New 700R4 transmission in my truck

[nedfunnell]

Hi,
I have a truck with a Turbo 350 transmission in it. The truck is an 82 GMC 1500 with a 6.2 diesel. It had a 700R4 in it from the factory, but it failed and was replaced with a Turbo 350. When this was done, a new driveshaft was made for the truck and some control modifications were made to get it to work right- something about a vacuum control valve. What will I have to do to put a 700R4 back in? I bought a 92 van with a 700R4 transmission in it, and I'm planning on putting it in. I'm not sure if its drive shaft might be the right length. I am not sure if the turbo 350 is a longtail or shorttail. How can I tell? Does anyone know what problems I might be able to expect putting a 92 700R4 into a truck which originally had an 82 one? Will there be a spline difference?

Your expertise is appreciated.

[MrEdd]

I'm 99% sure the mount location is different between the two. The difference is only a couple inches though if i remember right, so depending on what crossmember is in there you might just be able to drill it.

[nedfunnell]

Hmm, okay. That might not be a big deal- I've got a donor vehicle, so I can take whatever mounts I need from that and weld it right up. I don't think that's a showstopper. I am worried about control, however.

Can anyone tell me what the usual throttle position/shift point setup is for a stock 6.2L with a 700R4? I took some pictures of the transmission that's going in, here is one that shows the wires:
http://www.maj.com/cgi-bin/gallery.cgi?i=996112
http://www.maj.com/cgi-bin/gallery.cgi?i=996114
http://www.maj.com/cgi-bin/gallery.cgi?i=996120

Any ideas based on that? I don't have any pictures of the one currently installed in the truck, though.

[john8662]

Wires...

Perhaps the square plug that normally connects to the Transmission in the truck is still on your truck.

According to your images, you have two harnesses.

You only need the one that plugs in above the valvebody. The connector near the tailhousing is the Speed Sensor, which you won't be using in your truck, as your truck's speedometer is cable drive.

You will need the correct housing and gear to replace the speed sensor.

You can obtain that item at Bowtie Overdrives www.700R4.com

The other connector that you will be keeping is simply for Torque Converter lockup. I'm not sure how many wires you'll need tho, as some versions of the 700R4 having different wiring internally.

But the most important thing of all hasn't been mentioned so far.

The TV cable!

Is the bracket for the TV cable still on the engine in the truck? Hope so, but if not, no big deal, the one on the 6.2 in the van is the same.

I don't think you'll have any problems with the cross member.

The 700R4 and TH350 also have very similar lenghts, so I'm unsure why they had to alter the driveline, unless a short tail was used.

I don't know the difference though, just that they exist (before my time in tranny dealings).

J

[More Power]

I bought a used 6.2L diesel GMC in the mod 80's that also had its original 700R4 replaced with a TH350. To get it in, they used an adapter to mate the NP-208 transfer case to the TH350. The adapter made the lengths between the two transmissions equal to one another. No change in driveline lengths were necessary.

I eventually re-installed a TH700R4 in this truck, which was the best mod I could have made. The 700 was modified to eliminate the electric operation. Shift scheduling and TC lockup were based solely on engine rpm and TV cable. Worked great!

Jim

[JohnC]

If your donor vehicle is not a Diesel, you also have governor and torque converter differences to deal with...

[nedfunnell]

Yes, let my clarify- the donor vehicle had a gas 350 V8. I have the torque converter from that vehicle, but I could also use the one that I have in the truck now with the 350. Not sure if that will help, since the one in there may be a gasser torque converter as well- probably is.

Why do I need to replace the speed sensor? There is a cable coming out of the other side of the transmission which can be seen hanging over in the pictures. Is that the speedo cable? If not, what is it? Please excuse my ignorance, I'm learning yet.

Thanks for all your help!