strengthening the IRS
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Polishing smooths out the surface which is where most cracks start. I'd think that a good shot peening after polishing would be even better as this compresses the surface, inhibiting cracks. Folks have been doing this to OEM connecting rods for years and swearing by the practices.
Tech Contributor
Joined: Aug 1999
Posts: 15,166
Likes: 3,967
From: Connecticut, USA
It's not a dumb question. If you look at the cracked posi case above you'll see it is in it's stock form, rough ground on the flashing and that's it.
Tuning and polishing a posi requires grinding all the edges, the internal seams, and windows. I also polish the OD and the flange. The RG holes are countersunk as well. I'll never say they're bullitproof as there are some big guns out there, but it is better then a stock casting. The theory is to smooth out the stress risers that lead to cracks. The clutches should be solid steels, no fiber or snowflakes, and tuned without the plates and springs. Outside of Tom's, Mike, myself, and the people I trained I don't know of anyone else that does this. Main reason is money, it takes me about 4-5 hours to polish and tune a posi alone.Done right they out perform any vette posi, done wrong they'll hammer or break.
Iron diff's can be built many ways. Most of what you see are in the $500-$800 range are not custom built but rather standard stock rebuilds. They are not bad for a mild street car but few owners fully understand the differences on how things are done today with respect to these.
If you're going to build a 500+ hp car and push it hard then you might look into the various ways to add strength to them, but remember time is money and it will not be a $800 job.Fitting a steel cap alone is a few hours work( doing it the correct way).
Many have acheived great results at home building their own diff's with the correct parts and local machine shop help. Given some coaching I have helped a few guys build units that were well beyond what they could have exchanged theirs for.
As with anything, do your homework before you decide. Don't get fooled by some of the advertising out there, with some knowledge you'll see through a lot.
Good luck with your car.
If you want more info on this, PM me and I'll get you the link.
Tuning and polishing a posi requires grinding all the edges, the internal seams, and windows. I also polish the OD and the flange. The RG holes are countersunk as well. I'll never say they're bullitproof as there are some big guns out there, but it is better then a stock casting. The theory is to smooth out the stress risers that lead to cracks. The clutches should be solid steels, no fiber or snowflakes, and tuned without the plates and springs. Outside of Tom's, Mike, myself, and the people I trained I don't know of anyone else that does this. Main reason is money, it takes me about 4-5 hours to polish and tune a posi alone.Done right they out perform any vette posi, done wrong they'll hammer or break.
Iron diff's can be built many ways. Most of what you see are in the $500-$800 range are not custom built but rather standard stock rebuilds. They are not bad for a mild street car but few owners fully understand the differences on how things are done today with respect to these.
If you're going to build a 500+ hp car and push it hard then you might look into the various ways to add strength to them, but remember time is money and it will not be a $800 job.Fitting a steel cap alone is a few hours work( doing it the correct way).
Many have acheived great results at home building their own diff's with the correct parts and local machine shop help. Given some coaching I have helped a few guys build units that were well beyond what they could have exchanged theirs for.
As with anything, do your homework before you decide. Don't get fooled by some of the advertising out there, with some knowledge you'll see through a lot.
Good luck with your car.
If you want more info on this, PM me and I'll get you the link.
Team Owner
Joined: Jul 2004
Posts: 40,381
Likes: 789
From: Redondo Beach, California
....
About the latest posting. Shot peening and polishing the diff case prevents stress cracks from forming. Don't know that much about crystal fracture mechanics, but it works.
Drifting
Joined: Oct 2005
Posts: 1,527
Likes: 148
From: East London/SW Essex UK
I am really hoping that torque 'does it for me'. At the lower end of the scale the engine dyno showed 220 bhp and 470 ft/lbs @ 2500 rpm which may help compensate for the low numerical gearing.
Thread Starter
Safety Car
Joined: Nov 2007
Posts: 3,570
Likes: 0
From: bottom of the sea
If you have a stick shift and over 500 HP, the only way to have a strong enough rear setup would be to either install a Tom's 12-bolt setup or a solid axle. With stick and less than 500 HP or less than 700 HP with automatic (without transbrake), you can do the following:
1) stronger half shafts (preferably 3 inch thick wall half shafts)
2) solid Spicer U-joints
3) have your posi case polished and hardened spider gears installed
4) install a 400+ lbs/inch rear spring and QA1 shocks to prevent excessive squatting. Squatting is one of the major issues.
5) lower the strut rod mount (special bracket available) in order to prevent camber change when rear is compressing.
those mods shift the weakest link to the axles. However, without going to Tom's setup, I don't see how you can upgrade to larger axles. Those 17 spline stock axles just won't do the job with high HP applications.
1) stronger half shafts (preferably 3 inch thick wall half shafts)
2) solid Spicer U-joints
3) have your posi case polished and hardened spider gears installed
4) install a 400+ lbs/inch rear spring and QA1 shocks to prevent excessive squatting. Squatting is one of the major issues.
5) lower the strut rod mount (special bracket available) in order to prevent camber change when rear is compressing.
those mods shift the weakest link to the axles. However, without going to Tom's setup, I don't see how you can upgrade to larger axles. Those 17 spline stock axles just won't do the job with high HP applications.
good sounding advicei just installed drag light rims with MT drag radials and they do not spin at all. ive got a very stout 383 with a 5 spd TKO. so now im concerned about the axles
Last edited by rebc3; Jul 9, 2008 at 01:34 PM.
