3 speed auto transmissions
 

Do any three speed automatic transmissions only use one planetary set to get the three forward gears plus reverse? I know it's possible, just don't know if it was ever in production.

Also, is there a good website that shows exploded views of various automatic transmissions?

Thank you,

Chris

Re: 3 speed auto transmissions
 

www.wittrans.com has some pretty good exploded views for a lot of different trans makes.

Ryan Walther
Stock 315

Re: 3 speed auto transmissions
 

Thank you.

Re: 3 speed auto transmissions
 

Chris, I don't recall ever working on a 3 speed automatic with only one planetary set. And I worked on most every domestic 3 speed built since around 1955.

Re: 3 speed auto transmissions
 

If nobody has produced a three speed automatic with one planetary set yet, there must be a fundamental reason why. It is possible though.

Just haven't figured out yet what it is...

Re: 3 speed auto transmissions
 

Possible how?

Re: 3 speed auto transmissions
 

I've been thinking about this all day and then it hit me , Renault had what was called a ravignaux planetary assembaly that had compound planet gears ..used on a type 4139 trans
I'm looking for one of my old AMC school books,[ they were way better than the Frenchie's manuals ] for a blow up of it. if I remember correctly it had 2 sun gears , 1 annulus gear and compound planet gears.
I'll have to dig thru the stuff I had hoped I'd never have to use again!



Found a description and an excellent engineering web site.

http://www.mathworks.com/help/toolbo...avigneaux.html

Re: 3 speed auto transmissions
 

You have to connect two pieces together, say the sun gear and the ring gear. If they are connected by a clutch and the input is the sun, the ring gear would have to spin at the same speed.

This is an odd way of doing this, but I think it would work.

Re: 3 speed auto transmissions
 

The issue is gear ratio spread with a single, simple planetary set.

Using VERY ROUGH calculations with a 70 tooth sun and 100 tooth ring gives the following:

Low gear= 2.43:1
Second gear = 1.0:1
High Gear = 0.59:1

These are pretty unrealistic gear ratios for a small block chevy as a three speed. But it was a good thought experiment.

Re: 3 speed auto transmissions
 

Looking at the obvious mechanical disadvantage of a planetary overdrive of that configuration, I feel strength would be a major issue. What's on paper doesn't always hold up on the track.

Re: 3 speed auto transmissions
 

Seems to me that when the 700-R4 came out,the instructions in the owner's manual stated that the consumer was not to tow in the overdrive range. Subsequently, nearly all if not all the automatic overdrive transmissions since then seem to all state the same thing. Driving back through a set of planetaries seems to create a reliability issue when under that much load.

Re: 3 speed auto transmissions
 

Greg, with the 700R4, it was a matter of a lack of clutch pack and band capacity, as well as a weak over run sprag. You do not see a lot of planetary failures with the 700 R4, or at least I have not seen more than a very few in the 20+ years I've worked on them. The over run sprag failed regularly, as well as the sun gear shell.

The problem with a single compound planetary would be size, weight, and complexity. I don't think there'd be enough of a reduction in rotating mass/weight by replacing two planetary sets with one larger more complex compound set. If there was a lot to be gained, the OEM's would already be doing it a lot, just for the fuel economy and emissions gains, as even a minuscule gain for them is big, spread over their unit production run.

Re: 3 speed auto transmissions
 

After 209,500 miles, the direct clutch pack in the 700 4R trans in my Chevy Silverado started slipping,flaring on the upshift, as it failed completely. The clutches were burnt up, the fluid stinks,this trans went the distance and owed me nothing. It's time for a rebuild. I did tow with it, used this truck for everything, no complaints. The 4L80 E in the shop truck at work came with a towing guide that specified not to tow in the overdrive position. It makes sense that that would put more stress on the direct clutches and the overdrive planetary set. Ford and Chrysler say basically the same thing about not towing in the overdrive range. That also prevents constant up and down shifting under varying road conditions under load which can't possibly aid longevity. Planetary gearsets are pretty reliable anyway,since they are in constant mesh. Heat and load seem to do in a trans more than anything else.Just ask a motorhome shop.