Chevy 700R4 1991 diesel trans- electric hookup ??

Anybody out there have a Chevy or GMC factory service manual for 1991 pickups?

I'm trying to figure out what I have to do, to use a 1991 700R4 trans in my 1986 K5 diesel Blazer mini-motorhome that also has a 700R4.

My 86 already has the 700R4 (but it's blown). TV control and valve-body controled converter lock-up. I know that the 700R4 got many improvements in 1987, and many more as years followed.

I have a 1991 diesel Suburban with a 700R4 - NOT a 4L60 or 4L60E. But . . . the 1991 trans appears to be partially computer controlled - so I'm a bit confused at this point. If not too difficult, I'd like to rebuild this 1991 trans and use it in my 86. If I had a wire diagram, I'd know more about what this entails.
From what I've read, 1989 and newer 700R4s use computer-controlled converter lockup - even though they are called "non electric" transmissions. This 1991 diesel Suburban has a few added engine-controls/sensors that my 86 diesel does not have. The 1991 has a throttle-position sensor on the fuel injection pump and also have an RPM sensor on top of the engine-driven vacuum pump. The 86 has none of these things. I've got no problem swapping the parts in, IF I knew how to tie in the computer. I'm assuming the RPM sensor and the throttle-posistion sensor are there for transmission control.

My other option is to use a different trans. I also have a 1988 diesel Blazer up in my field with a 700R4 that is set up like my 86. I'm just inclined to use the 1991 trans since it's likely to have more improvements in it.

Main thing is, I need to see a schematic for 1991. I have diagrams for 82, 83, 84, 86, and 88. Nothing newer.

I MAY have a new enough diagram in my MOTOR auto tranny manual... I'll take a look later today.

Another quick and easy (but costs $25.00) is a subscription for the vehicle at ALLDATA.

The extra wiring is for pressure switches to tell the 'puter what gear the tranny is in.

Simply whittle it down to the "fourth gear pressure switch" like your old tranny has and the wire now going to your current tranny will function as it always has to control lockup.

I would THINK you could transfer the internal harness and pressure switch(es) from your old tranny to the new.

I just went down to the very old and very small Chevy dealer down the road from me. I kind of hit the jackpot. He just lost his Chevy franchise, but hasn't made it public information yet. He let me look through his many, many stacks of OEM Chevy service manuals, manual supplements, etc. Ends up I took a huge stack of books dating from 1987 to 1992 for V, P, G, and C/K trucks. Paid $30 for the whole mess. Took several trips to carry it all out. Service manuals, wiring diagram books , component rebuild books, etc.
So, it seems I've got a lot of reading to do, but the info I need must be in there somewhere.

Also, with a quick glance, I noticed that none of the 1991 GM manuals show any info on the 700R4. They only mention the 4L60 and 4L80. They show the 4L60 having the RPO code of MD8. That is the same RPO code they used previously for the 700R4, so maybe it IS a 4L60. I have no idea how to determine that, and maybe it doesn't matter anyway.

700R4 was just the old designation before they started calling 'em the 4L60.

Now, 'bout yer wiring.

Flip that '91 tranny upsidedown and pull the pan. We gotta rewire it to marry to the '86 control switches.

I'm going by memory here, so bear with me. :>)

All we're dealing with is a hot wire and a ground wire at the tranny case connector. The "juice" comes in, routes thru the solenoid, thru the control switches and then back out to be grounded by the computer on a '91 model.

That ain't a gonna work on an '86.

Replace the 3-4 pressure switch with a normally open, 45 to 60 lb self grounding switch(if ya can't find a self grounding switch, ground one terminal to a valvebody bolt).

THEN, the white wire coming in (may be yellow on your tranny) goes to the TCC solenoid, other wire from the solenoid goes to the switch and then when the switch closes, it grounds thru itself at the valve body. When the circuit is closed, the TCC solenoid locks 'er up.

Just ignore the other switches at the valve body and the other wire at the case connector. The 86's vacumn switches will handle the breaking of the TCC circuit for acceleration and the 'brake' switch is already incorporated in that circuit anyway.

The way they wired those diesels from the factory was a nightmare......just don't need all that herky-jerky contraption; just a high pressure lock-in switch.

'Spose I'm clear as mud?

Allan

im pretty sure as soon as they had those electronics put on them they changed the name to 4L60

Somebody trued to tell me one time. That a non electric 4L60 and TH700R4 valve body would swap onto a 4L60E?

Thanks for the info. It all kind of makes me wonder why GM made it so complicated in the 91 diesel.

Guess I learned a few new things. One being the GM RPO codes, by themselves, don't tell the whole story - seeing how they use the same RPO code for the 700R4 and the 4L60. And yes, I realize it was basically just a name change at first, but it's still a bit confusing.

This rig has been a bit of a "slippery slope." Got it going last year, but it lacked power with the 700R4 and high gearing (3.08s). This winter, I stuck in a turbo. This year, it ran great, with power perfect for the gearing - but . . . then the trans blew. I already knew the trans wasn't really adequate, and also being an 86 - it lacks updates.

So, now I'm trying to do this right - or at least, "righter." 7000 lbs. weight on those 10 bolt axles and 15" tires also makes me a bit nervous for long-trips. So, I'm now thinking of beefing up that 4L60 to 4L65 status, and installing the 3.73 axles from my 89 3/4 ton Suburban. The rear is a 14 bolt semi-floater with more load capacity, and the 3.73s ought to make life much easier for the trans. It also means I'll have 16" tires. I like the 3.08s for fuel mileage, but I'm afraid it might be asking for trouble with an 700R4/4L60.

I've already got all these extra parts sitting up in my field, and I guess I might as well make use of them.

Reading all this reminds me about how glad I am that I sold off my GM's and bought my 1996 Dodge Ram used back around 1997. That Ram has really been a good truck !

I've got a 92 Dodge with the 5.9 Cummins and 5 speed Gertrag and love it. Absolutely the best truck I've ever owned.

That being said, nobody but GM ever tried to make a 1/2 ton rig with their own diesel engine, so for that I give the former General Motors credit.

Also, this is basically a one-of-a-kind vehicle, so I don't have a lot of options. K5 chasis, 4WD, diesel, pop-up roof, solar power, 6000 watts AC power, etc. If I had money and time to burn, I'd stick a four-cylinder Cummins 4BDT in it.

I'll also note that I still have my 83 diesel Blazer plow-truck. I've had it for 20 years and it's never skipped a beat. My favorite plow truck, due to the short wheel basis and good fuel mileage. The guy that had it before me didn't get 20K miles out of the original 700R4 in it, and converted it to a turbo 400 with a mechanical modulator. I've got 300K miles on it and it still runs perfect. Pulled a camper for many years with it, but now it's all rotted out.

Could not get any Chevy dealers to work on my 89 C70 around here unless took it to Kansas City. A mechanic said he could fix it if he had the repair manuals. Cost me $220 for a set of C/K truck manuals and they just run from 1990 to 1992.

Maybe this will help.
Tranny