Thread: LT85 Damage

Originally Posted by Rangier Rover

Id still use it again if uneconomical to replace it. Shouldn't be a drama in lower gears as will have less torque against it in most cases. Hard to say but that would likely have around 90% of it strength I would think. Its not Turboed is it?

torque applied to the gears is higher in lower gears ie: say first is 4:1 and fourth is 1:1 the engine produces 100NM of torque @3000rpm so the torque applied to first gear is 400NM as opposed to 100NM on fourth hence we change down gears going up hills to multiply your torque.

I agree with John the gear should be fine, gears don't drive of the tips they load up through the middle, you see gear that have broken tips that beacause bearing failure causing missalignment or pushing to much torque through it and the gears walk apart from each other causing missalignment.

Originally Posted by lambrover

... gears don't drive of the tips they load up through the middle, you see gear that have broken tips that beacause bearing failure causing missalignment or pushing to much torque through it and the gears walk apart from each other causing missalignment.

Gears do transmit load from the tips of the teeth, but it is reduced because there will be another pair of teeth in mesh at the same time that are sharing the total load. This is even the case with spur gears (straight cut), but more load is shared with helical gears.

I disagree John, when you look at tooth contact say on a diff set up correctly the contact is in the middle, you may get some wiping action as the teeth disengage but load has already been taken up by the tooth behind.

if gears are driving of the tips they are set up incorrectly or have had a bearing failure, like wise if driving of the rute of the tooth.

hypoid gears =/= helical gears

helical and spur gears are often heavily chamfered on the outside edges of the teeth to remove the unsupported corners because they chip off under load

Originally Posted by lambrover

torque applied to the gears is higher in lower gears ie: say first is 4:1 and fourth is 1:1 the engine produces 100NM of torque @3000rpm so the torque applied to first gear is 400NM as opposed to 100NM on fourth hence we change down gears going up hills to multiply your torque.

I agree with John the gear should be fine, gears don't drive of the tips they load up through the middle, you see gear that have broken tips that beacause bearing failure causing missalignment or pushing to much torque through it and the gears walk apart from each other causing missalignment.

I assumed it was the input shaft torque on the given gear is relative to engine out put, in final constants.... yes that is the case indeed.

Originally Posted by lambrover

I disagree John, when you look at tooth contact say on a diff set up correctly the contact is in the middle, you may get some wiping action as the teeth disengage but load has already been taken up by the tooth behind. ...

We are discussing helical gears here, not hypoid or spiral bevel gears.

Originally Posted by lambrover

...if gears are driving of the tips they are set up incorrectly or have had a bearing failure, like wise if driving of the rute of the tooth.

You are mistaken!

The mating gear teeth make contact and transfer load over the full flank (excluding the clearance space at the root radius) as they rotate in mesh. There is quite a large amount of the rotation where the teeth only contact near the tips and roots - can you explain how the load transmission ceases in these regions.

Teeth wear more near the tip and root, than at the pitch line. This due to the fact that sliding friction occurs in these areas - near the pitch line it is closer to rolling contact.

Sometimes the involute profile has to be modified near the tip of the tooth to account for tooth deflection . But this is not done to provide clearance.