Hi my 91 corvette transmission broke, I went to the junk yard and bought a 87 transmission. Everything is identical except for the valve body blood on the 91 is square with 4 prongs and the 87 is round with 5 prongs. I need advice on how to connect this to my harness? Or how to make it work in general?

 

Take the plug, internal harness, and all the switches from the trans you had and put them in the trans you're going to use.

If that junkyard trans didn't come out of a corvette they are not the same. I'd take the whole corvette valve body, seperator plate, governor, and servo and put those in the junkyard trans.

 

The 700r4 was redesigned in late 1987 and there are vast differences between the earlier and later transmissions. You do NOT want the earlier version. The later version has an auxiilary valve body, which is much better than the earlier version.

Also note that the Corvette valve body is much different than the non-Corvette transmission. You can tell the Vette version by the large V cast into both sides of the bell housing.

The round 5 pin connector sounds suspicious. I have an '86 and '89 Corvette 700r4 and they both have exactly the same connector (squarish 4 pin connector). On my car TCC (Torque Converter Clutch) lockup and the OD switch are the only connections to the transmission.

 

Hi

Here are some pictures from my shop manual, it shows the wiring to the early T700R4 square plug.

I got a weather proof square four pin connector set and used that on the transmission, as my plug had the clip broken off.

Check the gearbox year, look on the other side for the identification.
You can see my old one started wit 5 which means it was made in 1985, Y means a Corvette trans.
see link below for T700 identification.

http://www.hotrodders.com/articles/T...ification.html

A. Purple.
B. Light blue 4th gear signal to ecm
C. Blank.
D. Tan with Black stripe.

 

Early 90's had a round connector, up until the 4L60E.
The early 90's connector has the pressure switches for 3rd, 4th, 4-3 downshift and the lock up solenoid. There was more communication between the trans and engine computer.

 

'92 was the first production year for the 5 pin connector in the Corvette.

OP - You need to do some more research on what you've purchased. I don't know that I'd start ripping out and replacing yet. Is there a LARGE V cast into the case like Cliff mentioned.

I'd relax and with some more information it's likely much easier to ID what you've got. It's likely easier to just look inside the pan and see how the harness is wired internally and what switches are actually in the valve body and wired. There's a couple different approaches to the way to proceed I'd think and just to start removing and replacing is foolish.

When you post back mention any information that you can find on any thing. Is there a tag? On the rail of the case like in the snapshot, is there something there. There should be a label or some information on the converter, what is that?

A couple questions, did you actually see the car it came out of? Did the transmission at the JY have the correct Corvette only extension or did that have to be exchanged? Most JY these days include a VIN on the invoice for major assembly purchases. Is there one.

Your old transmission should have some information also if original to the car. A code on the transmission I'd expect to be likely YDM or YHM.

A possible scenario - the transmission has already been rebuilt (the one you bought) and the builder used what he wanted in the build and likely just used a correct mating connector to adapt to the car. That could conceivably be a potential solution for you.

 

Most people who rely on books and websites might be surprised at how generic the 700R4 is in real life.
The V cast into the case and lack of a transmission mount provision are the only difference in the transmission cases of this year range.

The calibration is more specific and thats built into the valve body, governor, 2nd gear servo.

Nothing was said about a torque converter, stall speed is going to be lower in a non corvette specific V8/4.3 V6 application.

 

Without ID'ing what the OP actually ended up with it's pretty difficult to advise. Advising him to "rip things out accomplishes" NOTHING

When the OP returns with some information it might be quite easy to advise him. It seems this was intentioned to be an "INEXPENSIVE" make run and serviceable request. It may very well be just that - everything the OP needed.

 

"rip things out"
Sounds like you never did any transmission work.

Ok OP, gently remove all of your corvette specific parts from your old transmission, clean and inspect, carefully install........

Thats just how it's done, I don't need to refer to any literature to know that the "controls" stay with the vehicle. Remove, clean and install the said parts and it will work provided the "newly aquired" trans is in good mechanical condition.

Or just install it as it is and have it shift like a truck. Who cares, it's not my car. Do whatever the hell you want with it.

 

Lots of gratitude for all the help and information, I realize that my 91 corvette already had an 87 transmission that was blown out, the transmission I bought was actually 92 instead of a 87. How can I connect the 92 to the 91 body/ harness?

 

It's real easy to do, I've done it more times than I care to think about.
BUT, according to this site, if it's not written in a book it's wrong. So, figure it out.
I already answered the question.

More important...does the '92 trans even work?
The plug is only for torque converter lock up.

Yes, I did say the 700R4/4L60 is surprisingly universal. BUT the torque converter wiring....it seems like every vehicle is different.

I suggest you adapt your new wiring to function as the old wiring. It's simply UNBOLTING a few pressure switches, etc....BUT according to some people thats going to make the world come to an end. So figure it out.

 

Yes the 92 looks like it got just rebuild inside, the filter was spotless and the oil smelled so refreshed . Can you please explain or elaborate more with details, I know you've explained it but I don't understand a lot of the things, like the switches.. Etc. I would like to know your opinion and what to do with the square plug and round plug. Thanks for replying back, I feel like I can do it with your help, I appreciate it.

 

I've seen a lot of transmissions that were worn out with clean pans. You have to break open the filter to find the real condition of it.
Is it a corvette transmission?

Take the pans off both. It would help to have two engine stands.
Take a picture of both valve bodies and post them here.

 

You need to have the same pressure switches as the original transmission. In some years the engine computer wants to see what gear it's in and the pressure switches give it that signal.

A lot of times the ports are there but plugged. So the plugs can be removed and switches put in as needed.

If a replacement valve body had one port only it might work but since the engine computer is looking for signals from the other switches it might get an error code. I've never had to swap in the wrong valve body so I'm not sure. Usually I would get the right one.

This is why I say use your old valve body, it obviously worked as far as switches are concerned. It was probably a corvette valve body.

I have no idea what you have for a replacement transmission. But I do know this: the only difference between a 700R4/4L60 out of a 1989 to 1992 4.3 liter S10 pick up truck (as an example) and a 1992 corvette transmission is the valve body calibration (meaning certain springs and valve sizes, and switch combinations), valve body seperator plate, boost valve and spring, rev/int valve (in the pump), governor, 2nd servo, output shaft, extension housing. And the internal wiring harness.

ANY 90 degree V6 or V8 auxillary valve body type 700R4/4L60 will work just as the original corvette transmission worked by easily swapping out these parts (except for the output shaft which requires the whole trans to be disassembled).

And if you do anything it's a good idea to check the throttle valve spring, make sure it's not too long or too short. I think bowtie overdrives has info you can read on this.