Trans swap from T400 to Overdrive

[Eyegore]

OK this is transmissions for dummys, me being the dummy. If I want to change the exisitng T400 to a overdrive unit, whatever the 4l80 is, but without a computer to run it and w/o changing tailshaft and cutting down the driveline but only changing the selector to in OD, can it be done? And what is the most inexspensive way to do it and what year of tranrmission should I be looking for?
This is for a 82 3/4 ton w/ 6.2 diesel

Tom

[jimbonice]

Well, I believe the 4l80e requires the 'puter to run, either factory or aftermarket. I don't believe 6.2's ever came with the 4l80, but 6.5's did in the early '90's squares and had a stand alone computer for the trans. Not much getting around that. I know they make full manual valve bodies for competition; I don't know how street friendly they are and shifting the transmission may get tedious after a couple thousand times

And that brings up the much maligned 700r4, which would be the cheapest o\d swap. No computer needed, can be mildly modded to live in a truck - I've had on in my 454 C30 dually for 30,000 miles - and has a great first gear with a low 3.06 ratio compared to a 2.48 for just about everything else. A 6.2 would not be any harder on it than a 454 in a crew cab dually. It makes pulling the boat out of the water much easier, as well as taking off with a camper on the back. With my 4:10's it makes an effective 1st gear ratio of 12.5 to 1. In a 4l80e it would take a rear gear of 5 to 1 to match it.

You'll end up doing driveshaft mods irregardless of what is swapped, so plan for it. It is not necessary to change the selector as the detents in the transmission determine where the selector pin end up.

Maybe someone else will chime in here, but an o\d trans is no guarantee of better economy in these full size trucks and may never pay back the cost of the swap. In the 6.2's, lugging along out of the powerband in overdrive might return the same or worse economy. If you tow or work your truck alot of the time, I'd be tempted to leave the t400 in, because you won't be using o\d anyways.

good luck with your decision.

[Edahall]

Originally Posted by jimbonice

Maybe someone else will chime in here, but an o\d trans is no guarantee of better economy in these full size trucks and may never pay back the cost of the swap. In the 6.2's, lugging along out of the powerband in overdrive might return the same or worse economy. If you tow or work your truck alot of the time, I'd be tempted to leave the t400 in, because you won't be using o\d anyways.

good luck with your decision.

My experience with these engines has been that keeping the RPM's down definitely gives better economy. For best results on these engines, you want to cruise right around 1800 rpm's where the torque curve is at its highest. My 1982 Suburban has a 700R4 over drive transmission and I'm running a 3.08 rear end. This truck returns 30 mpg on the freeway driving conservatively. However, I don't like the 700R4 transmission. It is way too weak behind this engine even with all the mods. I've dumped way too much money into transmissions for this vehicle. For my latest Suburban, I switched over to a NV5600 manual transmission and could not be happier.

Eyegore,
Since you're looking for inexpensive solutions, here's my recommendation. Keep the TH400 but install the lowest stall torque converter you can find. The low stall converter will keep the slipping to a minimum and transfer more power to the ground which will give you better fuel economy. Is your truck 2 wheel drive, 3/4 ton? If so, find a 3.08 rear end out of a 1st generation 3/4 ton Dodge truck. Afterwards, get some 235/85/16 tires. These tires are large diameter and will bring your rpm's down. The above setup I mentioned will bring your RPM's down just a tad under 2000 rpm's at 60 rpm which isn't too bad.

[veinbar]

Originally Posted by Edahall

My 1982 Suburban has a 700R4 over drive transmission and I'm running a 3.08 rear end. This truck returns 30 mpg on the freeway driving conservatively.

Is this a typo? What engine / transmission are you running? I need to swap to whatever you have.

[Eyegore]

Originally Posted by veinbar

Is this a typo? What engine / transmission are you running? I need to swap to whatever you have.

No typo the 82 6.2 diesel I have gets 18 mpg in town, that is why I am looking into the overdrive to bump it up to 30 ish like mentioned but stout enough to do some heavier hauling though the 6.2 was not made for heavy hauling

[Edahall]

Originally Posted by veinbar

Is this a typo? What engine / transmission are you running? I need to swap to whatever you have.

Originally Posted by Eyegore

No typo the 82 6.2 diesel I have gets 18 mpg in town, that is why I am looking into the overdrive to bump it up to 30 ish like mentioned but stout enough to do some heavier hauling though the 6.2 was not made for heavy hauling

It's not a typo. The 6.2 diesel, can get very good fuel economy if equipped correctly and geared correctly. The earlier 6.2 diesel versions got better fuel economy than the newer versions because the heads had larger valves and smaller precombusion chambers. The smaller precombustion chambers limited power output but maximized fuel economy. The later 6.2's with larger precombustion chambers can be fitted with smaller precombustion chambers to maximize fuel economy but power will be reduced. When I first got my 1982 Suburban, it got mid 20's on the highway and didn't have much performance. So I made some mods that increased power and economy.
1. Exhaust headers
2. Free flowing dual 2-1/2" free flowing exhaust with H pipe.
3. J code intake manifold (no EGR)
4. Ported the heads
5. Gear Drive for camshaft
6. Advanced the timing

If you do a lot of high speed driving, another mod that helps out a lot with mpg's is a lowering kit. I haven't done this to my Suburban so if I drive 80 mph here in TX, gas mileage goes down.

Eyegore,
If you're looking for a transmission that has an overdrive and is stout enough for heavier hauling, look for a NV4500 manual transmission. It'll set you back about $1k for the tranny and you have drive line changes to make. However, you can also do what I mentioned in a previous post and probably get very close to spending the money for a different transmission.

[veinbar]

Originally Posted by Eyegore

No typo the 82 6.2 diesel I have gets 18 mpg in town, that is why I am looking into the overdrive to bump it up to 30 ish like mentioned but stout enough to do some heavier hauling though the 6.2 was not made for heavy hauling

That's insane... I had no idea we were dealing with a diesel in this scenario, which I know can turn impressive numbers. This forum makes it difficult to daydream sometimes... There are too many "dream" drive line combinations to choose just one. Thank you for explaining.

[Edahall]

Originally Posted by veinbar

That's insane... I had no idea we were dealing with a diesel in this scenario, which I know can turn impressive numbers. This forum makes it difficult to daydream sometimes... There are too many "dream" drive line combinations to choose just one. Thank you for explaining.

The 6.2L can turn impressive numbers with respect to fuel economy but that's not as true regarding HP. The limiting factor on these engines for building power is the bottom end. Keep the HP down to 180 or less and they'll purr forever and sip fuel.

[jimbonice]

Originally Posted by Eyegore

No typo the 82 6.2 diesel I have gets 18 mpg in town, that is why I am looking into the overdrive to bump it up to 30 ish like mentioned but stout enough to do some heavier hauling though the 6.2 was not made for heavy hauling

What is your description of "heavy hauling"? It makes some difference on what trans you're looking for. My heaving hauling is 10,000 lbs, for some people it is 3000 lbs, for others it is 15,000 lbs. Also, you're rear gear is going is going to come into the picture as well. Irrespective of what transmission you choose you will need a compatible rear gear. 10,000lb loads are going to require steep gears, like 4:10's or maybe 3.73's to keep the 6.2 happy in 3rd gear on the highway. If you have 3.08's in the back, then I don't see heavy hauling in your 6.2's future without a gear swap.

[Edahall]

Originally Posted by jimbonice

What is your description of "heavy hauling"? It makes some difference on what trans you're looking for. My heaving hauling is 10,000 lbs, for some people it is 3000 lbs, for others it is 15,000 lbs. Also, you're rear gear is going is going to come into the picture as well. Irrespective of what transmission you choose you will need a compatible rear gear. 10,000lb loads are going to require steep gears, like 4:10's or maybe 3.73's to keep the 6.2 happy in 3rd gear on the highway. If you have 3.08's in the back, then I don't see heavy hauling in your 6.2's future without a gear swap.

Just for reference, my 1982 Suburban 6.2 diesel non aspirated, 3.08 gears and 15in. 30x9.50 tires is happy towing my 26 ft. Airstream trailer weighing approximately 5000 lbs all day. I tow in 3rd gear (direct drive) and when going up hills, I shift downshift into 2nd gear. I have a switch to lock up the torque converter and it'll pull 50 mph in 2nd gear.

[502ss]

I am thinking about a 4l80e and a shift control system called optishift. http://www.optishift.com/

I currently have a 400 automatic in my c30 1 ton with a 454 which I use primarily for towing my 10,000lb speed boat. The problem is all the lakes I go to are over 2 hours away and all the traveling is highway. With my current setup the engine is turning 3500rpm on the highway and only gets 6mpg. I am thinking the 4L80e with the shift controller would give me a solid setup and the overdrive needed for the highway. The other benefit is you can pickup 4L80e all day long for short money and the shift controller module is also short money!!
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[hatzie]

The Optishift computer should work. I like the level of detail provided in the manual.
You'll need to install TPS on your carburetor.
You'll need to work out the speedo cable. The 4L80E is setup for VSS only.

[rruss86]

Originally Posted by Edahall

My experience with these engines has been that keeping the RPM's down definitely gives better economy. For best results on these engines, you want to cruise right around 1800 rpm's where the torque curve is at its highest. My 1982 Suburban has a 700R4 over drive transmission and I'm running a 3.08 rear end. This truck returns 30 mpg on the freeway driving conservatively. However, I don't like the 700R4 transmission. It is way too weak behind this engine even with all the mods. I've dumped way too much money into transmissions for this vehicle. For my latest Suburban, I switched over to a NV5600 manual transmission and could not be happier.

Eyegore,
Since you're looking for inexpensive solutions, here's my recommendation. Keep the TH400 but install the lowest stall torque converter you can find. The low stall converter will keep the slipping to a minimum and transfer more power to the ground which will give you better fuel economy. Is your truck 2 wheel drive, 3/4 ton? If so, find a 3.08 rear end out of a 1st generation 3/4 ton Dodge truck. Afterwards, get some 235/85/16 tires. These tires are large diameter and will bring your rpm's down. The above setup I mentioned will bring your RPM's down just a tad under 2000 rpm's at 60 rpm which isn't too bad.

ok so i have a 1987 suburban 3/4 400 trans with 4.10 gears. i am in truckin so my burban only goes to shows and drag fests.. i have a 29" tire. what gears can i run to get better mpg...

[nekkidhillbilly]

easiest would be find a 91 truck and swap in the 4l80e and its controller. 700 will work but its not very stout. however before id spend a grand on a nv4500 i think id find a used 80e and buy a controller be about the same money. most t400 trucks have 4:10s which is perfect for the 80 also. i doubt you will see big mpg on a diesel until your on the highway however.

[Edahall]

Originally Posted by rruss86

ok so i have a 1987 suburban 3/4 400 trans with 4.10 gears. i am in truckin so my burban only goes to shows and drag fests.. i have a 29" tire. what gears can i run to get better mpg...

The gears for best fuel economy with your setup would be 3.08's. However, good luck finding a 3/4 ton 3.08 axle. The only truck I know that came with it were the 88-90 Dodge with the Cummins engine.

Another idea is installing a Gear Vendors OD unit. They're pricey but with the price of fuel these days, it might not take long to pay it off.

For best fuel economy, go with a 700R4 transmission and 3.73 gears. The downside is the 700R4 is not nearly as robust as the 400 transmission especially when it comes to heavy towing.

[rruss86]

Originally Posted by Edahall

The gears for best fuel economy with your setup would be 3.08's. However, good luck finding a 3/4 ton 3.08 axle. The only truck I know that came with it were the 88-90 Dodge with the Cummins engine.

Another idea is installing a Gear Vendors OD unit. They're pricey but with the price of fuel these days, it might not take long to pay it off.

For best fuel economy, go with a 700R4 transmission and 3.73 gears. The downside is the 700R4 is not nearly as robust as the 400 transmission especially when it comes to heavy towing.

ok so can I just re gear my rearend with a 3.08.... it won't ever pull again.
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[Edahall]

Originally Posted by rruss86

ok so can I just re gear my rearend with a 3.08.... it won't ever pull again.
Posted via Mobile Device

What engine do you have under the hood? If it's a 454, you might even consider 2.73's.

Yes, you could re gear the rearend to 3.08. Yes you'll lose a lot of pulling power in 3rd gear especially if you have a 350. However, you'll get better fuel economy on the hwy. Also, keep your speeds down on the freeway. These trucks are not very aerodynamic. I lose nearly 30% fuel economy driving 70 mph rather than 55 mph on my Suburban! That said, I find 60 mph to be a happy medium on the freeway.

As far as pulling, my 82 Suburban 6.2L diesel has a 3.08 rear end and it pulls my 26 Airstream weighing around 5k lbs just fine. It's a little anemic in 3rd gear pulling that kind of weight but once I downshift into 2nd gear, I have plenty of power to pull over the 7% grades. However, a 6.2L diesel that's been modified does have somewhat more low rpm grunt than a good running 350. With 3.08's behind a 350, I would say it would be good for towing 3k lbs. With a 454, maybe 6k lbs.

[kevinr1970]

I had seen a '91 crewcab 6.2 truck (older body style) before and it had the O/D tranny.
I was told by a knowledgeable person on here that for that year only, the 4l80 (no "e") was a rare tranny that was sort of desireable due to no electronic controler? (the "e" meaning it was electronicly controlled)
I am no tranny expert, but more recently I had seen a guy parting a '91 3/4t 4x4 burb and he mentioned something to the effect of it having a 4l80e tranny that was "the one you wanted" for ease of instal in the 73-87 trucks.
Again, YMMV?

[Rogier]

Not a Diesel, same challenge!

I've taken out the old transmission and replaced it with a 4L80E. It is a HD version that has some OEM beefed up parts, like additional cooling and bigger pan, etc. The version I stumbled upon was a 4x4 version that has a different bobtail to attach the 4x4 gearbox. pay attention to get the right one for your application, mine is not usable as a 2 wheel drive trans.

I've looked into options to run it without a computer, but this requires a lot of work (if you have the expertise) or a lot of cash to buy a converted one. I've bought an Optishift and this appears to be working. I will continue the project in a month. The Optishift people are very responsive and have sent me a set including the throttle sensor and prefab harness. I would recommend to buy the harness, it is spot on and saves you a lot of hassle.

The speedo is something that you can solve with a conversion box that turns a digital signal and converts it into movement. Example: http://www.abbott-tach.com/cablex.htm . I think it's expensive, so I will be doing without a speedo for a while, I've got the navigation to tell me the GPS speed for now.

[Rogier]

Oh by the way: don't forget the flywheel. I had to replace some of the parts there to make it bolt up to the bellhouse. Nothing that is hard to acquire, but I don't know all the names of the parts. I Just replaced it comparing it to an engine that originally had a 4L80e connected.

[DetroitDan]

Very interested, I have a th400 behind a 454 and I hate it. I've been told the 700r4 is totally fine for a stock or mild 454, and I've also been told the 700r4 is going to explode the instant you put it into gear for the first time. I don't know who to believe. But, putting the 700 in will require moving the t-case back, shortening the rear driveshaft and lengthening the front. Then if I do break the trans, I can only replace it with another 700. I'd be tempted to do it, using a big auxiliary cooler with an electric fan and a temp gauge, like I always did on my plowtrucks. But, leery because I am going to tow 10,000 and I am not known for being gentle with trucks.

I like the 4l80e a lot, had one in my 97 diesel and whipped it like a rented mule for ten years plowing. Since the 4l80e is built on a 400, aren't the dimensions going to be the same? So the driveshafts can stay the same? I can find a 4l80e cheap enough, the controller would be the big expense for me, I'm pretty poor. What I really want to know is what kind of economy gains can be had by swapping to either a 700 or 4l80? I don't want to spend thousands to save hundreds. I hardly even drive the truck, mostly because it is so terrible on fuel, I'd guess I'm getting around 8 mpg around town. And seriously, how good is it going to get? It's still a big thirsty motor, even at idle. I've seen brand new, perfectly tuned carbed 454s with th400s pull down 14 mpg, but I'm lucky to get half that with my lifted truck with a loud pedal. If I could get upwards of 12 mpg, I'd drive it all the time.

[gramps77]

May not be that hard
http://www.summitracing.com/parts/HLY-534-202/
I havent used one but should work if you are carb'd and running a Holley

By the way, I realize you guys are talking about installing the 700 into a truck and possibly towing......as long as you have a large enough cooler for the grades, its not going to "blow up". Ive installed 2 700's and 3 2004Rs (only mentioned since we're talking O/D) but they were all into 63-70 Chevy Novas. some of which though are/were drag raced. As long as you keep the heat from building up, I dont see why you'd need to worry excessively. Get a trans temp gauge installed, monitor it, and if it gets hot, install a bigger cooler.

[Edahall]

Originally Posted by DetroitDan

Very interested, I have a th400 behind a 454 and I hate it. I've been told the 700r4 is totally fine for a stock or mild 454, and I've also been told the 700r4 is going to explode the instant you put it into gear for the first time. I don't know who to believe. But, putting the 700 in will require moving the t-case back, shortening the rear driveshaft and lengthening the front. Then if I do break the trans, I can only replace it with another 700. I'd be tempted to do it, using a big auxiliary cooler with an electric fan and a temp gauge, like I always did on my plowtrucks. But, leery because I am going to tow 10,000 and I am not known for being gentle with trucks.

I like the 4l80e a lot, had one in my 97 diesel and whipped it like a rented mule for ten years plowing. Since the 4l80e is built on a 400, aren't the dimensions going to be the same? So the driveshafts can stay the same? I can find a 4l80e cheap enough, the controller would be the big expense for me, I'm pretty poor. What I really want to know is what kind of economy gains can be had by swapping to either a 700 or 4l80? I don't want to spend thousands to save hundreds. I hardly even drive the truck, mostly because it is so terrible on fuel, I'd guess I'm getting around 8 mpg around town. And seriously, how good is it going to get? It's still a big thirsty motor, even at idle. I've seen brand new, perfectly tuned carbed 454s with th400s pull down 14 mpg, but I'm lucky to get half that with my lifted truck with a loud pedal. If I could get upwards of 12 mpg, I'd drive it all the time.

Don't even consider a 700R4 if you're going be towing that kind of weight with it. Yes you might be able to get by with 5000 lbs and keeping it out of O/D. The 700R4 is very weak in O/D so only use it for solo cruising. You would be better off paying for the fuel than paying for constant rebuilds on the 700R4.

The 4L80E and 400 are different lengths so you'll be into driveline changes there as well.

A different transmission is not going to change your fuel economy around town very much. It's a heavy truck and it takes a lot of energy to get it up to speed.

However, a different transmission with O/D can help your fuel economy on the highway because it lowers your rpm.

A less expensive option that would also give you the ability to tow would be the NV4500 transmission. But you'll have to shift.

Your lift also hurts your fuel economy especially on the highway. Keep your speeds down to 60 mph or less for best fuel economy. I lose 30% fuel economy driving 70 instead of 55 mph.

Take a look at my signature to give you ideas on what it takes to get good fuel economy (in the mid 20's) with these big heavy trucks. It's not cheap though.

[gramps77]

Its all a cost comparison....how often do you plan to tow, how much do you plan to tow, etc...
If you are using your truck and towing as a moving company then yes, you probably wouldnt want to use a 700. Its irritating for the constant blanket statements, not just here but other forums as well, that a tranny will simply blow up or just plain sucks for use at all.
One of the main issues with the 700r4 and towing is a lot of them lock up in OD. If you are towing, you probably wont have it in OD anyways. If the percentage of NOT towing is greater than towing......do some more research before accepting the "its gonna blow up". Everything can reach its design breaking point if you push it hard enough or use it incorrectly. I wouldnt worry towing up to about 5000 with a 700. please see here.....
http://www.gm-diesel.com/vbull/non-t...h-a-700r4.html

[DetroitDan]

see, I've been told not to even consider a 700, and I've been told that the built ones are fine. Obviously I wouldn't two in OD, I didn't use OD towing when I had my 97 4l80e. I would love a 5 speed manual, but it looks like it would be even harder to get all the parts together and make everything work. Plus I dont know which trucks I can swap out of, which ones to avoid, I don't know much at all about hydraulic slaves. But I'd sure like to drive one. I wouldn't consider an sm465, hate those clunky trannies. It's really just a 3 speed anyway, so no improvement over the th400.
So, no thoughts on how much an overdrive auto can help with fuel? I have looked at Gear Vendors, but they won't save you enough to pay for it for years.
I really don't drive on the highway, and the towing is only pulling the camper a handful of times a year. Which is why the 400 is still in there. I even considered swapping the 454 for a 6.2. But diesel is so much higher now it wouldn't be worth it.

Maybe I should start looking at nv4500s... Oh, one other thing, I've got an NP205 transfer case and auto locking hubs. I would love to keep this case in it if I can.