[scott70]

I've been thinking about swapping in the tkx from the original m21 I have in my 70 gto. The 2.87 first gear and the overdrive sound real appealing. I'd keep all the factory clutch linkage and bellhousing. Firsr off all I'd like to know if one of the vendors has a shifter handle that looks the same as the original Hurst competition plus shifter(roundish) and of course comes up through the floor in the stock location. Second is I have 3.31 gears with a 255/60-15 rear tire which is around 26.5 " tall. My car runs around 2800 rpms at around 65-70 mph. The .81 OD drops it around 500 rpms which to me sounds ok. The .68 looks like it would drop it additional 200 rpms more. I think I'd be more inclined to go with the .81 OD but not positive. Motor is the original 455 with a ra4 sized cam. Thanks for any opinions.

One part I'm pretty sure wouldn't work anymore would be how now you put it in reverse and turn the ignition key off and it locks the shifter so you can pull it out of gear unless you have the key on. The original anti theft device...lol.

[Formulajones]

Yes, they do make round bar handles that look stock. In fact, if you have a Comp Plus round bar handle already, you can simply unbolt that and bolt it directly to a TKX shifter. They use the same sticks and interchange.

It's the shifter itself you'll want to buy with the correct offsets to work properly with your car to come up in the floor in the correct location. They make various offsets depending on which brand you go with.


Yes the back drive linkage will no longer be functional with a TKX. What I do is keep that in the locked position so the steering column won't move and you can remove your key. For the back up lights you'll just jump a couple wires off the switch on the column and run them down to the switch on the side of the transmission. Tremec sells a small weather sealed plug for that connector on the side of the trans to make it simple, or you can make your own.

On the gear stuff, I've posted about that many times and have been pretty set on the .68 overdrive deal. Especially now that Tremec has decided to raise it to .68 instead of the previous .64 In my opinion that was a mistake as I now don't like running as much rear gear as I once did with it. The whole idea with an overdrive is to get the highway cruise rpm down, not up. I mean you'll be investing $4000+ so lets take advantage of what it has to offer. I don't even look at the .80 overdrive deal and have never sold/installed one for anybody either. Quite simply if that's all the overdrive you want, you're pretty close at this point of just making a small rear gear change or maybe tire height adjustment to get the same result at far much less cost $$$ But you hurt the other end of the spectrum. 5 speeds cure both ends, but take advantage of what it has to offer.

What you really gain with the swap is the 2.87 first gear, and the overdrive to boot. Drivability on both ends is improved.

If you're worried about the 3.31's and a .68 overdrive, I wouldn't be.

I run the same 255/60-15's on the back of our camaro and use a TKO .64 overdrive in that one. I'm just running 3.55's out back, and even with the little 302 it's perfectly fine cruising as low as 35 mph in 5th. A big 455 Pontiac will have no issue at all pulling your car around with the 3.31's , especially since the new TKX is now .68 overdrive. In fact with that small overdrive change it comes out almost exactly the same as our Camaro. So in your case, in overdrive it's essentially like cruising in 5th with 3.55's now that they have raised the 5th gear ratio. Not anything I would be concerned with in your case.

[jhein]

I have the TKX with 2.87 1st/.81 OD. 467 cid, 3.31 rear, 27 inch tire.

I totally respect FJs comments and I'm sure you would not go wrong with his advice. But, I think it depends on how you drive the car. If you do a fair amount of driving, cruising at 75 or more, then the .68 OD is probably a good idea. If you rarely cruise that fast for prolonged periods then the .81 would be as good or dare I say a little better. The roads I drive on are 55 mph roads. At 65 mph I'm at like 2100 RPM and I can do that all day long. 75 mph is around 2500 and is still very comfortable. I think if I had the .68 OD I would use it less, but maybe I'm wrong. But, I'm very happy with my overall gearing.

You could also do the 3.27 1st/.72 OD. But even with the 2.87 1st, traction is an issue so I'm not sure how the 3.27 would do.

[65madgoat]

Do it and don't look back. No point having a weak 4 speed with no OD anymore these days.

Makes the car so much more fun.

Plus with the new TKX you don't have to cut your floor. So every reason to do this swap today.

[ZeGermanHam]

Originally Posted by 65madgoat

Do it and don't look back. No point having a weak 4 speed with no OD anymore these days.

Makes the car so much more fun.

Plus with the new TKX you don't have to cut your floor. So every reason to do this swap today.

This is my view as well. Unless you're concerned with utmost originality, put the Muncie underneath the work bench and bolt in a TKX.

[grivera]

I have the TKO with 2.87 first/.64 OD, with 3.89 rear and 255 60 15 tires. First gear is a bit much and someday I plan a change maybe to a 3.50 rear. The .64 OD is perfect with the current rear gear though cruising 70 mph at about 2200 rpm

I assume you've seen this new TKX in the sales section? It has the it is the 2.87/.81 combo: http://forums.maxperformanceinc.com/...d.php?t=866159

[Scarebird]

One bad thing about numerically lower OD's with deep rear gears is your driveshaft spins that much quicker - not good if too close to critical speed.

Better to do this in the trans, a 2.87 1st with 0.81 OD would work quite well with your 3.31's.

[jhein]

Another way to look at this is to compare what your equivalent ratios would be between the M21 and the TKX. With your M21's 2.2 1st, the 2.87 TKX would be like having a 4.32 rear with the M21 (or like a M20 with a 3.77 rear). The TKX in OD (.81) would be like a M21 with a 2.68 rear. 2.68 is a pretty respectable highway gear. But again, if you're cruising for long periods at > 75 mph then maybe the .68 which would be like a 2.25 rear in the M21.

[Dragncar]

How much power are these TKX transmissions good to ?

[jhein]

Originally Posted by Dragncar

How much power are these TKX transmissions good to ?

600 ft lbs stock. They can be modded for more.

[tom s]

I have 3.31s with the .68 OD in y 69 bird with a mild 455.Tom

[Formulajones]

To Scarebirds comment, when doing this swap, do yourself a big favor and just have a nice beefy custom driveshaft built so you don't have to worry about critical speed and such. Also with a trans capable of the abuse these things will take, you really should have a driveshaft capable of the same abuse anyway.

In every swap I do I have the driveline shop up the street build me a custom driveshaft that's good for anywhere between 600hp and 1000hp, usually with 1350 joints.

[scott70]

Originally Posted by jhein

I have the TKX with 2.87 1st/.81 OD. 467 cid, 3.31 rear, 27 inch tire.

I totally respect FJs comments and I'm sure you would not go wrong with his advice. But, I think it depends on how you drive the car. If you do a fair amount of driving, cruising at 75 or more, then the .68 OD is probably a good idea. If you rarely cruise that fast for prolonged periods then the .81 would be as good or dare I say a little better. The roads I drive on are 55 mph roads. At 65 mph I'm at like 2100 RPM and I can do that all day long. 75 mph is around 2500 and is still very comfortable. I think if I had the .68 OD I would use it less, but maybe I'm wrong. But, I'm very happy with my overall gearing.

You could also do the 3.27 1st/.72 OD. But even with the 2.87 1st, traction is an issue so I'm not sure how the 3.27 would do.

Most of my highway driving has a speed limit of 60 which means I drive at around 65 mostly. Only occasionally do I go on I95 which is a limit of 70. Before my post I went on the wallace site and plugged in a bunch of different senarios but I wanted to hear what real world experiences were from you guys. Didnt want the car running like a high idle at 60-65 mph,,,I dont mind some rpm ,,,2800 cruising is just a bit much for me. Also the 2.87 VS 2.20 with my 3.31 gears sounded like a nice change for taking off whether its a hard or easy take off. With the iron exhaust manifolds it dynoed 480ish hp and 560 trq. Headers it was a little over 490 hp and 570 trq. I do play at the 1/8th mile now and then on bfg t/a street tires and the 2,20 1st gear sucks.

Yes I would definitely have a custom driveshaft done and not cut up my original. Also my original shifter was mentioned. On mine the chrome handle isnt a simple bolt on. and the rear gear ratio and back tire size are not going to change.

[scott70]

Originally Posted by tom s

I have 3.31s with the .68 OD in y 69 bird with a mild 455.Tom

How do you like the .68? If you changed it which way would you go? Im assuming you dont run a short tire?

[Formulajones]

Originally Posted by scott70

Most of my highway driving has a speed limit of 60 which means I drive at around 65 mostly. Only occasionally do I go on I95 which is a limit of 70. Before my post I went on the wallace site and plugged in a bunch of different senarios but I wanted to hear what real world experiences were from you guys. Didnt want the car running like a high idle at 60-65 mph,,,I dont mind some rpm ,,,2800 cruising is just a bit much for me. Also the 2.87 VS 2.20 with my 3.31 gears sounded like a nice change for taking off whether its a hard or easy take off. With the iron exhaust manifolds it dynoed 480ish hp and 560 trq. Headers it was a little over 490 hp and 570 trq. I do play at the 1/8th mile now and then on bfg t/a street tires and the 2,20 1st gear sucks.

Yes I would definitely have a custom driveshaft done and not cut up my original. Also my original shifter was mentioned. On mine the chrome handle isnt a simple bolt on. and the rear gear ratio and back tire size are not going to change.

We do a lot of driving with ours on 65 mph roads, which is only 1800 rpm (.64 overdrive, 3.55's, and 27" tire) and the 302 is fine with it. 70 mph is roughly 2000 rpm if I want to squeak a little more in a 65 zone. On the major highways it's 75mph here and I can easily float along at 2200-2300 going 75-80mph but the best part is that it will knock down just over 21 mpg whether I'm doing 65 or 80, it doesn't really care. What many also forget is how quiet the car is now that the engine isn't buzzing 3000 rpm down the freeway. The lower you keep the rpm the quieter the car is. I even find myself using 5th gear in the 35-45 mph zones all the time.

Your 455 makes a ton of grunt and should not have a single issue lugging your car around at lower rpm, even below those highway speeds.
No worries on the chrome handle if it's the factory push in Hurst style. They do reproduce the round bar handles that bolt on to the aftermarket Hurst and Tremec shifters. I run one in the Z since the original Hurst shifter has that push in handle and I didn't want to modify that, those original sticks with the specific Hurst part number on them bring some serious coin. Plus I wanted to save all that with the Muncie and driveshaft as a package deal since it's born with that car.

[chuckies76ta]

Here is my opinion on these O/D transmissions. You need to take into consideration your Driving style, Speed limits, Engine rpm which I think is the most important, Rear gear, and Tire size. Where is most of your driving gonna be, on the highway or around your City or Town. I guess if you want the best of both worlds you could move up to the T56 with 6 speed and two O/D's.
I was gonna go with the .72 O/D but that first gear ratio of 3.27 was no good for my setup. A good Friend of mine that is much better than myself with numbers talked me out of it. and he was right. I'm very happy with my current setup.

Anyhow, point is that one size doesn't fit all. Find yourself a rpm,tire calculator online and go from there.

https://purperformance.com/p-29669-rpm-calculator.html

I'm running the new TKX with .81 O/D, 275/60R/15 tire, and 3.73 rear gears. My engine like to cruise at around 2200 rpm. The after market shifter I went with is from Modern Driveline. It uses bellville washers for centering the shifter which I'm very impressed with. https://www.moderndriveline.com/shop...y-rear-socket/

[grivera]

Chuckie- what first gear in your TKX?

[Formulajones]

Originally Posted by chuckies76ta

I'm running the new TKX with .81 O/D, 275/60R/15 tire, and 3.73 rear gears. My engine like to cruise at around 2200 rpm.

Wow that's only 60 mph....yikes You'd still have to buzz 2700 rpm just to do 75 mph.

[chuckies76ta]

Originally Posted by grivera

Chuckie- what first gear in your TKX?

It has the 2.87 first gear

[scott70]

Most of my " normal" driving is around town,55 mph and 65 mph. The 2.87 first gear is appealing to me as much as having the overdrive. I will admit I'm not much of a putt putt. The car has its original drivetrain but I put it through its paces. Have been since 1986.