3 gen rear axle in a 2 gen

I did have one bad speed sensor on the new axle, which lit up the traction control light on the dash. We just pulled the sensor off my old axle and swapped it in.

 

Interesting that this worked for you. I took an 8.4 out of a second gen because I wanted a TrueTrac on my 3rd gen. I had driveline vibes that started at 75. Pretty sure it was due to pinion angle, which was odd because according to the junkyard I got it from, it apparently came out of a DCSB 2nd gen. No idea why it didn't work out but it was a big bummer.

 

Either a bad part or install error because the pinion angle wasn’t changed.

 

It was hard to say, but my testing pointed straight to pinion angle. I could not get a good enough measurement to really confirm that, but I did run in front wheel drive mode with the rear driveshaft removed up to 85 mph and it was smooth as silk. Reinstalled driveshaft, vibes immediately returned at 75.

If it was an internal rear end part bad, then it wouldn't have made any difference removing the driveshaft. The diff itself was assembled by Zuk, so I knew that was done right.

After the driveshaft test, I said screw it and swapped back. I don't know how it could have been anything besides the pinion angle with how that test went.

It was a strange problem and made no real sense, but I didn't have time to keep messing with it. I did sort of wonder if something internal to the TrueTrac acted up under torque at high speed, but I had no way to confirm that.

 

you put the axle or the third

if the axle fits, that makes 100% sense. That's why it's called a turd gen. They took the 2nd gen, fucked up a bunch of shit, and called it a different vehicle.
However, as opposed to most of the things they worsened, maybe one they got right.
That being the rear axle is larger meaning stronger.

Is that needed? It depends. 8.4? No. 8? Yes. I believe turd gen is 8.75".
So yeah this is good to know.
If you can find one for a good price and it fits, great.
Thing is, I don't think they generally do come available as a good price.

 

Everyone can make mistakes, including your differential builder. At that point in testing, it would have been way easier to shim the leaf springs to rule out a pinion angle problem than swap the entire axle assembly again, but I digress.

I’m still curious about this elocker custom harness. Because the topic of this whole thread is still a great low budget upgrade for 2015 & older trucks.

 

I believe all non-locker AT 3rd gens inherited the 8.4 axle from the 2nd gen Tacoma, so that might not have been the source of your vibrations.

I will note that

1.) I have not yet taken my own truck much above 70mph, because I cruise at 65. It’s been buttery smooth at the speeds I have driven.

2.) My truck is lifted 2.5 inches in rear, and I have already been running a carrier bearing drop and pinion angle shims.

3.) The rear 3rd member housing for the 3rd Gen OR is .25 inches shorter than the 2nd Gen housing it replaced. That suited me fine, because the driveshaft easily telescopes .25 inches, but, going in the opposite direction, if your driveshaft was too long for the 8.4 housing, that might have caused some vibes.

Just guesswork here, because again, I believe there are plenty of 3rd gen trucks with the 8.4 axles under them — all 3rd Gen trucks, in fact, except for the manual or locker rear ends.

 

Non-locker AT 3Gs received a newer version of the 2G locker axle. AKA the 8.0" locker, or TV6, only now without a locker of course.

The 2nd gen "8.4" is also an 8.0" axle but it has more ring gear bolts and a carrier bearing brace. Nobody really knows where the 8.4 name came from, but somehow it stuck. It does not measure 8.4" no matter what it's known as.

I believe the axle people call the 8.4 is actually what the new 8.75 derived from. They are pretty similar in design. 8.75 has a beefier housing. Drain plug and fill plug are in the same spots. Similar 3rd member stud pattern. Similar flange and driveshaft bolt pattern. No carrier bearing brace on 8.75. Both are shimmed carrier bearings and no threaded adjusters.

I did compare the pinion length, and the "8.4" vs the "8.75" were exactly the same length.

The 8.0 locker axle from the 2nd gen used threaded adjusters, as does the 8.0 non locker in the 3rd gen. Those two diffs are very similar, aside from the big funky locker on 2nd gens that is no longer there on the 3rd gen version.

 

The 8.75 axles are definitely not cheap, especially the 4.30’s. That said, AS LONG AS the gear ratio is what you want/ you were intending to regear anyway, this is indeed the cheapest way to get a beefier rear differential with a locker.

The whole reason I did this swap is I grenaded my 8.0 on an obstacle it should have taken without problem, and I know too many other people who have also grenaded their 8.0’s.

 

Got it, good info. I am upgrading from a 2nd gen OR axle, not the “8.4”. The 3rd member housing for the 2nd Gen OR was indeed ~.25 inches longer than the 8.75’s. This has caused me no issues, even though my axle was already moved backward an inch or so, due to Deaver u402 springs being slightly longer than OEM. I have already flexed my truck out to be sure, but I haven’t taken it above 75mph.

 

Did you have to do anything for the driveshaft to pinion flange? For some reason I thought I remembered the 2nd gen locked axle having a 60x60mm pattern. I know for sure 3rd gen OR axle is 66x66. Did yours bolt up?

 

They are exactly the same. Except for the wiring harness to operate the locker, no special provisions are needed. All the sensors are the same — everything.

FWIW, my truck started life as an open “8.4”; I swapped in an 8.0 because I wanted a locker (also a direct swap); broke that, moving on to 8.75.

 

Here is my write-up for installing a 3rd Gen OR axle assembly under a 2nd Gen truck. Posts #1-3.

https://www.tacomaworld.com/threads...on-a-2nd-gen-tacoma-or-non-or-3rd-gen.842862/