Older 700R4 vs newer 700R4

[mckpaul]

Got into my tranny over the weekend, pulled the valve body and cleaned it up, thought I might find a stuck valve, and replaced some of the springs. My truck isn't a daily driver, kind of a project for now. Been hearing a slight knocking from the engine on occasion. The '84 doesn't have an ECM, the only thing it has is the knock sensor system (EST?) and it's all been disconnected. In the back of my mind was hoping the knocking was related to that. Well, went out for a test drive after the transmission work. The transmission still had the same upshift problem AND got about a mile from the house and the engine died at a stop sign with a slight squeeking noise. Wouldn't turn over after that, strong battery, good heavy "click" sound when turning the key. It did finally turn over one more time and started for about 10 seconds and stopped again with the same squeeking sound, hasn't turned over sense. Have a feeling the engine's locked up now in addition to having a transmission that needs help.

Enough whining... so about my question. I know I can get another 305 or even rebuild mine if I want to, but as for the 700R4, it's the original one that came with the truck with the small input shaft. Looks like it's had several hands in it before, stripped pan bolt, one of the valve body bolts was stripped too, has a piece of stainless wire in the bolt hole. I was installing a shift kit that I bought that suggested enlarging some of the holes on the valve body spacer plate, some were already sloppily drilled out. Was thinking about going to a newer 700R4 when I pull the engine. But looking in the transmission book (700R4 rebuild book from a transmission parts house), there were about a dozen different wiring/switch setups for various valve bodies. If I get a newer 700R4 with the larger input shaft, even though the my wiring harness will probably plug in, wouldn't the newer transmission be wired internally set up for a newer truck with ECM? My harness has three wires on a 4-pin plug, in the book they all seemed to have that, but the switches on the valve body were different for the newer model diagrams. If I put a newer 700R4, will I have to modify my wiring, or possibly pull the pan on the newer 700R4 and change the switches and wiring on the valve body to match my truck? I want my lock up to work in a normal way. Was wondering if anyone had put a newer tranny in an older year model truck before.

I'm hoping to run across a running 305/700R4 combo maybe in a wrecked vehicle and get both together.

[1FaastC10]

dont mess with rebuilding a 305, there's way more power potential with the larger bore of a 350, and parts will be cheaper for it to boot. cant go wrong there. as for the 700R4, you shouldnt have a problem, as long as it is a pre93 unit. the post 93s were fully ecm controlled.

[Captkaos]

If you are buying a used 700R4, avoid pre-87 like the plague.

[pkbinplano]

Whats up with a pre 87 700r4 ? Thanks

[swervin ervin]

Somewhere around mid 87 they started using an auxilary valve body, which would help cushion engagement into drive. A ton of improvements had been made by this time. The early 700's were more or less junk. I highly recommend using a 88 up 700R4, or as they called them by this time, 4L60's. By this time, GM had figured out what was wrong with them and fixed most everything to where they would last.

[mckpaul]

Yep, I knew miine was one of the original ones, and read about all the problems the older ones had. I want to go with a newer one because they did seem to get the bugs out, and the newer ones have a larger input shaft. I just hope it will work right when connected to my wiring harness. Maybe if I stick with one older than '93 like Jeremy mentioned I'll be OK.

[TooMany2count]

Originally posted by Captkaos
If you are buying a used 700R4, avoid pre-87 like the plague.

swervin ervin----The early 700's were more or less junk.

MMMMM lets see, I have a 84 burb w/a 700r4 in it w/about 200,000 miles on it & it has NEVER BEEN TOUCHED, other than changing the fuild & filter, & w/at least 125,000 miles of it, it had a fully loaded 6,000 lbs trailor behind it. I just dont understand WHY everyone says they're JUNK, unless I'm just one of the lucky ones, and just so you all know
"I dont use my truck, I ABUSE IT"
always have & always will....joe

[swervin ervin]

You are just one of the lucky ones. I tell you what, put some torque in front of it and see how long it lasts.

[gchemist]

I agree. BAD BOW is on its third 700R4 since I've bought. This last one though is holding up because it was rebuilt with performance in mind. Can't wait to see how it will hold up to the 350.

[gchemist]

I agree. Lucky, very lucky. BAD BOW is on its third 700R4 since I've bought. This last one though is holding up because it was rebuilt with performance in mind. Can't wait to see how it will hold up to the 350.

[apstguy]

My truck still has the original TH700R4. It DOES need to rebuilt though. It still works like a champ!