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Re: School me on overdrive [Re: dogdays] #1393260
02/27/13 01:54 PM
02/27/13 01:54 PM
Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
patrick Offline
I Live Here
patrick  Offline
I Live Here

Joined: Jan 2003
Posts: 16,123
Grand Haven, MI
Quote:


At this point I must mention the Doug Nash 5-speed, which was an interesting design concept. If you study gear power losses, you come to the conclusion that a 4.56 rear gear wastes a lot of energy. There is a lot of friction in a hypoid gear setup. So Doug Nash designed a 5 speed transmssion with a 1:1 Fifth gear, and a 3.something to one First gear. It was intended to be used in front of a 3.07 or 3.23 rear. More gear reduction in the transmission starting out, with less friction in the driveline in Fifth. For some reason that idea never really caught fire.

R.




Quote:


One thing to watch out for with overdrives: Propshaft RPM. This can cause shaft to go over the critical RPM and blow up (regardless of torque), it also exacerbates vibration problems from balance and angularity defects. This is the biggest "bolt on" OD problem: The shaft is too short, U-joint angles go crazy.

Rick




I've never understood why OD's gained popularity for these reasons...

1) a higher (lower numerically) rear end is stronger, as the teeth are larger
2) a higher (lower numerically) rear end has less frictional losses
3) the most efficient transfer of power in direct drive (input and output shafts locked together), any overdrive is sending power through a countershaft of planetary gearset, which has frictional and inertial losses
4) the propshaft/driveshaft speed. there's a reason crown vic cop cars are electronically limited to 124mph....because of driveshaft speed.

I do understand why, from the standpoint of trying to base it on an existing product (i.e. 518 derived from 727, etc), but for a clean sheet design, a non-OD tranny with a deep 1st gear seems like it would make more sense....

Ideally, I'd like a 5 speed with say, a 4.5:1 first, 3:1 2nd, 2:1 3rd, 1.5:1 4th and 1:1 5th, and run a 2.2 or so rear end....

I like the gearing of the A580/NAG1 in the LX's, with their 3.59 first, 2.19 2nd, 1.41 3rd, 1:1 4th, and .83:1 OD...with my charger's 2.65 rear end, it gives an overall 1st gear the same as a 727/A518 with 3.88's, and OD gives an effective 2.2:1 ratio, about the same as an A518/42RH with a 3.20 rear end, but driveshaft speed is some 20% lower than the A518/42RH....

Last edited by patrick; 02/27/13 01:57 PM.

1976 Spinnaker White Plymouth Duster, /6 A833OD
1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!***
2011 Toxic Orange Dodge Charger R/T
2017 Grand Cherokee Overland
2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
Re: School me on overdrive [Re: patrick] #1393261
02/27/13 02:50 PM
02/27/13 02:50 PM
Joined: Jan 2003
Posts: 27,116
Rio Linda, CA
John_Kunkel Offline
Too Many Posts
John_Kunkel  Offline
Too Many Posts

Joined: Jan 2003
Posts: 27,116
Rio Linda, CA
Quote:

Ideally, I'd like a 5 speed with say, a 4.5:1 first, 3:1 2nd, 2:1 3rd, 1.5:1 4th and 1:1 5th, and run a 2.2 or so rear end....




Pretty close to the Porsche 928S4 which has 5-speed gear ratios of 4.07 first, 2.71 second, 1.93 third, 1.46 fourth and 1 fifth with a 2.20 axle ratio.


The INTERNET, the MISinformation superhighway
Re: School me on overdrive [Re: Rick_Ehrenberg] #1393262
02/27/13 02:56 PM
02/27/13 02:56 PM
Joined: Jan 2003
Posts: 16,376
D
dogdays Offline
I Live Here
dogdays  Offline
I Live Here
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Joined: Jan 2003
Posts: 16,376
Yeah, Rick, my point was to illustrate the development of the 4-speed manual in American cars. Some of the Board members are not old enough to realize that just getting a decent 4-speed in an American car was at one time impossible. And, four-speeds were added to US cars for performance.

Both the A833OD and the Ford Toploader OD transmissions were quick cheap fixes to the quest for a "gas-saving" gear in the early to mid '70s. They were cobbled together at a time when engine power was going down and you could get an optional 400 in place of the regular production 440 in a Chrysler car to "save gas."

R.

Remember the magazine articles about installing an overdrive unit from a Saginaw 3-speed onto/into a Saginaw 4-speed? It would have been trick if the transmission was strong enough to take the torque of a 327!

Re: School me on overdrive [Re: John_Kunkel] #1393263
02/27/13 03:53 PM
02/27/13 03:53 PM
Joined: Dec 2007
Posts: 2,714
Des Moines IA
S
Soopernaut Offline
master
Soopernaut  Offline
master
S

Joined: Dec 2007
Posts: 2,714
Des Moines IA
Quote:

Quote:

there was a short lived two speed Dana 60 on Mercury Cougars years ago




That wasn't a Dana 60, it was a Ford 9" with a Hone-O-Drive installed from the factory. Read about it:

http://www.stangerssite.com/honeodrive.html




It was a Dana 53 and probably never went into production.





1970 Dodge d100/eventually going on a 77 D100 frame
Re: School me on overdrive [Re: Soopernaut] #1393264
02/28/13 06:58 AM
02/28/13 06:58 AM
Joined: Jan 2006
Posts: 8,162
USA
3
360view Offline
Moparts resident spammer
360view  Offline
Moparts resident spammer
3

Joined: Jan 2006
Posts: 8,162
USA
thanks for posting that.

might Mercury and Dana Spicer
have made another attempt in the 1970s?

i wonder what the
smallest lightest two speed differential
being made anywhere in the world
right now is?

with so much money being spent
to improve engine fuel efficiency by 1%,
or to improve tire rolling resistance,
shouldnt there be equal interest
in improving driveline efficiency by small amounts?

"Rust never Sleeps
Friction never fails to pick your Pocket"

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