Power Train Swap for 1977 J10 Questions

[dljlobos]

Greetings. I'm new here but have already learned a lot from many of you.

I have a 1977 J10 with no engine but it still has the original BW1339 transfer case and passenger offset axles. I want to install a fuel injected engine and overdrive transmission and am hoping to hear others opinions on what would be the most straightforward and economical approach.

I'm leaning towards a 5.3 LS engine and I know there's been a lot of discussion about doing that swap. But the part that I'm not sure about is whether to (i) keep the BW1339 quadratrac transfer case and the passenger offset axles, or (ii) use the transfer case that comes with the LS motor and tranny, and find axles with driverside front and centered rear diffs that will work with the newer chevy transfer case.

If I stick with the BW1339, I will probably need to have it rebuilt, and also buy an adaptor kit, which may cost as much as new axles.

If I use the transfer case that comes with LS engine (241c I think), I will need to source new axles. I know that there is a lot of discussion about 3/4 ton axles, but here's the thing: I want to stay with 1/2 ton axles and make my truck a nice daily driver. I've been looking for 1/2 ton axles from an 1980-86 J10 that I think would bolt right up to my existing leaf springs, but I haven't been able to find any in my area they seem very scarce.

Any thoughts or suggestions? Thanks for reading this if you made it this far and thanks in advance for sharing any thoughts or wisdom from your experiences.

[sierrablue]

I'd go Quadratrac or Dana 20. Or you should be able to get a cheap pass drop part-time case (which is what you want for a daily driver). That does mean swapping the rear axle still though.

Probably not much help but just my thought process on that.

[cu4whln]

So much to answer here...

I used the original pass side drop axle.
Ratios were about right for the 6L80 trans.
Axle re-gearing is expensive.
I did a 5.3 LT.

Anyway, mine is a 77 as well... I have a long build thread you could look through as reference. .

remember, from the B pillar forward, it's all the same...

Expect this to be a very involved project...

However, its a huge improvement when complete.


http://www.ifsja.org/forums/vb/showthread.php?t=188457

[cu4whln]

Another resource for you . . .

Reference:

https://www.fsjnetwork.com/forum/vie...hp?f=35&t=9446

[dljlobos]

Thank you. I understand that the only cost effective option for daily driver passenger drop transfer case is 208 from 80s chevy? Are there any other good options out there that I should consider?

[dljlobos]

Excellent. Those are great resources. Thank you.

[tgreese]

My understanding - there is a NP241C that is passenger drop. Supposedly the 208 and 241 are very similar. Both have a centered output (unlike the BW1339), so you'll need to deal with that.

Look at this thread on fsjnetwork - https://www.fsjnetwork.com/forum/vie...216804#p216804 - it's mostly about putting a 700R4 in a Quadratrac Jeep, and the driveshaft interference issues. Apparently the overdrive automatics have a pan that sticks out on the passenger side.

The TH400 is an excellent transmission; it's not as efficient as a more modern automatic, but it's strong, durable and shifts nice. Parts are cheap and widely available. You can swap in the case from a Chevy TH400 and bolt up your choice of modern SBCs. You could then take the money you'd spend on a fancier upgrade and spend it on gasoline ...

[tgreese]

Also, what's your axles ratio? A '74 J10 had 3.54s standard, and that's most likely. I'd think that's plenty tall for the highway, especially with taller tires. I'd say there's no need to go to an overdrive transmission with that final drive ratio.

[sierrablue]

Not sure on the most cost effective (other than that you want a part-time case and not a full-time for a daily driver), sorry. Probably the NP241C, though you could also just buy the drivetrain from the donor truck and get the axles from a post-1979 rig, might be cheap especially if you can work out a trade with somebody (for the Qtrac axles and maybe the Qtrac itself).

[cu4whln]

Thank you. I understand that the only cost effective option for daily driver passenger drop transfer case is 208 from 80s chevy? Are there any other good options out there that I should consider?

I used a Dana 300.

As mentioned earlier, it has a centered output for the rear. A new driveshft will be required.

[sierrablue]

I used a Dana 300.

As mentioned earlier, it has a centered output for the rear. A new driveshft will be required.

Doesn't it require a centered rear axle too? Or is that just recommended?

[cu4whln]

Doesn't it require a centered rear axle too? Or is that just recommended?

I made it work with the original axle... details in my powertrain build thread.

Double, double carden. ie one at each end

[babywag]

Ditch the QT, while it was well ahead of it's time and an excellent transfer case, they're 40+yrs old. New parts for them are stupid expensive, and the pool of good used stuff is virtually non-existent.

[tgreese]

Ditch the QT, while it was well ahead of it's time and an excellent transfer case, they're 40+yrs old. New parts for them are stupid expensive, and the pool of good used stuff is virtually non-existent.

In this vein, I'd say the Quadratrac would be ok for you if you are willing to understand it and work on it yourself. Yer random drivetrain or 4x4 shop won't do any better than you can do, and very likely worse. Nobody cares as much about your build as you. There is a lot of discussion online in these forums about these transfer cases, and you can expect some expert responses if you ask.

The main issue with these transfer cases is chain life. Unfortunately, the chain drives both the front and rear axles. Modern chain-driven cases use the chain to drive just the front axle - that's why they are all centered rear output. The load of the rear axle makes the beefy Quadratrac chain wear out in maybe 60 to 100 thousand miles. There are quality replacement chains available today from Ramsey (?); the import chains are not good and wear out quickly. Again, yer random shop would likely install a junky chain ... not good.

I would also not invest in a part-time kit for an existing full-time Quadratrac. My opinion - run it full-time or change your plans for the Jeep.

JMO - Jeeps this old are both oddballs (different from common makes) and dinosaurs (old or obsolete technology). Most shops will not want to work on them. Very hard to own them unless you have deep pockets or can work on them yourself.

Lots of discussion here and at fsjnetwork if you search old threads.

[dljlobos]

Thanks for all the great responses. You've opened my eyes to more info and details that will be very helpful. I'm also impressed with the effort and skills on those build threads!

At this point I'm leaning toward replacement the axles with driver side drop in front and centered in rear so I can use the newer transfer case that comes already mated with LS engine and transmission.

So far I've only found those axles in a salvage yard in California. They call them M44s and say they will bolt up to my existing leaf springs. I've heard of D44s but not sure what the M44s are from. The price is about $1500 for the set plus shipping. Does that sound like a reasonable price or any suggestions on other places to search? There used to be an AMC jeep salvage yard in Phoenix but it closed down a few years ago.