I'm an engineering student doing a full analysis on the rear differential of my 75 vette. i would like to know any of the hardening/tempering techniques used in a stock rear diff if any. could any of you guys give me some input. called and e-mail GM everything is automated so i don't think they'll be getting back to me anytime soon

 

talk to mike dyer /Tracdogg2

 

Try this http://jimshea.corvettefaq.com/

 

Most of the parts in the differential are required to be hardened (via one method or another), because of the high unit loading and stresses applied to them. The cast iron housing (later aluminum units got similar treatment) were tempered to relieve internal casting stresses prior to machining. Bearings, hardended spacers, bearing retainer blocks, and similar parts were carburized and provided moderate core hardness throughout the part for toughness and overall strength (ie, Rc 30-45) ; then they were surface hardened and quenched for higher hardness at the surface for wear resistance (ie, Rc 60+ for several mils at the surface).

Gears were similarly processed to provide the core strength for the teeth to absorb the loading stresses of constant use, and then surfaced hardened on the wear surfaces for good abrasion/cracking resistance. For this process, most of the gear surfaces were copper plated prior to carburizing [except for tooth and wear surfaces] so that only those needed wear surfaces would be surface hardened. The roots of the teeth were Cu masked so that they did not become over-hardened and too brittle, thus cause cracking [and later propagation] from bending moments during operation. After hardening the wear surfaces, the Cu masking was then stripped from the part. Tooth surfaces may also have been nitrided for additional wear resistance.

In that differential unit, there were likely dozens of different heat treat process formats used [differing furnace atmospheres, temperature levels, time, quench types, etc.] on those parts used to produce a product that is no larger than it is, could tolerate the loading and wear of use [and sometimes 'abuse', like we prefer to do ] for many years with only occassional lubrication changes. If the general population knew what it actually took to produce that differential, they would surely be totally dumbfounded.

Good luck with your project.

 

Contact Eaton. They made them for GM and almost certainly have records on what was required in the process.

 

Check the S.A.E. handbooks, they will have an outline of the processes used.

 

Good luck with your project, and when you get into it, find out what they didnt do after 75 on the axle stub shafts. They aint worth a crap.

 

Paper must not be due for a few weeks.

And, it's the weekend and PIZZA NIGHT!!!