Rear drivetrain strength
Racer
Joined: Aug 2007
Posts: 267
Likes: 0
From: Brinnon Washington
Your 73 diff isn't much different then the 76. It will have the better RG bolts but the posi is the same. The earlier side yokes were better as well. I have rebuilt some early diff's with over 100k miles that I was able to reuse the yokes on.
I have seen stock engined cars pushed hard that wrecked the posi clutches. All in all the 63-79's aren't bad but there were changes thru the years that need to be addressed when rebuilding. Like any job, this can be done fast and cheap or fully detailed, much more labor intensive and better built.
Sorry, just answering the question not trying to hijack.
I have seen stock engined cars pushed hard that wrecked the posi clutches. All in all the 63-79's aren't bad but there were changes thru the years that need to be addressed when rebuilding. Like any job, this can be done fast and cheap or fully detailed, much more labor intensive and better built.
Sorry, just answering the question not trying to hijack.
Burning Brakes
Joined: Oct 2007
Posts: 816
Likes: 107
I really do not think you will have rear end issues even with a drag radial, with that little of a stall the car will not leave hard enough to break a spindle or anything else. These rears do and will break but they are still pretty tough especailly using and auto trans.
Team Owner
Joined: Jul 2004
Posts: 40,408
Likes: 792
From: Redondo Beach, California
I believe that the L88 engines produced about 550 HP. Also, I think the 68 and 69 L88's came with the same IRS package that the standard production cars had, including I believe 2 1/2 axles. So if this is true, it seems that the standard production IRS should hold up under a HP levels comparable to that produced by the L88. However, the L88 cars were really configured for road racing. I gather from what I read in this thread, the real threat to the C3 IRS comes from heavy acceleration under full power and particularly with sticky drag race tires. I also remember someone in this forum, some time ago, quoted Tom (Tom's Differentials) as saying that the standard C3 IRS could tolerate HP levels up to 650. Don't know if I'm quoting this person correctly, and of course, the person quoting Tom may have been mistaken.
Anyhow, I'm going to build a 502 and I'll be using a lot of Toms good stuff just to prevent an expensive IRS failure. I remember with my L88 clone (compression dropped from 12.5 to about 11.5), I revved the engine up with the car standing still and then pulled my foot off the clutch. Instead of wheel spin, I got a big clanking bang. The passenger's side U joint broke. I think the car went about 20 feet.
Anyhow, I'm going to build a 502 and I'll be using a lot of Toms good stuff just to prevent an expensive IRS failure. I remember with my L88 clone (compression dropped from 12.5 to about 11.5), I revved the engine up with the car standing still and then pulled my foot off the clutch. Instead of wheel spin, I got a big clanking bang. The passenger's side U joint broke. I think the car went about 20 feet.
Thread Starter
Pro
Joined: Jul 2005
Posts: 517
Likes: 7
From: Peoria IL
Thank you guys so much for your input. The transmission doesn't worry me, if it breaks chances are it won't be catastrophic, and it can be fixed- I have a good transmission guy if needed. The rear end was much more of an unknown to me, and I'm not convinced I'm making any more than a mild 454 makes, I won't be shock loading it with a manual transmission, and I don't have the extra weight of a BB car. It's just intended to be a (more) fun street toy with a couple "hero passes" at the strip.
I'll pick up all six U-joints from Mike Dyer in a couple days and put them in before the break in period is over.
Is the 10 bolt differential inside the housing the same as any other GM rear end?
I'll pick up all six U-joints from Mike Dyer in a couple days and put them in before the break in period is over.
Is the 10 bolt differential inside the housing the same as any other GM rear end?
Burning Brakes
Joined: Oct 2007
Posts: 816
Likes: 107
I believe that the L88 engines produced about 550 HP. Also, I think the 68 and 69 L88's came with the same IRS package that the standard production cars had, including I believe 2 1/2 axles. So if this is true, it seems that the standard production IRS should hold up under a HP levels comparable to that produced by the L88. However, the L88 cars were really configured for road racing. I gather from what I read in this thread, the real threat to the C3 IRS comes from heavy acceleration under full power and particularly with sticky drag race tires. I also remember someone in this forum, some time ago, quoted Tom (Tom's Differentials) as saying that the standard C3 IRS could tolerate HP levels up to 650. Don't know if I'm quoting this person correctly, and of course, the person quoting Tom may have been mistaken.
Anyhow, I'm going to build a 502 and I'll be using a lot of Toms good stuff just to prevent an expensive IRS failure. I remember with my L88 clone (compression dropped from 12.5 to about 11.5), I revved the engine up with the car standing still and then pulled my foot off the clutch. Instead of wheel spin, I got a big clanking bang. The passenger's side U joint broke. I think the car went about 20 feet.
Anyhow, I'm going to build a 502 and I'll be using a lot of Toms good stuff just to prevent an expensive IRS failure. I remember with my L88 clone (compression dropped from 12.5 to about 11.5), I revved the engine up with the car standing still and then pulled my foot off the clutch. Instead of wheel spin, I got a big clanking bang. The passenger's side U joint broke. I think the car went about 20 feet.
I am not 100% sure but I think that Toms quote is a little off, I seriously doubt a stock IRS can handle 650hp. My little small block has broken two sets of spindles with drag radials and that is on the street not even at the track
I really doubt my engine is making that kind of power....for sure it makes it on the spray but it is not on the car. As a matter of fact the car has not even been tuned yet and it broke the rear. I do not know if there is a hp tolerance number but if there is I dont think it is quite that high.
