cumminscruiser
Adventurer
SOR has FF axles for 4 bills, not so bad 2 bills would be better.
Stronger pinion
- Thread starter cumminscruiser
- Start date
Doesn't seem like the pinion is the problem here. Spring pearch just doesn't break easily..
cruiseroutfit
Well-known member
To give you a little insight to my FF experience. About 5 local LandCruisers in our 'group' of rigs were constantly breaking semi-float shafts, 3 on a Rubicon trip, 2 on a Moab trip, a combined 10+ shafts between us in just a year or two. I went and picked up 8 FF's in the back of my Tacoma and in short order they made their way onto the same rigs. Knock on wood not a single shaft failure! Seriously, not a single! I broke 3 rears in 9 months and then didn't break a single after that. Now, anything can break, I fully realize that and 5 years later I still pack spare FF shafts... but when they do break, with the FF you can drive it back to camp or even home. On the SF you fix it on site, be it in a snowstorm in Utah's West Desert or in the Little Sluice of the Rubicon (two of my more favorable trail fixes). When I was developing a build plan for my new 1HZ FJ62 project, you can bet your bottom a FF was one of the first products I installed, literally.
cumminscruiser
Adventurer
I am defenently looking for a FF rear axle, If I can't find one here in Northern California I'll drive south and get one at SOR. Stronger axles are great but mainly to be able to drive out and get to where I could do a repair. Looks like SOR is the only source.
Jonathan Hanson
Well-known member
Just to throw a little debate in here:
I've always thought the design of full-floating axles was optimized for carrying more weight, not transmitting more power. It's the arrangement of the bearings that constitutes the significant difference between the two approaches - the separation of load-bearing and torque-transmitting duties. All else being equal (shaft diameter and strength, spline count, etc.) I don't see how a full-floating axle would be intrinsically better at resisting twisting or shock loads. IIRC, the shaft on a semi-floating LC axle is actually larger in diameter than its FF counterpart.
I don't recall muscle cars in the live-axle era using FF axles, despite massive horsepower and torque loads. On the other hand, contemporary 3/4 and 1-ton trucks did, since they were rated to carry more weight.
Am I missing some design feature of FF axles that changes things?
I've always thought the design of full-floating axles was optimized for carrying more weight, not transmitting more power. It's the arrangement of the bearings that constitutes the significant difference between the two approaches - the separation of load-bearing and torque-transmitting duties. All else being equal (shaft diameter and strength, spline count, etc.) I don't see how a full-floating axle would be intrinsically better at resisting twisting or shock loads. IIRC, the shaft on a semi-floating LC axle is actually larger in diameter than its FF counterpart.
I don't recall muscle cars in the live-axle era using FF axles, despite massive horsepower and torque loads. On the other hand, contemporary 3/4 and 1-ton trucks did, since they were rated to carry more weight.
Am I missing some design feature of FF axles that changes things?
cumminscruiser
Adventurer
It would seem that a FF axle only sees torque loads, and not loads applied from the tire. Those loads are transmitted through the bearings to the housing.
ntsqd
Heretic Car Camper
What you're not seeing is the loss of the bending load on the FF axle shaft. The SF axle has to deal with both a bending load (that is revolving around the shaft - can you say cyclic fatigue!) due to the cantilevered nature of the wheel & tire relative to the outer bearing, and with the torsional loads of moving the vehicle.
The FF shaft has only to deal with the torsional loads. It can be smaller in diameter and still actually be stronger in the application. A by-product of the FF design is that the differential's side gears no longer carry any load and are not subject to nearly the wear that SF side gears are. Lest anyone think this isn't a large factor they should come and look at the oilite-bronze bushings that I had to install in my '84 Mini's rear Detroit case to fix it. Side gear loadings in that axle opened up the side gear counter-bores to the point that the exposed axle splines were starting to eat into the main diff case....
For reference, circle track cars use FF rear axles in the higher cornering speed classes, and the faster dragsters also use an FF design.
The FF shaft has only to deal with the torsional loads. It can be smaller in diameter and still actually be stronger in the application. A by-product of the FF design is that the differential's side gears no longer carry any load and are not subject to nearly the wear that SF side gears are. Lest anyone think this isn't a large factor they should come and look at the oilite-bronze bushings that I had to install in my '84 Mini's rear Detroit case to fix it. Side gear loadings in that axle opened up the side gear counter-bores to the point that the exposed axle splines were starting to eat into the main diff case....
For reference, circle track cars use FF rear axles in the higher cornering speed classes, and the faster dragsters also use an FF design.
cumminscruiser
Adventurer
That's what I was thinking.
Jonathan Hanson
Well-known member
Thanks - I understand the bending load part of the equation now. I'm still curious as to how much stress is induced by those bending loads in a large-diameter semi-floating axle, versus the reduced diameter/strength of a full-floating axle (at least in a Land Cruiser application). I can see that the bending loads could be a factor, yet most axle breakages I read about seem to occur at low speeds on rough trails, with a sudden application of torque. That would seem to indict simple shaft strength, or lack thereof, rather than high-speed oscillation and fatigue. Unless you're saying the oscillation might pre-stress a shaft?
I will say this: In my experience, and those of many acquaintances, the strength of a stock Land Cruiser semi-floating rear axle is more than sufficient for the vast majority of use.
I will say this: In my experience, and those of many acquaintances, the strength of a stock Land Cruiser semi-floating rear axle is more than sufficient for the vast majority of use.
cumminscruiser
Adventurer
When replacing the rear third member, remember Crack Kills.
cruiseroutfit
Well-known member
At the bearing yes, due to the restraint of the carrier bearing and side gear splines, the SF shaft necks down to nearly the same major/minor diameter just shy of the differential, which happens to be exactly where they shear, on perfect 45* planes.
In general theory your right, there should be not strength upgrade between the two. But a closer look reveals two factors. A stress riser created by the necking of the SF shaft as well as the combination of torsional and shear loads created by the axle. The metallurgy of the SF shaft differs than that of the FF due to its need to axle as a bearing surface, a seal surface, a drive surface and a shear beam. Its generally accepted that they are a more brittle structure than the FF shafts. Believe me this is an age old debate, we've had it on Pirate, we've had it on Mud and our local Cruiserheads have debated it. The load capacity is the commonly known benefit of the FF, but I can't really think where shear load has been an major contributing factor in the demise of a SF shaft, they always fail in torsion. If they were bending flanges, or commonly destroying the axle bearing it would be one thing but the LC SF is very robust for load capacity, being used even in 80 Series and 100 Series LC's.
Above that, real world testing really has put the nail in the coffin so to speak of the debate. FF's shaft failures are rare, even amongst users that have gone through dozens of SF shafts collectively. Could it be the softer material allowing for more torsional twist? Could it be the effects of shear load on the SF shafts over time?
On that note I really picked up my affinity for FF's when the PO of Cruiser Outfitters (Darrell) really started using them in the late 90's. He seemed to be on to something then but it had more to do with the FF's ability to use a Toyota e-locker or cable locker whereas these cannot be installed to the SF. When I got around to doing a FF in my FJ40 upgraded SF shafts were unheard of. At this point Poly Performance is building some rock-solid chromo shafts for the SF 40/55/60/62/80 applications and they have been very well proven thusfar. If one isn't worried about "theoretical" load capacity of the FF, I wouldn't hesitate to recommend they give PP a call and investigate some upgraded SF shafts.
Of course when things do break, it sure is nice to pull the driveline, pull the shafts and drive it back to camp
cruiseroutfit
Well-known member
Agreed, to an extent
Its that one time, that time in the middle of nowhere and your busted and stopped dead in your tracks. The FF smells oh so sweet that one time.
Otherwise, Tat's got a tool that would also smell pretty sweet that one time, but the damage that happens to your carrier and housing can easily cost double that of a FF. When I broke my first shaft we disconnected the park brake cable from the opposite side, engaged the cable and basically locked that side in place. Then using a chain wrapped through the wheel and around the leaf spring we 'bound it into place', I dissengaged the rear ARB and due to the snow on the ground was able to 3 wheel it to the pavement where I was able to secure a trailer to get it home. The 4-5 miles in the dirt destroyed my ARB carrier (wallowed out the bearing journal) and carrier bearing/carrier. All told the repair cost $500+ to fix.
jesusgatos
Explorer
I'm running a set of Longfield chromoly drive flanges with a set of custom 4340 Superior axleshafts in my custom Diamond Axles Tacoma/T100/Tundra rear axle with a FROR full-floater conversion kit. It's about as burly as we could build a Toyota-based rear axle.
cruiseroutfit
Well-known member
jesusgatos
Explorer
Thanks. Oh, and I forgot to mention: To he original poster, you might want to look into having your new R&P gears cryogenically treated. Seems to make a pretty measurable difference in how the gears hold-up in these axles. That's the one thing I kind of wish we had done to my gears.