Budman68

After disassembling the rear end tonight I ran the code on my rear end it is a OK. Dang it. All this time I thought I had the 3:55. Do I need 3:73 with the new 700R4 of is the 3:08 good. Right now my car pulls a 1.9 60 ft time and with the 700R4 it should drop to 1.8 or 1.7. Do I need more gear?

BeachinVette

I have a complete 3:55 I would let go for $425.00 + shipping. If you are interested let me know.

Bob

Budman68

Thanks, I probably will regear if necessary.

Schmucker

What's your overall 1/4 mile time? I think that you are probably fine with 3.08s. The car can move pretty well and you'll get better gas mileage (hopefully) than with some steeper gears when you travel. Plus that higher top speed is fun. I have a little goal to peg the 160mph speedo (and still run 12s)... I doubt I will anytime soon though (peg the 160. 12's by spring if all goes well :D)

frC3

Bob, Where are you located? Will this rear end fit my 1972? Fred.

BeachinVette

Fred I "IM'ed you. http://forums.corvetteforum.com/zerothread?id=485919

Bob

Alwyn678

Go with the 3:73's :reddevil

Ganey

The main advantage of O/D is for lower rear gears. You will have an effectively lower rear gear in 1st if you install the 700R4. Consider the 200R4.
If someone is not going to install lower gears, then the trans. can be fitted w/ 2.75 first gears which effectively lowers rear gear in 1st.

:cool:

gkull

IMO with the 700 or other OD trannies with a @ .70 top gear. 3.90 is the best choice. My 4.11 is a little overkill and 4.30 & 4.56 are for drag racers who use all four gears in the quarter.

3.73 is way overgeared in top gear for anything less than big blocks or low rpm big small blocks.

If I had it to do over again I would get a 5 speed manual without OD and install a 2.73 rear end

PatsLs1vette

i have 3.70 with my 700r4 might go to 3.90 later on,it luggs when in overdrive just running up the road around 45-50.

Budman68

That's strange, the mid eighties vettes had 3:07 gears with the 700R4. Pat are you sure your ECM is not shearching for a fuel map, because of a bad sensor.

PatsLs1vette

ill know better when i finally get to drive it more.

joe73vette

With the 3.06 first gear in the 700R4, the 3.08 rear will seem like you had a 3.80 gear with your old TH400. I wouldn't change it unless you like wheelspin. Joe
[or 3.74 if you had a TH350 before]


[Modified by joe73vette, 12:10 PM 2/4/2003]

gkull

Budman78. Pat has a zz4 cam and it lugs at low rpm. All those early to mid 80's vettes were low rpm motors and if you ever rode in one the first thing that you would notice is constant shifting in and out of OD 4th gear. They didn't have enough power to pull it and would shift down at the touch of the throttle.

I originally had a 700R4 and 3.55. In lockup 4th I had to drive 70+ mph to keep from lugging. Now with a bigger motor with 4.11 I don't have to worry about down shifting once I've over 45 mph


[Modified by gkull, 4:37 PM 2/5/2003]

Budman68

Forgot about the ZZ-4 hot cam. Mine doen't tend to clean up until after 2000 grand, so I will probably be experiencing the same issue. Sometime the O2 sensor jump in and out of loop when they are mounted in the headers and cause the same effect. lean/rich/lean/rich.

jdunne

My 74R has 700r4 & 3.08 behind a strong 383,i am struggling to control wheel spin as it is and i have tried with a 3.55...even on a drag strip,it spins all through first gear and most of second,so it was a total waste of time with 3.55......the best time i had with carb and traction problems is 13.5 @108mph......it will clearly go much faster when i get everything sorted...great fun cruising at 70mph and less than 2000 rpm....i dont put it into O/D below 50,but from 50 to 70 it will stay in O/D with a very light throttle.....john :chevy ;)

Jvette73

3.90 will fit in the 3 series carrier. Go for the max. The O/D will make up the difference. Im runnin 3.90 with 26"tire and locked in 4th I rev 2250rpm @65mph.

Mike Smith

Budman -

The only thing the code confirms is the gear set ratio originally installed in St. Louis. You could have any ratio from 3.08 to 3.70 in that case.

Suggest you jack the rear of the car up, place two jackstands securely under the frame, put the trans in neutral, and count the number of driveshaft revolutions per one complete revolution of a rear tire. You may need a helper to turn the tire while you observe the driveshaft.

This will equal the gear set ratio.

Budman68

Will count tonight. Looks original and never serviced. :crazy: Got the jackstands covered. Basically the only thing left on the rear is the pumpkin and brace.