Should the prop shaft be acting as a "fuse" ??
Discussion
I've almost finished swapping out the prop shaft on my lifted Suzuki Vitara for a double cardan prop from a Hilux Surf. This is a way bigger job than you'd think as the transfer box has to be fitted with a flange in place of the slip yoke.
Reason for the change is that the Surf prop shaft is double cardan so it better handles the steep prop angle caused by the suspension lift.
Somewhere I read that the prop shaft acts as a sort of "fuse" on the drivetrain, being the weakest part of the drivetrain, it breaks before anything more serious breaks, like the gearbox or axles. Is this true? In practice I've seen a few prop shafts break on the Vitara so it does seem to be the weakest point.
Now that I have a very beefy prop shaft, this fuse would be gone. Seeing as I probably will need to get the Suft prop shaft lengthened to finish the project, I could get the prop shop to create a hybrid shaft, having the Hilux Surf double cardan joint on one end, and an original Vitara UJ on the other end. This way I get the double cardan with it's high angle capabilities, and I still get the weaker Vitara joint on the other end to act as a fuse.
What do people think?
Reason for the change is that the Surf prop shaft is double cardan so it better handles the steep prop angle caused by the suspension lift.
Somewhere I read that the prop shaft acts as a sort of "fuse" on the drivetrain, being the weakest part of the drivetrain, it breaks before anything more serious breaks, like the gearbox or axles. Is this true? In practice I've seen a few prop shafts break on the Vitara so it does seem to be the weakest point.
Now that I have a very beefy prop shaft, this fuse would be gone. Seeing as I probably will need to get the Suft prop shaft lengthened to finish the project, I could get the prop shop to create a hybrid shaft, having the Hilux Surf double cardan joint on one end, and an original Vitara UJ on the other end. This way I get the double cardan with it's high angle capabilities, and I still get the weaker Vitara joint on the other end to act as a fuse.
What do people think?
Hmm, it's always been the prop shaft that's broken first on the Vitara's (mine and others) and I've seen the same happen with other 4x4s in comp safari competitions, especially when they take off, the props would break on landing. I've seen lots of prop shafts break. Aside from props the only other part of the drivetrain I've known to break is the chain drive on modern transfer boxes. All the earlier 4x4s, like Landcruisers, Hilux had stronger gear driven transfer boxes.
Stevie, yes sometimes it causes damage. On mine it flapped around and pulled off of the brake and fuel lines.
To clarify it's the UJ or the yoke that fails, not the actual shaft.
Stevie, yes sometimes it causes damage. On mine it flapped around and pulled off of the brake and fuel lines.
To clarify it's the UJ or the yoke that fails, not the actual shaft.
Edited by rcx106 on Saturday 19th September 09:51
failure is just a sign of inadequate part or a fault.
They should never break.
I've only ever broke one once, luckily shortly after a burnout/launch and it ripped handbrake cables off and punched a hole through the floor.
At speed it probably would have done a lot more damage.
No manufacturer ever would be insane enough to consider shaft breakage as a deliberate choice to prevent problems elsewhere.
They should never break.
I've only ever broke one once, luckily shortly after a burnout/launch and it ripped handbrake cables off and punched a hole through the floor.
At speed it probably would have done a lot more damage.
No manufacturer ever would be insane enough to consider shaft breakage as a deliberate choice to prevent problems elsewhere.
After tyre grip the next thing to go IME is the diff, prop breakage is usually a sign of doing work it's not intended for and manufacturers tend not to design for that, just because the prop is the weakest link it doesn't meen it was designed that way, a designed week point shouldn't really create so much potential damage, on road the diff "should" be the weak point (grip dependant), off road, lift kits and general abuse wil strain the prop U/Js and create a user made week point ?
for most vehicles the prop will not break first because it only handles gearbox output torque (and not wheel torque) and it's relatively speaking a large diameter! (compared to say parts in the cross axle differentials or halfshafts, that take full wheel torque, full wheel shock loads, and are a much smaller diameter.
However, on off road vehicles, that can experience high prop angularity then the joint do fail first as they are being asked to transmit high loads at high angles, especially on solid axled vehicles where those axles can tramp and nod massively as the tyres slip/grip etc
However, on off road vehicles, that can experience high prop angularity then the joint do fail first as they are being asked to transmit high loads at high angles, especially on solid axled vehicles where those axles can tramp and nod massively as the tyres slip/grip etc
Max_Torque said:
for most vehicles the prop will not break first because it only handles gearbox output torque (and not wheel torque) and it's relatively speaking a large diameter! (compared to say parts in the cross axle differentials or halfshafts, that take full wheel torque, full wheel shock loads, and are a much smaller diameter.
However, on off road vehicles, that can experience high prop angularity then the joint do fail first as they are being asked to transmit high loads at high angles, especially on solid axled vehicles where those axles can tramp and nod massively as the tyres slip/grip etc
Yup, it's just dawned on me that these 4x4s have all had big suspension lift which increases the prop angle which then puts a ton more strain on the UJs. Doubling the prop angle causes quadruple force on the UJ, it's an exponential relationship.However, on off road vehicles, that can experience high prop angularity then the joint do fail first as they are being asked to transmit high loads at high angles, especially on solid axled vehicles where those axles can tramp and nod massively as the tyres slip/grip etc
Anyway this means I don't have to worry about my now beefy prop shaft.
rcx106 said:
Hmm, it's always been the prop shaft that's broken first on the Vitara's (mine and others) and I've seen the same happen with other 4x4s in comp safari competitions, especially when they take off, the props would break on landing. I've seen lots of prop shafts break. Aside from props the only other part of the drivetrain I've known to break is the chain drive on modern transfer boxes. All the earlier 4x4s, like Landcruisers, Hilux had stronger gear driven transfer boxes.
Stevie, yes sometimes it causes damage. On mine it flapped around and pulled off of the brake and fuel lines.
To clarify it's the UJ or the yoke that fails, not the actual shaft.
On a jump, after takeoff the suspension is at full droop - the worst case for uj's. Add the shock loading from spinning wheels regaining traction, and it's not surprising the uni joints break.Stevie, yes sometimes it causes damage. On mine it flapped around and pulled off of the brake and fuel lines.
To clarify it's the UJ or the yoke that fails, not the actual shaft.
Edited by rcx106 on Saturday 19th September 09:51
The new Hilux Surf prop really is much beefier 
I'll be curious to see if the double cardan improves vibration problems, I've had mixed responses from prop shops. So far I've fitted the flange but the prop bolts don't clear the transfer box, so I have to drill the flange to fit countersunk head bolts. Then I have to see if the new prop is long enough, maybe have to get it lengthened. Then I need to see if there's enough adjustment in the axle rose joint to realign the rear axle to get it into the double cardan configuration which is different to a standard prop.
I'll be curious to see if the double cardan improves vibration problems, I've had mixed responses from prop shops. So far I've fitted the flange but the prop bolts don't clear the transfer box, so I have to drill the flange to fit countersunk head bolts. Then I have to see if the new prop is long enough, maybe have to get it lengthened. Then I need to see if there's enough adjustment in the axle rose joint to realign the rear axle to get it into the double cardan configuration which is different to a standard prop.stevieturbo said:
Very good demonstration. Interesting at the end the guy puts the UJs out of phase by approx 15 degrees and it totally messes up the constant velocity.When speccing a new prop for my 4x4 racer Bailey Morris did use the word 'fuse'.
In my case as the propshaft runs close to the gearbox and engine sump (fixed difs,it's independent suspension) failure tends to take out one or both sumps. My one and only foray into drag racing resulted in leaving the rear prop at the start of the Long Marsdon strip, way more grip than I'm used to
Once I pointed out that this type of failure was more expensive than a dif or gearbox failure, they came up with a solution that has as yet not failed.
I've gone to CV joints rather UJ which seems to offer more strength in a confined space.
In my case as the propshaft runs close to the gearbox and engine sump (fixed difs,it's independent suspension) failure tends to take out one or both sumps. My one and only foray into drag racing resulted in leaving the rear prop at the start of the Long Marsdon strip, way more grip than I'm used to
Once I pointed out that this type of failure was more expensive than a dif or gearbox failure, they came up with a solution that has as yet not failed.
I've gone to CV joints rather UJ which seems to offer more strength in a confined space.
The problem I had was that I didn't have room for anything bigger than a 1310 joint, one joint is right under the flexplate.
The only ones that lasted at all were GKN non grease. These were getting virtually unobtainable from GKN/HS. If I went for greasable ones they'd fail where the grease nipple screwed in.
Anyway. so far so good!
The only ones that lasted at all were GKN non grease. These were getting virtually unobtainable from GKN/HS. If I went for greasable ones they'd fail where the grease nipple screwed in.
Anyway. so far so good!
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