cool video on the innards of a CVT transmission...

[John in Santa Cruz]

... and why they really are not suitable for towing.

https://www.youtube.com/watch?v=_fBbNKUSvuU

[Terry G]

That's a great video about a really complicated device that must take hours and hours of machining, casting and assembly. So if anybody is wondering why we say that electric cars are going to take over, this is just one of the reasons. Electric cars don't need transmissions.

[John in Santa Cruz]

Originally Posted by Terry G

That's a great video about a really complicated device that must take hours and hours of machining, casting and assembly. So if anybody is wondering why we say that electric cars are going to take over, this is just one of the reasons. Electric cars don't need transmissions.

and those CVT's are far simpler than today's 7-10 speed automatics, which have a half dozen or more clutches in them, and like 3-4 sets of planetary gears....

[Raspy]

I don't understand how it can be said that the belt "pushes" the driven pulley. How can that be?

In Toyota's CVT, they don't take advantage of the infinitely variable ratio capability of their CVT. They move the belt to several predetermined positions. So, it simulates a geared transmission. Weird. Also, when you give it throttle the engine runs up to near redline instead of torquing it's way up to speed. That, to me makes the driving experience annoying.

It seems the main failure he mentioned was overheating and not enough oil changes, but is it really the belt that wears out? Or the sheaves? or is it just not strong enough? Don't know.

[Raspy]

Originally Posted by John in Santa Cruz

and those CVT's are far simpler than today's 7-10 speed automatics, which have a half dozen or more clutches in them, and like 3-4 sets of planetary gears....

The new 10 speed trannies are apparently not very efficient compared to simpler models, in that they have a lot of internal parasitic losses from so many spinning and slipping parts that are all pumping oil around as they move.

Terry makes a good point. A transmission is simply an adapter to make an internal combustion engine work with a car. They are not compatible without that adapter. The adapter is expensive, heavy and inefficient. Of course, engines are terribly inefficient too.

[ZachO]

I'm sure this is a completely different thing, but I thought I remembered reading on a forum at some point that a parking brake like that was illegal...I had no idea why then and still don't know. Anyone know what I'm talking about? Something people with older 4x4s who do a lot off roading would install, which I thought they called a transmission parking brake or something similar...
Maybe a t-case brake?

Anyway, that thing is crazy. Not that the inside of my transmission doesn't also baffle me, but man.

[Raspy]

Zach, Do you mean the parking pawl? It has to be on the driven side of the CVT and geared directly to the wheels. A transmission parking brake, as used on old Jeeps and Chryslers, held a band on the output shaft of the transmission, ahead of the driveshaft. If the driveshaft failed the brake did nothing to stop the car.

Whenever you put an automatic transmission in "Park", you are doing what is shown in that video. A dog holds a disk that is splined to a shaft. But the parking brake works directly on the rear wheels. Cars have both, a park and a parking brake, as long as they are automatics.

[Lynn Eberhardt]

And please don't confuse that transmission with what Toyota uses in its hybrids.

[John in Santa Cruz]

Originally Posted by Lynn Eberhardt

And please don't confuse that transmission with what Toyota uses in its hybrids.

yes, hybrids are NOT this style of belt driven CVT....

The belt driven CVT is found in most newer Nissans, Subarus, and many Hondas, Toyota Corollas. And I'm sure many others.

while they offer good fuel economy when driving very gently, they do NOT have good dynamics for sportier driving, they take too long to change ratios, usually causing the engine to spool way up before they start to shift to taller ratios, and if you even occasionally drive them in a spirited fashion you'll likely induce premature failure. They are rather unsuitable for towing trailers, too, as this will lead to premature failure.

[Mark J]

Thanks for that video. About all I can say is Wow, & how complicated can mechanical transmissions be - cvt or even standard trannys? No wonder cvt's fail while towing!

[ZachO]

Makes sense that "park" on an auto tranny has always been something similar. I think it was just him calling it a parking brake (or maybe I should go back and see what term he actually used) that triggered the memory.

Toyota people, so I'm guessing also Jeep etc installed some type of parking brake that clamped the t-case output, or driveshaft, or something. I don't think it was internal to the transmission and would maybe be a modification owners were making to bypass the drum-brake parking brakes that are often so unreliable when parking on steep slopes. I know I had a lot of issues when I was young and did less preventative maintenance...being on a dirt road, losing traction climbing a hill, and not being able to get out and lock in the hubs because the e-brake wouldn't hold on any kind of incline. So you either roll backwards till you hit flat ground to get out and lock the hubs, or put it in gear, shut it off, get out, lock hubs...etc.

Whatever people installed locked the transmission in place somehow, and I guess output shaft makes sense.

Anyway, off topic...

[Raspy]

Here's a pic of an "emergency brake" on an old Chrysler. This was used before the "park" feature came out in automatic transmissions. A drum is mounted on the output shaft of the tranny and a band is mechanically tightened to hold it. These will stop a car from a low speed on level ground, but that's about it. They are for holding it, not stopping it.

One of my first jobs was a tow truck driver. I went on a call where an old Chrysler had dropped it's driveshaft. It was parked at the top of a hill with a little stone under one rear wheel, about the size of a tennis ball. The emergency brake was useless because the driveshaft was disconnected. I backed up to it to hook up, and nudged it over the little stone. I can remember so clearly watching that car start off down the hill, from my rear view mirror. Oh no! Off it went, gaining speed. Nothing I could do. Meanwhile there was a nice gentleman sitting in his car near the bottom of the hill, waiting to give the owner of the Chrysler a ride home. By then I was out of the truck and watching. Here comes the monster! At the last second the guy looked up from reading his paper and threw it up into the air with a big gesture of panic. CRASH!! The poor guy's car jumped up onto the sidewalk. The Chrysler's rear end had a big frown and bent fins. It wasn't funny at the time, but now it sure is.

[ZachO]

Well I finally decided to just google it. Amazing how that option sometimes still slips my mind at first. Pretty similar to what you posted, but probably way more effective. T-case parking brake.

[Carl V]

My parents own a 1975 Travco motorhome (which has a fiberglass shell BTW) and the parking brake is as your described it, a drum brake at the output of the transmission. The vehicle is built on a Dodge truck chassis, with a 440 engine and the usual 727 TF transmission, which does have a Park selection like most cars.

[Raspy]

I guess a transmission "park" setting, a "parking brake", and an "emergency brake" are all different, but perform the same function sometimes. Only one, the emergency brake, can hopefully, be use to stop the vehicle, albeit from a very low speed and on level ground. The other two are strictly for holding it in place.

That picture Zach posted looks like a good idea for four-wheeler with a manual transmission and non conventional rear brakes that are not easily adaptable to a parking brake. A nice old school solution, in a modern form.

[k0wtz]

well i didnt do good research when buying our ford edge 2.0! No way to check the transmilssion fluids it drives me crazy!