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Planetary transmissions and differentials


Hal Davis (MODEL A HAL)
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A planetary gear system consists of a central (sun) gear surounded by multiple other gears (planets, if you will) joined together by a spider. This is surounded by a ring gear with teeth on the inside. The "planets" revolve aound the "sun", staying in constant mesh with the sun and ring. By holding any one of the three (sun, ring, or planet spider) still, and applying rotational motion to one of the another two, the third will rotate. Speeds, of course, are determined by the ratio of the system.

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I have heard the terms "planetary transmission" and "p. differential" used oftern and am really not clear on what exactly the term 'planetary' is describing. Is there a good definition/description/drawing that would make all this clear?

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Model A Hal's description is a good one. These were the choice for transmissions for many early cars such as the Model T, early Cadillacs and many others. For more information and drawings find an early Dyke's manual or other early automotive encyclopedias. You may also be able to get some drawings and descriptions from the AACA Library & Research Center.

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Ron,<P>You should have mentioned that a Dykes Manual is not a book on lesabans (sp) but an exelant book that covers most of the early cars. They cover things you wouldn't even think about. They puplished them fron about 1910 to about 1944. If you find one at a swap meet, used book store, flea market - - Get it. They are worth the money.<P>Dan

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DAN,YOU HAD TO BREAK MY BUBBLE,I HAVE READ THE DYKES BOOK MANY TIMES AND I REALY ENJOYED THE "DIRTY PARTS". PLANETARY GEAR SETS ARE STILL USED IN MODERN AUTOMATIC TRANSMISSIONS MUCH IN THE SAME MANOR AS IN THE OLD DAYS<BR>,WITH THE EXCEPTION THAT THEY USE OIL PRESSURE TO CHANGE GEAR RATIOS INSTEAD OF LEG POWER.PHIL<BR>

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I agree with the previous replies on the value of the Dykes manuals, however there is one caution - If you are interested in a specific year car, look for one of the versions a few years newer than the car. The same year and those published earlier might not have the needed info. They ususally lagged new developments by a couple of years. And some later editions dropped some older technology altogether. Get one two to four years after your model.

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