TH400 Vs 700R4 Vs 4L80e Vs gear vendor

[ScottyB]

I know this is going to cause some discussion because people seem to have strong opinions when it comes to transmissions. My 454 is currently followed by a TH400. This is great for a hard working or hard driving truck. My goal, however, is a gas miser. (My apologies to those of you who just spit your beverage of choice all over your computers.) I like the gear vendor idea and may just do that behind the TH400. The nice thing about the gear vendor is you can turn it off when you need to be a real truck again. I am thinking about converting to an OD transmission.

The 700R4 is the transmission that first came to my attention. The advantages to this that I see are that it keeps things simple for me. (Transmissions are the place where Voodoo happens.) I also have a friend that is very comfortable rebuilding these as that was his profession in a previous life. The downsides that I am aware of here are that it is not a heavy duty transmission. It can be hardened, but still isn't designed to hold up long term to heavy duty use. It also has a pretty big swing in ratios from 1st to 2nd gears. This means you end up running up your RPMs in order to make the shift to second. This is not condusive to fuel economy. A gear vendor in conjunction with this will negate the ratio swing but will not harden the transmission. Given that this truck will not have many occasions where I will require a heavy duty transmission I am less concerned here. I also like the idea of not having to take it into a shop to get it rebuilt.

The 4L80e on the other hand is a heavy duty transmission that has overdrive. The electronic component takes it out of my friends comfort level as he stopped working on transmissions before this evolution in technology took hold. I will admit that this is a superior transmission but suffers from a serviceability issue from where I stand.

700R4s also seem to be more plentiful in this area. I can find them all over on CL. While I don't trust the quality of the CL offerings I am less concerned there as we would be doing a rebuild on it anyway. A 4L80e would have to come from a trusted rebuilder. I don't intend to just slap a used transmission in that hasn't been rebuilt. I don't want to keep pulling it apart.

With my driving style and some maintenance I am hoping to measure the extended life of this truck in the decades and doing this right will certainly help with that. To say I have my mind made up isn't exactly fair. I am leaning in a direction but I throw this out as an honest debate. I can see going in any of those directions and regardless of which way I go I can see that I will kick myself at sometime or other. So what say you about these evil voodoo boxes?

 

[marks86]

don't no much about the gear vender so I have no opinion on that... butttt

the th400 sucks with only 3 gears unless you have a really tall gear like 3.73 or you never drive you truck over 55

the 700r4 is a half ton transmission so don't plan it lasting very long with the 454 unless you build you build one which costs some $$$$

the 4l80 is a no brainer IMO heavy duty electronic so it shifts nice the only prob I can see is you need some knowledge for an install you will need a stand alone computer system Im pretty sure TCI makes one

 

[skysurfer]

similar discussion was done here...http://www.gmsquarebody.com/forum/showthread.php?t=3137&highlight=gear+vendor

 

[ScottyB]

similar discussion was done here...http://www.gmsquarebody.com/forum/showthread.php?t=3137&highlight=gear+vendor

Thank you. I am still working my way through the different topics and threads here and hadn't seen that one yet. I was pretty sure it wasn't a unique question though. I'll give it a few more posts and then let you know which way I am leaning (this week until the wind changes direction again).

 

[kleedus]

the only overdive transmissions I would put behind a big block would be a 4l80 or a nv4500.

I bought a built 700r4 rated at 500 horse from mad dog transmissions and was going to put it behind a 454 then I learned about the 4l80 that 700r4 went in my jimmy behind a 350. if you plan to tow or any hard use a 700r4 will not hold up to the torque of a 454

if your friend can rebuild a turbo 400 and a 700r4 the 4l80 would not be any harder it is basically a 400 with overdrive they share a lot of parts

automatic transmissions kicked my ass for years until I bought the atsg manual off ebay for the 4l80 and tore into one and rebuilt it. and it was the first auto tranny I have ever rebuilt not bad at all that atsg book is awesome

I adapted a 205 t case to mine and put it in a 90 crew cab I have some pics and details in my build thread http://www.gmsquarebody.com/forum/showthread.php?t=2329

the computer to control them is kinda spendy I am running a 96 vortec engine in mine so I am using that computer for mine

 

[Jims86]

Yeah, 4L80 and controller, and be done with it. 1Low4x4 just completed the swap in his 85 C20 about 2 months agao, and is happier than a ***** in a dick tree. Recently upgraded his engine with a carbed Vortec top end too.

 

[HotRodPC]

Yep, 4L80-E or nothing if you want OD Auto behind a FoFittyFo !!!

Only way I'd conisder a Gear Vendor, is if I acquired a used one out of an old motorhome for dirt cheap which can be done. But then you have to cut drivelines, add crossmembers unless it's alreay got an adapter for the Th400 which is very possible if it came from a GM motorhome, otherwise, big expense for either an adapter to run it, or use it divroced. Either way, headache and expensive mods. I'd just go 4L80-E.

 

[ScottyB]

Right now I am leaning toward the TH400-GV combo. I already have a working TH400 and the support to rebuild it. The GV will allow me to run that like a 6 speed most of the time. Keep in mind that this truck isn't going to be a work horse. It will on rare occasion be asked to work but not often. The GV will allow me to keep my RPMs down across the board, not just in OD. I like the idea of the 4L80e-GV combo which would give me the equivelant of an 8 speed transmission with double OD. While the GV unit is expensive, I would be looking at something similar in price by the time I bought the 4L80e and computer to go with it.

 

[HotRodPC]

Right now I am leaning toward the TH400-GV combo. I already have a working TH400 and the support to rebuild it. The GV will allow me to run that like a 6 speed most of the time. Keep in mind that this truck isn't going to be a work horse. It will on rare occasion be asked to work but not often. The GV will allow me to keep my RPMs down across the board, not just in OD. I like the idea of the 4L80e-GV combo which would give me the equivelant of an 8 speed transmission with double OD. While the GV unit is expensive, I would be looking at something similar in price by the time I bought the 4L80e and computer to go with it.

Unless you'll be driving 80mph or more, you'll never get to see a gain with a double OD putting you at about a .50 OD ratio or unless you're running 5.38 rear gears on a short tire.

Not going to be a workhorse is even more reason not to go thru the expense and mods of a GV, but to each his own. Gotta drive a whole lotta miles to recoop that investment.

 

[ScottyB]

I can do 70 MPH here legally if I take it on to the freeway. Double OD may not be that beneficial. That aside, 6 gears will do better than 4 gears. If the fuel economy goes up high enough I can justify driving more thus recouping my investment. That said, does anyone think gas is ever going back down substantially? With the increases in the last 8 years alone we have seen the ROI on something like this decrease significantly. I am also looking long term on this thinking of the truck running for decades rather than just years.

I can rebuild the TH400 now (when I get a job again as that just changed ) and maybe swap the rear gears to a 3.73 or 3.56 until I am ready to do the GV. The rear ratio change is cheap and I can still hold onto the original 4.11 gears.

 

[HotRodPC]

4.10's are about perfect with a .67-.75 OD. You running a 31 inch tall tire right? Keep in mind, lower rpm does not always mean better mpg. You can actually get worse mpg with lower rpm and putting a strain on the motor.

 

[ScottyB]

4.10's are about perfect with a .67-.75 OD. You running a 31 inch tall tire right? Keep in mind, lower rpm does not always mean better mpg. You can actually get worse mpg with lower rpm and putting a strain on the motor.

Granted, most of my experience in this is with diesel engines and not all of that crosses over. With no work load though, I stand by lower RPMs being better so long as you aren't lugging the engine. If I were doing this under load I definitely see your point. Remember, the taller gears are being talked about in conjunction with the TH400, so there is no OD. Once I have OD I would be switching back to the 4.11s. As for tires, I haven't done the calculations but they are just 16 inch wheels with 10 ply tires.

 

[Green79Scottsdale]

You can actually get worse mpg with lower rpm and putting a strain on the motor.

With no work load though, I stand by lower RPMs being better so long as you aren't lugging the engine.

You guys just said the same thing. In a somewhat related story, I owned a 2001 Monte Carlo for a brief time. I found I got better mileage by getting after more from a stop, rather than easing into. My dad didn't believe me until he got the car back and tried it himself.

I have seen countless reports of 454/4.10 combos getting better MPG than 350/3.42 combos for the very same reason you guys said, lugging or straining the motor.

I think the best way to approach this kind of situation is to figure out your motors power curves first and foremost. When you know were the torque peak is at, you can start doing math to figure out what gears to run to put your motor at the torque peak at those RPM's. Motor running at torque peak is where the best MPG's are at.

 

[HotRodPC]

You guys just said the same thing. In a somewhat related story, I owned a 2001 Monte Carlo for a brief time. I found I got better mileage by getting after more from a stop, rather than easing into. My dad didn't believe me until he got the car back and tried it himself.

I have seen countless reports of 454/4.10 combos getting better MPG than 350/3.42 combos for the very same reason you guys said, lugging or straining the motor.

I think the best way to approach this kind of situation is to figure out your motors power curves first and foremost. When you know were the torque peak is at, you can start doing math to figure out what gears to run to put your motor at the torque peak at those RPM's. Motor running at torque peak is where the best MPG's are at.

Exactly !!! Find the happy spot in the rpm power band and try to stay in it with your most traveled speed. Our Interstate speed limits here in OK are 70, but I drive 5-9 over, so I'd prefer to set up at 75mph, but I've also slowed down a bit due to high gas costs and will do 70 since it does seem I get a little over half an mpg better for the 5mph slower.

And the 5mph going 70 miles to my dads, the extra 5 mph is only about 5 minutes in time, but by the end of the round trip, saves me about $6 in gas. Do the math. If you save $6 in 10 more minutes of driving, that's equal to making $36 an hour tax free.

Now, if I'm working and the boss is buying the fuel, you can bet your ass I'm rockin'. Saving 5 minutes every 70 miles is equal to an extra job or 2 by the end of a 8-12 hour shift and when you get paid by the job, not hourly, over the period of a week, 5-10mph can be equal to $100-$200 more on the paycheck.

 

[Green79Scottsdale]

To further the "which transmission" discussion, if I ever have a failure with my TH400, I am considering 4L80E, 6L80/90E, and the 5/6 speed Allison transmissions. And before anyone says anything, yes I realize all the "problems" and obstacles that would come with each one.