I had a lecture on props and driveshafts yesterday and that is what got me thinking
How high tensile should the propshaft and driveshaft bolts be?
At the moment i only have 8.8 on the driveshaft and im thinking these may not be quite strong enough.
The ones I bought from the ford dealer says "Verbus 10.9" on the head.
Prop should be 10.9 and driveshafts 12.9 IIRC.
That said I ran with 8.8 grade bolts fitted to the prop anyway and it wasnt a problem.
I cant remember what torque they are done up to (prop bolts), but ISTR that its still well within the 8.8 grade range anyway.
Remember the torque generates a clamping force and therefore friction between the 2 surfaces and thats what transmits the power. The bolts themselves
don't. The clamping force at a given torque will be the same with an 8.8, 10.9 or 12.9 bolt. The difference is the latter can be done up tighter
before they shear therefore they can apply more clamping force with higher torques.
Ok, cheers guys.
I had a lecture on props and driveshafts yesterday and that is what got me thinking
ford use 10.9 for alot of parts (prop shaft, brake calipers, suspension.....)
they use 12.9 on the M8 driveshafts (torx heads) - but if you get normal cap heads (allan key heads) to replace them they'll most likley be 12.9
anyway
can't imagine that its always needed, but stronger bolts isn't a bad thing if you can get them 
incase anyone didn't know already the first number is the min. tensile strength (div by 100) and the second is the ratio of that to the min.
yield stress
in other words - the higher the first number the more load it'll take before breaking
- and a higher second number means it'll get closer to the first number before it starts to stretch/bend
According to wikipedia, my engine oputs out 325Nm torque so i think id better go for 12.9.
what do jags use on theirs
use the same and thatll be plenty as your cars gonna weigh loads less so the tourqe on the props never going to reach that on the jag
take it your worried about them shearing
youd be amazed at the shear stength of a 6mm bolt let alone 4 times 8mm or so
Ray
quote:
Originally posted by RAYLEE29
.......youd be amazed at the shear stength of a 6mm bolt let alone 4 times 8mm or so
)