Find Reviews by Make:
[thanks to Robstar for the link]
38 Comments on “What’s Wrong with This Picture: Differential Equations Edition...”
Read all comments
Latest Car Reviews view all
Latest Product Reviews view all
Recent Comments
- Lou_BC: @Carlson Fan – My ’68 has 2.75:1 rear end. It buries the speedo needle. It came stock with the...
- theflyersfan: Inside the Chicago Loop and up Lakeshore Drive rivals any great city in the world. The beauty of the...
- A Scientist: When I was a teenager in the mid 90’s you could have one of these rolling s-boxes for a case of...
- Mike Beranek: You should expand your knowledge base, clearly it’s insufficient. The race isn’t in...
- Mike Beranek: ^^THIS^^ Chicago is FOX’s whipping boy because it makes Illinois a progressive bastion in the...
Car Reviews By Make view all
New Car Research
Who We Are
- Tim Healey
Managing Editor - Matt Posky
News and Social Media Contributor - Timothy Cain
Sales Analyst - Murilee Martin
Junkyard Finds Author - Matthew Guy
Contributor - Chris Tonn
Contributor
- Adam Tonge
- Bozi Tatarevic
- Corey Lewis
- Jo Borras
- Mark Baruth
- Ronnie Schreiber
…to paraphrase my kids, “Dude, this is so like … math and stuff!!”
It’s a bit campy, typical for the era, but there is nothing wrong with it at all. It’s a great example of how spider gears allow a differential to be a differential.
I believe it was Chevrolet as well that invented “limited slip” which they later referred to as “Positraction”. The specific name Positraction for years became a generic term for a limited slip differential.
I didn’t catch the technical error, if there was one, but the part at the end where the narrator explains why the driveshaft cannot go through the interior was classic GM.
Why can an uncovered driveshaft not go through the interior? Horrible safety issues? Major NVH issues? No, says the narrator in a loud drunk voice (they must have had to go back and re-record that part after happy hour), because it could get in the way of the luggage.
It falls off at the end, but the technical part with the tinker toys evolving into cut gears is better than anything else I’ve seen visually explaining the differential.
This explains one of life’s great mysteries – just what goes on in that bulge in the middle of the drive axle!
What I would have given to see this when I was six years old, and trying desperately to figure this out myself. I knew the problem, I knew there had to be a solution, but it eluded me.
How many people today have a clue about what a differential is? Now that GM is Government Motors, they should re-issue this and make it mandatory. We need to stimulate future engineers!!
What’s wrong is that back whenever they made that film, they had managed to eliminate the driveline tunnel hump we have today. Of course those cars sat higher off the ground than cars of today too…
What I find really interesting is modern FWD cars with a driveline tunnel… what the hell for?
Oh, and the other problem being that without the limited slip, the differential “two wheel” drive is not much better than the one wheel drive it was supposedly “fixing”.
Wolven: What I find really interesting is modern FWD cars with a driveline tunnel… what the hell for?
The exhaust and its catalytic converter.
I saw this on autoblog. I love this type of stuff. I’m very fascinated by mechanical devices and how stuff works. With everything going digital it’s nice to see good old fashioned gears meshing!
Ah, thanx Paul… That makes sense. It WOULD be nice to get the exhaust system up out of the way on RWD cars too.
There is nothing wrong with it. The gears on 5:31 are the same ones used on my Aveo to this day.
Not sure I’d call it an error, but the beginning part shows the differential bass ackwards…it would require a CCW turning drive shaft to move the vehicle forwards, assuming this is a front engine/rear drive car like all Chevrolets of the day. In reality almost all RWD cars have a CW turning driveshaft when viewed from the front looking back.
rpol35, it wasn’t GM nor Chevrolet division which invented the limited slip differential. Positraction simply became a (semi-) household name because of the sheer market percentage that GM (51%) and Chevrolet (26%) had in the US market during the early 1960’s when it was introduced.
It was Studebaker-Packard, which introduced it in 1956. It was called “Twin-Traction” and starting about that time, until the early 1960’s, any Studebaker with it had a little chrome ring with two offset “T’s” in it on the rear of the car.
AMC was next in offering it (AMC manufactured their own differentials and rear axles, unlike Studebaker which bought them from suppliers, though as may be seen, they clearly did have engineering input into what they bought).
GM’s Positraction was merely a copy of what others had done. Likewise Ford and Chrysler and all the others.
Studebaker were first (in North America) with caliper front disc brakes. AMC was first (in N.A.) with dual-circuit hydraulic brakes (earlier, Hudsons had dual-circuit brakes with one hydraulic circuit PLUS mechanical cable back-up). Packard were first with many things including air conditioning (1938). Reo were first with a self-shifting transmission (1934) which beat the GM “Safety transmission” of 1938 and the first Hydramatic of 1939 by many years.
GM’s claim to fame in their 1966 Oldsmobile Toronado (front wheel drive) was laughably far behind the Ruxton and Cord of 1929, as well.
Like Carguy is saw this on AB. Completely fascinating. Wish GM had made more of these, but unfortunately this appears to be it. Just like the general; make something great then abandon the idea completely. Love the barrel roll at the end.
Nothing is wrong here.
That was an excellent “Differentials for Dummies”.
I can take apart a rear end and fix it but to understand the physics is priceless.
The exhaust and its catalytic converter.
Sometimes. Not all cars do this: the Honda Civic has had a flat rear floor for a while now.
Next week we’re all going to learn about Summing Gearboxes!
As soon as I find the video….
“What I find really interesting is modern FWD cars with a driveline tunnel… what the hell for?”
The exhaust and its catalytic converter.
I think there’s also some aspect of torsional rigidity; a flat floorplan (like a flat piece of paper) isn’t very rigid.
I wonder if GM still uses these videos for their current designers. Live axles, leaf springs and high center of gravity, lemme think what GM makes like that.
I’m not sure if I’m correct here, but I remember my physics teacher telling us that a differential is called thus because the output shaft rotates at a speed which is the difference between rotational speeds of the two input shafts. In an automotive application it is used backwards; the drive shaft is attached to the output and the half shafts to the inputs.
This has always been a favorite video of mine, in that it is a good example of boiling down a complex concept into its most basic parts.
I’m fairly technical/mechanical, but I’d really like to see something like this that explains the workings of an automatic transmission. Somehow, despite the number of times I’ve looked at static diagrams representing gears and torque convertors, I’ve never been able to visualize how one really works.
What’s wrong with this picture is some guy is sticking his finger in the gears! Oh well, he can probably get by without it.
This is the first time I have ever understood a differential! Thanks guys. Next, do a sewing machine and my life will be complete.
Marvellous film. Treats the viewer as intelligent and doesn’t try to make it hip or ‘relevant’.
Show that to a young person and they will forever have the pleasure of knowing how a differential works. A most elegant thing. It creates an interest in them. I grew up around lots of broken trucks and tractors but most kids don’t get to see how things work now.
It’s almost uncool to be interested in how things work. Toyota could do one on their epicyclic gear based synergy drive. But I’m sure the PR people would not allow it. Not cool – just talk about the ipod connection.
I despair of the functional illiteracy I see these days. I helped my neighbour start her motorbike the other weekend. Her battery was mostly drained and it was turning over very slowly. After about 20 minutes I got out of bed and went over. I suggested that we crash start it as we’re on a hill. Both her and her boyfriend (mid 20s) we’re a bit taken a back. Said they didn’t know you could do that with a motorbike. She got on, put it in second and we gave her a push down the hill. I was running alongside and said OK, try it now. So she again pressed the starter button :-)
cheers
Malcolm
One of my Lego Technic sets as a kid had a working diff in it (earlier sets had locked axles). Man, it was a revelation.
This is a very elegant explanation of the principles behind open differentials. I’d love to see one done for a Torsen differential -I’m still not 100% convinced those things don’t work by magic.
Very good film. Don’t see anything wrong with it.
@dmrdano: Best auto trans book I’ve seen is “Changing Gears” by Philip G Gott, copyright 1991 by Society of Automotive Engineers. Covers it all.
When I was 14, ordered a lot of gears from Meccano, a British equivalent of the Erector Set, but perhaps more complex. Made a proper differential and crashbox 2 speed, powered by a clockwork motor with governor removed. The car I fitted it in was also made of Meccano and had independent front and rear suspension, with RWD. It could hurtle down a gravel driveway.
Later in my final year of mechanical engineering at university in the ’60s, I was the only one in my class who knew how a differential worked.
Visualizing how a differential works just in your mind is not easy. Nor is how AWD drive cars (depending on the make and model) can apportion torque differently front to rear. It’s done with gears of different ratios that rotate together when the vehicle is moving in a straight line, just like a differential behaves in the straight ahead position. When you have different ratios, one gear is trying “harder” and transmits more torque. Very simple, but not intuitive.
I like gears – they’re non-digital.
Wolven: What I find really interesting is modern FWD cars with a driveline tunnel… what the hell for?
The exhaust and its catalytic converter.
Also the hump adds strength and prevents the floor from vibrating creating harmonics.
Where the heck was this when I was taking physics in high school? A book can’t convey the whole picture like this well done film.
Now, does someone have a similar video showing why inline-6 and v-12 engines are so inherently smooth? Wikipedia’s entry just doesn’t seem to give me the whole picture.
I can tell you what’s wrong:
60 years ago auto engineers (and the general public) realized that having a car that was too high off the road was a bad thing.
Now everyone wants a sense of “road command,” like they have some sort of lifeguard fantasy.
Nice vid!
Limited Slips are harder to understand… they smack of black magic, in fact… to some people (including me)…
Clutch types are the easiest to figure… the speed of the input shaft pushes the clutches outwards and progressively locks the output shafts to the input shafts… (picture the above video with another large gear opposite the big one on the other axle, and a system of spring-loaded clutch plates between them… okay, an oversimplification… so sue me )
I still have trouble visualizing how my helical differential works… I’m simply happy that it does.
malcolmmacaulay wrote:
I despair of the functional illiteracy I see these days.
I used to think it was a generational thing–that each generation just naturally thought the next to be less mechanically-literate, much as they always think the “younguns” have had an easier life than them, etc. But as I get older I realize how true it is. Our society is losing basic mechanical literacy at an alarming rate. First cars became black boxes for most folks, then computers, now kids brag about not understanding how the simplest devices operate. And I despair too.
What’s wrong with this picture? GM explaining how something works-correctly. Today they wouldn’t dare explain regenerative technology so thoroughly, someone might point out what the Emperor’s new clothes are really made of.
If you want your kids to learn stuff like this, buy them a RC-car kit and have them build it. Too bad even RC-cars are almost exclusively ready-to-run models nowadays.. As a kid i replaced the steering on my first rc-car(cheap rtr nikko) with technic LEGO. Worked just as “well” as the original, just with a cord instead of wireless. And crashes were much more spectacular with the lego steering :D
yeah i think the next video should be limited slip differentials
LSDs are the sorta holy grail for Baruthians for obvious reasons
no LSD, no care
Lego? Pfftt! Meccano was of course the superior mech/science toy.
PeteMoran–> I did have Meccano, or still do.. ..somewhere in in the garage along with a huge pile of Scalextric stuff. I used lego because i had a motor for it ;) And the pneumatic stuff was fun. Now that i think about it, i could have made adjustable air-suspension for the car as well!
@ geggamoya
Some of the components you could (can??) get for Meccano were remarkable.
Anyone remember Capsela? That stuff was great.
No one has yet mentioned the lower angle of the driveshaft as it enters the differential assembly, ostensively to eliminate the floorpan tunnel. I remember seeing this on some old cars but, for some reason, it was abandoned to the point that all driveshafts entered the differential in the center. Of course, this meant there would almost certainly have to be a hump in the back floor.
Seems like the driveshaft entering the differential at a lower angle might have a siginificant effect on strength and longevity.
As to why there is no flat floor in FWD cars, I think the primary reason is not to provide space for the exhaust and/or converter but the structural rigidity requirements of unibody construction. The original FWD Toronado and Eldorado actually had a completely flat floor but it could be done with those cars since they were BOF construction.
Paul Niedermeyer:
“Wolven: What I find really interesting is modern FWD cars with a driveline tunnel… what the hell for?”
“The exhaust and its catalytic converter.”
This allows the car to be lower to the ground for better aerodynamics (and you don’t have to worry about your exhaust system scraping the ground – at least most of the time). I may be wrong but I believe most FWD cars have smaller tunnels than RWD cars.
So Robert, what exactly in your opinion IS wrong with this picture?
What’s wrong with this is that the differental has no electronic LSD or torque vectoring.
Go Grandma! You ghost ride that whip!
(8:55)
Nice miniature work- lots of metal parts. Real craftsmanship.