Specifically, what does it take to swap one into an older pickup in place of a TH-400? What trans is best to use? What trans is strongest?
The truck is a '78 1 ton with a 454 and a 4.56 rear. It's screaming at 60 mph, and I'd like to add a gear to reduce sound and improve mileage.
I am going to suggest a Gearvendors overdrive unit instead.
A TH700R4 CAN be made to work behind a 454 but the torque will annihilate the overdrive unit.
A gearvendors unit will cost about twice what the truck is worth, so that's not an option. I figure I need to use a used trans or a used rear axle with a 3.73 ratio. I haven't been able to find a rear, so I thought I'd look into the trans option. My TH400 is rebuilt, so I thought if I could find a used overdrive trans I might be able to sell my TH400 and not have a lot invested. What about a 4L60E or 4L80E? BTW, the engine is stock, and I need to tow 9k lbs only very seldom and for short periods. Other than that, I haul top soil in it and once in a while tow a car on a car trailer.
700R4's also have issues with a temperature sensor inside failing, making the lockup clutch not engage, often depending on the ambient temperature. Fortunately, you can jumper two pins on the diagnostic port to make it lock up manually. 
Several years ago when my mother was still alive & had the truck I have now, she had the choice of getting the 700R4 in it rebuilt or swapping in TH400. I foolishly suggested she have the 700R4 rebuilt. Now that I've had the truck for 6-years, I'm really wishing I'd told her to go with the TH400. 
If you want to do a trans swap, I would find a first gen 4L80. It is weak, for a 400, but takes all the newest updated parts to improve the strength. Plus IIRC, it's still all hydraulic or very rudimentary electronics.
I'd rather do a complete rear swap to a 3.73-ish gear and just live without OD. You still have plenty of torque to get everything moving. But if it's a 4x4, nevermind.
Brian
The 4L80E with controller will be in the $2000.00 range easily (They need an electronic interface to work that is about $1400.00 and I figure $600.00 for a good used unit)
I have seen TH400 GV units used for $1200.00 on CL.
In reply to John Brown:
Thanks. I didn't know about the controller,so that changes things. There are several 4L80E's around here in the $200-400 range, which would have been perfect if that was all that was involved. I assume that these are the only choices in GM overdrive transmissions?
If so, it sounds like the most economical choice is to keep looking for a rear axle to swap. A GV unit would be nice, but it's 100% added cost, where I can get pretty close to breaking even on the rear axle by selling my current unit.
In reply to bravenrace:
The 700R4 is the non-electronic version of the overdrive trans. I don't know if they ever came behind big blocks.
I'm assuming the rear axle is a 14-bolt? Single rear wheel 14-bolts should be next to free, but I'm guessing most of them are 4.10. There's no difference between a 3/4 ton and 1-ton 14-bolt as long as they're the full-floating style. You'd also be safe with any Ford or Dodge 3/4 or 1-ton rear axle. They should all be about the same width and 8-lug. Big vans might have different ratios in the same axles also, but for some reason I think van axles are a bit wider.
A quick search on my local craigslist located a Ford Dana 60 rear with 3.73 gears for $250. I would think something like that would work, you might have to weld new leaf spring perches on the axle.
In reply to twolittlebroncos:
Actually, the rear cover has 10 or 11 bolts, not 14. I'm really not sure what type it is, as everyone tells me it should be a 14 bolt. There is no evidence that it's not original, but who knows. I'd prefer a unit that just bolts in, mostly because I have enough projects without making this one of them, but I suppose that would depend on the price, convenience, etc.. When you say theres no difference in the 3/4 and 1 ton, you are talking single wheel only, right? I'm thinking the width is different on the dually, no? Do you or does anyone know what rearends were available for this truck in '78? Could it have a 14 bolt, 10 bolt, dana, etc..? It is a crew cab dually and is a camper special.
Here's everything you could ever want to know about a 14 bolt. Some good pictures to help you tell whether or not you have a 14 bolt.
http://www.pirate4x4.com/tech/billavista/14b_bible/index.html
Could be that you have a Dana 70, but that seems unlikely to me.
After skimming that 14 bolt article it looks like SRW and DRW housings are the same, but the hubs are different. Also, it looks like the leaf spring perch widths are different on 3/4 and 1-ton axles.
Thanks, except my truck has a 10 bolt. 
If it is 10 bolt, it's a Dana series rearend.
Looking at car-part, you can go with 3.21, 3.73, 4.10, and 4.56 gearing. It also looks like the 14bolt is a direct swap, except for maybe the brakes. Also, looks like anything for 87-back is a direct bolt in.
Brian
I'm thinking it's an Eaton, but I'm surprised that you'd have an Eaton on a 1978 truck. Here's an Eaton:
If it's not an Eaton, it's got to be one of these:
Ranger50 wrote: If it is 10 bolt, it's a Dana series rearend. Brian
Uhhh no.
Dana axles are Dana axles and you don't usually find one in a GM application unless it's in the front.
A ten bolt is a GM Corporate rear axles, just like a 12 and a 14 bolt.
1-tons usually got the 14-bolt. 10-bolts were 1/2 ton axles.
There's plenty of stuff out there to beef up a 10 bolt and the carrier in that 10 bolt is already the one you want.
Shawn
In reply to Trans_Maro:
Well this one has a cover that has 10 bolts on it, but it's in no way the same 10 bolt rear that was in my Firebird. It's huge, and it's a full floater. My truck is also the heaviest duty pickup made that year, so I don't know why it would have an inferior rearend in it. Plus, there are two different 10 bolt rears that came in these, a GM and a Spicer 70HD.
I'm not looking to beef it up, I want a more freeway friendly gear ratio, and swapping the entire rear for one with a better ratio seems to be the cheapest way to do it, since using an over-drive doesn't seem to make sense.
Here's what it looks like:
According tho www.car-part.com there was a Dana 10 bolt DRW
4x2, DRW, 10 bolt cover, 3.21 ratio (opt HC8)
4x2, DRW, 10 bolt cover, 3.42 ratio (opt GU6)
4x2, DRW, 10 bolt cover, 3.73 ratio (opt GT4)
4x2, DRW, 10 bolt cover, 4.10 ratio (opt GT5)
4x2, DRW, 10 bolt cover, 4.56 ratio (opt HC4)
In reply to John Brown:
John,
That's the Spicer 70HD I mentioned above.
I believe that's the rearend I have in my truck.
Jim
Another angle: lots of trucks came with 2 speed rear axles. Even some cars were available with them, like the Cougar. Might be worth a look.
EDIT: Found this link to some Dana 2 speed axle model numbers.
http://www.vibratesoftware.com/html_help/html/Dana_Spicer_Eaton/Dana_Spicer_Axles/Dana_Spicer_2spd_single_axles.htm
ALL Dana axles use 10 bolts on the cover, it's pointless to identify it as a Dana 10-bolt.
Dana uses model numbers. Dana 30, Dana 44, Dana 60, Dana 70.
Call a diff shop and ask them for parts for a Dana 10-bolt and they'll tell you to put the pipe down.
If it uses a Dana axle, the number will be cast into the pumpkin on the side of front half of the housing.
From the cover gasket you're showing me, you have a Dana 60 or 70.
Here's some good info: http://coloradok5.com/axleguide.shtml
And for summary:
GM CORPORATE 10-BOLT This 10-bolt, with a larger 8 1/2-inch ring gear diameter, replaced the Dana 44 that was used in the front of some pre-1977 GMs. It can also be found in the back of 1983-91 1/2-tons and in the front of 1983-87 1/2-tons.
GM CORPORATE 14-BOLT With a 10 1/2-inch-diameter ring gear, the biggest 14-bolt GM rearend looks much like a Dana 70, and is but a few thousandths of an inch shorter in ring gear diameter. This axle is commonly used with big engines and/or overly large tires. It was used under 1973-87 3/4-tons.
DANA 70 Almost identical in appearance to a Dana 60, the Dana 70 is standard in heavy Dodge pickups and GM duallies. The large 10.54-inch ring gear diameter will tolerate much torque, and is suitable for diesel power and/or big tires.
If your truck has duals then it could have a Dana 70 and it would have 10 cover bolts.
If it's SRW then it should have a Corporate 14-bolt and yes, it would have 14 cover bolts.
a 4L80 of any vintage will hold a stock 454.. put a big trans cooler on it, as with anything.. and of course assuming its in good shape to begin with..
You guys are all wrong. The answer is Miata all the way.
In reply to Vigo:
Is there any way to run a 4L80E without a controller?
John Brown wrote: You guys are all wrong. The answer is Miata all the way.
I think the answer is get rid of the truck. Nearing the very end of the smog era, that 454 probably makes less hp and tq then a ~96 350 vortec... AND it probably only gets 10mpg downhill coasting in neutral. You can buy a 3/4ton model for as much as its gonna cost you to really do anything about your problem.
Just sayin' 
In reply to Trans_Maro:
Do you know the differences in fit? Can I put a 14 bolt in place of my 10 bolt? There is no identification on my axle.
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