Factory 489 8.75 Rear Gear Ringand Pinion?

[68Valiant440]

Anybody know how strong a factory installed 3.91 Gear set from a 489 case 8.75" Mopar rear can be? How much hp/tq can they handle with 35 spline axles/spool @3600lbs? Making over 600 hp/tq....
Are they a strong steel or weak?

Should I just buy after market gears? I already broke the stock axles!

Thanks
Adam

 

[SGBARRACUDA]

There are several threads related to the 8 3/4 and strength of the different cases. But i ran a 742 case 4.88 spool 35 spline in a BB Scamp for years with no problems. Ran 6.40's 1/8th.

 

[68Valiant440]

There are several threads related to the 8 3/4 and strength of the different cases. But i ran a 742 case 4.88 spool 35 spline in a BB Scamp for years with no problems. Ran 6.40's 1/8th.

Thanks but did they answer the question of is a factory ring and pinion strong enough to handle 600+ hp/tq?

 

[SGBARRACUDA]

Well that is a loaded question. Are you running slicks, 4speed or auto, street or race.
I can state that i ran the standard Richmond gears, not pro gears.

 

[68Valiant440]

Well that is a loaded question. Are you running slicks, 4speed or auto, street or race.
I can state that i ran the standard Richmond gears, not pro gears.

727 rmvb 4200 9.5"
275/60/15 MT Drag Radial....Mostly Street driven but gonna hit the track too..
I foot brake the car already been 1.52 60 with 4.30 (Richmond) gears and still tuning..Should go 1.4's with no problem..
I have a set of 3.91 dated 1970 and wondering how strong they are

 

[Supershafts]

The gear and axle are 2 different issues, but resetting them after they were running is a different issue and if it wasn't all noted exactly how they were you can have a failure.

 

[crackedback]

Like most things, with time and application of power, it will eventually fail.