Before/after comparison of 3.73
07-08-2010, 12:23 PM
#22
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
It has nothing to do with heat treatment of the steel, though I have seen that put forth in some silly explanations of why to heat cycle gears--however I never said it, as it would be nonsense as you have correctly pointed out.
What it does have to do with is that steel (and all materials) expand and contract as they heat and cool, and in newly assembled components they actually "move around" a small bit while expanding and contracting, repositioning themselves in their mountings and establishing their final operating relationships.
Heat cycling under moderate loads also causes all the newly installed pieces-parts to expand to what will be their normal operating dimensions, and establish their initial wear patterns under that moderate load--this is a good thing which will greatly increase their service life, and if done on a lift provides an opportunity to listen and directly observe.
Rear-ends are generally targeted to operate around 220°F to "burn-off" any moisture that might collect in the lube. If you installed the gears at 75°F then your 8.8" ring gear will expand in diameter by a bit over 0.009" when it's heated up, and in depth by 0.0015" or so. The pinion diameter will grow by 0.004", and pinion depth will increase by a like amount.
This is why the backlash and pinion depth settings are so important.
All that said, is heat cycling absolutely necessary on something as inexpensive, readily repairable, and not expected to last very long anyway¹ as an automobile rear-end?
Probably not.
Is it absolutely necessary for a gearbox on a multi-million dollar piece of production machinery (things I have been responsible for in the past) that will be expected to run 24/7 for the next 12 months without failure--or perhaps on a NASCAR racer that needs to last, running all out, for 500 (not 497.5) miles?
You betcha'!
It only takes a bit of time, does no harm of any sort, and may catch improper spacing and/or bearing preload before any damage is done. To my mind it beats the crap out of finding out 500 miles later that the rear-end has been overheating and the gears are shot...
---------------------------------------------
¹ - 100k miles is considered a long time for an automobile, a lousy 2000 hours at 50mph; 24/7 for 12 months = 8760 hours, at 50mph that would be 438,000 miles...
What it does have to do with is that steel (and all materials) expand and contract as they heat and cool, and in newly assembled components they actually "move around" a small bit while expanding and contracting, repositioning themselves in their mountings and establishing their final operating relationships.
Heat cycling under moderate loads also causes all the newly installed pieces-parts to expand to what will be their normal operating dimensions, and establish their initial wear patterns under that moderate load--this is a good thing which will greatly increase their service life, and if done on a lift provides an opportunity to listen and directly observe.
Rear-ends are generally targeted to operate around 220°F to "burn-off" any moisture that might collect in the lube. If you installed the gears at 75°F then your 8.8" ring gear will expand in diameter by a bit over 0.009" when it's heated up, and in depth by 0.0015" or so. The pinion diameter will grow by 0.004", and pinion depth will increase by a like amount.
This is why the backlash and pinion depth settings are so important.
All that said, is heat cycling absolutely necessary on something as inexpensive, readily repairable, and not expected to last very long anyway¹ as an automobile rear-end?
Probably not.
Is it absolutely necessary for a gearbox on a multi-million dollar piece of production machinery (things I have been responsible for in the past) that will be expected to run 24/7 for the next 12 months without failure--or perhaps on a NASCAR racer that needs to last, running all out, for 500 (not 497.5) miles?
You betcha'!
It only takes a bit of time, does no harm of any sort, and may catch improper spacing and/or bearing preload before any damage is done. To my mind it beats the crap out of finding out 500 miles later that the rear-end has been overheating and the gears are shot...
---------------------------------------------
¹ - 100k miles is considered a long time for an automobile, a lousy 2000 hours at 50mph; 24/7 for 12 months = 8760 hours, at 50mph that would be 438,000 miles...
Last edited by cliffyk; 07-08-2010 at 02:54 PM.
07-08-2010, 12:34 PM
#23
5th Gear Member
Join Date: Mar 2008
Location: Ohio
Posts: 2,994
Ahah! So we are both right...lol. I completely see your point with high end equipment, and likewise the opposite with our differentials...BUT-no one I have ever talked to knew anything about this...likely because they were mechanics, salesmen, etc and not flipping Mechanical Engineers lol.
Now, that being said, I think we both know the solution to this conundrum-
throw a bottle of Purple Ice in the dif. and call it a day! Wooooooooooooot!
hahahaha!
Now, that being said, I think we both know the solution to this conundrum-
throw a bottle of Purple Ice in the dif. and call it a day! Wooooooooooooot!
hahahaha!
07-08-2010, 04:47 PM
#27
6th Gear Member
Join Date: Oct 2006
Location: NJ
Posts: 6,817
You'll have fun. I know i am still enjoying my 3.73's... My enjoyment is bittersweet though. I would have probably went 4.10's, but i didnt want the 4.10's when i get the blower bc i want to keep my wheel/tire setup on and 4.10's would have had me shifting to 5th ... The 3.73's are much more enjoyable than the 3.27's though. Much more instant power and torque, more fun to play around with, definitely feels a lot quicker, and 5th gear can be used at 50mph no problem.. My exhaust sounds 10x better as well on decel and accel too. Idk the exact reason, but i have an idea as to why. I drove my friends stocked geared GT the other day and it feels SOOO SLOWWWW even though i ran better at the track with my stock gears as opposed to the 3.73 hahaha
Overall, i think You'll love them... Very noticeable. 3.27-3.73 was quite a step up
Overall, i think You'll love them... Very noticeable. 3.27-3.73 was quite a step up
Last edited by hpwrestler220; 07-08-2010 at 04:49 PM.
