8 1/4 rebuild

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EvanS

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Hi, I'm in the process of rebuilding an 8 1/4 to put into my valiant. I believe it came out of a 74 duster, but I'm not sure. This car is going to be a cruiser with an occasional lead foot. Right now it has 2.45 gears in it and drum brakes. I am going to be putting in a 360 magnum with either a 904 or 727 depending on what I can get when I'm ready for it. Goal for the motor would be around 400hp. I'm trying to keep it affordable and having trouble finding affordable new parts... With that I have a few questions...

1. I want to put posi in it, but I'm only finding the spicer trac lok at dr diff, or the yukon gear dura grip. The spicer says its good up to 350 hp and the dura grip is twice the price. Am I missing any other options?

2. Gear ratio, because it is a cruiser would I be doing a disservice to myself staying with 3.21 rear so I can keep my gas mileage up or should i go up to 3.55?

3. Brake options. I can't seem to find an affordable disc or drum brake option... has 10" now but they need to be replaced.

I have been searching for days for answers to these Qs and I haven't found the answers that I like. TIA
 
Talk to Cass at Dr. Differential...maybe he can answer most of your questions..Mopar costs more than all of em...
 
Go to the U Pull IT and grab a sure grip out of a Jeep. Not sure what year they changed the spline count.
 
1. & 2.) Hit the boneyards, look for Jeep XJs (Cherokees) and Dakotas with the 8.25 rear- up to 1996 or so they still use the 27 spline axles. Both of these commonly had SURE GRIP carriers and gears in the 3.5x -3.9x range.
3.) Brake options-
If you want drums, any 10/11" drum brake assemblies from B, C, E, F/M/J, 4.5 BC truck/van, and others will work.
Cheap discs can be had while you're at the pick 'n pull getting your rear end parts. Jeep Grand Cherokees up to about '98 or so and Jeep Libertys have rear disc brakes that are a bolt on for your rear. The only fab work is adapting the parking brake cables to your car.
 
3:55 gears with a 26" tire and a lock up torqueflight will net you 2800-3000rpm on the highway. 3:21 would be better on gas and still lively enough.
 
suregrip.jpg


All serious if that is a 2.45 in there you have to get another carrier if going with lower gears. We beat the 8 1/4 up pretty good here.

The 8 1/4 thread | For A Bodies Only Mopar Forum
 
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You mention your putting the ~400hp drivetrain in a Valiant. There’s more space in a Duster and you distinguish between the two in your post already. Without hacking the rear wheel wells, you’ll be limited on the size of rubber to utilize that power. I’m not sure if skinny tires can tell the difference between 300 and 400hp.
 
FWIW, there are quite a few people that say that you can switch a 2.45 gear 8-1/4 with its different pinion location to a lower gear ratio, but the handful of folks I have talked to who have done it strongly advise me against doing the same. Their exact words were that they couldn't get them to run quietly or keep them from making metal chips.
 
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