700R4 confusion

[Brisk]

ok let me start off by saying I'm not an expert with transmissions, especially automatics... but I do know I'm having a problem.

vehcile: 1991 Camaro Z28 350 5.7L 700R4 3:08 Rear Gears.

Taking off from a stop it drives and shifts normally through 4 gears and seems normal. However crusing at 80km/h (50MPH) in OD this car holds at a constant 2400rpm which seems awefully high to me.

In comparison, my IROC with a 5 speed and 3:45 rear gears cruises at 1200rpm at the same 80km/h.

Is the torque converter not locking up, or what could possibly be the problem? What can I check or look into?

Any help would be appreciated, thank you.

[89vert]

first thing I do is confirm your tach is acurate

[Brisk]

the tach may not be accurate, but I know a problem exists. I can drive my heavily modded 5.0L 5-speed iroc to work for 4 days on a 1/4 tank of gas, yet one trip will use 1/4 of gas with the stock 5.7L 700R4.

[89vert]

moderately accelerate on an open road, make sure you start in 1st and count the shifts, make sure you can feel it hit 2nd, 3rd then OD, you should then feel another engine rpm drop, when the converter locks up, you may have to lift slightly on the pedal to get he converter to lock

[Brisk]

I can feel and hear the 1-2 shift, 2-3, and 3-4... thats it, even when using cruise control or barely feathering on the gas to maintain speed.

[Brisk]

my 91 Z71 chevy truck with 3:73 gears and 700R4 wasn't this bad on gas, nor did it rev this high doing the same speed.

[89vert]

even if you aren't locking up, its not going to save you that much fuel,

you may have another issue,

2400 rpm seems like you converter might be stalling to high

[Brisk]

hum.. this has certinally got me scratching my head... how can I test the coverter to see if it is working properly?

and I think I'm going to pull the rear diff cover off and count the teeth, a pervious owner may have swapped out the gears.

[steveo]

you can find the rough stall point of your converter by applying full brakes and blocking the back wheels (anything you can do make sure the back wheels do not spin and the car doesn't take off while testing) and revving it up at a reasonably slow rate to see where it stalls.. you will feel the stall point.. just don't mash on it and don't hold the throttle too long and you shouldn't break anything

you don't have to pull the cover to check your gears, mark the driveshaft and spin the wheels to see how many wheel rotations per driveshaft rotation

[89vert]

like siad above, get on the brakes apply throttle but dont let the tires spin,

see what the rpm is, I thimk its like a 1200 or so stall

[Brisk]

ok I just thought I'd come back and update this...

I found a leaking vacuum hose and replaced it, the tranny now shifts properly. I also found my tach is very inaccurate, VERY. Lastly I reset the timing, which was set to 0.. I've now got it set to approximatly 7deg and it runs much better.

With the above problems resolved, the gas milage has greatly improved - as well as increased performance.