Hello all ,I have a stock 89rs with a 305 and not sure on the auto tranny. But my question is when is the or does the overdrive drop in? Mine is going in at 40 mph or so. Gets old in town too.....I did the adjust thing where you reset the spring on the TBI and then go full open with throttle but still same thing. Could this be a setting that the TPS gives ecm when to drop in? I did set the fuel to air mixure up a turn or to ... to get my idle up to around 1000 or so. If this could be the prob what is the correct idle for a 305 and what should the TPS sensor be reading? Thanks in advance for any info.

 

It's a fixed MPH number in the ECM

 

Put the shifter into drive and forget about it? The older three speed trannys had a kick down cable. The only third gens that I know that have three speed trannys were the very early ones 82 and some of 83. My 83 trans am has a 700r4, I do not remember when it shifts. I have a 89 iroc also it shifts around 40 if you are out of the throttle, I am confident that is the number GM decided on, at least yours is not broken. The cable you adjusted is called the TV cable. A small mistake in this adjustment could cost you a tranny.
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It has to more complicated than a fixed number, because it changes based on enigne load. In a drag race against a mud stain if it shifted into overdrive at 40 you would be a terd.

 

Well everything still works fine it just goes into OD at 40mph or so and if it is what GM put in then I'm fine with it. I'll just pull down one when driving around town to only shift the first 3 gears.

But one last crazy question, can I adjust the shift point in the ecm? Or reprogram the prom in the chip to say 55mph or so?

 

I know kurtrangen kind of touched on this already but it is most definietly NOT a fixed number on a 700r4 (which I am assuming is what we are talking about) it is based on engine load and throttle via the TV cable.

Also, no stock thirdgen has an electronically controlled trasmission, the ECM has no bearing on shift points. You can't reprogram or buy a chip to adjust them. You can adjust the fluid pressure by properly adjusting the TV Cable, tryadjusting the TV cable in small incriments until shifts "feel" correct. Not adjusting it properly can cause problems, but the ratcheting automatic adjusting sleeves, tend to wear out end up giving an inaccurate adjustment.

To raise the speed and rpms it shifts into OD try tightening it "SLIGHTLY" . But to really change shift points properly you would need to change internals in this case the governor and/or O.D. valve.

 

Of course it doesnt lock up at 40 when you going up a hill or when you are way into the throttle.

What I meant is that its set at 40 mph in low load, in town cruising situatiuons. Which is what jeep2creep is complaining about.

Yes, you can change it in the ecm. You can change the minimum temp need, the max amount of low speed cruising load (%TPS) all to suit your driving style.

 

Not on a 700r4, there is no temp. sensor for the transmission and no provisions in the ECM that effect the transmission whatsoever.

Why do you suppose no one sells an electronic shift kit for a 700r4?

Because it is NOT an electronically controlled transmission, open up the valve body, it entirley based on fluid pressure which is ONLY adjustable through a set of vavles/springs and the TV cable.

I don't mean to argue, just wanted to state the facts. The oldest camaro that would have an electronic tranny is a 93.

 

http://http://700r4.com/faq/computer.shtml

Quote:

Vehicles that came from the factory equipped with these transmissions did not use a computer to control the transmission. The confusion comes from the fact that the computer in the later models controlled the 12v circuit to the transmission for converter clutch lockup.

 

93 F bodies have 4L60 trans :-)

The 4L60E got into the F bods in 94 :-)

Any thirgen auto has athe converter controlled by the ECM. The trans itself and shift points etc are still controlled by the valve body via TV pressure and governor.

later
Jeremy

 

the only thing the ecu controls on a 700R4 is the converter. It simply locks and unlocks the converter. It has NOTHING to do with shift points.

 

To elaborate more: the governor pressure creates the shift. The faster you go, the more governor pressure. The detent pressure (throttle pressure) delays the shift. The more you're in the gas, the more detent pressure opposing governor pressure, the later the shift.

My OD comes in about 28MPH under light throttle. the converter clutch at 35MPH under light throttle.