Shot peening differential

[Peer81]

Hello eveybody,

I need some advice on this one. I want to let a company shot peen my differential and everything in it. I already have it apart. All the internal parts are new from Tom's. I begun polishing the carrier but a friend said shot peening was a better option. The housing from my 81 is aluminium so some added strength is also a good idea plus the nice finish shot peening gives on aluminium.

But now the question.
Do I need to tape off (or put plastic pieces into) all the parts that need to contact other parts like the surface on the carrier that contacts the ring gear? Or the parts where the bearings are on the carrier and housing etc etc?
I don't know how much the shot peening process alters the metal / aluminium surface? Of course I don't want to bearings to be spinning freely on the carrier / inside the housing or to have a ring gear with run out because of the shot peening process.

Google doesn't show me pictures from taped off parts that enter the shot peening process and all the parts that have been shot peening also don't show any untreated parts as far as I can see.
Thanks

Greetings Peter

 

[Hib Halverson]

What's the torque output of the engine?
What's the axle ratio?

 

[Vettehead Mikey]

I'd use the softest media possible- plastic bead or walnut shells to avoid damaging or altering surfaces. Taping over critical mounting or friction surfaces is mandatory.

Make sure your blaster triples washes all components when done.

 

[Peer81]

I put some plastic caps inside and over all the parts that don't need any shot peening and / or a few duct tape layers.
As I want to make the iron and alu better and stronger pastic or wallnut shooting isn't going to work.
As for the engine and diff ratio. I don't know why you need the info for this question but no problem. The engine is going to be a 400ci Dart SHP block (still need to build it) and the diff ratio is 3.07 or very close to that because I don't remember. As the Dana44 in 80/82 vettes aren't the strongest diffs around I think while working on it I can improve it to help it a little.

Greetings Peter

 

[Mac]

I put some plastic caps inside and over all the parts that don't need any shot peening and / or a few duct tape layers.
As I want to make the iron and alu better and stronger pastic or wallnut shooting isn't going to work.
As for the engine and diff ratio. I don't know why you need the info for this question but no problem. The engine is going to be a 400ci Dart SHP block (still need to build it) and the diff ratio is 3.07 or very close to that because I don't remember. As the Dana44 in 80/82 vettes aren't the strongest diffs around I think while working on it I can improve it to help it a little.

Greetings Peter

I did a bit of spot research on shot-peening aluminum. I didn't realize how effective of a treatment it was! Other than cost, there didn't appear to be any downsides... provided you protect the machined surfaces. Once it's done, do you intend to paint or otherwise protect the newly cleaned surfaces?

-Mac

 

[Vettehead Mikey]

As I want to make the iron and alu better and stronger pastic or wallnut shooting isn't going to work.

Shot peening will do very little for improving overall strength. Most of the benefit is to relieve residual stress in a component and put the surface in compressive load which may help with mitigating crack propagation.

 

[Hib Halverson]

Sorry...one more question.

What are you going to use for rear tires on this car?

 

[Peer81]

@Mac, no the aluminium will be as it is. As the diff goes back under the vette there is no need to paint it, it also wasn't painted from the factory.

@Hib, you sure make be curious about where you want to go with your questions so here it goes..
The rear tires will be stock ones 255/60R15 maybe a little bigger to 275 or maybe 17" rims if I need bigger brakes (no need for it now). I have in mind the weakest link in the driveline should be the tires. It's easier to get some new tires then a broken transmission. Btw the transmission will be a beefed up 700R4. I don't intent to go to a dragstrip just some normal road use and some autocross from time to time.

As the Dana44's (under the 80/82 vette's) have weak bearingcaps. A shop overhere is making a new billet one for the driversside (per Mike, Tracdogg's paper). I'm not looking for any miracles with the shot peening but as everything is apart right now I don't mind getting it done. As I don't want to lower the diff another time soon I don't want to take any shortcuts.

Greetings Peter

 

[Hib Halverson]

My opinion is your wasting time and money shot peening the axle case.

If your ring and pinion gears are ok, I'd take the diff apart, de burr the case, especially, the areas around the big window. Install new clutches packs and reassemble it.

D44s were not only used in 80-82 C3 but that diff was used from 85-96 in C4 manuals.

With the tires you have, the tall axle ratio and an automatic trans, I think it's highly unlikely your going to break that axle housing.

Now, if you had a manual trans, 4.11 gears, sticky tires and you were going to go drag racing on a regular basis, yeah...I'd see the drive axle as a weak link, but from what you say here, that's not your situation.

 

[Peer81]

Hello Hib,

Thank you for your heads up. But I already knew that's why I didn't ask
As for the Dana 44, the C3 44's are very different from the C4 44's! The C4 44's are about the best stock units you can get as for the C3 44's you need to remember they can fail if they have a coreshift or to much power on them.

Greetings Peter

 

[Hib Halverson]

Hello Hib,

Thank you for your heads up. But I already knew that's why I didn't ask
As for the Dana 44, the C3 44's are very different from the C4 44's! The C4 44's are about the best stock units you can get as for the C3 44's you need to remember they can fail if they have a coreshift or to much power on them.

Greetings Peter

Ok, you're talking about the drive axle case not the differential case–a symantics thing. A drive axle is the entire rear end. The "differential" is the device inside the ring gear which contains the limited slip and the side gears.

If you have a rear end case with "coreshift" shot peening isn't going to help.

Shot peening the cast aluminum drive axle case may offer a some improvement in reduction of stress in the metal, but considering the intended use–street driving and occasional autocross–and your rear tire package, I think you've got an expensive solution looking for a problem.

Spend that money on some other mod which will lower your time on the autocross course. For instance, upgraded limited slip clutches and a "tuned-up" limited slip will help you off the turns.