: Over drive

    At the switches on the gearbox, both have one side wired to ground, while the other side of both switches connect to the wire to the relay.

    If you don't have a copy of the workshop and owners manuals, you can download PDF from here https://drive.google.com/drive/mobil...13&direction=a

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    Re: Over drive

    Maybe this will help at some point:



    I used both the diode and the in-line fuse suggested by Randall. This is the diode I used:



    Several places to add it, I put it right in the harness:



    The fuse I put at the connection to the relay:



    Relay contacts should point down, I really should fix that someday.

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    Re: Over drive

    very nice

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    Re: Over drive

    Thanks for all the help ,

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    Re: Over drive

    Having accomplished the OD wiring installation with the addition of the diode and the fuse holder, I am wondering what an appropriate fuse rating would be? I think in this case I'm trying to protect the solenoid rather than the wire that goes to it?
    I own 1958 TR3A TS 26005L and have the privilege of working on 1960 TR3A TS 65587L.

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    Re: Over drive

    On a Triumph, I’d probably refer to it as “numbers correct”, since there are no numbers that actually match.
    John

    1955 TR2

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    Re: Over drive

    Thought I had remembered the Diode mod.

    What are the specks on the diode or will the Radio shack number correctly identify it also how high a fuse rating?

    David
    TR3A TS75524L

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    Re: Over drive

    The fuse protects both wiring and solenoid, but mostly the solenoid. Possibly less important now, as new solenoids are a lot less expensive than they used to be, but still a good idea, IMO.

    I use an MDL 8 fuse, which is an 8 amp "slow blow", mostly because I had a case of them on hand (discarded by a previous employer). But I believe even an ordinary 5 amp fuse (ie AGC 5) would work fine. Or if you want to use a more modern fuse holder, ATO or ATC, etc would work fine too.

    The solenoid draws a big burst of current at first (hence the relay and relatively beefy wiring to it), but normally the burst of current only lasts a fraction of a second; not long enough for even a 5 amp fuse to get hot and burn out. The problem is that if something blocks the motion of the solenoid plunger and it doesn't cause the internal contacts to open, the high current will eventually (in a few minutes) cause the solenoid to overheat and burn up. So using a smaller fuse means the fuse blows before the solenoid hurts itself, giving you a chance to correct the problem without needed a new solenoid. (In my case, it was a bit of gravel that had worked it's way inside and jammed the plunger.)

    The ratings on the diode are not critical at all; what I used is a 1N4004, which is rated 400 volts and 1 amp. (At the time, Radio Shack sold a bag of 25 of them for a couple of dollars, but they don't do that any more.) Any of the 1N400x series should work fine, and they are readily available at any electronics supplier (Digi-Key, Mouser, Newark, etc) or on eBay. Just for example
    https://www.ebay.com/itm/25-x-1N4004...0AAOxyFiRRzFEx

    The one Geo showed above will work just fine too, if RS still has them (and if there is still a RS available to you. AFAIK all the ones near me are gone now.)

    If you happen to be near Torrance, California (or passing through), I recommend Torrance Electronics on Carson Ave. All the other stores in the area have closed, but TE was still there last time I drove by.

    Note that the diode is polarity sensitive, installation will depend on whether your TR3 is still positive ground or has been converted to negative ground. The diode will usually have a white stripe on one end to indicate polarity, the stripe needs to go towards the positive side. So for positive ground, it would go towards ground; for negative ground it goes towards the relay output pin.
    Last edited by TR3driver; 09-11-2019 at 07:38 PM.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Over drive

    Hello Randall

    Thank you for that very informative answer.

    We do not have a RS here anymore but we do have a small electronic parts store. Will have to add a second fuse holder.

    David
    TR3A TS75524L

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    Re: Over drive

    I used an in-line holder, hanging off the back of the ammeter. You can see just the end of it, at the top of this photo (taken as I was parting out the wreck).

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    Re: Over drive

    Thank you randall!
    I own 1958 TR3A TS 26005L and have the privilege of working on 1960 TR3A TS 65587L.

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    Re: Over drive

    Hi would one of you gent's mind doing a quick sketch of a wiring diagram . from the switch to overdrive to relay including the inline fues and the diode , for us simple foke across the water

    Thanks Tony

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    Re: Over drive

    Does this help?
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Over drive

    Thank you Randall.

    Perfect.

    I knew how it went but that verifies my plan.

    David
    TR3A TS75524L

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    Re: Over drive

    Thank you , just the job ,
    At the miute i have the gear box drained of oil . will this also drain the ovredrive . ? is there an easy way to test if the overdrve oprates ,as the car is not running at the moment
    Regards
    Tony

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    Re: Over drive

    You need to remove both plugs to fully drain both gearbox and overdrive. Inside the OD plug is a screen and possibly some magnets that should be cleaned as well.

    To test the OD in the car, you'll need the engine running. Put the rear on jack stands, or disconnect the driveshaft. (Disconnecting is probably better.)

    Just a fast idle will do, 1000 or 1500 rpm. Select 4th gear and let out the clutch. Without OD, the indicated speed in mph should be close to twice the rpm in hundreds. Eg, 1500 rpm equals 30 mph. Then when you engage OD, the speed should jump up by about 20%. So, for example 1500 rpm should now be about 36 mph.

    This is a fairly basic test, it doesn't check things like hydraulic pressure. But it gives at least a first level check of OD operation. If you are worried about it, I suggest getting a gauge and checking the operating pressure. Low pressure can let the OD clutch slip under load, leading to rapid wear and eventually an expensive repair job.

    The Buckeye Triumphs site has some good articles on rebuilding an A-type od, which include testing and troubleshooting (and checking pressure).
    https://www.buckeyetriumphs.org/gearbox
    Last edited by TR3driver; 09-16-2019 at 11:23 AM.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: Over drive

    Here is a walkthrough an A overdrive, including testing at the end. Afraid photobucket is holding the pictures hostage again, but select them and they’ll link you to better versions.

    https://www.britishcarforum.com/bcf/...040-Here-We-Go!
    Last edited by CJD; 09-16-2019 at 02:56 PM.
    John

    1955 TR2

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    Re: Over drive

    Yep...Photobucket is up to their old tricks again. All the photos are blurred from your end. Last time I had to fork out $100 to get them back. Love you guys, but I don’t plan to fork out that kinda bucks, and re-posting would take months on all my threads.

    Oh well...fun while it lasted!
    Last edited by CJD; 09-16-2019 at 03:00 PM.
    John

    1955 TR2

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