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Spitfire & GT6 Forum

overdrive surprise

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GerryV8 Silver Member Gerry Reis
Brantford, ON, Canada   CAN
I bought a toggle switch that lights up when you turn it on... that way the idiot (me) will not wonder what that light means.

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Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, FL, USA   USA
In reply to # 1509340 by GerryV8
What I conclude from the advice is:-
While overdrive engaged in 1st or 2nd is not good, it is not catastrophic if done accidentally. I can try to avoid this.
Reverse with OD is catastrophic. I do not trust myself to never do this.

My plan is to inhibit overdrive using the reverse light switch on the transmission. I should be able to do that using a 5 pin relay. I will post a wiring diagram as soon as I figure it out.

Sounds like a solid plan to me!
I would want to power the unit (maybe with the tunel out, just a jumper wire set up or something), and know it works, before digging in too deep.



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible
2018 Jaguar F-Pace

booley Bruce H
Latham, NY, USA   USA
In reply to # 1509284 by mkivmarty I laugh only because I've done similar things and worse in some of my previous repairs...

Rotten floor boards in the same car? Watch where you park, the sign is missing.

What doesn't kill you makes you stronger, and hopefully a little smarter.

Marty

I once had a '65 Buick with a HUGE "STOP" sign in the trunk holding the gas tank up

I think they limited the O/D to 3-4 because they worried the torque multiplication in 1-2 would affect reliability. Although I knew a guy with a GT6 racer who ran an overdrive transmission with the o/d operating in all 4 gears.
I could have bought said racer for $2500, ARGH!!, but 40 yrs ago, that was alot of money...

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spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
In reply to # 1510128 by booley
I think they limited the O/D to 3-4 because they worried the torque multiplication in 1-2 would affect reliability. Although I knew a guy with a GT6 racer who ran an overdrive transmission with the o/d operating in all 4 gears.
I could have bought said racer for $2500, ARGH!!, but 40 yrs ago, that was alot of money...
Bruce,
The same OD unit is used behind the big Healey 3 liter six and some other strong engines. The Spitfire in the lower gears isn't going to be as much of a challenge as they are. ISTR Triumph eliminated the lower gear lock-out function on the rally Spitfires. So they weren't too worried about its reliability.
All the best,
Paul

mkivmarty Avatar
mkivmarty Marty Yanik
N.E.Ohio, USA   USA
In reply to # 1510128 by booley
Although I knew a guy with a GT6 racer who ran an overdrive transmission with the o/d operating in all 4 gears.

The oil pump runs on a cam on the main shaft / output shaft of the gearbox. The car has to be moving pretty good for it to develop enough pressure to engage the OD clutch. It might work in 1st once you get the car going, as long as you never stop!!

Marty

GerryV8 Silver Member Gerry Reis
Brantford, ON, Canada   CAN
wiring diagram
well now I see the the 2 diagrams do not agree.... one shows 87 is normal open the other shows 87 is normal closed.... I will test the relay to find out.... anyway the reverse light will be connected to the normal open pin



Edited 1 time(s). Last edit at 2018-01-30 10:46 AM by GerryV8.


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Tonyfixit Avatar
Tonyfixit Tony M
Duncan, BC, Canada   CAN
The wiring diagram looks OK, but remember that if you have a 'D' type O/D the solenoid will draw (momentarily ) 20 amps when engaged.

For this reason, the O/D was switched via a relay. I would also add a fuse on the solenoid power feed just in case the solenoid does not switch over from the 20amp engagement winding to the low amp 'hold' winding.

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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
Assume "reverse light" isn't the same as a backup light.

GerryV8 Silver Member Gerry Reis
Brantford, ON, Canada   CAN
modified wiring diagram... added another fuse and relay to the feed line

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