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Transmission, swap or not

T

Tx70Jimmy

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My '70 Jimmy's TH350 has a leaking front seal. I've convinced my wife it needs to either be rebuilt or replaced:cool1:. Question is, for a weekend driver (maybe sometimes to work) is it worth swapping to a 700R in place of just replacing the leaking seal? Are the trannys from Jet a good quality? I like the idea of a lower first and the extra gear, but the cost and modifiactions required may not make it worth while.
 
Same question for a '73

:confused: I want to remove the one from my wife's '86 K-5 when I get her a pickup. I wondered the same thing. How you get it to work without a computer. And if the 700/208 combo will work with minimum problems.
 
there is basically nothing computer controlled about a 700R4. 4l60e is a different story of course. There is one thing but I think thats the park/neutral safety switch. TV cable is important but thats simple.
 
lock up kit needed

you need to get a lock up kit and the tv cable and bracket some times the aftermarket adjustable ones are better to use . and lengthen frt shaft shorten rear shaft then move cross member and hook up the parts and run. if your tcase is a 203 or 205 the tail shaft may be to long then you half to change the shaft or just order the corect one when ordering tranny.
 
Don't forget about tire size and your gear ratios. It's easy to make the overdrive useless with the wrong combination. If your current ride runs above 2600-2700 rpm at say 60mph then a 700R4 will help.

My 72 has 35" tires and 3.73 gears. This combination doesn't work well with a 700R4.
 
I know it does have a lock-up torque converter (which I like) but how's ya get it to work? It hooked to the computer in my '82 K-10 I know and I assue the same for the '86 K-5.
 
Lock up in the '82 and '86 are both standalone systems.

Essentially just a vacuum switched system, I'd never buy a kit, the stock setup works excellent and is easy enough to find.
 
the only thing the computer controls on a 700 is the shifting servo(i think). i'm sure you can find something to make it work.


The 700 has a real short ratio in od. I mean real short. with a stock 350 it won't stay in od unless its on flat ground. You will spend alot of time doggin hills in third and eatin large chunks of your paycheck unless of course you have the hp to stay in od up the hills. otherwise the 700 is a great tranny. You will see the difference in mpg if you live in flat country or if you have the ponies to push it up the hills.
 
Computer controls nothing about the 700R4 in pre-TBI trucks, and I'm not even sure it controls lockup in the '87+ trucks.

Torque Converter Clutch is all there is to worry about, the stock system just unlocks it when vacuum is low. Very consistent way to do it, and on just about every 700R4 truck ever made.
 
Shift points are controlled by the governor (and TV) on all 700R4's.

If shift points are governed by an ECM, it's a 4L60E or 4L80E and neither was out in '88.
 
Chips don't change shift points, and the four prong plug is for lockup, and power to any of the pressure switches used on each particular year.

No idea what the pressure switches "talk" to, but until the 4L60/4L80E, the only thing the computer (PROM) cares about is whether its a manual or auto rig.
 
Im pretty sure the 88 700's used the comp for lockup and shift points but i can tell we are gonna have another finger fight on this so this is all im gonna say.

Have you ever opened up a 700 and taken a look at the shifting servo? The tv cable holds the shift points longer at more throttle it doesn't control the points when it needs to shift with no throttle being applied. I know auto trannies use governers but the 88's have an electronic servo in them.
 
Show me a picture of this servo. As a matter of fact, show me a picture of a factory diagram that shows this. I'm looking at a 1988 manual right now, and although there are at least 5 different wiring schematics for the inside of the tranny, none have any shift servo's.

If you are talking about the piece that is at the front of the tranny, in front of the valve body, held in with two bolts, typically white plastic with a solenoid attached, going into the tranny pump portion that extends into the case, two wires (IIRC), it's the TCC solenoid, and is what controls lockup, thats it.

As a matter of fact, a factory diagnosis chart mentions electrical for NO conditions, not up or downshift problems, EXCEPT those related to converter clutch.

As a matter of fact, regarding TV operation, the service manual states "A part throttle 4-3 downshift can be accomplished by depressing the accelerator pedal far enough to move the TV plunger to allow the TV oil to enter the part throttle passge...part throttle oil and the 3-4 throttle valve spring force will close the 3-4 shift valve against governor pressure, shutting off D4 oil to the fourth signal passage."

So if TV doesn't at least partly affect shift points, where does that fit in?

If you do any research and find that the 700 is in fact controlled by the ECM in any way shape or form (short of the TCC) I'll listen. I'm not trying to be a hardass, I'm just looking at factory documentation, my own experience with ECM's and truck wiring, and have had a few auto trannies apart, besides paying attention once in awhile when people talk about them.

Besides ALL of that, the trucks originally referred to by me were in the post regarding the 82 and 86, but I'm game, prove me wrong.
 
The tv cable holds the shift points longer at more throttle

it doesn't control the points when it needs to shift with no throttle being applied
Click to expand...

When my stock 350 took a dump i had the tranny looked at because second gear was slamming so hard it would sqeel my 35's with no throttle. I bet it was the reason my main bearing let go. I pulled it out and took it to my dads buddy who is a master mechanic at a chevy dealer and does a lot of tranny work on dirtbikes, trucks, cars, street bikes, and quads. This is what he told me.

I have a bad servo and this is why second was slamming into gear. Just the word servo implies "electric" but I couldn't find any diagrams that showed a complete 700. they only show the driver side which is not the side with the servo.

A four prong plug is usually something that controls multiple things for example: 1 prong per gear. Now that i think about it theres no way the tranny can control torque converter lock up. all it does is hook to the splines. I can't confirm any of this besides what im telling you right now because i can't find any 88 700 diagrams but it's common sense...theres nothing that controls the torque converter so what else is left? Not vss becuase mine is mechanical. that leaves shifts. All i can say. A mechanical tranny has no need for a servo, it uses centrifical clutches. A computerized tranny uses a servo. Since i can't give you a diagram you probably won't listen to this. They used em all the way to 95... I find it hard to beleive that in all that time they never went computerized.
 
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