gm 8.5 r&p

[K*A*B]

been having some problems with 8.5 ring and pinion durability
3450 pounds street driven , th400 , 780 hp to the crank (appr. 950 on spray ), drag radials this thing has been eating them up all summer , about 15-20 passes and some street miles then its time for a swap
they are installed properly and have never had this problem befor , now the engine makes a bit more power
i have seen more powerful cars with 8.5's but i don't know their maintanance and none were street driven
have tried a few different manufacturers all with the same results
is it time for a 9'' or dana 60 ?
really tearing up the backside of the ring gear

[Scott @ DLS]

I gotta say it's just the radial tire. If you chatter them you will break the gear and twist axles. You want to delay the NOS and keep the rear of the car soft for better weight transfer. I bet if you run with a slick you wont have these issues.

If you stay with a radial tire,
I would install a real goor solid spacer, not cheap Ratech junk, Set up the gear a few thousands deep, M/W states they would rather burn up a bearing than to have something come loose so preload the pinion bearings up to but no more than 40 inch lbs or rotational torque. If you are still breaking gears then yes it's time for a heavier duty rear.

[Louie L]

Scott,
Do you sell or know of anyone who makes 8.5 Pro gears?
All ive found is Tom Axles 8.5 gears with "Special heat treating"

Ive been lucky with the stock GM 3.42s on slicks. I was planing on going to a radial until u just mentioned the above.

[nosmech]

WE HAVE HAD GREAT LUCK WITH OUR CAR ON GEARS. 10.10 ON MOTOR AND 8.60 NITROUS. SET THEM UP DEEP AND TIGHT. WE HAVE ABOUT 120 PASSES ON OUR NEW GEARS IN OUR MALIBU. 1.43 60 ON MOTOR 1.32 ON NITROUS.

[K*A*B]

does have a solid spacer in it , but i'm not sure what brand , changed that last go round
really have not made many nitrous passes yet , typically in the high 1.30's on motor
it just started its typical whining while cruising down the road
just for shits and giggles added a quart overful of gear oil today , the whining has subsided , could there be a lubrication issue that has been overlooked

[OnABudget]

When I had the 8.5, new gears wouldnt last but 5-10 passes.Good seasoned used gears from the junk yard would go 80-100 runs..008backlash. I always used .1 delay from the hit for the nitrous,never saw a gain from turning it on at the hit,so use a .1 delay to get the slack out of the drivetrain before the 1st kit turns on.

2quarts of gear oil is plenty, 80w90 weight, no synthetic gave me the best results.

Radials will beat the ring gear bolts up no matter what rear you have.

[jester]

What are you using for axles and spool brand wise? 33 or 35 spline?

[dougd]

2 things , 1 add strange aftermarket cap for a 12 bolt, 2nd add 2 or 3 lbs to your tire air psi.. Your caps are flexing under load and moving the pattern up the gear and breaking.You may also consider sending your gear to a heat treater and reduce the rockwell to 45.

[Scott @ DLS]

Scott,
Do you sell or know of anyone who makes 8.5 Pro gears?
All ive found is Tom Axles 8.5 gears with "Special heat treating"

Ive been lucky with the stock GM 3.42s on slicks. I was planing on going to a radial until u just mentioned the above.


Nothing in the aftermarket is offered for a GM 8.5" pro gear. You can take a normal street gear and have it softened. I know a few racers in my area have done it with good results. I will check into in ana get back with you. If memory serve's me right you want a pro gear to be about 55-60 rockwell hardness.