fj80 axel swap?

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When you change ring gear ratios you need to add or subtract teeth from the ring gear/pinion..


So a 3.70 has 37 teeth on the gear and 10 teeth on the pinion (example)

a 4.88 has 39 teeth and 8 pinion teeth

the outer edge of a ring gear is tapered. When you reduce the pinion size (#of teeth) you have to make the ring gear thicker so that it mates up to the pinion properly. This is why certian Domestic nuits have carrier breaks (D60 for example) so as you make the ring gear get thicker you end up having a larger overall diameter of the ring itself.
It is not a huge number, but it does change.
 
Two things about 80 axles: small reverse cut diff, weird knuckles that only one comapany makes aftermarket arms for.

Here's a (bad) picture of a 8" reverse cut diff from a '97 HJZ75 (keep in mind the birfs are approx. the same size as your stock 60 birfs, not big like the 80 birfs). Truck had a blown rear pinnion and was back up a gradual slope when this happened. The Ring and pinnion were trashed, and the stock (two pinnion) carrier split in two.

So what's the weak part? Stock birfs or the 8"RC?
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ridgerunner said:
Here's a (bad) picture of a 8" reverse cut diff from a '97 HJZ75 (keep in mind the birfs are approx. the same size as your stock 60 birfs, not big like the 80 birfs).
Click to expand...

I always think 80 birf are more tough than 40 or 60 birf .. right . ?

And all 8" reverse cut diff that use TLC ( 80 or 7* series ) front have the same configuraction .. birf axles and R&P.
 
OK, late to the party.

Elocked 80 series rear axles usually do not get lodged when they break on the first break. Here is what happens. You break a longside axle and you fix the one side then two weeks later you are doing something mild and the short side breaks. It is the one that gets lodged in and is a PITA to get out. Also, most of these breaks are on 36" and larger tired rigs. 35s seem to be OK in the safety margin department. The nonlocked axles are a little bit stronger because they don't have the extra splines for the Elocker.

Comparing an 80 series elocked or nonlocked fullfloater axle to a 60 series as far as safety is a different matter. Even if there was a greater chance of breaking them I'd pick a fullfloater 80 over a US spec'd semifloater 60 axle any day. Then when it breaks you can get the benefit of being able to drive home with a broke axle. And you get rear disc brakes.

The photo of Zepp's broke front isn't typical. It can happen. But he broke the rear too. I was told that he broke the rear, then the front. And this was on a 79 series mine truck with a steel box on back. It wasn't a typical weight trail truck. It was definitely on the heavy side. I wasn't on the trail with him but that was the report I got at camp and I looked at the carnage.

Using an 80 front with leaf springs is going to be a PITA. That one company that made steering arms to make like a high steer set up no longer does. I know of nobody currently making steering arms for 80 knuckles. So unless you are going coils it would be tough to convert to it. 80 birfs are huge compared to even 60 series birfs. The one problem with 80 birfs especially used ones that haven't been cared for is that they have been driven on their whole lives so they wear. A 40 or 60 series birf almost never wears out, they do break but they do not wear out. An 80 birf will wear out because of the fulltime and it is accelerated due to lack of care. There have been failures with the third, most of them are in reversing situations with big tires. A lot of times these are also in situations where the locker is locked. If you take care and unlock the diff prior to backing up you most likely won't have problems. There are no guarantees in 4wheeling though.

Anyway, just some thoughts from the other side of Land Cruiser Lane.
 
I swapped a FJ80 rear axle into a FJ60 for TheFerg before he parted it out. It was a pretty easy swap. No offense but I really hate all the web wheeler "FZJ80 axle is weaker than a 60 axle" blah blah blah. What are the chances that you are really going to break a rear FZJ80 axle unless you are running absolutely massive tires... Also as Eric said full float, built in locker, being able to get home, disk brakes, and off the shelf or easily found used parts. So that is my $.02.. Also the axle itself is very large and heavy duty with trusses in the housing, much stronger (and heavier) than a 60 axle...

The swap was pretty easy and absolutely worth it in my opinion... The sky manufacturing width kit makes it look pretty good. But, I never liked the look of the FZJ rims on the 60 IMO, ferg's rig (imo) looked much better with black steelies. I would run some of the cheap 16 x 4 - 4.5 backspacing wheels all over the internet IMO...
 
Sorry to hi-jack...What is the best year(s) 80 axle to find i.e. discs, locker, most common, least expensive? I searched, but would like real world response...
Thanks!
 
dieselcruiserhead said:
I swapped a FJ80 rear axle into a FJ60 for TheFerg before he parted it out. It was a pretty easy swap. No offense but I really hate all the web wheeler "FZJ80 axle is weaker than a 60 axle" blah blah blah. What are the chances that you are really going to break a rear FZJ80 axle unless you are running absolutely massive tires... Also as Eric said full float, built in locker, being able to get home, disk brakes, and off the shelf or easily found used parts. So that is my $.02.. Also the axle itself is very large and heavy duty with trusses in the housing, much stronger (and heavier) than a 60 axle...

The swap was pretty easy and absolutely worth it in my opinion... The sky manufacturing width kit makes it look pretty good. But, I never liked the look of the FZJ rims on the 60 IMO, ferg's rig (imo) looked much better with black steelies. I would run some of the cheap 16 x 4 - 4.5 backspacing wheels all over the internet IMO...
Click to expand...


I think the guy over on 80tech that I can remember was running 35s when he snaped his. I dont think anyone here said that the 60 axle was stronger. We were talking about snapping a and axle and getting it stuck in the e-locker. Another factor is where you live and what you wheel. I know for a fact if i did not live on the east coast where the rocks are very low in traction I would break way more stuff.
 
dieselcruiserhead said:
fair enough... I have never seen a rear 80 axle break here in 'hig htraction' utah though FWIW....
Click to expand...


As said above from the Mr. Mace the 80 series have not been beat on as much as the 40/60s we will see what happens in the years to come.
 
I was with NW sick boy when he broke the rear. I believe he had 37s on at that time. Christo has broken at least one like I described above, I believe with 38s. Shawn Jackson also broke one but he was on 37s, I don't think it was after he went to 40s. Now that he is on 40s he running fancy axles. Christo is really the authority on this as he keeps track.

High traction isn't the problem Loose traction and then sudden traction is the problem.

On the trail NW sick boy broke his rear last weekend there were 8 broken axles on that trail within 3 hours. Mostly Heeps but there were two front Dana 60s broke on a Ford. It was just that type of day.

My 80 axles were spared because I never made it onto the main trail because of all the breakage. I was the official Ford tow truck.

How big of a tire are you going to run? I think even at 37s you could go a long time without breaking for a long time.
 
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