Transmission swap
 

Hi everyone. My interest in some Pontiac years/models seems to be all over the charts for some reason. A little unsettled. Not sure why, but now I find myself looking at '66 GTO's. Many out there and prices seem to vary according to condition. I found a few of interest but was slightly turned off because they had automatic transmissions. Then I thought more about it. Getting older now and do I really want to shift a 4 speed?? I have other cars with 4 speeds already, so it's not like I would be missing anything. And I noticed that automatic equipped cars usually were priced cheaper. For no particular reason, I'm not a big proponent of any 2 speed automatic equipped car. I was wondering if it was possible and how difficult, to take out the 2 speed automatic transmission and replace it with lets say a TH350 or TH400. It would be a must to keep the original console and use the original shifter. I don't think I would have any interest in an overdrive transmission if I had to modify the transmission tunnel. Any thoughts would be appreciated, Carmine.

The 350 trans is a direct bolt in meaning - crossmember / mount/ you / driveshaft/ is the same, you can re-use the 2 speed linkage & shifter but the inside shifter detent must be bent back a tad to get 1st. gear. 400 trans will require a different yoke & shorter shaft & crossmember has to be moved & frame drilled.

OK. Good to know. Thank you, Carmine.

My friend just put in a 200r4 in his 66. Loves it. Said it is the best think he has done. Used the same driveshaft..Shiftworks kit for modifying the shifter.

Step by step 4L80E, no floor modifications required in 68 GTO. Same swap done in a 67 chevelle in the super chevy link I posted, also no floor modifications. The transmissions that require floor mods are the manual 5-6 speeds ODs, not the 4L80E.

http://forums.maxperformanceinc.com/...d.php?t=823023

T400 durability, with OD, infinitely adjustability with electronic controls, or manual control if you want to shift the automatic manually.

Great guys. Good info. Nice to know. Thank you, Carmine.

Some good info. Thank you guys for responding, Carmine.

Best/easiest swap is the T350. Bolts in uses came t/converter, & same drive shaft etc. You need to fabricate a bracket for the throttle cable that the 350 uses.

Somebody probably makes a kit for this. Shift works makes a kit for the 2 speed to 3 speed console parts & shift cable etc.

This would be a huge and expensive mistake.

This ^ ^ ^ would be the best choice. The middle of the road choice would be a 700R4/4L60/4L60e. Basically a TH350 with an O.D.

Also have a friend that put in a 200r4 about ten years ago in his 69 convert.. Has put on about 20000 miles since and no problems

So spending $3-4000 to get a 200 with all billet parts is cheaper than taking a 4l80E that in stock form (add Trans Go shift improver kit) will easily withstand 5-600 HP, modified they can go to 1500 HP.

My stock 4L80E with 270,000 miles on it in a 93 turbo diesel 4x4 dually behind a turbo diesel will withstand all the abuse you can throw at it.

For about 2 grand you could have a 4L80E done and running in the car that will last as long as the car is running, you can run slicks if you want to, and never worry about it coming apart.

Myself I like all the safety margin I can get for the least amount of money expended. I also like to start with a platform that was engineered for abuse from the beginning, 440 lb ft of torque in stock form.

Notice 2007 post, where Jake is recommending a 4L80E over a 200 because the 200, even with billet parts is getting sketchy at between 550-660 HP.

Depends on what you want to spend, and how much HP/TQ you want it to withstand reliably. Are you ever going to run slicks at a dragstrip with the car? The car owner/OP is in control of the decision.

Frankly, I think 2 grand is about $500.00-700.00 too high unless you are factoring in everything including adaptor plate, crossmember, cutting the driveshaft, etc. But then again, I guess it all depends on location, connections, etc.

Unlike the 200-4R and 700R4, the TH350 cable is just a kickdown cable. If you don't mind manually downshifting, there's no real downside to not connecting it. So the TH350 (with the multipattern bellhousing) is easy peasy. With a mild gear out back you won't need OD, so there's a reason to consider A/C equipped cars?

Buying the aftermarket ECM and harness, shortening the driveshaft, or buying new. I can modify or build my own crossmember so some here can't, and making the speedometer work by electronic, or mechanical means would be included.

I can shorten or build my own shaft, but some here can't and have to pay to have it done. Even if you have a transmission shop go through the used transmission before installing it, you should be around 2 grand, give or take. But you should be good to go for a lifetime of mixed street strip driving with a very respectable engine in the car, without buying a host of billet and hardened hard parts to keep the unit from destructing prematurely.

Ultimately the power of the engine, and the traction out back, and how hard you intend to flog it will figure into the decision. With a mostly stock 400 engine you can obviously get away with less strength in the transmission, but if you ever intend to upgrade the engine, it never hurts to have room to grow without revisiting another transmission upgrade, on top of the engine upgrade. You can't build too strong, but you can definitely build too weak.

Getting back to basics, I'll add this: simply removing the original 2 speed auto with its anemic 1:76 first gear and replacing it with a cheap TH350 which is a direct bolt in will give you about a 2:50 first gear. The car will feel and drive like it picked up another 100 HP and get better fuel mileage to boot. You could do as the others say and upgrade to a later overdrive transmission and get even better performance. But your idea of getting a 2 speed '66 on the cheap and bolting in a better trans is a solid one. Easily done, cheap, and you'll end up with a great driving car.

I am familiar with the overdrive transmissions, and I appreciate everyone's experience and input, but I really don't have a desire for one. The car I am looking at presently, has the 2 speed automatic. As I mentioned in my initial thread, I'm not a big proponent of it. My objective would be to have a little bit better get up and go. Whatever I do buy, will never see slicks. Maybe a little red light action, occasional nostalgic drags, but that's it. I would never abuse or beat this car. I go on an interstate highway maybe twice a year, 40 miles round trip, so highway driving shouldn't be an issue. My normal driving is primary roads at about 45-50 mph. I think the ideal gear ratio, for what I want it for, would be 3.55's. No interest in any numerically higher numbers. My '71 GTO with the TH400 has 3.55's and it works well for me. I guess I'm leaning towards the TH350 because it's a direct bolt in, I can use many of the original parts, and I don't have to alter the transmission tunnel. I would never consider butchering that area. It's certainly good to know all the things that the members are sharing, so I guess I better get a car lol, Carmine.

FWIW, in 1967 GM did the swap for GTO owners and put the 440 ft.lb. rated T400 in these cars. A bone stock one can be broken with a healthy running 400 with street tires, from my own torture testing back in the day. Since you can break a stock T400 with street tires and a warmed over 400, I myself wouldn't recommend a T350 which is even less torque capacity than a stock T400, but the OP can decide for himself.

A short tail T 400 only needs a shortened driveshaft, and move the crossmember back (very easy to do, done at least a dozen of these swaps over the years). Everything else hooks to the T300 lines, shift linkage with minor tweaks to the shift cable bracket which have to be done with a T400 or a T350.

That right there is a text book example of an oxymoron.

Here is some food for thought as well as looking at this from an economical angle. That car with any non-OD tranny will tach at around 3800 RPM at 55 mph. With an OD, that same car, same engine and same rear gear will tach at about 2200-2400 RPM at 55 mph.

Now, without even talking about fuel economy, an engine that is running at a much lower RPM will last a hell of a lot longer because it is experiencing a lot less wear & tear.

There are also no tunnel mods necessary for a 700R4/4L60/4L60e.

The folks that designed the Powerglide back in 1950 would simply not believe the point to which it has evolved. I love the TH400, but even I have to admit the TH350 is quite capable.