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Discussion Starter · #1 ·
What are your Guys opinion on swapping out a TH400 for a TH700R tranny. I know the adapters from AA are very expensive but do you think its worth it?

Hoot

79' CJ-7,AMC 360, T400, Dana 300, D60 and D30 4.10, All Fiberblass.
 
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Discussion Starter · #2 ·
Only if you're interested in picking up some gas milage in my opinion. Sure the first gear is lower, but the torque converter helps compensate for this.

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John
95.5 YJ with "stuff"
http://SonsofThunder4x4.com
 

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The TH-400, (three speed) is a power hog of the worst kind. In some cases, depending on converter, they can consume up to 40 horse power. The gear ratios don't lend them selves particularly well to 4 wheeling, but they are tough.

The TH-700R-4 (four speed) 1st gear is lower than the TH-400. Lower gear ratio means slower rock crawling and snappy starts when trying to get into traffic.
The TH-700R-4 uses less than 1/3 of the horse power of the best TH-400 build, and according to the GM usage charts, the TH-700R-4 is only VERY SLIGHTLY less strong than the TH-400.
It has better gear spacing than any previous GM transmission, and that helps keep you in the power band of your engine. Not many people take this into consideration when picking a transmission.
The TH-700R-4 has an over driven 4th gear. Over drive means longer legs on the top end (higher top speed). Over drive also means much improved gas milage, and lower engine speeds (RPM) on the highway.
The TH-700R-4 has the added option of a lock up torque converter that increases it's efficiency, and adds fuel milage.
(The lock up converter will only engage in 3rd and 4th gear, and can be turned off with the push of a button, if you choose not to use it.)

This is a no contest comparison. It's like comparing the old breaker point ignitions to the better late model electronic ignitions.

You may be able to find the transmission you want, depending on your application and the transfer case you are using, in the junk yard. TH-700R-4 transmissions came out in several versions of GM 4X4's for several years. The adaptors for the NP T-cases grow on trees, and the tail shaft housing is the same as a TH-350, and there are literally millions of those out there for an adaptor source, but I don't know about the output shaft, my transmission guy is in Fla. right now. (I'm thinking most will though)

Hope this helps. Aaron.

So many cats, so few recipes...
 

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/wwwthreads_images/icons/tongue.gif Our TH400 is sitting here all "fresh and clean", ready to pop into the CJ7 behind the mostly stock 304. What, if anything, can we do torque converter-wise to improve the MPG?/wwwthreads_images/icons/smile.gif It's not too late to change to a different converter if there is one./wwwthreads_images/icons/tongue.gif

CJDave
I never believe any statistics unless my moonguys /wwwthreads_images/icons/crazy.gif/wwwthreads_images/icons/wink.gif made 'em up themselves.
 

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Generally, the larger the torque converter, the more efficient it is, when you are talking about car converters. more fin area and more fins = more efficiency. (Fin pitch can be altered, but this is correct as a general rule)
If you talk about truck converters, all bets are off. A lot of truck converters were made to 'slip' so you didn't do the drive shaft eject thing or smoke clutches when you took off with a load.
(Stock truck converters are the best kept secret in the aftermarket parts business for 'race cars' and 4X4's. Quick coat of paint, and a new sticker, and triple the price...)

Car converters were made to be more efficient. There is no lock up converter for a TH-400 that I know of, so you are stuck with a common converter.

I remember back in '87 when we were building a car for a coast to coast race, we used a GM parts guide that identified a 'BU-3' converter as having a good stall speed, but has the highest efficiency of all the converters at the time. It was LARGE though! A really big sucker. It was a stock item for a early 70's Impalas' with a small block 400 W/ 4 bbl. carb, and was used in the automatic corvettes, but I don't remember if it was for the TH-400 or the TH-350 transmission...
I don't know if it would fit in the modified bell housing of a TH-400 for AMC engines either...

My second choice would be the latest model of TH-350 gas miser GM put out with a 350 V-8. You know, like what ever the last year of Impala or Caprice Police car that has a non-lock up converter in it... It will take some research at the parts store, but I'm sure it's worth it...
Let us know what you find out CJ Dave...

Hope this helped, Aaron.

So many cats, so few recipes...
 

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To CJDave:
I recently had my TH-400 for my '70 Waggie rebuilt with low-end/towing/jeepin/economy in mind with all HD internals. The torque converter chosen was a GM Allison #TC-275. Cost was $255.25. This has all new bearings, furnace brazed fins and is balanced. I'm very happy with how the tranny turned out. Shifts slightly crisp, not jerky like so many of the reprogramming kits and aftermarket trannies available out there. Happy Trails.
Tim
'66 Jeepster Commando w/Buick 252/4.1L V-6 (soon to have a 700R4 & Atlas II)
'70 Wagoneer w/Buick 350 V-8
'76 Wagoneer w/AMC 401 V-8 (sold)

 

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2 things pop to mind that havent been covered:

1) the th700r4 MIGHT be easier to get a transfer case onto if your looking towards a later model New Process case

2) the Th400 has a switch pitch converter available for it, im not sure exactly how it works, but it equates to adjustable from low stall to high stall with a dash mounted control...

Id personally go with the 700r4, build it right, get the biggest cooler you can mount, and keep the converter unlocked everywhere but long highway trips and itll last and last and last...



ozarkjeep
1977 CJ5 looking for a Hard top near NW Arkansas!
 
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Discussion Starter · #8 ·
I am running a TH400. One thing I was told that could be a prob with a 700r4 is that the fluid pan is bigger and protudes to the passanger side more than the 400. This could cause front driveshaft interference probs if you are a passanger side drop front diff. Dont know how bad or if it is with certain cases or what, but it is somehting I have heard and you might want to look into.

 
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Discussion Starter · #9 ·
I have actually ahd both in my Jeep. I currently run a TH400 with a manual valve body. I like it. The 700R4 I had ended up being junk, but I did notice a 400 rpm drop at cruising speeds...but did't notice any milage gains. You have to make sure you hook up the lock up for high speed driving, otherwise it will cause you tranny to overheat and fry like bacon. I usually lean towards the simple route. I have a th400 with a np205 transfer, this is a couple inches shorter than the th350/np203 combo and ALOT stronger. Why did you leave out the th350 as a choice? I didn't really have to worry about horsepower loss that much, because my 350 engine is moderately modified. I probably wouldn't go that beefy with a smaller engine. I guess if you could have or find a 700r4 that was built for moderate four wheeling, I would lean towards that, but don't forget to order the lockup kit from Jegs/summit.

~TIM~

I'm not afraid of dying...I'm scared of not living

chevy-Cj-7
 
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Discussion Starter · #10 ·
I installed a 700R4 in a customers' CJ8, with a 360 AMC using the AA adapter. The performance is great. The only complaint is the cheesy adapter setup for the AMC engine. The starter needed to be shimmed to prevent excess noise, the spacers needed between the torque converter and flexplate come loose often, the bolts supplied had heads that were too tall and hit the adapter plate as the engine ran, and the cover for the torque converter required alot of reshaping to prevent it hitting the converter. It took me 2 weeks to get it working reasonably well, and the customer brings it by often to check the bolts. In my opinion, this trans would work well with a GM engine swap, but I wouldn't recommend it on an AMC engine.

 
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