Converting manual to automatic, best transmission to use?

[67ChevNut]

Need recomendations on what type of automatic transmission to use for my 72. It has a 350 with a 4 spd. manual transmission on the floor. This truck was originally manual, I believe it has high gears on the rearend. It feels heavy and slow on the street when driving on 4th gear.

I really don't want to swap the rearend since it is a posi rearend.

I have access to a 2004 4L80 and a 2002 4L60 transmissions, but those are too new for the old 350 in my truck, don't really know how to make them work with it. I also have 350 transmission, but because of my high rearend gears, not sure this one would make my truck run smoother. Thinking about using a TH400 transmission since those came on heavier trucks, although I would have to find one of those. Also, a friend wants to trade me a THM200-R4 transmission for my 4L60, wonder if that would be a good choice.

What should I use? Is there another transmission I should consider? I want my truck to run like it has a 3:08 gear rearend even though I am sure it doesn't.

[kwmech]

If you have no plans in the future to swap out the rear gears, then go with the T350. If you want heavier duty T400. You will not be too thrilled with an overdrive plus the 3.07 gears

[Step'67]

I made the same conversion, from the old 4-speed to an auto. Motor in the truck is a mildly built 355 with 3:73 rear gears. Despite the old tech engine, I wanted something modern for the transmission. I chose to go with a low mileage 4l80e. The thing is bullet proof for the power I'm putting through it and pairs nicely with my gear ratio. Because it's electronic, I used the TCI trans controller for it (also works for the 4l60e):

http://www.tciauto.com/tc/ez-tcutm-t...85e-to-09html/

A couple of other companies have come out with controllers since then such as MSD. Easy to use, just a few wires, couple options on the handheld controller, and it was up and running. The computer learns your driving style, and the best part of it in my opinion is you can fine tune the shift firmness, aggressiveness, torque converter lockup, everything from a few button presses. No messing with shift kits or mechanical mods.

Now in your situation you've got a different rear gear setup than I do. The overdrive isn't going to hurt performance when your around town or getting on it, but believe me it makes a huge difference on the highway. Worth it in my opinion. With your gears, if you want a little more pep, I'd consider either the 700R4 or the 4l60e. They are basically the same transmission, but the 4l60e is electronic and allows for the tuning via the controller. They aren't as tough as the 4l80e, but these two transmissions have a lower first gear than any of the other popular GM 4-speed autos most people choose (TH350, TH400, 4l80e, etc) and will help to make up for the rear end gear. The 200-4R has a lower first gear than the TH350 (still taller than the 700R4/4l60e), but it also has a really tall overdrive (you might be lugging the motor down in OD depending on your driving speed with it).

To help even out your tall rear gears, if you want simplicity - the 700R4. If you want a modern update, customization, and still relatively simple - the 4l60e. Just my $0.02.

[special-K]

I think you meant to say the gears are low, not the ratio. High gears are a low ratio (3.08:1) and low gears are high ration (4.10:1). So, you have low gears that make hiway driving slower and you want a more hiway-friendly situation. You would be miles ahead to change ratio vs going with an electronic O/D transmission. Why, because the transmission will need an ECM that doesn't accommodate EFI and an electronic speedometer. You'll find that to be far more expensive...and possibly less reliable. Gears is gears. Set 'em up and keep them in lube and they are virtually eternal.

700r4 is what came to my mind before reading through. I see you are wanting to select from the pool you listed. I'd go with the 200r4 out of those, but that could get expensive, too. At least for me it would. They can be "made into" a very strong trans but not so much stock...in a truck anyway. Making one beefy will also cost you. A good 700r4 is a good trans with no electronics involved

[Devins-step]

When I put in the 383 stroker in my '72 stepper I chose a 700R4 and am loving it. It handles the horsepower and gives me good street driving.
DW

[davepl]

Here's another vote for the 4L80E. I just wish there was a cheaper way to control it and to get a speedo signal. Since there isn't my next vote is for the 200-4R, which doesn't require any electronics and has a speedo outlet.

Then the TH350. Then the 700-R4, but I hear they're pretty weak in stock form. Then the powerglide.

[Spullar]

Originally Posted by davepl

Here's another vote for the 4L80E. I just wish there was a cheaper way to control it and to get a speedo signal. Since there isn't my next vote is for the 200-4R, which doesn't require any electronics and has a speedo outlet.

Then the TH350. Then the 700-R4, but I hear they're pretty weak in stock form. Then the powerglide.

I would think the 4L60E would be better with the 3.08:1 then the 4L80E

[Bigdav160]

200-4R would be my choice. All the other ones with "e" need a controller, vehicle speed sensor and throttle position sensors adapted.

[biketopia]

First off, we need to determine what rear gear the OP is working with and his intended use. He says he wants it to run like it's got 3.08's but no clue what's in it. Some previous owner could of gone crazy and put 4.11 or 4.56's in it and he'll never be happy with a non-od trans on the highway because they all have a final 1:1 ratio. And what's your budget, like stated the 200 is good, but needs help to live even in stock form in a car. 700's will hold up better stock but some people don't really like the gear ratios, usually a really short 1st. You've got the electronic trans's, if you know they are good and want to get the controller then either one will hold up, and hold up any future mods most likely as well. If it were me, I'd figure out what rear I have and slap in the TH350 you have and call it a day, plenty stout for a stock application, parts are cheap and plentiful, and you have it already, plus you can use any money savings to change out the gear set if needed to get you where you want.

[67ChevNut]

I believe I didn't explain myself correctly. Special-k got it right, I meant to say my gears are low and yes, I want a more highway friendly situation. I have not opened the rearend, but I am thinking it has 3:73's or even lower.

I like the idea of using the 350, easy and simple. I am also leaning towards using the 200-4R, but I wouldn't want to do so many modifications and spend a bunch of money trying to get it to work. This is a cheap daily driver work truck, I just want it to run good in town every day.

[biketopia]

My truck before i took it off the road had 3.73 and the stock 350 and a TH350. Very much an easy driving truck, nothing crazy on the RPM's at cruise and was just fine around town.

[Step'67]

Ah, sorry for the misunderstanding on what rear ratio you're currently running. Then yes, if you don't care for the OD and aren't pushing a ton of power, the TH350 would be fine. Though if you do any highway driving, the tall OD on the 200-4R would help bring the RPMs down.

[demian5]

I have a rock crusher sitting on my shelving and a complete running 355 with edelbrock heads under the bench. Been contemplating putting these in but a truck with stock clutch linkage and how long the shifter will be, sounds like a chore to drive....

[67ChevNut]

I want to drive this truck two days or more a week, I visit my mother everyday and need to drive at 60 mph for about 15 minutes. Maybe I should consider the 200-4R since I gather from the comments here is the easiest to use after the TH350, and it is an overdrive.

[RGT]

I used Bowtie Overdrives out of Hisperia, Ca to get the transmission and parts for my swap from a Turbo 350 to 200R4 and they were great to work with and I love the way the truck drives now. I have 3.73 gears. If I had been going to use the truck only occasionally on the highway I would have kept the T350 as that was a great transmission, but the extra 5 mpg and being able to hear the radio at highway speeds is nice for those several hour trips.

[Fraud]

Originally Posted by RGT

I used Bowtie Overdrives out of Hisperia, Ca to get the transmission and parts for my swap from a Turbo 350 to 200R4 and they were great to work with and I love the way the truck drives now. I have 3.73 gears. If I had been going to use the truck only occasionally on the highway I would have kept the T350 as that was a great transmission, but the extra 5 mpg and being able to hear the radio at highway speeds is nice for those several hour trips.

I've currently got an almost stock 350 with a TH350 and 3.73 gears, and would love to know more about this - seems to me that a 25% drop in rpm at cruising speeds and a lockup converter would be a night and day change for the better. Any regrets at all?

I'd be really interested to know what that conversion costs all in with converter and any linkage changes and the correct speedo drive for the gears etc..

[RGT]

I will dig up my receipts later, roughly for their trans/converter and wire wiring, shift indicater/linkage and linkage adapter for the carb it was around $1500. They provided me with the correct speedo gear already installed based on my gearing and tire size and my speedo reads what my gps shows and odometer matches the highway mile markers dead on. The transmission in drive wants to shift into OD too early so I drive around in 3 unless I am on the highway. I have a switch to lock up the converter in 3rd which is nice for extended back road use. Uses original driveshaft with no modification and you just slide the crossmember back to the already drilled holes in the frame and use the original transmission mount. the original speedo cable is a little tight reaching the new transmission but has not been a problem. I had to modify the new exhaust pipe I was installing to allow for the new crossmember position, I suppose I could have ordered a pipe that had been designed for a truck with a turbo 400 trans...

[arocars]

A 200R4 swap requires a new torque converter, dip stick, TV cable, adapter on the carb, crossmember, shifter alteration (to get all 4 gears) and potentially a shorter driveshaft. I did a T350 to 200R4 swap on my 69 Camaro. It cost $2k in parts. I created a custom crossmember. *** It was not worth it. I didn't drive the car often enough that I needed the overdrive.

The T350 has a deep first gear, so that would be an advantage over your 4 speed. But both the T350 and whatever 4 speed you have will both have the same 1:1 final drive ratio.

I have a sbc 350 and T350 in my 68 truck. I haven't actually checked, but I would guess it has 3.73:1 gears. I dont drive the truck enough that I care about gas mileage. So, I would not put an overdrive in it.

If you have 3.73:1 gears, your truck should not feel heavy and slow in 4th.

Too bad you're not closer. I would swap all my T350 stuff for all your 4 speed stuff.

[67ChevNut]

Very interesting comments on that 200-R4 swap. I am going to open the rearend tomorrow and find out what it has, think it may be easier. The 4th speed tranny the truck has looks big, the p.o. moved the floor shift lever closer to the firewall to make it work, thinking is not regular 4th spd. tranny and if so, maybe that's the problem.

[trac209]

Why does everyone always say you won't be happy with 3.07 gear and a 700r4? First off a 700r4 still has a 1-1 third and has a steeper 1st gear. You don't have to use od unless conditions are right like flat low load cruising. Not that I'm a fan of this trans but I've never understood the logic behind that statement. Plus since you shouldn't tow in od at least with less gear you're not towing in third at 3000 plus rpm just to keep up to traffic.

[67ChevNut]

This is what I have installed on my truck, I wonder why the shift lever is on a higher position. Also, the picture showing the view from the distributor area shows the transmission. It is very different from a 68 GMC manual transmission I have. Wonder if this is the correct transmission for this 72.

[wbc409]

The big shift boot closer to the firewall is correct. The hole and boot closer to the seat tell me there was either a 3 spd manual that was converted to floor shift, or someone put a car 4 spd in the truck at some point.

[67ChevNut]

Cool, thank you for letting me know.

[Nick2x2x]

What difference in a 4L80e and a 4L60e?

[LongBox]

Originally Posted by Nick2x2x

What difference in a 4L80e and a 4L60e?

The 4L60E is the 700R4 with electronic control. The 700R4 was essentially a TH 350 with the OD 4th gear.

The 4L80E is basically a TH 400 with an OD 4th gear and electronic control.

So, the 4L80E is a heavier-uty unit.