700R4 - essential to buy a newer case?

[spitfirenut]

Thanks, that's what I need to know.

[Robyn]

Good luck on your search for parts.
If you have any questions along the way just ask.

The 700 although not a difficult box to rebuild can present some challenges. There are a couple special tools that are a "MUST HAVE" to be able to assemble the clutch pistons.
These are the seal installer tools. Without them its a no go and you simply can't assemble without damaging the seals.

I made mine here in the shop. You can do the same or possibly borrow a set.
The cost to purchase was not inviting for a single unit rebuild.

Good luck
Robyn

[78Chev]

I have a Bowtie 700r4 in my 2WD. Very solid and works as advertised (even though I had to put a transgo kit in it to make it shift right). The trans locks up in OD automatically (it has a NO switch in the OD valve train) but with a toggle I can bypass the OD valve body switch and lock it up in any gear (including 2nd). Since the converter solenoid is what controls lockup exclusively, anytime the OD VB switch is bypassed the thing will lock the converter (except in 1st). The VB only has a port for a switch in the OD train. I would like to have more control over which gear I can lock/unlock it and also have some protection with a pulse switch so that the converter unlocks as it shifts gears. As it is if I have the manual lockup switch activated and it downshifts from 4th to 3rd it jars the tranny when under load and so I'm afraid of damaging it. Also, the decrease in RPM from 3rd unlocked to OD locked is huge, so being able to run in locked 3rd then unlocking as it shifts into OD locked would make for smoother running on the highway.

I have the VB switches that I need and can figure out the wiring harness. Can I drill and tap ports for these switches in the VB? What would be involved in changing the bushings and valve trains? Or should I look for a VB with these ports already there? If so what would I ask for (e.g., year; model)? Thanks for your ideas. --Randy

[Robyn]

You need to inbstall a 4-3 pulse switch in the VB.
Most VB will have the ports in them. Dont dril and tap these as you can make a mess of things.
Look in the ATRA tranny book for the 700 and cruise through all the diiferent wiring styles and pick the one you like.

The late 80's VB will have the valving in it so it will lock the converter hydraulically and the only need for the switch would be to shut off the lockup for town driving.
If your VB has the ports you can install the valves and make it all work.

Good luck

Robyn

[More Power]

I was told by my trans guy back in the 90's that the pre-87 700R4 can be built/modified to shift without any electrical control. In fact, that's what he built for my 6.2TD GMC. The TV cable was retained, but not electrics. Shift scheduling was controlled by the TV cable, speed and hydraulic pressure internally. Worked great...

Jim

[mhagie]

I also have a Bowtie 700R4 and I have noticed that it will also go direct from 3rd to OD and lockup together,however that occurs at light throttle if I am applying more throttle than normal it will do the 3-4 shift and then T/C lockup.
Down shifting has been no issue as lockup drops out around 35-40 mph.
I do have the optional 3rd gear lockup switch but rarely use it.
Merle

[Robyn]

Transgo sells a kit to allow a non electric lockup.

The Valve body must have the lockup control spools in the bore sot do this though.

Some of the 700R4 boxes have the bores but are fitted with aluminum plugs.
The plugs can be removed and the spools, springs and such then fitted.

Ther is also a solenoid that is hooked up along with the hydraulics to give an electrical control too.

The early setup placed a check ball under the solenoid valve and this allowed the shift valves (spools) to do all the work.
This was however a tad hinky in the way it worked.

The new setup allows much better control of the lockup in and out.


best

Robyn