Transmission recommendation - 68 GTO
 

I'm in the early stages of working on my 68 GTO (automatic) and I'm curious as to what transmission some of you guys are running. I currently have Paul (gtofreek) building my motor. He's using a standard bore 455. I'm not sure yet what kind of HP or torque it's going to have. The car currently has a 700R4 transmission, Global West suspension, 12 bolt 3.55 gears. I just ordered and received my wheels and tires. (Year One Rally ii's) Front: 17x8 - 245/45/17. Rear: 17x9 - 275/40/17.

I'm pretty new to cars and just want to hear opinions on the automatic transmissions you guys are using. I've read some good and bad about the 700R4. My car will mainly be driven on local roads but occasionally on the highway for some road trips.

Any thoughts or suggestions would be appreciated!

In my opinion if you want an automatic for crusing the 700r4 can't be beat except by maybe the 4L80E. If you want to row, a 6 speed conversion is made for that car. Personally I'd keep the 700r4
Ponchjoe

Run the 700...till you break it.

4L80 requires a shortened driveshaft, all else can be managed (i think).

If I'm not mistaken, Joe wants to do this once and done. The 455 .030 build Paul is doing for him has unported (for now) KRE d ports and I believe less than 10.5 comp; and a Hurricane intake (unk carb) It will have a yet to be determined HR cam. With this in mind, he needs a trans that will survive the combo.

I still say considering the cam, a TH400 with a 308 gear would be fine with what you're trying to do, and allow for somewhat friendly highway driving.

IMO the 700 is too much of a risk, it's not if it will fail, it's when.

Thing with an OD trans, with the dual gate shifter, OD moves to where N is, and N will be between N & P. Not optimal, and is a pain/confusing. This is why I changed directions on the 442, and am going to a 455 with 308 gears in it.

For the amount of money it costs to get a built 700 or 200 that will handle the power even somewhat reliably, you will be so close to the cost of a 4L80E, it would make no sense to do the 700/200.

I'm getting ready to sell my CompuShift trans controller and TPS setup, if you want to go 4L80E. Also have a Cable-X box so you can use the factory speedo.

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A rear gear change adds to the cost of a 1500+ th400, just something to consider but may not be a deal breaker...

Yeah, but it's not that much considering. He can drive it with the 355s for now, see what it's like, and if he wants more highway, he can do a gear change. Or that's what I was thinking.

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Btw, His tire height is 25.7"

Thanks for your continued help. This is certainly overwhelming for someone that is clueless about cars. I'm learning a lot but I never would have imagined every decision is so important and can effect future decisions. As I said from the beginning, I would rather do it once rather than regret "going cheap" with something. I don't want to build a show car but I do want a well put together, bullet proof car.

4L80E
 

I've always liked the ratio spread and the durability of the 4L80E.
Considering how strong the 455 can pull with 3.08s and the right converter, having a .75 OD allows you to go with 3.42, 3.55, or even 3.73 with less converter and still knock the final drive down below the 3.08 range with full lockup in OD. A little pricier on the front end, but well worth it if it's in the budget.

I'll echo the general consensus here- if you have the budget then the 4l80e would be the way to go. A more budget friendly option is the th400 with 3.08 gears. Be sure to get a good converter as that will realty bre key to maximizing performance with that combo.

My formula with 3.23s, th400, and a Coen converter is a blast to drive though I do wish the gears were a littler taller when I driver for any distance on the freeway

From what I've leaned here, a 4L80e is the way to go as it's based on the tough old TH400. The 700R4 is based on the TH350 which was designed by GM as a medium duty trans for lighter cars/lower power cars. Hence the 4L80e is a better choice since its based on a heavy duty design to begin with. (Used with big blocks, trucks, RV's, etc.) Hope this helps.

T5 5 speed transmission. You won't have to open up the transmission tunnel. All the parts are easily available. Will have to put clutch pedal in but that only takes an hour. You will have to shorten the drive shaft and change it for a Chevy or a Ford. I've had no problems with mine and I'm putting out close to 400 horsepower. Im not very easy on it and I am constantly doggin it. If it ever does grenade, you can buy another one for around 3 to $500 and it will take an hour to swap out. They have made them now for 25 years so there's a lot of them out there.
See my post in this forum and it will show you exactly how to do it

For us old timers, and anyone who is not familiar with the electronics/computer system required to use a 4L80E trans, will somebody please explain, in detail, exactly what is involved in the COMPLETE install, set-up & maintenance of this trans. I realize that this info can probably be Googled. But, it might help some, who may be considering this trans, to make their decision.

Personally, I'd just keep it simple, and go with the tried & proven, PROPERLY BUILT TH400, with the correct rear gear & converter, to meet the owners desires. Strong, reliable, simple, and well proven. No computer, TV cable, or kickdown cable required. Just a good gate or ratchet shifter is all that's needed, for street/strip use.

I have a 700R4 in my tempest. 389 Tri-power 282/292 camshaft. The transmission was built by Gearstar out of Akron Ohio. They put all of the heavy duty guts in it. At the strip I have more torque than traction in 1st. So I must baby the gas to launch. Great street manners, and I am turning 2000 RPM at 70 MPH. I did put a manual switch in it to keep the torque converter lock-up from hunting back and forth when climbing hills.

X3. A 4L80E with your current 3,55's, or a TH400 with 3.08's or even 2.93's. I run a 2.56 posi behind my very mild 406 with a TH400 and 1900RPM stall converter in a '67 GTO ragtop, and the car moves out just fine (for me). It'll burn rubber if I want, and RPM's are 2450 at 80 MPH. Fuel mileage is killer, too.

The T5 was designed for a maximum torque load of 300 ft/lbs. It won't live long behind a STOCK 455, let alone one with any modifications. Horsepower doesn't kill transmissions as quickly torque DOES... IMO, a 4L80E is the no-brainer if you want a dependable transmission with O/D. My second choice would be the old, reliable TH400 with a 3.08 rear gear if you're running a 455, a 3.23 with a 428/400.

I've not done a 4L80 retrofit, but have done other computerized OD trannys. They are all similar, as far as what you have to do.

First thing, when using a carb, is that you will need a TPS - throttle position sensor. There are a variety to choose from, mine mounted on the passenger side of the carb, and a tab bolted to the end of the throttle shaft operated the sensor. This sensor tells the TCU (the computer for the transmission) whether you are at idle, full-throttle, or where in-between. Instead of a kick-down cable, or a TV-cable, it uses the TPS.

Then you have the computer. You'll need to wire it to a switched power source. It will have outputs for your neutral safety switch and your back-up lights, and it will have an output for a digital speedometer. Depending upon what transmission you get, who you get it from, etc. it may or may not be compatible with a cable-driven speedometer.

What I LOVE about these transmissions is the tenability. You can program it drive like a Cadillac around town, but like a full-race tranny at WOT - or however you like it. Want to drop the 1-2 shiftpoint by 200rpm, but raise the 2-3 by 500rpm??? Simply and quick, just go to the controller (or plug in your laptop, depending upon the system), change a few points on a graph (or data points in a table), hit "enter" and it is done. Line pressure can be altered at different TPS/RPM, upshifts and downshifts can be tweaked, converter lock-up characteristics tuned...

I love computer controlled transmissions. WAY easier to tune than having to mess around with governor weights/springs and such.

Awhile back when I was going deep into my Firebird I was pondering what OD transmission to use. I had a issue with going from a strong Th400 to something that had to be built up just to get in the ballpark of the Th400's strength. Yes, I could get much better gas mileage with an OD but the gas savings would never pay for the transmission. I decided to put 3.08 gears in it and have never looked back. Another way I look at it is I would never pull my Pontiac 400 for a 350 Chevy, the engine is a classic ...a Th400 is a classic also.

I would get a good converter. In my case I have a Switch Pitch converter but I realize they are not easily found.