Why did Toyota get rid of the 9.5" front diff for the 80 series? (3 Viewers)

[SaturnAscends]

As far as I know, Toyota got rid of the 9.5" front diff after the 62 series, opting for the high-pinion 8" instead, which as I understand it was essentially a minitruck diff, or at least adapted from one that was originally used on 3000 lb pickups with 80 horsepower. I'm curious what led Toyota to downgrade to a weaker front end when introducing a heavier and more powerful series of Land Cruiser. Why retire the venerable and proven 9.5"?

Many have experienced failures when driven hard on bigger tires, especially when they ostensibly become the point of failure after fitting stronger birfs and shafts.. This became even more apparent on the IFS 100 series, which were known to break R&P and spider gears even in stock form in some cases.

Forgive my ignorance, but I'm trying to understand why Toyota appears to have a habit of using undersized minitruck parts in 2.5-ton 8 passenger wagons - the 8" rear in the 120 series and R-series boxes in the 105 and HZJ75s also spring to mind.

I'm not trying to dog on Toyota here; I know all OEMs are forced to make compromises from time to time to cut costs, comply with regulations, etc. I'd appreciate any insight. Thanks for reading.

 

[Diesel-Runner]

I don't know what analysis went into why they chose the HP 8", but would offer that the 80 front axle is pretty robust, especially when you factor in that toyota designed it with a 32" tire in mind. I've wheeled an 80 a lot on 35s and 37s and never had a single issue and know a bunch others with the same experience. Additionally the 8" ring gear was used on the rear end on mini trucks not the front.

 

[matzell]

I don't know what analysis went into why they chose the HP 8", but would offer that the 80 front axle is pretty robust, especially when you factor in that toyota designed it with a 32" tire in mind. I've wheeled an 80 a lot on 35s and 37s and never had a single issue and know a bunch others with the same experience. Additionally the 8" ring gear was used on the rear end on mini trucks not the front.

79-85 mini trucks and 4runners had a 8" front and rear and solid axles front and rear. The reverse rotation means it is driving on the drive side of the gear, rather than the coast side like most low pinion units. They needed a high pinion reverse rotation diff for the packaging and keep driveline angles better being all wheel drive.

 

[Diesel-Runner]

79-85 mini trucks and 4runners had a 8" front and rear and solid axles front and rear. The reverse rotation means it is driving on the drive side of the gear, rather than the coast side like most low pinion units. They needed a high pinion reverse rotation diff for the packaging and keep driveline angles better being all wheel drive.

You are correct. Sorry I was thinking about what Toyota was offering when the fj80 was being developed (1988-89). By that time all the mini trucks were IFS 7.5". I could be wrong but I believe the reverse rotation HP 8" was first offered on the 80 series and is something toyota specifically designed to serve in that application. I believe they did good job. I don't worry about my axles.

 

[Marvelicious]

If you're concerned, slap some 30 spline birfs in there and quit worrying about it.

 

[SaturnAscends]

If you're concerned, slap some 30 spline birfs in there and quit worrying about it.

Well I’d rather have the birds be the fuse instead of the ring and pinion.

 

[Marvelicious]

Well I’d rather have the birds be the fuse instead of the ring and pinion.

I watched this argument go back and forth back in the day on Pirate, whether it made sense to run a part as a fuse, or to just run as much beef as you can. 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.

 

[Camotubebender]

I've seen a few threads on mud where they modify a rear 9.5" axle to work in the front of an 80 series

 

[SNLC]

Patrols are a 9.5” HP, FYI.

Cheers

 

[OGBeno]

100% weight savings and less NVH and more robust reliability paired with available power trains. All of the 70 series trucks went to the same setup as well At roughly the same time (phased in by market and platform).

Toyota knows what they are doing.

 

[Broski]

The 8" HP is pretty strong going forward, just be careful in reverse..

 

[SaturnAscends]

Patrols are a 9.5” HP, FYI.

Cheers

Yeah a lot of Aussies swear by those. Cruisers have better engines and gearboxes though.

 

[SaturnAscends]

The 8" HP is pretty strong going forward, just be careful in reverse..

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.

 

[use2bn83]

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.

My theory/opinion with the 100 series is 2 fold. (2 vs 4 pinion aside). 1. They come from the factory with less carrier bearing preload. So this allows for more deflection. 2. By the time a 100 series has 200k miles on the front diff, the bearings are worn enough that there is no preload left… in fact, usually less than zero allowing for a tremendous amount of ring gear deflection. Combine that with more powah and a heavier truck and things go sideways quick.

Because the 8” in the front of an 80 is a high pinion RR, it’s much strong going forward than the 8” in the back of your typical mini. However, the compromise is it’s strength going in reverse as mentioned above.

 

[SaturnAscends]

My theory/opinion with the 100 series is 2 fold. (2 vs 4 pinion aside). 1. They come from the factory with less carrier bearing preload. So this allows for more deflection. 2. By the time a 100 series has 200k miles on the front diff, the bearings are worn enough that there is no preload left… in fact, usually less that zero allowing for a tremendous amount of ring gear deflection. Combine that with more powah and a heavier truck and things go sideways quick.

Because the 8” in the front of an 80 is a high pinion RR, it’s much strong going forward than the 8” in the back of your typical mini. However, the compromise is it’s strength going in reverse as mentioned above.

Interesting. I suppose that’s why an aftermarket carrier/locker is often suggested for those.

 

[use2bn83]

Interesting. I suppose that’s why an aftermarket carrier/locker is often suggested for those.

That’s usually to replace a 2 pinion carrier. But having fresh carrier bearings and adding a bit more preload always helps.

 

[TheBussman]

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.

 

[mudgudgeon]

This became even more apparent on the IFS 100 series, which were known to break R&P and spider gears even in stock form in some cases.

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

Yeah a lot of Aussies swear by those. Cruisers have better engines and gearboxes though.

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

Interesting. I suppose that’s why an aftermarket carrier/locker is often suggested for those.

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

 

[matzell]

Because the 8” in the front of an 80 is a high pinion RR, it’s much strong going forward than the 8” in the back of your typical mini. However, the compromise is it’s strength going in reverse as mentioned above.

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.

 

[PEOPLES]

A pity is, that the parts are not interchangeable anymore. On my J4 i can use the fwd Diff to repair the rear one, if necessary. And I only need one set of spares in stock for the diffs.