# Triumph overdrive



## etischer (Jun 16, 2008)

probably not much of a ratio change to make it worth it.


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## jackbauer (Jan 12, 2008)

yeh possibly. Also looking at a 4wd transfer box....


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## sunworksco (Sep 8, 2008)

I have the same over-drive on my 4-speed Jaguar transmission.
You get about 78% overdrive ratio.They are similar to a planetary sun-gear in an automatic transmission operated by an electric switch and solenoid.Mine is in a 1975 XJ6-C.I bolted the trans into the car with zero mods.I bought a very rusty German spec XJ6 sedan parts car for the conversion to change an automatic slush-box to a zippy 4-speed over-drive trans.
Regards,
John


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## esoneson (Sep 1, 2008)

After looking at what folks have been using when installing a manual transmission, most say that they use 2 and sometimes 3 years forward. Usually 2. Which brings up why everybody seems to be trying to locate a decent 2 speed transfer-box or 2 speed overdrive unit to replace the transmission. Then using motor reverse to go backwards.

Each time I think I have found the solution, I compare it with the features of a Chevy Powerglide tranny. So far Powerglide privides ALL of what I need.

Powerglide can be shifted manually (with no manual clutch) or automatically with quite a variety of options for tuning shift points. And the ratios available for low gear go from 1.65:1 to 2.11:1. While high gear is 1.00:1. Normal ratios found in stock tranny is 1.76:1 or 1.80:1 depending on year and model.

Plus the Powerglide gives you parking pawl and neutral.

At present my goal is to use the Powerglide unless someone can find another inexpensive, light weight, functional alternative with reasonable low/high ratios. I'm all ears for suggestions......I just haven't found one yet.

Let me know if you find one.

Thanks,

Eric


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## sunworksco (Sep 8, 2008)

Have you thought about using an ac motor with a 10 to 1 belt-drive system.No trans required at that point.
http://www.thunderstruck-ev.com/index.php?dispatch=categories.view&category_id=36
Regards,
John


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## TX_Dj (Jul 25, 2008)

One thing to keep in mind, if you want to use an overdrive unit, you'll have two ratios, direct and overdrive. 

Many EV drivers rarely use overdrive, instead shifting 2nd/3rd or 2nd/4th.

Only one EV driver I know uses 1st/3rd/5th as his shift pattern.

Depending on your axle ratio, direct may be too tall to start from a stop without burning things up or using too much energy from the pack, and overdrive may be right out.

The key thing is to understand what the overall gear ratios will be when figured all the way from the tires back to the motor output shaft. Tire size does make a (big!) difference.

For instance, if you have a tire that turns 700 revolutions per mile, that means your axle turns 700 RPM at 60 mph. If you have 3.73 diff gears, and lets say a choice of 1:1 (direct) or 0.78:1 (overdrive) as your only gear selections, that means that at 60 mph your motor is spinning 2611 RPM in direct, or 2036 RPM in the overdrive ratio.

Similarly, this means that at 30 mph, your motor is turning 1305 RPM in direct or 1018 RPM in overdrive. That's a bit slow, perhaps, depending on the motor.

This information all changes depending on what your car actually has, but I picked those numbers because they are common.

If your car is light weight enough that you don't require too much torque to start off in 4th gear, then direct will work for you, but it will always consume more energy than a lower ratio when starting out.

Another option for some would be to buy a compatible pair of under/overdrive units, then you end up with at least 3 ratios (actually 4). For example, if you have an underdrive of 2:1 and an overdrive of 0.78:1, and if these are your only gears besides the differential, you'd end up with the following combinations:

1st: 2:1 (underdrive only)
2nd: 1.56:1 (under & over)
3rd: 1:1 (direct)
4th: 0.78:1

These units tend to cost about $3000 each, so that would then be a $6000 transmission. A $150 pull from a junk yard would not weigh much more, and would be far less expensive.

*NOTE* Most likely a 4x4 transfer case WILL NOT WORK AS EXPECTED, as they are not synchronized gearboxes (usually) can cannot be shifted from Low to High while in motion.


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## Woodsmith (Jun 5, 2008)

I have pondered, on here, the use of an overdrive and have been told that it probably wouldn't handle the torque and rather then getting a high ratio the transmission should really be providing a lower ratio.

I have also looked at using a transfer box and have obtained a Lada Niva box

It would make an interesting transaxle. The ratios are 1.2:1 and 2.135:1.
It has prop shaft flanges as outputs and inputs so would be easy to adapt to drive wheels.
It is also a permenant 4x4 and so has a centre diff with a diff lock.


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## jackbauer (Jan 12, 2008)

Woody thats interesting. Kind of what i'm thinking about. Can it be shifted while in motion?


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## Woodsmith (Jun 5, 2008)

Well, I've always been able to shift Tboxes in motion but I am used to driving old trucks with no syncro. It is all sliding mesh gears.









I figured that, like some people with no clutch, a change can be made while stopped so that there is an 'urban' ratio and a 'motorway' ratio that you select when convenient on the basis that the motor will move off in either gear.


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