Hand-assembled by our trained technicians for an unbeatable combination of quality and value, Precision assembly for the correct backlash, preload, and proper amount of pinion shims to ensure the correct pattern on the ring gear teeth on all of our Ford 9 inch limited slip differentials, 9 inch Ford posi units are ideal for street tires and medium horsepower applications, Nodular iron housing is stronger than OEM “gray” iron and has 4 lbs of additional reinforcement, Clutch style positraction differential gives limited slip performance and quiet operation (no gears clicking!)
Ford 9 Inch Posi Differential 3rd Member, 31 Spl, 4.56 Gear Ratio Speedway Motors
Ford 9 Inch Posi Differential 3rd Member, 31 Spl, 4.56 Gear Ratio
Sku # 91049345-31-456
Mfr. Part # 91049345-31-456
Condition
New
Brand
Speedway Motors
Sold
Each
Details

As featured on Classic Truck’s Week to Wicked. Watch the transformation !

Assembled by Professionals

Hand-assembled by trained experts in-house, our Ford 9-inch third members are built from quality components with an exact step-by-step process. We bring this combination of precision assembly and quality components to you at a price that can’t be beat. We trust these third members so much, they’re the go-to choice for our own rides, from the street to the track. 

Tough, Nodular Iron Center Section

Our Ford 9 Inch Nodular Iron Third Member Center Section Carrier starts with a NEW casting with over 4 lbs. of additional material in critical areas. Nodular (ductile) iron is much more resistant to fracturing than OEM “gray” iron. Extra ribbing reinforces the case and rearmost pinion support (pilot bearing). 

Thick, forged steel bearing caps surround the carrier bearings, all securely held in place with precision Grade 8 cap screws. The improvements continue with rugged billet steel adjuster nuts and heavy-duty keepers to ensure your ring gear settings are maintained. All mounting surfaces are precision machined to ensure a consistent, flat surface for a positive gasket seal (no more leaks on your shop floor). An oil fill plug is included. 

Precision Assembled for Proper Ring Gear Teeth Pattern

Getting a proper pattern on the ring gear teeth is crucial. Our time-proven, step-by-step process ensures the correct backlash, preload, and proper amount of pinion shims to ensure the correct pattern on the ring gear teeth. Our gears use cold-rolled 8620 steel, known for its long-wear and durability.

To ensure a proper gear pattern, we use a stronger “Daytona” style pinion bearing support to maintain that critical pinion depth setting. Stronger due to its larger bearings, our Daytona pinion support also uses the spacer-and-shim setup to maintain critical pinion depth settings under high load, unlike traditional crush sleeves which often compress further, take out your preload and lead to failure. With solid bearing spacers and the proper shims, we eliminate this problem and make setting preload easy and repeatable during installation, service and gear changes. Since preload is already set, simply torque the pinion nut to 160 ft./lbs. and you’re good to go. The pinion gear is connected to our new, forged steel “Ford short”, 1310-type pinion yoke. 

Note - Speedway Motors Differential 3rd members come with a 1310 Universal Joint (U-Joint) series yoke. No other Yoke size options are available. 

1310 series U-Joint and Bearing Cap Reatainers Not Included - 1310 Series U-Joint Options

Clutch-Style Posi Differential with Proven Performance 

Our clutch-style posi differential gives you maximum traction. Based on the original limited-slip designs of the OEMs, these differential units provide the added benefits of experience over millions of miles and decades of proven reliability. A clutch-style operation means no clicking around corners and our posis feature heat-treated spider gears in a forged steel case. We’ve taken this posi to the next step in performance with increased clutch pressure and holding power, suiting it well for heavy-duty street car applications.

Speedway Clutch Style Differential has performed well in our Week to Wicked 1952 Chevy Truck, handling the job of transferring a 430 HP GM Performance LS3 to the ground.   

  • Clutch style, spider gear differential = proven reliability 
  • Spring-loaded clutch pack with improved grip over OEM designs 
  • Ideal for street tires and medium horsepower applications 
  • Housed in a Fully Machined, Reinforced Forged Steel Case 

Proven Reliability

We run what we sell. Our third member units are the go-to choice for our own rides and we have built these units to last with high quality hardware and components. Tapered steel roller bearings minimize friction, better handle thrust loads and increase load carrying capacity. The ring gears are assembled with Grade 9 bolts with a tensile strength of 180,000 psi, a 15% increase over Grade 8 hardware.  Heavy duty Grade 8 carrier cap bolts, a lock-style pinion nut with pre-applied Loctite and high-quality grade 5 pinion support bolts make our third member near-bulletproof. 

Units include a Viton® pinion seal providing long lasting oil and chemical resistance. This seal retains elasticity up to 399°F (204°C) and intermittently up to 600°F (316°C) This high temp seal helps eliminate pinion leaks, reduces maintenance and keeps the third member properly lubricated. A carrier-to-housing gasket is available separately. 

Our hand-assembled Ford 9 inch third member assemblies are made-to-order. We keep a supply of the most popular gears in stock, with most units built within 2-3 days. Our third-member units are shipped in a durable, reusable poly storage case, perfect for keeping multiple gear sets stored and ready for the track.

Features

  • Hand-assembled by our trained technicians for an unbeatable combination of quality and value
  • Track-tested durability in our own cars – we race what we sell
  • Precision assembly for the correct backlash, preload, and proper amount of pinion shims to ensure the correct pattern on the ring gear teeth 
  • Ring and pinion gears of 8620 cold-rolled steel for long wear
  • Nodular iron housing is stronger than OEM “gray” iron and has 4 lbs of additional reinforcement
  • Large “Daytona” style pinion bearing support for strength and reliability
  • Spacer and shim setup maintains critical pinion depth settings and easier to service than traditional crush sleeves
  • Clutch style positraction differential gives limited slip performance and quiet operation (no gears clicking!)
  • Ring gears assembled with Grade 9 hardware, 15% stronger in tensile strength than Grade 8
  • Viton® pinion seal, resistant to chemicals and high temperatures
  • Grade 8 Carrier cap bolts
  • Lock-style pinion nut with pre-applied Loctite®
  • Grade 5 pinion support bolts
  • Includes form fitted, reusable red poly storage case
Specs
Differential Type
Limited Slip
Housing Material
Nodular Iron
Gear Ratio
4.56:1
Axle Splines
31
Yoke U-Joint Series
1310
Yoke Width
3-7/32"
U-Joint Cap Size
1-1/16"
Spool Weight
Standard
Ring Gear Weight
Standard
Weight
78.55 lbs.
MFG. Part #
91049345-31-456
Sold in Quantity
Each
Gear Material
Steel
Yoke Included
Yes
Ring and Pinion Included
Yes
Carrier Style
Clutch Style Posi
Reviews

yes

Rated
Product Rating
by Ricardo on January 31, 2026

Summary: Pro street Mustang, perfect gear ratio and quiet, smooth on the street.

No, I would not recommend this product.

Very happy with posi

Rated
Product Rating
by Jamie on January 30, 2026

Summary: Great case to protect casting. Everything looks good so far. Thanks!

Yes, I recommend this product.

Great Product

Rated
Product Rating
by Jp on January 21, 2026

Summary: Item came In wrong box with the wrong Info wrote on box Item seemed to work out it is in the vehicle and working fine .. definitely a good product

Yes, I recommend this product.

Yes

Rated
Product Rating
by Vg on January 19, 2026

Summary: Very well put together a little tigh on the preload but not bad

Yes, I recommend this product.

9" Differential

Rated
Product Rating
by Country on December 12, 2025

Summary: Differential for 1965 f 100. Part fit and working great

Yes, I recommend this product.

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Tech Support
We're here to help before and after your purchase. If you have a question or need assistance with one of our products, please contact us through eBay Messaging and a knowledgeable Speedway Motors team member will be happy to help.
About
Speedway Motors is America’s Oldest Speed Shop® and has been a trusted source for specialty rodding and racing products and friendly expert advice for more than 74 years. Founded in 1952 by “Speedy” Bill Smith – a racer and street rodder himself – Speedway has grown from a one-man operation to become the world’s largest manufacturer, distributor and retailer of street rod and racing products. Our industry-leading fast delivery is the result of same-day shipping from our state-of-the-art, centrally located 500,000 sq. ft. headquarters. Speedway’s size offers customers unmatched product selection and low pricing, while our excellent technical support and customer service have made us a recognized leader in the rodding and racing industries.