Inliners International Forums General Discussion Drive Train School me on auto trans please

I've always preferred manual transmissions but my left knee is telling me it's time to start getting familiar with autos. I have an '81 gmc jimmy 2wd that currently has no engine or transmission. I'd like to put a 250 and 200-4R in it. I'm considering the 200-4R because I've read that it's more efficient than a 700-R4. The rear currently has 2.73 gears but I'll change that if I end up with an overdrive transmission. I have the engine already but haven't gotten a transmission yet. Please tell me what I need to know to make sure I get the right transmission and what is critical to make it work well. Thanks.

I think a 200-r4 with a 4.11 rear end would be a lot of fun. You can play around town and still cruise out on the highway.
2.73 gears would cause it to lug down more than I like.

Will Willis

I agree with Will. I think you will like the 200r4. I'm not sure if it is as touchy about the throttle cable setting as the 700r4 but suspect it is. Just find some good instructions and follow them.

The tough part: Be honest with yourself about what the vehicle will be expected to do and chose the rear end gears to suit your needs. My '68 C20 has a 700r4 and 3.54s (350) never lacks power and does 70+ all day. Towing/hauling no problem. No reason your setup won't do the same. 3.73 or 4.11 might be a bit better for the 250. Just take a little off the top and add it to the bottom. Tire size matters too. There are calculators out there that will help. I'd make my choice based on being at the best rpm for MY engine (all mods figured in) in OD at highway speed.

I Agree and I feel the 200r would be better for the 250 , And I think the 700 would be to big of a tranny. And the 200 is not computer controlled and can take more heat then the 700r.

I like the 700 over the 200. Having worked in a transmission shop that did R&D for a major converter and racing parts manufacturer, we found that the 7004R was more versatile AND durable.

I'm running a 700 behind a virtually stock 153 Chevy II engine in my little rat rod and it's been trouble free!! Downtown traffic or interstate highway, the backroads and hills of Tennessee, nothing seems to phase it!!

I just experimented with the detent cable adjustment until it ran and shifted the way I wanted it to and it's been perfect!! It was a little tall in overdrive with the 3.00:1 for hills and such, but a change to a 3.50:1 was superb.

That is very interesting to know with it behind something that small.

Yep! I figure with the header and the tiny NASCAR Holley 390 4bbl, it MIGHT make 120 hp!! The car weighs 2300 lbs with me in it. I'm in the process of assembling a new engine displacing 174 cu. in. and hoping to produce between 200 and 250 hp. I have NO DOUBT that that same 700R4 will work splendidly behind it.

The transmission, incidentally, is a used one, straight out of an old pickup truck, converter and all!! I just changed the fluid and filter and put a new detent cable on it!!

Blackwater,
What rpm was the engine running at say 60 or 70 mph with the two different rear ratios?
Also, if I understand right, a Powerglide is more efficient than a Turbo 350. (more of the power going in comes out the output shaft). How do the 200R4 and 700R4 compare?
For me the extra gear in the T350 is well worth whatever extra power it might consume compared to P/G.
Thanks

Blackwater is that 700r a Non computer?

Sorry to take so long to answer! Been out in the shop.

With the 300:1 gear, the engine was turning around 1,800 rpm at 65mph in overdrive and the tcc locked up. That's on flat ground cruising. the numbers for the 3.50:1 gear may be slightly skewed because I swapped rear tires too, but under the same conditions, it was running about 1,950.

The PowerGlide "takes less horsepower" to operate. The numbers aren't totally accurate, but a 'Glide takes about 19hp and the 350/400 take around 40hp. Most of your three and four speed automatics are similar to the GM offerings. The 200 and 700 both pull about the same hp. Where the PowerGlide shines is on the drag strip and stop light to stop light. In a light car, the 'Glide will outperform even a good manual transmission, given all other thing being equal. We replaced the Richmond five speed manual transmission with one of our racing PowerGlides in a record holding D/Gas Camaro, just to prove our automatics were capable of being competitive. With the exception of adding a transmission oil cooler and a different drive shaft and shifter, NOTHING else on the car was changed!! Same driver, same track, same weather conditions. The car was actually 0.10 seconds faster on the eighth mile and 0.13 faster through the quarter mile!!

YES! For daily driving the TH350 is probably better, particularly around town and in heavier vehicles. On the highway the overdrive transmissions, of course, have a distinct advantage, simply because of the better effective gear ratio. As my little rat rod experiment proved however, you CAN have too much of a good thing!!

YES!! The 700R4 is NON computer!! The detent cable is the only control for shifts and TCC lockup outside of the gear selector. The 4L60E is the electronically controlled version of the 700.

The 200-4R is a good transmission and if you already have one, I probably would go ahead and use it. IF you're still in the looking around phase, I recommend the 700!!