1973 Piggy trans questions? (1 Viewer)

[prbsurf7]

Hello All,
I haven't posted on the forum much, ever. But I do spend time reading posts and tech how-to's. I am hoping to get some advise on transmission choices for my 73" Piggy 3-speed replacement.
I am trying to decide what to put behind a 383 stroker I built just for the 55. I have a recon HF55/t-case combo for for another project. Also have a junk yard Th400 w/NP205. Or maybe a NV4500 or Tremec?? The rig is going to be used for off-road trip in BC ( If I can get into BC), but being driven from my home in the Santa Cruz Mtns. Any and all suggestions would be greatly appreciated. Especially first hand experience with recommendations provided. Thanks much! prbsurf7

 

[3_puppies]

first you need to figure out if you want an auto or manual

I would go with a trans with overdrive

 

[Hobbs81]

If highway use is one of your goals I would go NV4500 because you have adequate wheelbase. I've done a couple in CJ-7s. You would want to have the overdrive "big-nut-problem" fixed during the swap. Basically the large nut that holds one of the OD gears on the shaft can come loose and cause you to lose at least OD. The 4500 shifts well, has a decent granny (better if you can find an early GM model, they have a better granny ratio). If trail use or secondary roads are all you are worried about then the older T-18s or NP-435s are really compact and cheaper.
I have an automatic and mine and I'm on the fence about it. Easier to drive obviously, but no good compression braking. Biggest issue with auto is it generates a lot of heat. The small allowable space for a radiator makes this a tricky one. I'm paranoid about transmission temps (added a separate gauge) but this also takes away from engine cooling capacity because the hot cooler in front of the radiator obvioulsy heats the air that is getting to the rad. Plus I have AC...I'm not running as cool as I want.

 

[B y r o n]

My vote is for the NV4500. I have one in my FJ40 behind a 350 ci Chevy. AA makes an adapter to mate it to your original transfer case. As previously stated the NV4500 gives you a lower first gear for off-road, not needed on the street, and also gives you an OD for highway traveling. In my mind this give you a low gear for off-road and an OD for freeway flying! Go for it!

I forgot to mention, it also gives you all Chevy parts for engine and trans and all Toyota for transfer case back. That should make finding parts easier if need be.

 

[archie73]

My vote is for the NV4500. I have one in my FJ40 behind a 350 ci Chevy. AA makes an adapter to mate it to your original transfer case. As previously stated the NV4500 gives you a lower first gear for off-road, not needed on the street, and also gives you an OD for highway traveling. In my mind this give you a low gear for off-road and an OD for freeway flying! Go for it!

I forgot to mention, it also gives you all Chevy parts for engine and trans and all Toyota for transfer case back. That should make finding parts easier if need be.

What size tire are you running? I lust after the NV4500, but I keep reading overdrive is useless with anything over 35’s. I have a SM465/4.10 and it’s great, but seems like the old 350 revved high on the highway. I haven’t gotten the 5.3 up to speed, but I assume it’ll seem high at cruising speed.

 

[Hobbs81]

Concerns about the NV4500 not being of value with bigger tires are valid. My second CJ-7 with NV4500 had little 5th gear time. But it had horrible 2.73 gears (never got around to the gearing). I also had a pooch TBI 350. I would think with 4.10 gears and a healthy 383 you'd be able to pull 5th quite a bit. Of course if you have 44s probably not.

My (limited) experience with 383s is that they are great torque motors, but also have pretty high cooling needs. I don't think you'd want an automatic behind one with the small radiators we have to work with. Have I mentioned I'm paranoid about heat from automatics?

 

[B y r o n]

What size tire are you running? I lust after the NV4500, but I keep reading overdrive is useless with anything over 35’s. I have a SM465/4.10 and it’s great, but seems like the old 350 revved high on the highway. I haven’t gotten the 5.3 up to speed, but I assume it’ll seem high at cruising speed.

Have 4.10 gearing and 33-12.5x15 tires. Depending on how and where you're driving you may not get a lot of use out of 1st or 5th; not much off road 1st isn't needed around town and if you're just driving around town then probably won't see 5th very often. That doesn't mean that the NV4500 isn't worth the cost to swap it in though. It's like having a factory 3 spd except that you have that option to use a lower first when starting up long inclines or moving heavy trailers and it gives you the ability to drop RPM when on the highway and cruise easily at that lower RPM which will save gas. No regrets installing mine.

 

[pb4ugo]

Concerns about the NV4500 not being of value with bigger tires are valid. My second CJ-7 with NV4500 had little 5th gear time. But it had horrible 2.73 gears (never got around to the gearing). I also had a pooch TBI 350. I would think with 4.10 gears and a healthy 383 you'd be able to pull 5th quite a bit. Of course if you have 44s probably not.

My (limited) experience with 383s is that they are great torque motors, but also have pretty high cooling needs. I don't think you'd want an automatic behind one with the small radiators we have to work with. Have I mentioned I'm paranoid about heat from automatics?

The reason to run an NV4500 is to maximize the crawl ratio and still have highway gearing. A friend in his YJ, added a lift and 33' tall tires, he had the same result, 5th gear was useless with stk 3.08:1 diffs. The YJ has an AX15 trans which has a similar 5th gear overdrive ratio as an NV4500. Later he decided to upgrade to beefier axles with 35" tall tires. So a diff gear swap was in order. We 1st looked what the stk rpms the manufacturer designed for the YJ w/a stk 4.0L 6 cylder 3.08 diffs and 29" tires running 65 mph using an rpm calculator on the web. Then looked at what diff ratio we need to get the rpms needed for the 4.0l for 65 mph with 35" tires. We found 4.11's to 4.56:1 would put the gearing back to stk. Yes a sbc should pull 5th gear fine with a NV4500 and 4.11's on 33's. My street 40 will be running an NV4500, 3.70:1 gears and most likely 33" tires. This should put my rpms around 1900 at 60-65mph. Soon I be able to confirm if that works or not.


This will be a little bit out there. If I had the FJ55 with a sbc, I would most likely run a NV4500, then consider a split case to make it easy or either a Dana 300 or the stk NP241. I would stay a way from the 1 piece Toyota case, and IMO, orions are too exspensive with minimal benefits. I think the NP241 would be stk for the NV4500 so no adapter would be required in the drive line. The Dana 300 would require an adapter but the 300 would offer frt dig and is shorter. I believe the 300 offers a 2.62: 1 low range and the NP241 offers a 2.71:1 low. These are center rear output t/cases but with added length of the FJ55 this may not be an issue. If it was an issue., I would swap in a stronger centered rear end or center the stk rear end. You may have to alter the tranny hump to deal with added length of the drive line, especially with the NP241. I'd want a very robust drive line for a built sbc and the weight of the pig.