Before you purchase parts…

Please read this before you buy parts from us.

At West Coast Differentials we have always supported our wholesale customers by not competing with them. We do not sell parts online, and have never gone out of our way to pursue retail sales. Nonetheless, we do sell parts to retail customers on a will call and mail order basis to those that are capable of installing parts themselves.

That brings us to the point of this post…

If you are planning to have a shop install your parts, we strongly recommend that you have the shop / installer purchase the parts.
Here’s why:
  • Most shops will not provide a warranty on parts you buy elsewhere. This creates a hassle for everyone if the parts fail, not to mention the delay caused when customer provided parts are incorrect or incomplete.
  • The professional mechanics at your local shop can order just the high quality parts they need for your job without paying for extras.
  • Most shops are owner operated family businesses that make a small profit on the parts they sell in order to pay for the tools and equipment needed to install them.

Help keep your local shop in business!



REM Polish ISF Gear Finishing Race Polishing Service

Isotropic Superfinishing – Ring & Pinion Gear Polishing

In-House Gear Finishing Service

Simply put, Isotropic Superfinishing significantly reduces the surface imperfections that remain after a Ring and Pinion Gear set is manufactured. The result is a cooler, quieter and longer lasting gear set.  At West Coast Differentials, the process we use is chemically accelerated vibratory surface finishing. This is technically not a polishing process, however the resulting finish does have a polished appearance. This process eliminates surface imperfections without removing material or changing the physical dimensions of the part.
This finishing process is widely used in racing applications where a conventional break-in process is not feasible, and where optimum performance is not an option.


  • Reduced Friction
  • Reduced Contact Wear
  • Reduced Heat
  • Increased Durability
  • Improved Oil Retention
  • Lower Operating Temperature
  • Reduced Noise & Vibration
  • Increased Fuel Economy
  • Reduced Break-In Requirements
  • Reduced Maintenance



We can Superfinish Ring & Pinion gears for practically any vehicle. Our extensive inventory of OEM and Aftermarket gear sets allows us to process and deliver your gears in the shortest possible time. Normal processing time is 1-2 days, depending on current scheduling.

Please call our Gear, Axle and Differential Parts specialists for details, pricing and scheduling.

(800) 642-0950

Gear Polishing REM Polish ISF Gear

Off Road 4x4 Differential Cover

ARB Differential Covers

ARB Diff Covers

ARB’s nodular iron Differential Covers have been engineered to protect the differential and ring & pinion from off-road hazards.


  • Computer optimized cross brace design increases the structural rigidity of the whole axle
  • Additional housing strength helps keep the ring & pinion gears meshing on the flat faces of the teeth, greatly increasing ring & pinion life and overall maximum load strength
  • Top quality, high power neodymium magnets are used in both the drain plug and the dipstick to collect metallic wear particles
  • Magnet location in the end of the dipstick allows the oil to be checked for tell-tale signs of internal damage
  • Prolonged carrier bearing life due to extra support to the bearing alignment
  • Approach/departure angle optimized by angled exterior surfaces
  • Unique dipstick/filler cap design allows differential oil level to be adjusted for customized high driveline angles

Available for:

  • Dana 35
  • Dana 44 (except Aluminum)
  • Dana 50/60
  • Chrysler 8.25″
  • Ford 8.8″
  • GM 10-Bolt

ARB’s Diff Cover will protect your differential against the hazards of impact during competition or extreme off road use and are designed to counteract flexing of the axle assembly When off road, it is inevitable that obstacles will be encountered that could potentially inflict expensive damage on your differential. To prevent this, ARB’s Differential Cover is available for a range of vehicle models, and has been specifically engineered to protect the differential and ring & pinion set from any off road hazards.

  • High tensile nodular iron structure protects the differential and ring & pinion set from off road obstacles
  • Computer optimized cross brace design increases the structural rigidity of the whole axle
  • Approach/departure angle optimized by angled exterior surface
  • Prolonged carrier bearing life due to extra support to the bearing alignment.
  • Top quality, high power neodymium magnets are used in both the drain plug and the dipstick to collect any metallic particles in the oil. This makes the dipstick an easy location to be checked for tell-tale signs of internal damage or water contamination without the need to drain the oil.


Ring Pinion Gear Break In

Ring & Pinion Gear Break In Procedure

Rear End Gear Break-In

In addition to proper differential setup, the correct break-in procedure is an important part of ensuring the long life of your gears.

New Gear Break In is an important step. ALL new ring & pinion gear sets must be properly broken in to prevent damage & premature failure.

Improper gear break in procedures may cause overloading and overheating of the ring and pinion gears as well as break down of the gear oil. Failure to properly break-in a new gear set can be identified by inspection, and may void the manufacturer’s warranty.

If you’re replacing the ring & pinion gear set, don’t plan on heading up over that mountain pass or hooking up that heavy trailer just yet….. Following the simple steps outlined below before you head out can prevent potential noise issues or gear damage.

After driving the first 15-20 miles at around 60 mph, it is best to stop and let the differential cool completely. Maintaining a speed below 60 mph and driving conservatively for the first 100 miles is also advised. The gear oil should be changed after 500 miles. We recommend that you drive at least 500 miles before any heavy use or towing. During the first 45 miles of actual towing, only drive 10-15 miles at a time before stopping to let the differential cool.

These steps are necessary to prevent damage to the new ring & pinion gear. Any heavy use or overloading of the differential during the first 500 miles may cause irreparable damage to the gear set.


Ford 9 Limited Slip Posi 35 Spline

Ford 9 Detroit Truetrac – 35 Spline 5 Pinion

The Ford 9 Detroit Truetrac 35 Spline is perfect for use in Ford 9″ axle applications that are being upgraded from 28 or 31 spline to 35 spline.

This unit is also ideal for custom powertrain builds. The 5-pinion design of the Ford 9 Detroit Truetrac provides incredible strength, smooth maintenance-free performance and proven durability. Available NOW!! Call the differential experts at West Coast Differentials for more information. Representatives are available to help Monday thru Friday from 8am to 5pm Pacific Standard Time.

Ford 9 Detroit Truetrac

Check out the Detroit Truetrac FAQ’s page for more information.