How to tell if 700r4 has lockup converter (and what does that even mean..?)

[benbloom]

Hey guys, im just looking into buying a truck with a 700r4 / 350 combo, the thing is, the owner says that it is not a lockup converter running currently in the trans. firstly, what is the big deal with lockup/not lockup, i understand that it lowers rpms at freeway speeds, but is this really such a big deal? what if i just drive at 65 instead of 70, is that effectively the same as having a lockup? let me know if you guys would install lockup if it was your truck, the current owner claims its unnecessary...but i would hate to buy a truck with a fried trans or fry it myself.
thanks!

[Alex V.]

Lockup converters, at a certain speed, usually only in 3rd or 4th gear - in some early ones, only in 4th gear - receive a hydraulic or electric signal from the transmission at a certain speed after which they lock rigid allowing full power transfer into the transmission without any slippage, hence improving efficiency and decreasing heat. For instance, in an older 3-speed automatic w/lockup TC the lockup point can be felt at a point where it feels like the tranny shifted again, but was already in 3rd gear. Non-lockups have their "stall point" where fluid pressure in the vanes causes them to go stiff, but it isn't a true lock-up and still allows some slippage. Good for torque multiplication, but not beneficial to heat generation or fuel economy.

[along for the ride]

mopars had them in the later model torqueflite transmission the input shaft is different. The splines go all the way out on a lock up, and they stop about 1/4 of an inch from the end on a non lock up transmission. you can not use a lock up converter in a non lock up transmission. Don't know if Gm is the same they are new to me.

[BLT gmc]

To tell if the converter is locking up in the early GMs try this- Once at interstate cruising speed(no load other than cruising) , very lightly touch the brakes with your LEFT foot, while maintaining your current speed and accelerator position. When you doing this procedure, you should feel the transmission "downshift" and the engine RPMs bump up ~300. When you let off the brake, the trans should "shift up" ie-TC lock and engine RPMs return to previous cruising speed/RPM. No harm running a non locking TC that I know of, just missing out on some benefits. Bruce. This braking method must work in locking TC , or else your engine would stall if you jumped on the brakes.
Posted via Mobile Device

[dennislbrooks]

If the lockup is enabled hydraulically is there still a switch tied to the braking or does it sense a change in pressure to release the lockup?

I thot that my 42 700r4 was lockup but not sure one way or the other yet. It has a wire that hooks to the switch for overdrive. I have a switch to allow or not allow in OD. But nothing is connected to the brake for lockup release. Again I do not think i have lockup feature. Will ask trans shop that build it.

On my olds 442 --- I got a Raptor 700r4 that has no electronics to it. It shifts haydraulically into OD between 45 and 50 depending on accelleration or cruising and kicks out about 45 mph. I do not think it has lockup as I have not experienced it at 60+mph. The 455 would have no trouble lugging a lockup. --- Would do a 200r4 next time.

[VetteVet]

This ought to be a big help.

http://www.73-87.com/7387garage/drivetrain/lockup.htm

another good one.

http://purplesagetradingpost.com/sum.../techinfo.html

[67 chevelle]

if the wire plug is in the side of the trany , the answer is probably yes , if not , no , it is unnecessary , but If you have 411 gears and short tires , a great thing to have , its still an overdrive transmission ,without the lockup