The Stovebolt Site Forums The Shop Area Engine Shop Quick Tranny Question!

Hey all, my Dad has a 1973 1/2ton Chevy pickup with a 350 3spd auto transmission. The truck really needs a 4th gear, I was wondering what tranny I would use thats a 4 speed automatic. Thanks -

Shane

Shane,

For questions about more "modern" trucks, you'll probably want to post here: http://www.67-72chevytrucks.com

The short answer, though, is to swap your th350 for a 700r4.

Nothing will help unless you add an overdrive trans or change the rear end ratio. All manual and automatics have a 1:1 (direct) ratio for top gear, unless they have an overdrive.

Fab,

If I'm not mistaken, the 700r4 is a more modern GM transmission that has a .70:1 overdrive and shares a bolt pattern with the th350 which he almost certainly has now.

Brian

200R4 will also work. It is 4spd, overdrive and the same length as the 350TH. The 700R4 would require a new drive shaft. It was used in Chevy's '84-'90 in various Monte carlos, Malibu and Impalas. Olds used them the same years in 88, 98, and Cutlass, but you have to find one that has the universal Chevy and BOP bellhousing bolt pattern. I'm told the '84-'85 had issues, but were much improved by '89-'90.

Hey Brian, thanks for the help but I just wanted to double check on what you said about going to that website. Did you say that because they may be able to better help me, or that you dont think I should post here about more modern trucks? I have posted here about my 1979 chevy as well a couple of times. Im not trying to argue or anything, so please dont take it the wrong way.

Also, I think I asked the question a little wrong, this is my question: What tranny would I look for to swap with my current th350, that is compatible?

If anyone else has any input about the tranny question...well please input! Thanks -

Shane

Shane - he's just sayin you'll find more folks over there that are up on the later automatics and slightly newer trucks, and would better know what the easy swaps are - tho there seems to be a few here w/ an opinion too!

Bill

Thats what I was thinking, and then I thought, I hope hes not saying that I shoulds only post about stovebolts. Anywho, thanks for your help people.

- Shane

700r4

Are you positive that the 700r4 will bolt up to the current engine & driveshaft without problem, as well as fit correctly into place without any fabricating? The engine is a 305, out of a 77 nova if that matters. And the truck is a stock 1973 1/2 ton chevy. Thanks again, I will look into the 700r4.

- Shane

Mine is in a 55 2nd series,with a 350 CU.from a mid 70s truck.It bolted right up to the 350,and I had no clearance problems.I had to modify the trans.mount and have the driveshaft shortened. The overdrive output from the 700R4 tranny is around .78 to 1 compared to 1 to 1 with your 350 turbo.You should have more clearance in the 70s truck than I did in the 55.hope this helps.

the 700r4 is the way to go. best to look for 86 and newer. easy getting it in the truck but i hear that the problem area here is getting it wired and adjusted to get the overdrive to work right. my 69 and i drive 60miles round trip to work and with gas being what it is its a swap i'm getting ready to make too. so far i dont have the details on the wiring and adjustments.

I have done 2 of them. A 63 & 70. The main thing is to get the thottle cable right. It controls everything except the lockup converter. You can run without the lockup but its almost like a 5th gear. There are kits for the lockup. K.C. steet rods has the one I like best. This makes a great conversion.

I've been told that the cable adjustment is critical. If it's wrong you'l destroy the trans real quick.A friend just swaped the Chevy V6 and 700R4 into an English MGB and had it trailered to the trans shop for that adjustment.He was told not to even start it up.
John

Got to have that torque converter able to lock up in a 700R4. I have seen them burn trucks down when not operating right. The torque converters generate a lot more heat in a 700R4 than the 350, 400, even the 2004R. They are also longer than a short tail 350 so a drive shaft has to be made to fit. A 2004R built right will hold up well under a 350 and is so close to the same lenght as a TH350 it will bolt right in. Simple to wire up for the lockup torque converter, and more forgiving on the detent cable adjustment.

so with my truck being mostly on the hiway and lightly loaded on occasion (200lbs or so in the bed) the 2004r would work as well and is easier on the install?