If you've installed a 700R4....

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.


UP of MI.
Jan 28, 2003
UP of Michigan
I'm days away from installing a 700R4 in my '70 FJ40 and "conversed" with one of the tranny guys doing the work today and he said that it may not be any better than the 3 speed because of the 4:11 gears. Personally, I think he's a dipsh*t, but if I'm wrong, and anyone out there can give me any sort of relevant heads up, I'd appreciate it. I've already built the R4 and have the AA kit for SBC 350, guess I'm still going to do it, but what the heck, let me know something.

(I reckin it's a foreign type-uh jeep)
Yikes,::) I hope this trany guy is just sweeping the floors. Pull up a chalk board for him…Gear ratio’s are mathematics…

Trany guy Lesson A. If you have a 1:1 out the back of your T350 auto and your ring and pinion is 4:11 you get 4:11 at the axels.

Trany guy Lesson B. IF you have a 1:0.7 (70% OD or 30% depending on how you look at it) out the back of your T700R4 auto and your ring and pinion is 4:11 you get 2.887 at the axels! One heck of an over drive! Whoo hoo! Even better with the 700R4 it’s the 3 to 1 first gear.. (W/O considering anything else) with a 4:11 rear end you get 12:33 to one… monster low end. (Where as the T350 is around the 2:1 first only 8:22 to one )

Bottom line, a properly built 700R4 is perfect for what we do.

BTW: If tray guy has a perplexed look, talk about how it would be better to sweep up the floors if he had a 30% bigger broom. ;)

You probably already know this. but since I'm fixing on using a 700r4 also I've noted that its very important when hooking the r4 up to have the TV cable adjusted correctly. I understand that when not adjusted right its real easy to burn up the trany.
good luck and keep us posted on how it works.
i have 700r4's in my 40 and my 45.. they are the way to go... just be sure to get an 1988 or later.. it has a larger shafts and valve bodies etc.. shouldnt be hard to come by.. and you will have to fab a bracket to get the kick down cable adjusted right.. but it isnt a big deal... you will also need the converter lockout kit.. but there are ones on the net for 60 bucks.. far cheaper than the painless wiring kit...

if your going to do a 700r4 i suggest doing the 203 dual case set up.. it will be cheaper than the AA kit for the 700r4 to toy case and you get a two transfer setup in the process.. when i am in low low.. and in OD on the tranny i am still only going 15 mph.. plenty low...

I also run a tranny cooler in the front then back to a second cooler with a fan ( derale ) and a temp switch.. that does the trick for me.. even in moab last weekend when it was 95 deg plus...

if you have any other ???'s hit me with an email

good luck
This 203 set up you speak of, forgive me, but shed some light on it, because I've already ordered the AA kit, but haven't cracked into installing it yet. (Plenty returnable). This project is going down this week or next, so I'm lining up ducks by writing you guys. Truth lies, however, in the experience end of the job, but we can all appreciate a good heads up.

Either way, I'll be sure to post head aches and heart throbs.
hey man i am assuming you have a fj40//

the np203 is a chain drive chevy truck tcase.. you can get one with a broken chain for next to nothing.. you will only use the gear reduction part and toss the rest so you dont need a good one... a core will do... the gears in the case are HUGE so they will take the load... when you get the 203 you need to ask to get the stock adapter plate from the auto tranny to the tcase.. they sometimes throw it in for free... I got two core tcases for $25 buks

then AA sells a kit.. its pn 50-8801 for a 10 spline case and 50-8802 for a 16 spline case.. its $489 and you will need the output shaft they sell for the 700r to make it look like a turbo 350... then the tranny will bolt up to the gm adapter which bolts to the 203 which bolts to your LC case.. this gives you a second tcase so you will have hi n low on the 203 and hi n low on you lc case.. pretty cool and only 2" longer than the AA adapter but you now have a stump pulling low range...
you will have to make a setup for your shifters but i sat mine side by side.. all three fit out the stock tcase hole in the tranny hump in the floor

here is your gearing...

a typical 40 with a 4 speed case

700r 1st gear... 3.06 :1
203 box 2:1
LC case 2:1
gears 4.1: 1

total 50:1 ... it would be 57:1 with a 3 speed case

not bad for an auto figuring the torque converter will get you even lower.. and you will have an OD to go 75 mph on the highway

I would suggest flipping your rear springs around to lengthen the wheelbase by 3.5".. it makes a big difference on hiway stability and on steep hill climbs...

then later you can swap in fj55 springs.. by flipping the rear mounts... but you wont have any driveline changes
i've had an r4 in my 40 for about 4 years.it is the way to go, my low gear in 4w low is very slow great for off road.the o/d for hwy is good for cruisin at 70mph.but you do have to set the cable in the right position or it wont work correctly.you will also have rear drive shaft probs.it will be pretty short,you will probably need a c/v joint for the angle.
why haven't you guys written a paper in the tech section?
i like the sound of this auto-trans duel case setup.

Users who are viewing this thread

Top Bottom