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Pierce Arrow overdrive - How did it work?


m-mman
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Many years ago I got to drive a very original 36 Pierce 8 sedan. It had Overdrive. When you got up speed you lifted your foot and it shifted into OD

 

I am very familiar with the Borg-Warner OD set up as installed on many late 30s into the 60s cars, repairing and troubleshooting plenty. These set ups are electrical in nature. 

 

The (parked for many years) Pierce did not consistently drop into OD and I was thinking that it was dirty electrical or other contact issues. I was told that the Pierce system did not use an electrical solenoid, etc to work. I did not see the typical relay or kickdown switches under the hood. 

 

The Pierce owner could not explain exactly how it functioned without using an electrical system. 

Purely mechanical??? How did that work?

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It uses a planetary with a sprag. It’s adjustable by turning a shaft that changes pressure on the spring. It works great, and is bulletproof. Many were disassembled and welded together to remove the free wheeling. The unit was a Warner gear model W-1. It was attached to a T83 gearbox. There were no electrical components associated with it. It was 100 percent mechanical. Adjustment was from 38-48 mph. Almost every one I set up is at 44 or 45 mph. 

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Edited by edinmass (see edit history)
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AND......

 

* The clutch gear, about 3/4-inch thick, with the 8 or so sort-of-oval-shaped dogs, is unobtanium except from another purely-mechanical B-W OD.  Individual dogs get broken off.

 

* The root cause of these malfunctions is that the rear end of the OD shaft rides in a bushing, which wears into an ovoid shape and allows the OD shaft to wobble; the front end of the OD shaft gets the greatest movement, which causes destruction of the clutch gear mentioned above.  If you have one of these cars, remove the OD housing (without having to remove the transmission itself--difficult due to X-frame but easier than pulling the whole tranny), have it disassembled, and substitute a BEARING for the bushing at the aft end of the OD shaft; this will probably require machining out the housing a bit.

 

* Only the cast iron transmission and OD cases are unique to Pierce.  A Hollanders manual will find you interchanges for gears and shafts.

 

* 1936-38 Pierces, 8s and 12s, had the OD as standard equipment.

 

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1 hour ago, edinmass said:

It uses a planetary with a sprag. It’s adjustable by turning a shaft that changes pressure on the spring.

 

There has to be a overunning clutch (aka freewheeling) so that the output shaft can spin faster than the input. . . . 

 

On the electrical versions when the solenoid is powered (28 mph) it pushes in to hold the sun gear. (which causes the OD ratio) How does the mechanical set up hold the sun gear? Thinking that it is a centrifugal type of clutch . . . 

Edited by m-mman (see edit history)
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4 hours ago, m-mman said:

Purely mechanical??? How did that work?

Yep, all mechanical. The Graham in my picture has Overdrive, and being a '38 it is also a mechanical only system.  It Works!👍

 

It was balky when I first got the car, so I changed the fluid and all is well. So I have not had a reason to take it apart and see how it works.😄

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3 hours ago, m-mman said:

 

There has to be a overunning clutch (aka freewheeling) so that the output shaft can spin faster than the input. . . . 

 

On the electrical versions when the solenoid is powered (28 mph) it pushes in to hold the sun gear. (which causes the OD ratio) How does the mechanical set up hold the sun gear? Thinking that it is a centrifugal type of clutch . . . 


The sprag is an overrunning clutch.............by definition. The rollers in the first photo are the lock up.

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image.png.061051537508f71b6470b940f2cd05b9.png

 

The 1934 Chrysler and DeSoto overdrives (Borg-Warner units, developed in conjunction with Mopar engineers) offered a good compromise solution to this problem, and between 1935 and 1942 eight other marques jumped on the bandwagon with the same Warner overdrives, which soon acquired reputations for both high speed and economy.  written by Don Frolich

 

Graham-Paige used the Borg-Warner units

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Hudson used it in 1940.

Speed of engagement was adjuatable thru access hole on top.

Two screw head heads on opposite sides of govenor, one with straight slot and a cross slot, to adjust tension and thus operating speed.

Very desireable unit.

 

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