Swapping 8.4" axle for 8" pros and cons

Hey Guys,

Came across a wrecked Tacoma that came from the factory with a locked rear axle. My Tacoma has the open diff 8.4" axle on it and I was curious about swapping it for a locked axle. Some one has already grabbed the 3rd member off of it so I would just be purchasing the axle housing for $250 or so. From what I understand if you have the 8" axle housing you can use 4runner 3rd members which would open up the option of putting a 4.30 or maybe even a 4.56 factory locking third member in. My truck has a mild lift on it, 1.5" with a front arb bumper without winch, an allpro rear bumper and a topper with bed. I am currently running 245 75 r16 tires to try to help with gas mileage but now my gas mileage is suffering. Would like to maybe put 265/75 r16 tires on the truck at some point if it doesn't bog it down to much. I read my door code and I currently have 3.91 gearing in my truck. I do not wheel the truck, and don't plan to, it is mostly used as semi daily and to go camping, hunting but sees a lot of highway miles to get to dirt roads. Having a locked rear axle would be nice to have some of the places I go but I am curious if it is worth it considering how I use the truck. If it is worth it what gearing should I look at putting in there to help pep the truck up a little bit? I know I will have to find a matching front diff too.

 

It seems like you would be ahead to just add a locker to your current setup. The bare axle would require you to source a locking rear 3rd, the wiring, and matching gears for the front.

 

A 3rd Gen 4Runner with rear locker will be a 4.30

 

been there, done that...just get an arb for the 8.4 and be done with it. the e locker isnt worth the swap at all. bonus points for you if youre planning on regearing down the road, get the arb install and regear done at the same time (obv will have to do the front as well)

 

What gearing would be good based on my intended use for the truck? With an arb you have to have an on board air compressor correct?

 

Uhm...weight would relate more to 'what springs should I use with my coilovers' and 'should I install an AAL' etc.

Gearing shorter than what you currently have, will move you up in the power band so you will feel a bit more 'get up and go'. The downfall would be that your RPMs will be higher at the same speed your currently at which will mean you'll get worse MPG's than you do now.

 

Where are you getting weight from?

 

Why else would you mention your bumper earlier?

 

Proper gears for your setup would depend on which engine (3.4), which transmission(MT) and what tire size(265/75R16) you will be running. You want your final drive ratio to be similar to the stock final drive ratio to keep your truck in the same power band as it was designed for. But I believe what @Kwikvette is getting at is that if your truck is significantly heavier than stock you would to compensate for that so your truck doesn't feel like a slug. I'm not smart enough on 1st gens to tell you what would be your best option, but I'm sure there are some threads here with enough smart conversation and real world experience to lead you in the right direction.

And to answer your other question, yes, an ARB Air locker will require an on board air source. There is also a Harrop E-locker that doesn't require air but is a bit more expensive.

 

I would put an ARB or Detroit locker into the 8.4. Not worth the effort to source all of the parts to swap the entire elocker axle -- if you put a 4 runner third in it you'll have to swap your front diff to match as well.

 

honestly, if the extent of your driving is county/FS roads to go hunting, and you dont plan on wheeling and only want to go up to a 265/75 tire...dont even bother regearing or adding a locker. your truck in 4lo with good tires will be just fine for that. You dont need a locker to go on dirt roads to go hunting. Spend the money on a good winch and recovery gear, and that will be a much better option for your purpose than a locker. Itll help you be more self reliant in getting out of "oops" situations, where as a locker is better at getting you into "oops" situations for fun. It doesen't sound like you intend on getting into "oops" situations for fun.

 

Doesn't weight affect the over all choice in gearing correctly?

 

Weight can be a factor, but it's more relatable to suspension choice.

Tire size is a much more discussed factor when choosing gearing.

 

If your weight is at the Max payload plus of the Truck all the time it can factor in to what gears you want.

Then how much driving do you do at 60 mph or above can play into deciding as well

 

Not really, no.

While yes, if you weigh down your vehicle with a bunch of heavy stuff, a lower gearing would “help” it’s not the proper way to deal with it.

Firstly, you shouldn’t be going beyond the gvwr anyway, but lowering your gears just makes you go slower. Youll be reving higher at highway speeds.

Power is really what you need to compensate for added weight.

You get different gears bedause you got significantly bigger tires, or you want to adjust your crawl ratio, i.e. go slower in the rocks.

That said, nothing you’ve described really pushes you towards needing lower gears or especially a locker.

I’ve been running 265/75s for many many years with stock 4:10 gearing. Especially for normal driving or even just forest road non technical rock crawling, it’s more than sufficient.

Hopefully by now you realize you don’t need a new differential. All you would need is the appropriate ring and pinion gears for front and rear. But again, it doesn’t really seem all that necessary for your use case.

 

TL;DR

40s and tons

 

True. But keep stock gears.

 

That all makes sense. Saw the wrecked truck and my brain got to thinking and scheming. Couldn’t help but think of the possibilities but thanks to you guys my wallet might be saved for something else!

 

e-locker swap is worth it if you find a good priced axle that doesn't need any work. You can essentially break even on the swap if you do it right. If you find one at a junk yard you should really swap the bearings and seals while you have it out.
At that point the hardest part for people seems to be the wiring, but that was easy for me.
https://www.tacomaworld.com/threads/tiffany-the-taco.374490/page-5#post-14771682

 

True. Elocker swap is worth it. The swap will be cheaper than buying an arb air locker and paying someone to set it up. Plus, you can sell your 8.4 axle for a few hundred buck to recover some loss. Yes, many will say arb is stronger and provide an instant lock. But try telling the other folks who uses the Elocker with 37" tires and the few with 40s. Technically speaking, the 8" elock and 8.4" both use 8" ring and pinion and that's what break, not the locker itself btw.

Downfall of arb:
You'll need OBA. And the arb I have and 5 other guys I know who run arb leaks air. It's a common arb problem. Ask @Fernando

Downfall of elock:
You must turn it on at least once a month.