4.3 Build Advice

While waiting for the motor for my 68 CJ5 build, I decided to start another using spare parts. I have the following (with little or no cost in them):

• SM465
• Dana 18
• NT Dana 30 front with 4.88
• Flanged Dana 44 rear with 4.88
• Dana 27 front with 3.73
• Flanged Dana 44 rear with 3.73

Wanting to run a 4.3 TBI V6. Purpose of the Jeep will likely be 70% offroad, 30% on road. Nothing crazy, but I want a capable trail rig that can also be driven to or between trails without being the slow poke. Most likely go with 32" or 33" tires.

I'd like to use the D30, but thinking to re-gear to 3.73. I believe the 4.3 motors redline around 4500 rpm. Only 4.3 I have ever had was in a boat and it seemed happy cruising around 3000 rpm iirc. So by my math:

Crawl ratio with 6.55:1 granny gear, 2.46:1 D18 low range and 3.73 axle is 60...respectable. Same set-up in 2H, 4th gear would put engine rpm's around 2,470 @ 65mph or 2,659 @ 70mph with 33" tires.

By contrast, 4.88 axle ratio would be a crawl ratio of nearly 80...rock crawler status. However, engine rpm's would be 3,231 @ 65 and 3,480 @ 70.

All theoretical of course for planning purposes, but I am leaning toward the 3.73 option for all-around usability. The 4.88 seems a bit deep on the low end (read as breaking stuff) and too many rpm's on the top end. 3.73 would also allow me to go to a 32" or 31" tire and likely still be in an acceptable rpm range at speed. Like to stay away from overdrive for simplicity.

Thoughts welcomed.

 

I think the 3.73 and sm465 would make a good DD/Trail rig. I think the Higher (numerically) transmission ratio compliments the lower (numerically) gears.

 

70% off road...I'd go with the 4.88's. You get all the advantages of a dana 30 as well: Better steering, better choice of lockers, stronger shafts, great availability of parts, better clearance for larger tires.

Ive got an 84:1 crawl gear with 33's. And its perfect. Terra low gears would take me to 100:1, and I'm tempted. Slowing things down and not spinning the tires is good style IMO and keeps you from breaking stuff.

An overdrive is so simple to put in there, and in my mind, a big advantage to the 18 case. I really dig being able to split all my gears.

For driving around, the SM420 (sm465 jsut as well), the OD and the 4.88's & 33's are very road-able. I can go 60mph with no worries. Its a capable, well-balanced set up off road that's also fun and safe to just drive around...

EDIT: Just reread your post that you're not into an OD...can we change your mind? Its not that complex. FWIW, I don't think the 4.88s will lead to breakage, especially with flanged axles.

 

Go with the 3.73's and sell me the D30 and offset 44 with 4.88 gears

 

4.88s on 33s gets my vote. The 4.3s are so cheap and common, killing one from high RPMs isn't that great of a loss. Although, I don't think it's too much to ask of one to run 3400 RPM all day. Fuel mileage might suffer, but I doubt engine longevity would as long as you keep clean oil in it.

As far as tire size goes, I've found the step between 32s or less and 33s or greater is huge for traction. 33s seem to be the magic size.

 

I am working on a warmed over 4.3 on my build. T-90 short term then sm-465 long term.
Overdrive and 5.38 axles. The t-90 is not deep enough using an RV cam grind.
The biggest problem with the 4.3 is it has two main oil galleys where as the v8 has 3 main gallerys and 4500 rpm is all you really want to run stock before you start starving the engine of oil. the 3.48" stroke is a lot easier on the bottom end components compared to the 134 which can do 3600 on a good day.

 

if you're not going to run an OD why even go with a D18? No OD means you can run a D20 or D300 and not have to deal with only offset axles.

 

I wondered how long it would take for someone to help narrow my choices by offering to lighten my parts pile. The winner is James at 9 min!

I really appreciate the excellent feedback everyone.

Very solid points James. Going 4.88 would avoid the D30 re-gear, funds which could go toward an OD. This would also allow for better gear selection offroad. The 3.73 only allows the low crawl speed in granny 1st gear, fairly big jump to 2nd gear. Staying in granny 1st and shifting to 4H would kind of split the difference, but much easier to shift the transmission than the t-case in a hurry. Having ridden in your set-up, no arguing its capability. Was kind of hoping to save the OD money and put toward BDS springs based on how well yours performed. Funny thing is, I actually do have an OD, but it is on my 69 with 4.88's. I could steal it for this build, but that would definitely relegate the 69 to the slow lane. Not planning to keep that one long term, but it is the only running/driving Jeep I have at present.

Based on the feedback, now kind of leaning toward 4.88's for better gear selection offroad, then maybe do the OD at a later time if engine RPM's at speed becomes an issue.

Thanks Chris. Re-considering OD as an option. Starting from scratch I would definitely consider other t-case and axle options, trying to use up parts I already have on-hand.

 

Thanks James, who better to go to for number crunching and rock crawling advice than a Teacher/Geologist?

The SM465 to D18 adapter from Novak includes the mainshaft and can be ordered in 6 or 10 spline. I am rebuilding the SM465 now and need to order the adapter/shaft soon. Kind of why I am trying to plan this out as the D18 is nearly complete as well pending which speedo gears will be appropriate before I button-up the rear output housing.

 

I am running almost the same combination. 231 V6, SM 465, D18, D30, flanged D44 with 4:88's and a Warn OD. I see maybe 85% to 90% off road and wouldn't trade it for anything. The crawl ratio is absolutely awesome and with the OD I can still cruise at around 2400 RPM at 65 mph.
I used Novak's kit for the SM 465 to D18. They sell top quality stuff and their customer service at the time was great.

 

Yes, the adapters are pricey for either transmission to D18 ($515 or so from Novak). One little tidbit I will share from my research is that while the SM420 is shorter than the SM465 (10.7" vs 12"), the adapter for the SM420 is 4.4" long whereas the SM465 adapter is 1". So, overall length transmission + adapter is: SM465 - 13", SM420 - 15.1". The stock T14 is 8.7", so you lose the following in rear driveshaft length (SM465 - 4.3", SM420 - 6.4"). Deeper granny gear in the SM420, but I was worried about the driveshaft length/angle. Just food for thought.

Thanks jzeber, you just had to go and make it real! I see in your signature line that you also run 33's. Nice that your real life experience lines up pretty much with my calculations. Being in Arkansas, I had to use my toes to count and everything, so I wasn't completely sure on the math

Seriously though, I really appreciate it. You guys about have me convinced on the 4.88/OD combo.

 

Second Dibs here.

 

The SM 465 is tied for best upgrades ever with the Detroit Locker. I am still happy I did it. I lucked out and bought my Jeep with the OD. The rear drive shaft is a bit short at just over 12" but it has never been a problem. I know a great driveline shop here in town. I went from 32's to 33's and I kick around the idea of 35's. I have a really hard time justifying a 1" over height increase. This is not a cheap upgrade. After it was all said and done mine cost about $1,500. New driveshafts, new clutch and all that goes with it and I added a disc parking brake and got rid of the drum. I think I even did a write up on it some where on here.
Looking forward to seeing what you end up with.

 

Looks like it's ready to bolt up to a D300!

Edit: I don't know how the head-scratch emoji ended up on my first draft.

 

Those look like pretty fair deals. They tend to have an issue popping out of 3rd gear, but the Novak rebuild kit includes a fix for that. It is a beast of a transmission compared to the T14; pretty sure my T14 will fit inside of the SM465 case! Getting it mounted in there correctly will be interesting, but having seen how beefy everything about it is, pretty sure everything else will break on the Jeep 4 times over before that transmission gives up.

 

Just for fun, T14 vs SM465 case...