Overdrive Do's and Don'ts

Leave the shifter in D for all driving (2wd, 4wd, on-road, off-road, etc.) except heavy hauling or towing, during which I'd leave her in third.

Doc

Please clarify: [D] or D?

He mentioned he'd put it in 3rd, or D, when towing or hauling, all other times would be in [D] then, based on your understanding of the shift sequence. I can see the fog on his statement, my 94 Jimmy had PRN[D]D21, my 2000 S-10 has PRND321

Gotcha.

Same here.

I put mine in OD (1.47:1) for regular driving but if I tow anything, I put it in D (1:1). I have an '89 silverado with the TH700R4.

davemeek

Actually, isn't OD .47:1?

My bad; been driving 3-speeds too long! Mike was correct, by D I meant [D] and by third I meant D.

Doc

No it's 0.7:1 if it's a 700R4, 4L60e or a 4L80e with torque convertor locked.

Doc

OD is 0.69 : 1, Braniac

I thought I read somewhere the ratio was closer to 1.47:1 (1 being the crank, and 1.47 being the driveshaft) BUT was way off!! "The 700R transmission's principal new feature was a 30% overdrive. It also sported a lower first gear of 3.06:1."

So, you are correct Don the final drive ratio in OD is in fact .7:1 or 30% overdrive.

davemeek

Not according to the GM spec sheet for the TH700R4. Don is correct. First gear is 3.06, second gear is 1.63, third -OR- drive is 1:1, and overdrive is

sorry.... Braniac

so shoot me over 0.01

GM is 0.70, Mopar is 0.69 in OD

both of which are a long way from 1.47

actually, if you do the math, 0.7:1.0 is 1.428 overdriven, not 1.300

'30% overdrive' is a mis-statement, engine RPM drops 30%, but driveshaft speed is 1.428 of engine with TC locked in 4th

I had a healthy chuckle when I read in one of the above posts that D was 1:1 and [D] was 1.47:1. Always nice when overdrive is numerically HIGHER than third............................

Doc

Yeh, I *was* completely backwards on that wasn't I... oh well...

Dave

And, if you do the math the other way, 1.47:1 is very close to .69 final ratio.

correct. First