[hotrod3z]

i have a 700r4 that 90% of the time wont shift in to overdrive if i hit 70mph it will and i was told it had a shift kit when i bought the truck84 chevy could it be a vacume problem or what could it be any advice would help im not a trans person thanks eric

[Crosley]

Originally Posted by hotrod3z

i have a 700r4 that 90% of the time wont shift in to overdrive if i hit 70mph it will and i was told it had a shift kit when i bought the truck84 chevy could it be a vacume problem or what could it be any advice would help im not a trans person thanks eric

there is no vacuum to a 700r4 trans.

the other 2 shifts are timed / shifting correct speeds.

Do the shift points increase in speed as you step on the gas pedal harder?

to verify ; the shift to over drive is late .... Not the converter clutch lock-up?

could be several items with the late shift to Over drive;

sticky shift valve

sticky or worn inner TV valve in the v-body

some person installed a stiffer spring into the OD shift valve assembly in the v-body

[1930u]

Originally Posted by hotrod3z

i have a 700r4 that 90% of the time wont shift in to overdrive if i hit 70mph it will and i was told it had a shift kit when i bought the truck84 chevy could it be a vacume problem or what could it be any advice would help im not a trans person thanks eric

Crosley is the guy when it comes to the trans issues. He helped me through a 700 conversion a few years back...if you listen and do what he says you will be happy.

Thanks again Crosley!

[hotrod3z]

so there is not supposed to be a vac on the tranny on a 700r4 because there is one going to the modulater valve and yes shift points do change at higher speeds

[briscoe]

Where on the trans is this modulator located?

[Crosley]

Originally Posted by hotrod3z

so there is not supposed to be a vac on the tranny on a 700r4 because there is one going to the modulater valve and yes shift points do change at higher speeds

IF there is a vacuum modulator on the trans in your vehicle... the trans is not a 700r4.

A 1984 chev truck could have a t-350c trans. this is a 3 speed trans with an internal locking converter clutch.

Your truck may have been built with a 700r4 and the 700 was replaced with a 3 speed automatic.

[Jmark]

Guess that 'splains where the other missing gear went! LOL

Mark

[hotrod3z]

the truck came from the factory with a v6 and a 3 speed trans but the guy i bought it from put in a v8 and he said it was a 700r4 but when i hit 65 it shifts in to 4th gear so it really cant be a turbo350

[hotrod3z]

the modulater valve is on the passenger side at the back

[Crosley]

Originally Posted by hotrod3z

the modulater valve is on the passenger side at the back

you describe a t-350.

Perhaps a t-350C or a t-250C trans is in the truck with a lock up torque converter.


as i posted before If the trans has a vacuum modulator on it, then it is not a 700r4 trans,.

NONE of GM's over drive transmissions have a modulator on them.... not the 200-4r , 700r4 , 4l80e

[randywr]

Hey, crosley is right. A 700-R4 runs via TV cable, or "kick-down" cable that ties to your throttle linkage. That last shift your feeling is prolly a lock-up converter kicking in. They can start acting funny and go bad. However, if your vehicle puts a significant load on the tranny at highway speed, the converter will purposely hesitate to lock-up. They work off of vacuum and load. When your throttle is to far open with a significant load on the tranny, your vacuum is down and your load is up, so the converter is un-locked. When the vaccuum goes up and the load goes down, it will lock. Your setup may be hung in the middle of these situations. Too high of a gear ratio can cause this, especially at highway speeds, but it could just be a bad converter.

[hotrod3z]

thanks for all the info guys the truck has 6cylinder gears in the rear end

[randywr]

6-cylinder gears? If you mean the truck was geared for a 6-cyl engine, that doesn't mean a whole lot. It could still have a big number of different axle ratios, or they could even have been be changed by someone.