700r4 or TH400 with gear splitter?
 

Alright guys I have a 1970 gmc with a 454 and a TH400. which is better changing out the transmission to a 700r4 or just adding a gear vender gear splitter to the existing transmission to add the extra gears. the goal is to get better gas milage and be able to run it at higher speeds with lower rpms. what do you all think?

Re: 700r4 or TH400 with gear splitter?
 

You may be able to cruise better at highway speeds.

But forget about mileage. The best you will get is 8-9. I get 9-10 with 3.73, overdrive, and modern fuel injection.

Another option would be a different ratio in your rear diff. I assume you have 4.10 or 4.56 back there.


If you do decide on the 700R4, it would need built to last behind a big block.

You could also do a 4L80E with a stand alone controller.

Re: 700r4 or TH400 with gear splitter?
 

Have you considered how long it would take to get your return on investing 3K on a gear vendor piece. I installed a 700r4 in my 1972 c10 with 3.42 gears well under the price of the piece you are looking at spending 3K. If money is no issue, bombs away on the credit card.

Re: 700r4 or TH400 with gear splitter?
 

The GV will lower your rpms, but not your mileage.

Cheapest solution is new gears. If yours is like mine it probably has 4:10s in it.

I would do a 4l80 instead of the 700 if you just want to change something. Still less than the GV.

Re: 700r4 or TH400 with gear splitter?
 

If those were the only 2 choices, I'd go for the 700R4 for the advantage of having a lockup converter. A 700R4 built will every available upgrade will be less than a GV.

GV does give you the very cool option of splitting gears though.

As others have suggested, a 4L80E is really the way to go.

Re: 700r4 or TH400 with gear splitter?
 

lol. Yes lowering your cruise rpm will gain mileage. If it didn't the oem's wouldn't have done it seeing as no truck accelerates with a load in overdrive meaning they added no usable gears with overdrive except at cruise.
700R4 with a 454 is a joke. Not an option IMO.

Re: 700r4 or TH400 with gear splitter?
 

:agree:. What Tom said.

Re: 700r4 or TH400 with gear splitter?
 

In most cases it will, but not with big blocks.

I get 9-10 all the time. It doesn't matter if I am driving empty, towing 8,000 pounds in third gear. The same is true with my rollback. It gets 9-10 when empty(9,000 pounds) and gets the same when fully loaded(15,000 pounds) and in fourth gear. That has 4.88 rear axle and an NV4500.

You can look on this site and many others and see what kind of mileage big blocks are getting.


You don't buy a truck with a big block for mileage. You buy it to haul/tow.

Re: 700r4 or TH400 with gear splitter?
 

In my opinion, 700s should NEVER be considered in a truck for any type of work. It is a passenger car transmission. The very last thing I would do is put one behind a big block. I've had enough trouble with them behind small blocks, special drums, vette servos, shift kits heavy duty this and that...they just don't last long term when asked to anything heavy duty, such as towing. Go with a Gear Vendor or a 4L80e. I am converting my Suburban from a 700 to a 4L80 and I have a gear vendor in my 69 flat bed. Flat bed has a built big block and the suburban is a stock 350 tbi soon to be a 400 next year if money allows

Re: 700r4 or TH400 with gear splitter?
 

as said big block engines are for WORK not mileage .

and a good cheep way to optimize fuel mileage is a simple gauge like this .

you will be amazed how much you can gain by watching this little guy . not saying you will get a ton but it will improve .

Re: 700r4 or TH400 with gear splitter?
 

No its actually very much a truck transmission. Cars used the 200-4R except for full sized caprices.
That's a terrible statement. Just because you buy something to work doesn't mean you can't or shouldn't maximize its efficiancy where possible. And I know this may sound crazy, but some people buy big blocks for fun, not work. Not too many 48yr old trucks being put to real world, daily business type work these days.

Re: 700r4 or TH400 with gear splitter?
 

Whatever they're still junk in my book. I've wasted a quite a few grand on 3-4 700s, only to have them either break, slip, not shift correctly etc. All built by professional "700 experts"

Re: 700r4 or TH400 with gear splitter?
 

What mileage are you averaging right now?
What would you consider an acceptable increase in MPG?
How much are you willing to spend, to achieve this increase?
What speed are you trying to run, and what RPM are you running at that speed?
What gears do you have?
How tall are your tires?
Is this a 1/2 ton, 3/4, 1 ton?
2wd, I assume?
What Carburetor or FI system are you running?
Points or HEI
Is this thing properly tuned?
Are you sure you need OD?
Would taller gears and/or some tuning get you close enough?
A properly tuned 454 will twist some pretty tall gears.

Keep your expectations low. It ain't EVER gonna get great mileage.

Re: 700r4 or TH400 with gear splitter?
 

If the engine makes any power, a 700R4 won't live. The GV unit will.

Re: 700r4 or TH400 with gear splitter?
 

I run a 700R4 behind a big block in my 72 Blazer and my 72 swb 383 c10, never had a issue with my 700R4 transmissions.
But I do not abuse my equipment nor do I expect things to last for ever.

Not sure why so much hating on the 700R4's but I will take all of the ones everyone dont want. Thanks.

As far as gas mileage, big block and gas mileage should not be used in the same sentence. If its your daily driver than I would look to buy another vehicle with better mileage.
Should this be more of a debate on a 700 vs 400 with GV ? 70 LWB truck with a 3000 dollar GV, I dont think I would spend the cash on a GV....Ask yourself what the truck is worth, its a LWB truck right ? the GV is worth half as much as the truck. I already know what I would do but again these forums are so much fun to hear other opinions.

Re: 700r4 or TH400 with gear splitter?
 

History. Yours are living. Most don't.
I'm sure others are like me in that the value of the vehicle doesn't mean jack s**t. We aren't building them to sell and make money. We build them to enjoy. You never get your money back on upgrades, that's life.

Re: 700r4 or TH400 with gear splitter?
 

Like I said in my previous post, its fun to hear other opinions.

Re: 700r4 or TH400 with gear splitter?
 

Nv4500

Re: 700r4 or TH400 with gear splitter?
 

I think we scared the OP away.

NV4500 is a good choice if you like rowing through gears (actually have one sitting on the garage floor to replace the TH400 behind the 454 in my R30). If I ever get around to the diesel swap in it, I'll ad a GV behind the NV4500.

Honestly though, if the OP wants an automatic he should be looking at a 4L80E. Not only is there way more strength than a 700R4 (not knocking the 700...I have one living behind a diesel that is making 500+ ft/lbs of torque and it is fine), but the ability to tune lockup and shift points with the controller can really make for a nice driving experience.

Re: 700r4 or TH400 with gear splitter?
 

Agree on the 4l80. Now...if I could just win the current lottery.

Re: 700r4 or TH400 with gear splitter?
 

I just like em, all four of em :smoke:

Re: 700r4 or TH400 with gear splitter?
 

A question to ask when considering a GV is "Can the gears be split PROGRESSIVLY"?
I've asked this question lots & GV dances around the answer.
Yes it will "Split" the gears, but if it won't split them "PROGRESSIVLY" then all you're adding is an OD box that will go from direct to OD & back again.
Also remember that the GV box is very small & uses it's own lube reservoir, not the trans lube & there's no way to cool it.
Not bashing GV units but it's a lot of $$$ to spend & not know the answers.

Re: 700r4 or TH400 with gear splitter?
 

If you are asking if it will do this...

1st
1st OD
2nd
2nd OD
3rd
3rd OD

It won't do that in automatic mode, but it is fully capable of doing that with manual control.

If that isn't what you mean, then please explain "progressively".

Re: 700r4 or TH400 with gear splitter?
 

DieselSJ that's xactly what I was talking about. Some transmissions & splitter boxes aint compatable ratio wise. Having said that, ALL my experience is with Class 8 truck equipment, not the GV splitter, although I did drive a truck once with a Doug Nash Under drive in it but it was an auto trans.
Have you owned / driven a GV w/ a std trans & shifted it progressively? Sure be interested to know how they perform!

Re: 700r4 or TH400 with gear splitter?
 

Yes, we had a shop truck with a NV4500 and a GV. The NV has some fairly large splits so the GV worked very well with that trans. Drove that truck fully loaded towing an enclosed trailer with a race car with a full set of spare parts and tools from the shop in San Diego out to Colorado Springs. We had the manual switch for the GV mounted on the gear shift so it was easy to shift both units at the same time.

If you are concerned about the split ratios, it is easy enough to figure out what the splits would be if you know the ratios in your transmission.