Original Ford 7.25" Rearend with 3.5:1 Gears (top) compared to 8" with 2.79:1 Gears (bottom)
Ford 8" Rearend Swap
Original Ford 7.25" Rearend with 3.5:1 Gears (top) compared to 8" with 2.79:1 Gears (bottom)
I was at a local Pull-A-Part self-serve salvage yard looking for parts when I noticed an early Maverick with a 4-lug rearend. I made a few notes from the data plate and did some research when I returned home. I found out it was a 1970 model year and that was the only year the 8" came out with 4-lugs. Most were 5-lug. The gear ratio is 2.79:1 which is a great number for highway cruising and not too bad for take-offs when behind my recently rebuilt C4 tranny. The 7.25" was not having problems but I've been told they are getting more and more expensive to repair and parts are hard to find.
The 7.25" is referred to as a "Salisbury" type. Salisbury rearends have an access plate on the back side and the carrier is an integral part of the housing. They were Fords low-cost, low-performance units. The 8" rearend is what is called a "Hotchkiss" type and the carrier is easily seperated by removing nuts on the front side of the carrier. The 8" is a good choice because it is tough, you can easily change gear ratios (though not necessarily cheaply), and they are not as expensive to maintain as some are, at least for the near future. They can also handle up to 300 hp.
This swap is basically a very easy drop-in aside from a few points. Foremost is the width. The 8" is 1/2" wider than the stock 7.25". The spring perches are the correct distance apart but the tubes are a little longer between the perches and the backing plates. You'll also notice the tubes on the 7.25" are tapered at the ends and the 8" are straight so you will need the shock absorber plates from the Maverick to accommodate the wider u-bolts. This increase in width may not be an issue depending on the wheels and tires you're running but I found a local race shop (Ron Piercey Racing) who had many years experience and the right jig for narrowing these rearends so I had him take out 3/8" on each side for a total of 3/4" overall. The other issues are shortening the axles, modifying the driveshaft and the length of the rubber brake line which are addressed below.
With the price of gas increasing so quickly, doing a mod that should eventually pay for itself is always a big bonus. Here's a page of my calculations to show the decrease in RPMs at highway speeds.
Take the Full Tour or click on the links below to view individual photos.
|
|
|
|
Helpful Links
8" Rearend Swap Expenses (includes taxes and shipping)
$57 - 1970 Maverick 4-lug 8" Rearend Assembly
$22 - U-Bolts
$35 - Axle Seals
$54 - Axle Bearings
$30 - 3/16" Brake Lines & Fittings
$31 - Soft Brake Line
$35 - Drums
$27 - Brake Shoes
$20 - Brake Hardware Kits
$34 - Wheel Cylinders
$25 - Earl's Solo Bleeders
$13 - Driven Gear
$167 - Shorten Driveshaft, Weld Yoke, Balance, U-joint Kit
$50 - Misc. parts, hardware, tools, paint, fluids, etc.
$600 Grand Total
