Why did Toyota get rid of the 9.5" front diff for the 80 series? (1 Viewer)

[Broski]

Well, it seems quite vulnerable in the 100 series from all the discussion of blown front diffs on those - maybe because of the shockloads of ATRAC and/or reduced travel with the torsion bar IFS.

The RCVs let go before the 8" third on my rig and I'm rockin 39s for the last few years and 37s before that. She a hard core trail rig.
And there's 3 or for Minis rocking 40s in our Wheeling group they seem to be holding up just fine.
I can't speak of the hundred series.

 

[SaturnAscends]

100 series used a two pinion carrier. The carier is no where near as strong


The patrol diff centre is regarded as being stronger, but the nissan birfs ABS knuckles are quite a bit smaller and weaker and less turn radius.
Some guys build hybrids, nissan centre, 80 knuckles and birfs


4 pinion carrier, aftermarket, or 80 series, plus more preload, and solid pinion spacers make them more reliable.
There's plenty of HP 8" 80series diffs used in competition winch trucks etc in aus without issues.
Extra preload, deeper contact pattern ( no good for a street truck), carrier studs upgraded to 10mm, solid pinion spacer

Aussies don't have Dana 70s or 14 bolt, 1 tonnes etc laying around in wrecking yards, so we gotta make the toyota stuff work

Isn’t the 80 series 2 pinion as well?

 

[SaturnAscends]

None of us will know the real reason unless somebody from Toyota engineering is on here. If i was to guess i would say it was cost/weight savings. I'm a fan of the 8.4" I wish they made a HP version and used it instead.

Good point, was the 8.4” around back in the 80s?

 

[Speedytech7]

Isn’t the 80 series 2 pinion as well?

No, it's 4, also get off this forum and go back to the other, you're gonna give these nice folks a headache and yourself even more nervous chihuahua energy

 

[SaturnAscends]

No, it's 4, also get off this forum and go back to the other, you're gonna give these nice folks a headache and yourself even more nervous chihuahua energy

lol I’m not nervous about it, just trying to understand as I’m not an engineer.

In any case, that also begs the question why they bothered going to a 2 pinion unit in 1998, only to backtrack after a couple years..

 

[TheBussman]

Good point, was the 8.4” around back in the 80s?

93 is the first year i think.

 

[MoCoNative]

Keep in mind also the 80 introduced the new coil sprung axles, they had to redesign the entire system compared to the 40, 55, 60, 70. The regular big carrier occupies the same spot that the tierod has to pass through on the 80. The tierod most likely went to the rear of the axle so the track bar would not interfere with it on the front side. Couldn't run it above the diff as it would interact with the sway bar and probably frame. Its actually a pretty neat design overall.

The argument of blowing them out, they designed the truck for the power installed and the stock drivetrain. Extra capacity is a waste of resources in vehicle design, plain and simple. Same reason I suspect the low gear range in Toyotas has always been what it is, that is the limits of torque for the drivetrain. For example, the early 40 had a 3-speed with a higher first gear, but a lower transfer case ratio for low range. When the 4-speed came out, 1st gear was lower, low range got slightly higher and that ratio remained about the same across all the truck lines. It is the designed limit.

If Toyota intended the trucks to have 37" tires, they would have built the drivetrain to fit, or more HP, etc...

 

[Broski]

Haha the 80 fits 37s like it was made for them!

 

[use2bn83]

In theory, both the front RR and the rear low pinion diff will both be driven forward on the drive side of the gears making them the same strength. In reverse they will both be on the coast side, which is the weaker side.

Bad phrasing on my part. I was talking about running a standard rear 8” in the front vs a HP 8”. We agree.

 

[Mrtwooooo]

Isn’t the 80 series 2 pinion as well?

I’ve seen diagrams that show the non locker diffs are 2 pinion and the locked diffs have 4 pinions. But no one ever talks about that

 

[Broski]

I’ve seen diagrams that show the non locker diffs are 2 pinion and the locked diffs have 4 pinions. But no one ever talks about that
View attachment 3534930

Very interesting, one more reason to go with OEM lockers.
I have them and like them !!

 

[suzuguru]

Personally, if I was going to pick a part as a fuse, I'd run some manual hubs. Seems a lot simpler to swap than birfs. Either way, I just don't see people tearing up that many rings and pinions.

Maybe I'm not understanding. Are you saying that the manual hubs will be the weak link and keep the birfs from breaking? If so, that's not necessarily the case.

 

[Broski]

Maybe I'm not understanding. Are you saying that the manual hubs will be the weak link and keep the birfs from breaking? If so, that's not really the case.

That would depend on what kind of axles you’re running

 

[suzuguru]

That would depend on what kind of axles you’re running

Certainly true. I was assuming stock axles.

 

[Marvelicious]

Maybe I'm not understanding. Are you saying that the manual hubs will be the weak link and keep the birfs from breaking? If so, that's not necessarily the case.

Yeah, in the context of running something as a fusible link, we were talking 30 spline birfs, and I guess I just assumed that in that context, you may as well give the credit card a good workout and get the full meal deal (RCV 300m ultimates). The theory back in the day on Pirate was that if you went all out on everything else, the Aisin manual hubs would be the weakest point. I don't break enough parts to swear to that one way or the other, but it always seemed plausible. If I were going to calculate a weak point, that's where I'd want it to be.

 

[suzuguru]

Yeah, in the context of running something as a fusible link, we were talking 30 spline birfs, and I guess I just assumed that in that context, you may as well give the credit card a good workout and get the full meal deal (RCV 300m ultimates). The theory back in the day on Pirate was that if you went all out on everything else, the Aisin manual hubs would be the weakest point. I don't break enough parts to swear to that one way or the other, but it always seemed plausible. If I were going to calculate a weak point, that's where I'd want it to be.

Yep…. that’s where I would want it. Back in the day, when I used to wheel Samurais, we had it worked out where the driveshafts were the weak link. It worked out real well, since they were plentiful, relatively cheap, and easy to swap out.

 

[mudgudgeon]

I’ve seen diagrams that show the non locker diffs are 2 pinion and the locked diffs have 4 pinions. But no one ever talks about that
View attachment 3534930

You may be right I had it in my head that early 80s were 2 pinion (4 pinion with lockers), later they were all 4 pinion. Now I'm not sure.

 

[mudgudgeon]

Maybe I'm not understanding. Are you saying that the manual hubs will be the weak link and keep the birfs from breaking? If so, that's not necessarily the case.

I've seen hub studs torn out and hubs destroyed when locking hubs have broken and the shrapnel jammed in the hub

 

[Broski]

I run the 300Ms and purposely run the stock drive flange as a fuse.
It hasn’t quite worked out

 

[baldilocks]

I read this entire thread up to here and there has been zero reliable theories/info posted save post #10 which addresses the original question. I've broken random bits including rear nitro shafts but never an RCV and never hub studs, front R&P, cracked Aisin hub gears (37's and air lockers). Over the years many have reported failures of every single part and component of these 80 series axles. One guy snaps hub studs twice in a day running stock hardware on 35's while the next guy explodes a front diff running Aisin hubs that most think will give up first (which i've also seen) and then there's the guy that manages to destroy two front RCV axles simultaneously while the diff and flanges are unharmed. Anything can happen on any given day spent running rugged terrain including the demise of 9.5 diff's which I've also seen on the trail.

A question I've asked myself is; why did Toyota go to a smaller diff and much larger Birf's in the same design change? Is the 80 that much heavier or that much more powerful than it's predecessors?? Pairing a theoretically weaker diff (based on less material used and leverages involved) with considerably stronger knuckles/Birf's???????????