Thread: Drive Flange Bolts

Originally Posted by roverrescue

From a wise sage forum member

"An 8.8 bolt has a shear strength of 375 N/mm2"

M10 in grade 8.8 would be 29000N or the shear of 5 of them 145,000N
I dont think even your 4BD1 could generate that Dougal
I agree though its the tension or lack of that would lead to failure, I was worried that a helicoil would be a weak point and continue to fail.

Thanks for all your help!
Steve

Good of you to work it out, I was hoping someone else would.
So 5x145kN at a radius of 0.0475m gives 34 kNm.
But that's not the failure mode, if they can move then they're going to slog the holes, slog the threads and fatigue the bolts in bending.

M10 bolts gr 8.8 torqued almost to yield (60Nm approx) gives around 35kN clamp. With friction of 0.3 I get an axle torque of 2.5kNm to make the joint slip.
On a 33" tyre that's 600kg of driving force which seems sufficient but doesn't have much spare to deal with shock loading.

I'd helicoil it, put in grade 12.9 cap screws and torque them to ~90Nm. This will give you about 25% more than the original torque capacity, rave shows 65Nm which will yield grade 8.8 bolts.

Just a comment - one thing I have found guaranteed to loosen the drive flange bolts is loose wheel bearings - could be worth keeping in the back of your mind; if the flange bolts come loose, check the wheel bearings for free play.

John