45MPH in 4th? What are my tranny options?

[Slingmaster]

I have got a pretty much stock, J-10 4X4. It's nice, but I don't live exactly close to my weekend crawls. I've got the T-18 but I'd like to get an automatic. In order of most affordable, what are my options. The T-18 is in great shape and will make someone very happy, but I need a little more versatility. Also, what else will be necesssary for the swap. Personal accounts or links would be greatly appreciated!

[Lindel]

with a 76, your best option for an automatic is an AMC TH400. You can get one from a donor rig, or find an older AMC car that might have one.

If you swap engines, then you might have more options on automatics

[joe]

45 mph top speed in 4th gear has nothing to do with your tranny. All trannies in FSJ's are a 1:1 ratio in high gear be it a T18/T90/TH400/TF727 blah blah...whatever. Opps the T-5 had an OD gear but that doesn't apply to you.
Axle gearing will seriously limit your top speed though but the only rig I've had that was maxed out at 45 had 5.38 gears and a 53 Dodge flathead 6 truck motor(not a powerhouse).
The lowest "stock" gears(optional) in a 76 J-10 were 4.09's and they'll do better than 45 mph. I can run 65 easily with my 3 FSJ's that run 4.09's and one is only a tired 230 OHC six banger.
You're top end(or lack of it) problem isn't your tranny...it's either really low axle gears(non-stock) or a really weak nippled motor(as in: worn out or way out of tune).
A 76 shouldn't have a catalitic converter but who knows what folks(DSPO's) add to there rigs for whatever reasons. If you do have one it may be plugged.
Find out "why" you can only run 45 mph in 4th before you spend bucks on a not-needed trans swap cause your T-18 ain't the prob. Again the T-18's high gear is identical to the TH400/TF727 automatics.

[Slingmaster]

Thanks alot Joe. I'll check the tuning. I'll probably sound like a complete newbie FSJ owner, but... its the axles not the tranny, okay then that makes a little more sense. Thanks :D

[Lindel]

It's very possible that the transfer case is in low range. What are your speeds in any of the other gears? Does the truck accelerate alright?

[joe]

Lindel brought up a good point to check. Never considered being in LO range. 45 mph in LO range...wow! Acceleration I bet would be "snappy" at the least smile.gif

[Mikel2]

Thatīs a good point smile.gif
My Dana 20 got stuck once in low range, and thatīs about how fast I could go (4500RPM). But I tried to stay under 3000 most of the time... People behind me didnīt appreciate it :D

[Mikel2]

When you drive your truck, does the tranny whine (gnnnnnnnn) a lot? Low range gears in a dana 20 are straight cut and make a lot of noise. That would be a good indicator.

Can you move your shifter? Shift pattern should be

2H 4L

4H - N

And the shift sequence is 4L, N, 4H, 2H and viceversa. Getting the shifter out of 4L can be... problematic sometimes. Good luck smile.gif

[Slingmaster]

I have had trouble with the T-Case. Those are really good ideas. I woulda never thought about it but I have some trouble shifting. :cool: Thanks again

[jeepbob]

A quick note on automatics if you still want one. AMC cars used the toqueflyte or a borg warmner trans and that would be useless unless converted over to 4x4 use and a dodge 203 or a jeep 300 transfer case were used. The borg warner tranny is totally useless. The T400 are mostly q/tracs or can be set up for D20 although you must either get an adapter kit or find a D20 for an automatic as the input gears were different.
BTW if you still want an automatic tranny, I will trade your t18/D20 for a rebuilt t400/bw1339 with new chain and good low range w/shifter.

[ December 29, 2001: Message edited by: jeepbob ]