Please let me preface with: I'm new! I've just signed up and promptly ignored the "New Members" section entirely so please feel free to give me a deserved earful of all the etiquette I'm breaking. I'm also new to owning anything GM from this time period as of three weeks ago. Have mercy, thx!I just bought a gorgeous 1991 S10 Blazer from an estate sale, 50k miles, garaged, custom order, hasn't been driven since 2000-2001ish. Automatic, 4x4 capable. It has overdrive. (As well does another '91 GM car I just bought that I'll mention below when relevant) The lovely folks I bought it from seemed almost scared to talk about it and have very little knowledge on what it even is, and until now I've never heard of it.

Now, I get the gist, it's higher gearing? But what do I use it for? Highway? Always? Not towing, that much I've found out through Google. It feels like it shifts with a different "brain" in OD and not particularly comfortable for small-town driving. D is much smoother and well timed (traditional feeling?) What I'm used to in most cars, for feel anyway. (This different "feel" is consistent with my 1991 Pontiac Firebird Formula and it's Overdrive, in fact I'm hoping any knowledge here is relevant there too, Pontiac being a GM manufacturer) Is this normal for OD? Do they wear out consistently in some way that causes this to happen or is this just what OD is?

Lastly,
Can I switch into OD while I'm in motion? Playing around with the transmission in an automatic while driving feels very foreign and uncomfortable to me and I don't want to break something 31 years old that I'm sure there's lots of spare parts for.

Any and all knowledge or resources is greatly appreciated, Thank You!

-91GM-

 

Overdrive works automatically. But you can go into out of drive using the shifter at pretty much any speed or whim without any problem. You can start with the selector in Drive or start in OD. If you're in town and like the feel of driving in "drive", no reason not to do it.

 

Traditionally, the top gear ratio through transmissions is 1:1. I think for our Blazers 3rd is 1:1 with the overdrive ratio being about 0.73:1 so that the output shaft spins once every time the input shaft spins about 73% of a full rotation.

I had a 92 a long time ago and I would generally just keep it in overdrive unless I was towing my boat.

As for your feel, that is seems consistent with your other 91 GM product indicates that it is likely fine.

Now, for a vehicle that has been sitting around for so long, you might want to take it to a transmission shop to have them look at it and check it over. After sitting for so long, the transmission fluid simply old and also could have absorbed water and/or lost some of its volume from evaporation of some of the lighter compounds.

And these overdrive systems do not wear out. Gears 3 and Overdrive ("4" on the later models) are on the same gear circuit. What does cause problems with the 3/4 gear circuit is if the transmission is allowed to overheat and some critical seals get hard and allow fluid to leak past and contaminate the 3/4 clutch pack causing the transmission to slip when trying to go into 3rd from 2nd. I know this from having learned it the hard way by towing my 2,200 lbs of boat and trailer in overdrive and not having a transmission cooler. This was about a $3,000 mistake! You've been warned!

 

Welcome, you'll get the answers your looking for here... But I'd love to see this hidden gem you speak of! Sounds like she's a beauty