[db flyer]

Hey you trans/rear gears pros. I have a th350 and a little 283ci in my 56 chev. with 3.36 rearend. I want better overall gas mileage. I`m thinking about putting in a 700r4. About what speed does the overdrive kick in?
50 mph or? Most of my driving is around town near 40/50 mph. Would I be better to stay with the th350 and just change to higher rear gears such as
3.23 or? Comments welcome. Thanks

[blwn31]

With the 700, you can manually lock up the converter in any gear, if you wish. Many people will manually lock up in 3. But, you have to remember to unlock it when you are coming to a stop. Third gear is 1:1 like your TH350. Fourth is overdrive, then you have converter lock up. I have my car set up to lock up automatically when the trans shift into 4th. Most of the time the trans will lock the converter at about 45 mph under light throttle and about 60 mph under mild throttle.

Keith

[db flyer]

Do all 700r4 have the lockup feature? Is this standard or is this a special torque converter feature? As you can tell, I know very little about this trans.
You mention that you have yours set to lockup at 4th gear shift, isnt that the overdrive gear [4th] ? I dont know much about converters either. As I mentioned before, I want the best all around gas mileage I can get around town. Thanks for any help.

[blwn31]

Yes, I believe all 700's have the lock up converter and, 4th gear is overdrive. Lock up is just that, drops the RPM about an additional 250 revs.
If you are just wanting the best mileage around town, and your speeds are under 45 MPH, I would say the TH350 that you have is the best bet. I don't know if I would change gears in the rear end. 3.23:1 is a pretty good gear.

Keith

[db flyer]

Well, I drive about 65% in town, but even in town, my speeds average about 40/50 mph. I wonder if the 3.23 gears would be better than the 3.36 gears I currently run now. I have heard a couple guys on the forum say somthing like they have 3.08 gears. I dont know if I got the numbers right. Thanks

[F-BIRD'88]

Before you run out and spend big bucks on a OD trans or swap rear gears ,, try this.
Install some rear tires on your car that are 10%or so taller in diameter than the present rear tires.
This will reduce the effective gear ratio and hiway cruising rpm.
Drive it around for a month or so and measure the real overall fuel mileage change.

Trying taller rear tires is easy and cheap and can be effective.

The th2004r is a real nice OD trans for your purpose.
The gear ratio spread is way better than a th700r4.

The real fun and bang for your buck deal with adding a OD trans (especially with a small motor)
is to combine it wiht a gear ratio swap like a 4.10.
Now your lil 283 really hauls when you rug it and cruises at low rpm in OD.
the .67:1 OD ratio of a th2004r tames down a 4.10 to a hiway cruiser friendly 2.74:1 gear

tames a 4.30 to a hiway cruiser friendly 2.88:1 cog.



Use the GM special high stall lock up converter that is from the 1987 Monte SS w 305HO and th2004R trans.
Just right for the 283 w a th 200r4 and 4.10's to 4.30's.

Now you will love your lil 283 '56 Goes like a bat out of hell from a light and cruises efficiently too.
It will be a whole different car.

[db flyer]

Thanks for your reply F-Bird`88. I would`nt mind trying a 10% taller tire, if it would help mpg overall some. Sure would save some money on trans. cost.
I think my current tires are 205 75 15. Wonder what ratio difference I would be looking at. Thanks