How to Check Your Cars Differential Gear Ratio! Easy!

[@CampTlangram]

Genius, but simple to understand.

[@RobertBeck-pp2ru]

Your method is good to know. Thanks

[@CatfishMotorsports]

Thank you, though this one has been around for a while so I can’t take credit for it. I made the video because I didn’t think the other videos I saw for it explained the difference between the open and limited slip diffs in the test. So I was just trying to get more complete information to people so they don’t have to piece it together.

[@ROMAN-oy5ju]

Wow this is the best gear ratio video I've seen

[@CatfishMotorsports]

Thank you!

[@tedsmith3061]

I figured this one out 50 years ago and he's completely right. Nice work youngster. However we knew this one a hundred years ago. Literally.

[@CatfishMotorsports]

It’s a gear ratio, Archimedes probably had this one worked out more like 2000 years ago lol. It’s more the couple of videos I looked at before I made this one I felt didn’t tell you about the difference between an open rear and limited slip. So really I was just trying to quickly put all the information needed in one place.

[@tedsmith3061]

@@CatfishMotorsports I did note that too. Stoll good work. We didn't have screwtube 50 years ago. Probably wasn't around 2000 years ago either. You're the first to compile the 411 into a gigitized video.

[@thud9797]

Yes I did this on my first car, a 71 Firebird Formula 400 but that was easy since it was a GM clutch posi and both rear wheels were locked together so it was easy to do. Driveshaft turned 3 1/2 times for the 3.42 gears that it had. Newer vehicles with different types of limited slips it sometimes won't work with the wheels off the ground.

[@thud9797]

In my Pickup with a GM Eaton Locker none of this worked so I taped everything up like you did and pushed the truck slowly down the driveway while counting driveshaft revolutions, this was easy on my truck but maybe not on other vehicles, anyway it turned a little over four revolutions so it's a 4.10 gear and the GM service printout confirmed that.

[@CatfishMotorsports]

That works. Though I’m not sure why it wouldn’t have worked without rolling the whole truck.

[@thud9797]

@@CatfishMotorsports I think the other wheel was rolling backwards and the turning wheel only turned about 3 turns which I knew wasn't right. Who knows, maybe I did something wrong but rolling it slightly downhill was pretty easy. 😀

[@mikeeiben3430]

If the transmission is in park, would the wheels on an open differential rotate opposite?

[@CatfishMotorsports]

It wouldn’t work for this test anyway because the driveshaft wouldn’t spin, so you wouldn’t be able to count. My immediate thought is to say with the DS locked neither would spin, but it’s been a minute since I’ve owned an open rear end so now I’m questioning that.

[@JuiceboxOffroad]

I'm going to try this out on my jeep wrangler. My question is, I have e-lockers front and rear, does it make a difference whether or not they are locked for this test?

[@CatfishMotorsports]

I’m not 100% certain but I think e lockers operate as open when they aren’t locked. So in that case you would need to spin the wheel twice and may need to leave one tire on the ground. If locked then both tires should spin in the same direction and you would only need to go one turn around.

[@JuiceboxOffroad]

@ thanks ! i'm going to try it with the lockers engaged

[@jimmiebroadbrook1057]

Does it make a difference if the car came with 14 inch tires and you put 15 inch tires on it the rear end I put in my car is out of a 69 firebird 400 and I have a 78 Pontiac Phoenix kind of like a Nova

[@CatfishMotorsports]

No. 360 degrees of rotation is still 360 degrees of rotation. It could have a small effect on your rpm while driving because of tire size differences but not for this test.

[@pace0086]

LSD is good brother. 👍👍

[@CatfishMotorsports]

I was shocked to find out I had a limited slip in that old girl.