8" axle diff gears strong enough for 37" & Marlin Crawler Dual 2.8:1? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 09-16-2019, 05:36 PM   #1 (permalink)
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8" axle diff gears strong enough for 37" & Marlin Crawler Dual 2.8:1?

Short version: How much torque is too much for the gears in a 8" axle?

Long version with more specs: I've got a '95 Pickup with stock rear axles on 37" tires. Running the 3.0L V6 (already rebuilt) and dual Marlin Crawler transfers, both 2.8:1. Diff gears are 4.88. Stock rear end, front end is a matching 8" axle, uncertain from where.

At the start of the summer, I was coming into Rubicon from Loon Lake and got halfway up the slab when I lost my rear end. Later, off the hill, I saw my entire ring & pinion gears in the rear were totally destroyed. Several teeth were chunked off. This older set was 4.56.

I ordered a new set of 4.88 gears (since that's all I can get, and I didn't want a smaller pinion that 5.29 would've gotten). On a second trip out, the same thing happened! A bunch of teeth got chunked out of the ring gear again!

Amongst other discussions, I was told that the 8" axle can't handle that much torque. It's only a half-ton axle and should be upgraded to something sturdier, like a D60. I understand other people run that kind of a setup on the 8" axle with no problem. So I thought I'd come here and see if any of you had a similar setup and/or experience, and whether you made some choices to reduce torque on your setup or something.
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Old 09-16-2019, 05:50 PM   #2 (permalink)
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Iím guessing itís the shock loads killing the diff. Who is setting up the 3rd? 5:37 is what my buddy runs and he wheels hard, had a lunch box locker take out a set of gears. Other than that, itís holding up to 37s.

My 4:88s hold up to 4.3 vortec power. So it sounds like you have a lack of gearing to maintain a crawl, causing shock loads in your drivetrain exposing the weak link.

Itís cheaper to throw gears in the rear case than to throw tons under your truck.
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Old 09-16-2019, 05:50 PM   #3 (permalink)
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No one runs +31" onna yota axle.
never been done.
Check the bible???
I beat my 37" 5:29' threw doubled 2:28x4.7 duals,w59,2.7 3rz in my
taco from buck in rear wheel driving to loon
Aka toyota bible in the stickies????
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Old 09-16-2019, 05:59 PM   #4 (permalink)
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I run 39s on dual cases (2.28x4.7) but i have a 22re. Everything is in how you setup the gears. The picture in this post is what not to do, fortunately caught it before it took out the front ring and pinion. Use a solid pinion spacer, one thick shim if possible (multiple small ones got chewed up and caused a noticeable amount of play in the pinion) and set the appropriate preload. Once the pinion loses preload everything goes boom. Also, make sure you dont shock load the axle, if you look putting on a show, this is not the axle for you.



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Old 09-17-2019, 09:22 AM   #5 (permalink)
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Gear setup is critical. Who is setting up yours?

Here is some quality reading for you. Toyota Gear Install Harrop
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Old 09-17-2019, 12:26 PM   #6 (permalink)
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I agree, gear setup is critical, and your driving is too. It's a small gear set, so you'll have to drive accordingly.

In my 66 FJ40 I was running a V6 8" in the rear and high pinion 8" in the front. Dual cases, 4.8L Chevy V8, and 38.5Ē swampers. 5.29 gears.

Both diffs were setup at Marlin's shop. Probably 8-10 Rubicon trips, never a gear failure... But I drove it carefully and let my low gearing do the work instead of my gas pedal.

I did once find a chipped tooth on the rear ring gear. I think it happened when the studs holding the 3rd failed. I replaced the gears in that diff as a precautionary measure.
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Old 09-17-2019, 03:22 PM   #7 (permalink)
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Just because it was set up by Marlin doesnít make it gold. I had to rebuild the brand new third that I purchased from them years ago. The backlash and carrier bearing preload was good.... for a mall crawler, not a crawler.
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Old 09-17-2019, 03:23 PM   #8 (permalink)
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Quote:
Originally Posted by mistermocha View Post
Short version: How much torque is too much for the gears in a 8" axle?

Long version with more specs: I've got a '95 Pickup with stock rear axles on 37" tires. Running the 3.0L V6 (already rebuilt) and dual Marlin Crawler transfers, both 2.8:1. Diff gears are 4.88. Stock rear end, front end is a matching 8" axle, uncertain from where.

At the start of the summer, I was coming into Rubicon from Loon Lake and got halfway up the slab when I lost my rear end. Later, off the hill, I saw my entire ring & pinion gears in the rear were totally destroyed. Several teeth were chunked off. This older set was 4.56.

I ordered a new set of 4.88 gears (since that's all I can get, and I didn't want a smaller pinion that 5.29 would've gotten). On a second trip out, the same thing happened! A bunch of teeth got chunked out of the ring gear again!

Amongst other discussions, I was told that the 8" axle can't handle that much torque. It's only a half-ton axle and should be upgraded to something sturdier, like a D60. I understand other people run that kind of a setup on the 8" axle with no problem. So I thought I'd come here and see if any of you had a similar setup and/or experience, and whether you made some choices to reduce torque on your setup or something.
If you have V6 3rds, set up correctly you should be fine as long as you arenít bouncing or dumping the clutch.
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Old 09-17-2019, 03:55 PM   #9 (permalink)
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also a more robust than stock housing will help tremendously by minimizing deflection. even the 8.4" 8" does better with the added bearing girdle

there is a reason diamond/ruffstuff/trail-gear all do well selling housings, and it is only ~60% people who like to just spend money :flipof2:
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Old 09-17-2019, 04:14 PM   #10 (permalink)
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there is a reason diamond/ruffstuff/trail-gear all do well selling housings, and it is only ~60% people who like to just spend money :flipof2:[/QUOTE]

clarification please?!
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Old 09-17-2019, 05:22 PM   #11 (permalink)
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there is a reason diamond/ruffstuff/trail-gear all do well selling housings, and it is only ~60% people who like to just spend money :flipof2:
clarification please?![/QUOTE]

well, the joke is that most folks (60% may be off ) buy those blingy aftermarket housings just for a name, while the remainder are doing the typical upgrade as needed, lowest cash at the moment route of building. who spends $5k on a toy axle? nobody should all at once, but over several years it is easy to do, and a housing is a big chunk of that coin.

not concerning the joke the thicker tubes and thicker mounting flange and more rigid pumpkin reduce deflection. similar but reverse concept to the anti-massive front axle truss argument.

the stock rear housing can allow for some flex, it really doesn't take much at~36" length to the end of the axle, that can impart force to the bearings, that can increase the natural desire of the pinion and ring gears to seperate/walk out under load. this loss of contact between ring/pinion gears under load is one thing that really helps accelerate destruction

also why good setup matters, so that you aren't on the edges tostart. also why an ARB carrier can help due to robust design, also why the 8.4" was factory upgraded with the girlde, also why industrial/drag/some rock stuff run load bolts behind the ring gear, also why big bearings make a v6 diff, and a pinion snout bearing make other diffs stronger than their diameter peers
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Old 09-17-2019, 05:33 PM   #12 (permalink)
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Old 10-02-2019, 02:00 PM   #13 (permalink)
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well, the joke is that most folks (60% may be off ) buy those blingy aftermarket housings just for a name, while the remainder are doing the typical upgrade as needed, lowest cash at the moment route of building. who spends $5k on a toy axle? nobody should all at once, but over several years it is easy to do, and a housing is a big chunk of that coin.

not concerning the joke the thicker tubes and thicker mounting flange and more rigid pumpkin reduce deflection. similar but reverse concept to the anti-massive front axle truss argument.

the stock rear housing can allow for some flex, it really doesn't take much at~36" length to the end of the axle, that can impart force to the bearings, that can increase the natural desire of the pinion and ring gears to seperate/walk out under load. this loss of contact between ring/pinion gears under load is one thing that really helps accelerate destruction

also why good setup matters, so that you aren't on the edges tostart. also why an ARB carrier can help due to robust design, also why the 8.4" was factory upgraded with the girlde, also why industrial/drag/some rock stuff run load bolts behind the ring gear, also why big bearings make a v6 diff, and a pinion snout bearing make other diffs stronger than their diameter peers
Probably the most helpful run of comments here. Thanks a bunch. Next time I need to get into the diff, I'll consider upgrading the housing.

Last edited by mistermocha; 10-02-2019 at 02:02 PM.
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Old 10-02-2019, 04:51 PM   #14 (permalink)
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Just for a little additional info - the primary cause in my experience of diff failures due to pinion flex and/or carrier flex. I'm not sure how much an axle housing would help. I don't think much load is born by the housing, but I suppose some flex is possible there. I can definitely see how it might happen. I've never had an issue with that that I'm aware of. And setup is of course critical. Not just pinion depth and backlash, but also the preload on the bearings is very important for a stout differential.

This is a picture of a Toyota 8.2 (2010+ 4Runner) compared to an 8" pinion. You can see that the newer setups have a much larger pinion and associated bearings. I don't think the 8.2 is a great option for an upgrade because they only offer 4.56 or 4.88 gear sets for them, so you're limited. Otherwise they're a similar size axle with a much stronger diff.



The newer 8.2 pinion is also a fair bit shorter.


The ring gears are nearly identical in size though:
8.2 on top, 8" on bottom:

Last edited by jetboy; 10-02-2019 at 05:07 PM.
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Old 10-02-2019, 06:20 PM   #15 (permalink)
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the housing helps stiffen the whole mounting location for the drop out third, think V6 ribs vs 4cyl ribs, same concept. the tubes help limit the flex from the shaafts at the bearing ends, those are transferred directly into carrier flex.

huge world changing difference? no. i wheeled for years on a stock housing without breaking stuff. I also broke a few diffs :shrug:

Difference? yes, in the sense that every little bit helps and they all add up to a bunch.

again, i don't think a $4k+ toyota axle is a great option for a hardcore pickup rig all at once. a full float diamond housing with "8.4" or "8.2" diff and ARB with chromo shafts and treated gears is dope. buying it all at once? nah, better options exist. buying one thing every couple years to spread it out? easy to end up there.
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Old 10-02-2019, 06:45 PM   #16 (permalink)
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Make sure axle is straight. Have
Someone who knows what they are doing set up your diffs. I would upgrade the stud size that hold the rear diff to the rear axle. I have a similar setup. And gear breakage did not start until 40" iroks.
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Old 10-02-2019, 09:57 PM   #17 (permalink)
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every little bit helps and they all add up to a bunch.

this x10000

there is no single solution
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Old 10-03-2019, 08:08 AM   #18 (permalink)
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I didn't make it very clear - my main point in posting those pictures was to show how Toyota re-designed the 8" diff to handle a lot more power when there were similar issues in the FJ Cruiser with rear ring gear failures. They primarily upgraded the pinion assembly and the carrier. And those diffs seem to handle v8 power in the GX and 400hp/400tq in the supercharged 4Runners with almost zero failures. They're remarkably robust for how small they are. Basically the newer front and rear axles from stock tacomas and 4Runners, although roughly similar in size, have been reworked to become much stronger. So it might be worth considering over an aftermarket assembly that could cost a lot more.

Not really suggesting an axle swap over a properly build diff. I'd start with a well built diff. But if I were looking to upgrade to something better on a budget and didn't want to build a custom land cruiser 9.5" axle, the 8.2 is a decent option that's almost universally overlooked. The 8.2 is just the stock axle in my daily driver 4runner, but I do wheel it. It's been through the Rubicon twice. With no broken parts. The last time loaded up with 3 people and all of our gear for a week. So probably running at ~ 6k lbs. If it handles that, I'd think it would hold up reasonably well to a light weight trail rig even with low gears.

I would think a stock 8.2 rear axle from a 4Runner would be a pretty good budget upgrade. They're a better overall axle than any Tacoma unit because they come with pretty good sized rear discs that are factory fit and have parking brakes. So the overall swap cost to a more modern brakes system along with a substantially improved differential is probably about as cheap as you could do it. A complete e-locker axle 8.2 goes for something like $1500-2k. So it's not cheap, but it is a lot cheaper than blowing up ring and pinions every year. And it's a much more reliable locker than an ARB, so you also get a benefit there. The non-elocker 8.2 rears are cheaper. I'd guess $1k would get you a complete axle assembly, but then you're still short a locker. And the non-elocker version uses shims for the carrier preload, so that kinda sucks to setup. I don't think you could realistically build any other comparable aftermarket axle with OEM quality disc brakes and a locker for anywhere close to that. You'd still need to do gears - but you can buy a set of Revolution gears for about $200. And all the 8.2 gears are the same circle K gears, so it really doesn't matter what label is on the box. And the 8.2 uses the threaded carrier bearing design, so setup is a breeze.

One down side is that they probably won't fit a 15" wheel. The brakes - even on the rear - are probably too big for 15" wheels to clear.

Last edited by jetboy; 10-03-2019 at 08:17 AM.
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Old 10-03-2019, 09:47 AM   #19 (permalink)
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Originally Posted by mistermocha View Post
Short version: How much torque is too much for the gears in a 8" axle?

Long version with more specs: I've got a '95 Pickup with stock rear axles on 37" tires. Running the 3.0L V6 (already rebuilt) and dual Marlin Crawler transfers, both 2.8:1. Diff gears are 4.88. Stock rear end, front end is a matching 8" axle, uncertain from where.

At the start of the summer, I was coming into Rubicon from Loon Lake and got halfway up the slab when I lost my rear end. Later, off the hill, I saw my entire ring & pinion gears in the rear were totally destroyed. Several teeth were chunked off. This older set was 4.56.

I ordered a new set of 4.88 gears (since that's all I can get, and I didn't want a smaller pinion that 5.29 would've gotten). On a second trip out, the same thing happened! A bunch of teeth got chunked out of the ring gear again!

Amongst other discussions, I was told that the 8" axle can't handle that much torque. It's only a half-ton axle and should be upgraded to something sturdier, like a D60. I understand other people run that kind of a setup on the 8" axle with no problem. So I thought I'd come here and see if any of you had a similar setup and/or experience, and whether you made some choices to reduce torque on your setup or something.
I run heavy Toyo 40's on a 8" hi pinion, 2.28 x 4.71. I drive it like it has an 8" and everything is fine. Pinch a tire, bounce a tire, shit will break. I've broke an 8 inch rear on 35's driving like an idiot.
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Old 01-08-2020, 05:25 PM   #20 (permalink)
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I've been running 5.29s in my 2nd generation pickup, on toyo 37 x 13.5 x 17r MTs for 7 years. I blew up one set of rear gears with an Aussie locker on Wrecking ball. I went spool, 5.29s and have not had any problems since.
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