Build Dirty Koala Build - Cummins Common Rail + NV4500 + HF2AV Swap

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cruisermatt said:
Wow that’s some good carnage. Will you be selling the air locker and 9.5” 4.88 gears?
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The 9.5" ARB is going to go in the front diff of my BJ42, The 4.88 gears I could sell as I wont be using them in the 42.
 
fireball said:
How am I going to know you're behind me when wheeling without your air compressor constantly cycling on and off?!
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You will just have to rely on the tacka-tacka-tacka of the Cummins to keep tabs on my locale.
 
I knew I was going to regret saying the rear will go quick. I just zipped off the axle shaft nuts only to find that who ever setup these diffs used RTV to seal the axle shaft and all the little cone washers are good and sealed in place...this is going to be more work that it should have been.
 
orangefj45 said:
Yum. Silicone everywhere ...... sadly we see that at the shop a lot. And the factory gaskets are literally $2 each ......

Georg @ Valley Hybrids & Cruiser Brothers
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I soaked the studs/cones with some solvent from my parts washer and let it sit overnight. Yesterday the shafts came out without too much persuasion. I will be putting a gasket back in when this goes back together.
 
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orangefj45 said:
Yum. Silicone everywhere ...... sadly we see that at the shop a lot. And the factory gaskets are literally $2 each ......

Georg @ Valley Hybrids & Cruiser Brothers
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I’m sure that despite the price, you almost always have to order said gaskets and people don’t want to wait for them to arrive.
 
Dubbinchris said:
I’m sure that despite the price, you almost always have to order said gaskets and people don’t want to wait for them to arrive.
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If you bust an axle on the trail and need to pull it and replace it or run in 3wd then RTV is a good trail remedy...but if you are planning any rear axle work, you likely have had to order and wait for other parts anyway. Whoever setup these gears and ARB's used a bunch of RTV on the 3rd's as well...I am pretty sure that was the last time the rear axkes where pulled...no reason to not have ordered the correct gaskets.

Also, if I had to pull these axles out on the trail with all that RTV I would have be quiet grumpy.
 
Dirty Koala said:
Been very busy with family duties...going from 1 toddler to 1 toddler and a newborn is quiet the experience!

Anyway, I have been driving the 80 in 2wd for ages since I knew the front diff needed to be torn apart to see what I broke when out wheeling Iast. I finally got around to yanking the diff out last night when the kiddos went to bed...I was moving fast since I only had 2 hours to spare so not a ton of pics...but here is what I found.

13 teeth are busted on the crown wheel and every tooth on the pinion is toast...the ARB locker isn't looking to good either
View attachment 1598656

View attachment 1598657

I was decending a steep hill in 1st low range using the engine as a brake...all that weight riding on the coast side of the gear set combined with the 4.88 gears and a super low NV4500 1st gear was just too much for this little diff to handle...I also don't know who set these gears up...it's possible they weren't setup properly.

These are the parts I am sending to Zuk/Ken @gearinstalls.com to work his magic. I will pull the rear diff out tomorrow but that should go really quick since there are no knuckles to tear apart.
View attachment 1598658

I have a pair of Harrops from @orangefj45 @wardharris @beno and a pair of 4.10 gears and all the associated accoutrements waiting with Zuk/Ken @gearinstalls.com just waiting for the empty 3rds to be shipped out.

Since I was able to destroy this little 8" diff we have cryo treated the new gear sets for a-little extra protection.

I had been wanting to switch from ARB's to Harrop's for a while now since I manage to break air lines like it's my job...this carnage just accelerated that as a priority.
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Congrats on the newborn
 
Dirty Koala said:
If you bust an axle on the trail and need to pull it and replace it or run in 3wd then RTV is a good trail remedy...but if you are planning any rear axle work, you likely have had to order and wait for other parts anyway. Whoever setup these gears and ARB's used a bunch of RTV on the 3rd's as well...I am pretty sure that was the last time the rear axkes where pulled...no reason to not have ordered the correct gaskets.

Also, if I had to pull these axles out on the trail with all that RTV I would have be quiet grumpy.
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3rds are often installed with rtv. Its only annoying to remove but it works better than a paper gasket IMO
 
New Paper gasket with the red gasket tack goo from Napa... both sides, is what I did on mine. idk would that be considered a good compromise? I haven’t needed to take apart yet and have no leaks but I feel that red goo will be irritating to remove?
 
I keep a roll of paper gasket for the times I don’t want to order something for $2. Also have fiber paper to make gaskets for oil changes since I always forget to buy a gasket before draining.
 
I am not opposed to a very thin layer of rtv or similiar in conjunction with the paper gasket. What I am dealing with is an RTV overdose...less is more!
 
I got my 3rds back from Zuk but haven't had a chance to slap them back in the 80 yet. I have to say those Harrops are sexy though.

Today I broke out the spreadsheets to calculate a bunch of gear ratio options for the Xfer case and then went deep down the rabbit hole with variables for Xfer case high and low range gear options, Diff gear ratio options, tire size variables and since I am running an NV4500...the 5th gear ratio had to also be factored in.

The ultimate goal of this analysis was to confirm that my engine RPM will be in the prime operating range based on the new 4.1 gears and the 9% Overdrive Xfer case gears that I have sitting on the bench.


Based on my calcs moving from 4.88 gears to 4.10 gears and replacing the stock high range gears in the HF2AV with a 9% Overdrive gearset, will drop my RPM's down to a much more pleasing range. 1783 RPM at 70 MPH sounds good to me:steer:

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Just be aware, if your RPMs are too low, you might lug the engine or not spin the turbo fast enough to create enough boost. My Cummins performs best between 1900 and 2000 RPM.
 
If I don't install the 9% OD, then my RPM's at 70MPH would be 1955. I think I will put the axles back together and drive it for a while before I make a decision on the OD install or not. I originally bought them to reduce RPM's since the engine was spinning too much with the 4.88 gears..now that I have 4.10's its possible that the 9% OD will be too much. In any case I will be going into the xfer case since I also have 3.12 low range gears that need to get installed.
 
I think I’m cruising at +/-2,100 on 35s and 8% overdrive. I would run it with the 4.10 and stock gears first.
 
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