8.25 gear install

[texas charger 73]

im switching from a 2:76 to a 3:55 gear in my 8.25.. its open rear( cant find a good used SG i can afford).. i know how to set backlash.. my biggest concern is pinion depth and pinion preload? is there special tool for pinion pre load or how can i measure pinion pre load.. i believe its like 6-7" lbs...  this will be my first rear i am doing myself... i could use all the help and tips i could get....thanks guys..

[TommyGun]

Im not familiar with 8.25 diff but pinion preload is set either with a crush sleeve or shims.  You measure preload with a dial type torque wrench.

https://www.summitracing.com/parts/wmr-m195?rrec=true

[Birdflu]

im switching from a 2:76 to a 3:55 gear in my 8.25.. its open rear( cant find a good used SG i can afford).. i know how to set backlash.. my biggest concern is pinion depth and pinion preload? is there special tool for pinion pre load or how can i measure pinion pre load.. i believe its like 6-7" lbs...  this will be my first rear i am doing myself... i could use all the help and tips i could get....thanks guys..

Pinion depth is going to be determined by the print or contact pattern you have during your set-up. Always start by using the original pinion depth shim that was removed from the housing that you're using. If you're fortunate enough to start with an OE installed gear set along with it's original thickness pinion shim, you've got about a 60-70% chance you won't have to change it. Since ring and pinion mesh are engineered off of a 'nominal' pinion depth, you're always best off starting with the pinion depth shim the housing was born with.
Typically, we always recommend using new bearings when setting up a new gear set. At a minimum, I'd surely use new pinion bearings. It is somewhat critical that the pinion remain fixed in its bore and not allowed to move for and aft once the bearings break-in. New bearings will allow more pre-load from the get go (20-25in lbs), and are less prone to burning up from having their lifelong pre-load changed even the slightest. It's not uncommon for used pinion bearings to fail if their pre-load is increased as little as 5in lbs! If your pinion bearings are in great shape and you choose to re-use them, install a new crush sleeve, use a new pinion nut and shoot for around 10in lbs of rotating 'drag'. This is measured using a dial type torque wrench (as mentioned above). We use a 0-150in lb Accutorq dial torque wrench. Tighten the pinion nut until you measure 10in lbs of rotating 'drag' NOT including the break away torque (the amount of force required to get the assembly moving). Get yourself some prussian blue, a dial indicator and you're well on your way!      

[Vegas_Nick]

Just check this guy's video series. He explains it all:

https://youtu.be/s7upD4HZzkw

[Kern Dog]

I have never seen a 2.76 in a 8 1/4" axle. I've seen the 2.71 ratio. Are you sure that you are not working on a 7 1/4" ? They did come with a 2.76 ratio.

[ACUDANUT]

I have never seen a 2.76 in a 8 1/4" axle. I've seen the 2.71 ratio. Are you sure that you are not working on a 7 1/4" ? They did come with a 2.76 ratio.

They did ?

[440]

Not sure about Mopars but most aftermarket gear sets are marked with a pinion depth figure from when the gears are lapped from the factory. My Motive gears said to try and stay within .002 of this figure. I think setting the pinion depth to the gear vendors specs saves a lot of hassles and makes gear set up much easier. Set the pinion depth followed by backlash, maybe a slight adjustment, call it done.

[John_Kunkel]

I have never seen a 2.76 in a 8 1/4" axle. I've seen the 2.71 ratio. Are you sure that you are not working on a 7 1/4" ? They did come with a 2.76 ratio.

They did ?

[Kern Dog]

That is great, John.
I have never seen a 7 1/4" axle with anything but a 2.76 even though I have read that other ratios were available. EVERY one of the A body cars I've had were equipped with a 2.76 ratio if it had a 7 1/4" axle.
The 8 1/4" axle is a good unit for moderate Hp applications. I'm buying a 1970 383 Charger with an 8 1/4" axle. I'll bet that one is also the dreaded 2.71. I'll use that axle in some A body project.