'71 C20 with 402 NEED transmission advice

[jamesmadconductor]

Hi, everybody. Truck is in Phoenix, the original TH400 is absolutely spent and ready for a rebuild. I was thinking of going to a 700r4 simply for the highway gear, but have been reading a lot of suggestions to not use a 700r4 with the big block. I understand that thought for those running any speed equipment on their big blocks, or hauling stuff, etc., but my truck is for pure enjoyment. I do like to drive it up the mountains around Arizona. Since I'm not heavy-footed, would the 700r4 be a good option, or should I stick with a very well rebuilt TH400?

[bigmac73]

I say it is your truck , DO what you want.
I would look at some of premium builders like Extreme Automatics or Phoenix Transmissions in weatherford texas

to ensure your tranny is built for the big block. also consider your ring and pinion , need to make sure it is good for the overdrive ratio

[kwmech]

Don't even waste your money on a 700r. They do not hold up behind a big block, I don't care what anybody else says. They can be built up, but they don't last the duration. Go 4l80. BUT you may have to regear depending on which rear axle you have

[LockDoc]

Originally Posted by jamesmadconductor

Hi, everybody. Truck is in Phoenix, the original TH400 is absolutely spent and ready for a rebuild. I was thinking of going to a 700r4 simply for the highway gear, but have been reading a lot of suggestions to not use a 700r4 with the big block. I understand that thought for those running any speed equipment on their big blocks, or hauling stuff, etc., but my truck is for pure enjoyment. I do like to drive it up the mountains around Arizona. Since I'm not heavy-footed, would the 700r4 be a good option, or should I stick with a very well rebuilt TH400?

I say put the 700r4 in and drive it. If you don't have a lead foot and don't plan on doing any burnouts it will be fine. If you drive your truck a lot you will love it.

If you change it you are welcome to post back here in a year and tell everyone if I was wrong. I don't think you will be..... I used the BowTie Overdrives install kits for the lockup and kickdown.

http://bowtieoverdrives.com/catalog/...BCAT&CATID=WA3

The TV Made Ez kit you need depends on what carb you are using.

LockDoc

[Bigdav160]

The torque of a big block exposes so many weaknesses in a TH700/4L60

Properly built, with the correct throttle linkage geometry, they'll last for a little while.

[bigmac73]

Originally Posted by kwmech

Don't even waste your money on a 700r. They do not hold up behind a big block, I don't care what anybody else says. They can be built up, but they don't last the duration. Go 4l80. BUT you may have to regear depending on which rear axle you have

My question is why is it justlimited to a big block??

500 Ft/lbs is 500 regardless of a big block or big stroker sbc

[Sheepdip]

Originally Posted by bigmac73

My question is why is it justlimited to a big block??

500 Ft/lbs is 500 regardless of a big block or big stroker sbc

My exact thought also. For a driver that see's no drag strips or heavy towing.

[too much stuff]

I say go for the 700r. If you are not beating it and just making a cruiser, i think you will be fine.
I had a turbo 350 behind a big block in my 70 4x4 and most people said that trans wouldn't hold up... It out lasted the engine.

[some383]

You'll be fine. Just watch for transmissions with electric speedo. You'll want to get the TV cable adjusted properly as well. They put the 2004r transmissions behind Buick Grand Nationals so that might be another option. I went with a gear vender overdrive in my Big Block truck but they are pricy. However, you get absolutly everything to install it. In my daily driver truck I went with th350 and 3.08 gears and it seems great. So you might be better off going with a 3 speed and just changing the rear end gear. LOTS of options. Best of Luck.

[Wrenchbender Ret]

I had a 700R4 in a 63 pickup with a 454 big block. It held up fine. I had it for about 2 years & sold it. I got on it hard one time to get out in traffic & in a few seconds I looked down at the speedo & was doing 95 mph. Scared me.
George

[tim_mc]

I love my 700R4 with hydraulic converter lock-up. If you research them, you'll find that later years (87 or 88 & up) have a larger 30-spline input shaft - those are the ones you want if you're looking for a core to rebuild. It will be fine, especially when built with better internals than stock.

[davepl]

I put a 4L80E in mine and the mechanical speedo tailhousing, and couldn't be happier. I used a stock converter though which is almost too tight, but drives like stock.

It's not a cheap setup... the stupid tailhousing is $700 on its own. But it's basically a TH400 with overdrive, which is what we should have