700R4 vs TH350...

[Nova70]

I'm turning 35's and have been thinking about switching to a 700R4 but I'm not sure. My dad has an adapter for my T-Case so it will mate up to the 700, but is it going to make a big enough difference in daily driving to swap them? I'm hoping for a little better MPG and some lower R's on my 2 hour trip to the dunes I take bi-weekly during the summer... What do you guys think?

[mrein3]

35s are tall. Stock tires are 28 inches. A 700r4 will drop your highway rpms down 30% +/-. I added +/- because the final gear in a 700r4 is .7:1 where your th350 is 1:1 but in the 700r4 you also get a lock-up in your torque converter which drops your r's even further.

All that being said you don't want to drop your rpms so far that on the highway you'll be lugging the engine. With your current 35" tires you're already kinda getting about a 20% decrease in highway rpms over stock height tires. So unless you're running 3.73 or 4.11 rear end gears you might want to steer clear of the 700r4.

Also if you do get a 700r4, I would look at getting one with an Advanced Adapters 700r4 in place of a th350 output shaft and stay away from extra bolt on things that are out there. The Advanced Adapters output shaft allows your 700r4 to bolt right to the existing transfer case adapter. All you have to do is move your engine forward a bit and put the 700r4 in there.

[Nova70]

I'm running 4:11's and at 65 I'm at about 2500 RPM.

[chas350]

Another benefit to the 700r4 is I believe it has a lower 1st gear, which is nice to have with a truck running 35's

[Nova70]

Originally Posted by chas350

Another benefit to the 700r4 is I believe it has a lower 1st gear, which is nice to have with a truck running 35's

Yeah it is. That's another reason I'm contemplating it. My truck doesn't do horrible but it is a pig from a stop. Especially when I'm towing.

[67ChevyRedneck]

My truck has a 700R and 3.73 and I'm spinning around 2000+/- @ 65 and 2300+/- @75.

I have much smaller tires too, 237/75/15.

[chas350]

Originally Posted by Nova70

Yeah it is. That's another reason I'm contemplating it. My truck doesn't do horrible but it is a pig from a stop. Especially when I'm towing.

Towing, thats exactly why I would want that lower gear...

[Nova70]

That's the reason I want it as well, but 95% of my towing is 1 1/2 + hours highway. My dad hauls the camp trailer and I haul the toys. We usually go every other weekend but sometimes we go one after another. I'm more concerned if it will drop my R's a few on @ 65. I don't want to lug it, but my truck doesn't do much more than 4 grand. The guy who built it made it pretty solid for low end. If I could get the R's to right around 1900-2100 when towing @ 65 it would be perfect.

[Nova70]

Bump. Any other input? Would appreciate it.

[mrein3]

I'm not too certain you want to tow with a 700r4. I had some email communication with bowtieoverdrives a few years ago. They claim their built 700r4 will take towing and I know the current version of GM auto overdrives has a tow/haul mode but I'm still from the old school where you were taught to tow in 3rd if you have a 700r4. That will still drop your r's verses your th350 because the 700r4 will lock up in 3rd gear.

You need to start doing math. If you spend $1500 to put a 700r4 into your current truck, how long will it take to recoup that money? That .7:1 final ratio doesn't mean diddly if you are towing in 3rd - which is 1:1. You're not going to see a 30% increase in mileage but you will see an improvement. IF however you are looking to reduce the noise that small block is putting out at highway speed you might justify the expense that way.

Long story short - it will take a LOT of miles to recover the initial cost of a properly built 700r4. However that doesn't take into account the reduced wear and tear on your engine from not having to spin 30% faster when you are on the highway and aren't towing.

[Big-Blue]

Have you thought about the 200-R4? It is the most direct fitting overdrive for the TH350.

[68 C-10 Panel]

I have a 700r4 in my 89 blazer and its running 38.5's. The trans is a great way to go but you have to have the rear end match up to the tires. The 4.56 in the diffs make the whole thing humm on the freeway. And with the first gear the way it is I can get this thing to get air with just a little run and a hill There are a couple of youtube videos of me jumping and mudding it if interested I can track em down. Anyway what I was getting at was that oversized tires are like a mild OD but then its a dog out of the hole. If you have big tires and an OD make sure you do the math and match up the ring and pinion set. Just my $.02 good luck

[Burb]

Just dropped a "Monster" 700R4 with a lock up converter switch in to my '71 3/4 ton Suburban. Will bark tires in 2nd gear.

With the lock up switch engaged my RPMs drop down to 1900 @ 65 mph, without the switch engaged it runs about 2200.

And I know what ya mean ... when I first got the Burban it had a TH400 w/ 4.56 gears on 16.5 wheels @ 32" tires .... we are talking 60 mph @ 3200 rpm praying there were no hills to climb.

[Nova70]

Thanks for all the comments guys. My dad bought the trans for $200 and said I can have it if I want to use it, so it's free to me. It's had a fresh rebuild on it, the guys wife wanted him to clear out his garage. lol.

[blazin]

Originally Posted by 68 C-10 Panel

I have a 700r4 in my 89 blazer and its running 38.5's. The trans is a great way to go but you have to have the rear end match up to the tires. The 4.56 in the diffs make the whole thing humm on the freeway. And with the first gear the way it is I can get this thing to get air with just a little run and a hill There are a couple of youtube videos of me jumping and mudding it if interested I can track em down. Anyway what I was getting at was that oversized tires are like a mild OD but then its a dog out of the hole. If you have big tires and an OD make sure you do the math and match up the ring and pinion set. Just my $.02 good luck

so your 700r4/4.56 gears are a good match with 38 inch tires.. how would it be with 35s? i have a 72 blazer with a 700r4 35's and i havent picked a gear yet.. not sure what would be a good choice.

[68 C-10 Panel]

Well to be honest I think they would be a little steep. When my truck is in 4 hi the rpms are normal to low on the hiway. if you are running 35's they may cross past the "normal" area into the high zone. I think if you were to keep it at 70 you would be ok but if you want to get somewhere in a hurry you would be back to burnin the fuel. You may want to look at one step down to a 4.11 ( I think thats one step?) If the motor has any trouble in the dunes the 4-lo more than makes up for it if your not looking to go to fast. The 350 in the beast is really built and in 4-lo with the 4.56, the trans goes through the gears in a big hurry. So unless i"m going up a really steep hill (like 60 deg plus) the 4-hi and shifted into 2nd or 3rd seems to work best Here are those vids on youtubehttp://www.youtube.com/watch?v=yJt73Jx-VY0# The jeep is my friends, I just put in a lockrite in the front and an ox locker in the back for him when we rebuilt the axles last year. good luck!

[DigDugDale]

Can anyone help me determine what kind of mileage I would get with a 2006 5.3L Vortec motor matched to a 4L60E tranny in a '71 C10? Thanks!

[Mt Man Chad]

Gear Vendors!!

The best over drive setup hand down.
700R4 suck with high HP and heavy rigs!

[CB24]

Originally Posted by Mt Man Chad

Gear Vendors!!

The best over drive setup hand down.
700R4 suck with high HP and heavy rigs!

I was set on going the gear vendors route until I saw the price! I think I'll just keep the bad gas mileage.

[ksbeatty]

I have placed the 700r4 in mine with the advanced adapters with 285's or 30-31 inch tires. It works great. I have not done a bunch of towing. I also have a GV on my RV but i wanted the extra gear between 1st and 2nd for pulling Monarch Pass. I have 4.10's and I think the RPM is about right for the highway. Gas mileage is a matter of how you drive. The faster you want to go at lower rpms will still burn at a rate that you may not see a huge difference. From what I have read and driven don't expect a huge difference, remember you still have to push that front end through the wind resistence.

I have been through this scenario a bunch of times. I still like the lower rpm's to save equipment but unless you plan on driving a rice rocket nicely don't expect big gains.

IMO i would use the 700r4 with 4.56 because 4.10's will not pull it depending on the motor which I did not see the discussion on. If it is a BB then you should be fine but a SB is a ?

[jeffro788]

I am running a 700r4 with what I believe is 4:10 gears, it is tacking about 2200-2300 at 70mph, as opposed to th400 turning nearly 3200. However, I have a 2wd. If you are running 35's, you might want atleast 4:10's, but I would be sure to go ahead and have corvette servos put in the transmission to hold up to the torque. I actually will not drive around town in overdrive b/c it does lug a little before it will kick down unless you goose it.