Overdrive suggestions

[trkfrmr]

Thinking of trans swap in my 67,currently 355 q jet w/th400 3.54 30 inch tire,have 70 mile interstate commute,and would love to lower 70mph engine rpms,would like feedback on 4l80e/4l60e/700r4 options such as if the increased investments in electronics for electric shifts are worth it,etc.truck is about 3000 rpm hwy speed,thanks in advance.

[Andy4639]

I'd do the 700R-4 if you don't want all the eletronic's to go with the others. I had a 305 TPI with 700r-4 for several years and it did great.

[KyFarm]

Depending on how much you want to spend and how mechanically inclined you are, a overdrive transmission would be great, I'm adding one in my drivetrain re-build.

A simpler solution though would also be getting bigger tires (if you need tires anyway AND they would fit) this will only help a very little,

Also, changing your diff gear to a numerically lower numbered gear should also lower highway RPM at the same speed. IF i understand correctly how that works, all other things being equal, i.e. tires, trans, speed etc, changing the diff to a 10% lower gear should lower RPM 10% at the same highway speed. So 3000rpm would become 2700rpm. Truck would feel slower from a stop though.....

If anyone needs to correct what I've said, feel free, I'm often mistaken

[68Stepbed]

Thw 700R4 is going to be the easiest to swap in and get operating quickly. The 4L60E is technically the same as a 700r4, but electronically controlled, which means you'll need a trans control box that uses a throttle position sensor(TPS) attached to the carburetor.

The 4L80E, although actually different, is essentially a TH400 with an overdrive gear and electronically controlled. If you don't plan on making serious horsepower and torque, or do any major towing, I wouldn't do the 4L80E. From what I've learned, they tend to take more power to operate, which tends to rob a tad more fuel mileage compared to the 700R4/4L60E.

Of course, if you really want to save on fuel mileage and reduce RPMs, go with a 6 speed manual!!!

[3767]

Based on your set up, u should b turning about 2200 rpm to get 2 55. With an overdrive of.7, you will now be going 79 mph at 2200. The 700r is the cheapest way to go. It’s also the easiest. You don’t need to change your tire height nor rear gear if you take this route. The 700 has a 3.06 first gear so you will have plenty of take off with what u got. The others you mentioned all will need a computer to operate. In the aftermarket, they will cost you a grand so they will take along time to recoup the savings. The 700 doesn’t need this to work. Plan on $800 for a rebuilt 700r4. You will need a core so look for one in the $100/150 price range. You will need a cable to hook to the side of carb but those are plentiful. You can change you tire height but you will lose bottom end pulling . By the time u pay someone to change rear gear to say a 3.08, you could have done the tranny swap. And u will still lose some pulling power as well. As Matt stated, the 4l80 will rob you of some mileage due to the weight and all thats involved getting it moving. With the 4l80 being the exception, the others all have a lot of the same internal parts so 1 is just as strong as the other. Since you drive a lot of highway miles, the 700r will pay for its self much faster than the rest.

[LS short box]

If you are so inclined and have the cash I would do mildly built 4L60E and maybe a bit of stall converter. The reason I like the 4L60E is because you con "tune" all the shift points under part throttle and full throttle. Also converter lock. And when the overdrive kicks in. All with out turning a wrench.

[KyFarm]

yep, built 4L60E is the 4L70E i'm putting in. factory rated to 495ft/lbs

much more than the $800 re-built 700r4 tho.....

[Rick Bollinger]

I did the 700r4 373 gears and 29" tires. B&M torque converter lock up through the brake switch and very happy with it. Run a big cooler and should last a long time. Your gears are a little taller so highway should be even better.