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.

Twice a year, 40 miles, round trip.

Stop telling him what you would do. SBC, 700R4, 9 inch. :rolleyes:

We're not talking toques and back bacon here. Please chime in when you can speak "transmission". ;)

Thanks for the info on the overdrive transmissions. What I said in my last post, I would never consider it an oxymoron. Occasional action at a red light and a trip down the 1340 once a year, if that ever happens, is far from abuse or beating this car. No slicks. No headers. No 4.33 gears. No motor changes. Just a little more get up and go with a transmission change would be fine with me. These cars when purchased new back in the day, I'm sure were subjected to abuse. Seen alot of them at the drags. Different story now, at least for me, Carmine.

From a core standpoint, the 2 transmissions are going to be near the same price point. GMs engineering department already made the determination over 5 decades ago which transmission was superior in a muscle car.

Any muscle car near 400 CU IN came from the factory with the T400, not the 350, (until the smog era choked engines, where GM reconsidered using a 350 in Trans Ams). The reason was warranty claims, and the 400 would survive long enough to get a muscle car past warranty. In interest of longevity, the monetary investment is going to be close to equal, why wouldn't the OP go for at least what GM deemed adequate at the time the car was new? Shortening the driveshaft a couple inches, and moving the crossmember back a like amount, would surely be worth the added torque capacity to avoid breaking parts.

I fail to understand why when talking muscle cars, and the abuse they sustain, (because that's why people own them in the first place), the attitude is to use inferior engineered parts today, because it might be a little less work, or someone might save a couple hundred or so dollars over the stronger engineered parts.

It might seem like a great idea initially, but when you're laying on your back the second time under the car, removing a broken transmission that you thought would be adequate, the false economy of the original decision somehow fades quickly. I've been there and done it, and comments I post here on PY are a lifetime learned as a mechanic, and muscle car owner of nothing but Pontiac muscle cars, and racing them, and thrashing them for decades. First muscle car owned was a 67 326 HO Firebird bought in 1969 from the dealership I worked at, and I have owned and worked on literally dozens of my own, and other customers Pontiac rides to gain my knowledge and pass on recommendations.

Street use, oval track, autocross, road course, and yes more than a few straight line acceleration contests. Been there, built them, broke them and fixed them until the breakage was at a bare minimum. Conducting the torture testing so others could profit from my testing...……………:)

My testing program was done from my own wallet and making my living twisting wrenches on my own, and other peoples mostly Pontiac musclecars. The third picture in my signature shows the backdrop of Pontiacs in the late 70s and early 80s of my service station and garage where we specialized in Pontiacs. Now if someone has done more breaking of parts, and cost them more money, and time than my own testing program has, I'll gladly yield to their opinions, fair enough? I'll return to the earlier comment I made, "You can't build too strong, but you can definitely build too weak."

If you only knew. Ha Ha! There was a parking lot between 2 buildings where Pontiacs were being built. That parking lot was known as the dragstrip.

We did the TH350 swap as it was just so darn easy., which is what we needed. We don't have a lot of resources to do much else. It certainly does everything we need it to. We were considering the 200-R4, but they are pretty hard to come by used. They haven't been made in a long time. We rarely venture far from home with the car, but if we ever do, it would be nice to have the overdrive. So it's on our wish list for now.

FWIW, the 4L80E was made from 1991-2013, tons of cores out there in GMC, chevy light duty trucks and medium duty motorhomes etc. Up to 18,000 lbs chassis. A stock 4L80e is nearly as strong as a built 200 is, more work initially, but reliability is worth something.

Question about the TH350...I did the swap to TH350 but am having trouble finding the right tube...anyone have any idea what will fit a '66? Ordered one aftermarket and tried a couple others and none fit.

If you are talking about the dipstick tube, then I can tell you that aftermarket sucks. Every one that we tried didn't fit and they leaked like a bugger. We finally found a used GM dipstick tube on eBay and problem solved.

Look for a factory dipstick and tube from an A-body (‘72 and earlier) that originally came equipped with a TH350. I found one here on the forums by posting a ‘parts wanted’ ad, from a 1970 Tempest or Le Mans to fit my ‘64 Le Mans with a TH350 swap.

I used a similar strategy when I put a TH400 in another ‘64, using a ‘69 GP TH400 dipstick and tube which is the same a an A-body in this regard.

I owned a 66 GTO since 1968. It rusted so bad that it was unsafe to drive about 20 years ago. During that time I had 12/13 motors in the car, from 326/389/455. And 350/400 SBC and 454 BBC. Transmissions ranged from 350/400 and the 4 speed muncie and a TKO600 5 speed OD. [ In my present 66 Lemans with a Ford 3:50 9". The 350 is an easy swap. It will bolt right in. Course a different flywheel is needed. The drive shaft will bolt right in. Watch out for a BOP case as chevrolet bolt pattern is different if you are buying one used. Also watch out for the ones with a lock up converter as they are not built to take the horsepower as the early ones. Also watch out because someone may try to sell you a 200 transmission as they look close to the same. The 200 has no modulator if I remember right. Rear trans mount bolts right in. The 2 speed rear mount is the same if I remember right. If you only go 40 miles out of town then the 350 is the way to go. If not I would put a 200R4 in it. I have never done that swap, but from what I read, [ I use to get every performance GM andHot Rod magazine. I still get 8/10 ] it is also a bolt in. Remember, they used it in the Grand National Turbo's. Example 3:55 rear gear 70 MPH 350/400 3200 RPM 4 speed 2900 RPM 5 speed OD TKO 600 2400 RPM and 1200 RPM at 40 MPH. I haveto hit 42 MPH before I put it in OD. Since you are stayig stock on the motor, You do not need a high horsepower transmission . I hope this info helps you.

Good info. Thank you, Carmine.

242177P: Yes, the 400 is a better trans, but 350 is a good trans. I have never broken one yet. I never put it behind a high horsepower motor tho. LOL, To put the 400 in 66, the crossmember must be moved back and different yoke and shorten the drive shaft. It was years ago like early 70's I put in a 455 and 400 trans. In order to mount the trans, we had to weld an extension on the crossmember and bolted it straight to the frame. Needless to say, even back then, finding a crossmember for a convertible was not eazy when I changed it back.

Are you aware that the top dog GN was the GNX? And are you aware that the GNX only had 276 horse and that did not come in at the hit of the throttle? Even low horse GTO's had considerably more horse than that. And are you also aware that no 200 GM tranny was ever used in any heavy duty or other performance application? Are you also aware that GM killed off the 200 in short fashion due to warranty claims? Why? Because they simply do not hold up. Unless you sink $3000.00+ dollars on one, changing almost every internal part, they are junk.

Only fools and those that have already wasted their money on one believe in them. And using the "drops right in" excuse is lame at best.

What a maroon...
 

Bwahaha! My cheekbones hurt now.
Armchair quarterback. :pound:

Okay. How about you explain? Did the GNX have more that 276 horse? NO. Did Pontiac make a GTO with less than 276 horse? Not that I am aware of unless perhaps a '73 or '74, but this thread is about '66 and '67. I will wait for your enlightenment of the day.

Explain? Not a chance. You clearly have NO clue, and that's hilarious.
(BTW, 255 horse in 67 but that isn't even the funny part :D)

So you have no clue. Thank you for your words of wisdom. I will cherish them.

If I can slip in a question to you knowledgeable fellas...swapped my 300 for a 350 but can't find a dipstick/tube to fit...any idea what will fit? Will a tube from any after 67 fit? Thanks

Since you’re not going to find anything earlier than a ‘68 TH350 dipstick tube from an A-body Pontiac I’d be looking to try one of those. For my own ‘64 Le Mans with TH350 swap I procured a dipstick and tube from a ‘70 Tempest to try, haven’t done the installation yet but pretty confident it will work.

After having done a couple of TH400 swaps into ‘64 A-body Pontiacs using ‘69 GP dipstick tubes successfully I am again pretty sure anything with a similar/identical firewall profile should be a good dipstick tube donor. The ‘69 -‘72 GP (G-body) and possibly a few years later were essentially an A-body on a lengthened frame, so you can safely assume the firewalls were nearly identical. Even found out not long ago that a ‘70 GP TH400 dipstick tube was a perfect fit in a ‘68 Firebird.

Good luck.

Yesterday we switched to a different dipstick tube for our newly installed TH350. It was a huge pain. But the old one was leaking badly where it slipped into the tranny. We ordered this TCI "Trick stick"because of it's reputation for not leaking. And it does not leak now it's a huge relief. But the installation was difficult due to just the slightest difference in bends from the original. We massaged the heck out of it and then I see that the tab used to grab a bellhousing bolt is nowhere near anything bolt-able.
So I'm going to try again but at least the leak has stopped. The next one will definitely have the seal that looks like a hat at the tranny end of the tube not the O-ring.

Sorry, late to this party...

In what alternative universe to you live in Chief?

With tires close to the OE tire height (27" - maybe a common 255/60/15 ), with a non overdrive transmission will tach a little over 2400 RPM at 55 MPH.

Even with 26" tall tires (say a 235/60/15), that car would only hit a little over 2500 RPM.

Or if it was being run with 14" wheels with the widest available 245/60/14's (25.6" tall), it would only be reading 2566 RPM at 55 MPH.

To hit 3800 RPM, the tires would have to be around 17" tall or the car.

Can I point out that the car would be traveling over 80 MPH with the 245/60/14's or 86 MPH with the 27" tires.

The amount of incorrect information you post here is legendary. I won't even go into the other wildly inaccurate info you have posted in this thread...:rolleyes:

Carry on, I need the laughs...

Laughs is what I get from reading this ^ ^ ^ because I owned these cars when they were stock.

Must not have been able to find high gear then? :pound:

Par for the course. Canadian takes the advice of a Googling parts pusher. :rolleyes:

https://www.cartalk.com/sites/default/files/Oreilly.jpg

Wallace's calculator shows at 55mph a TH400 w/3.55s turns 3735 rpm in second gear (slightly more with convertor slippage).

Driver error?? Blame the machine. :rolleyes:

Maybe now you can see it.

Uh huh. Still not high gear.

How about you show us your math instead?

200r4
 

i just had a friend put one in his 65 goat, (200r4) no mod in trans and he been running it now 3 month and he love it and he beats the hell out of it. (konwal455gto)

200r4
 

Art Carr would laugh at that statement/ https://www.cpttransmission.com/ is as nearly as strong as a built 200