What is the correct way to measure my bolt circle for my wheels? 

It depends on the stud count of your bolt circle. If it is a 4 or 6 lug then you measure from the center of the 12 o’clock position stud to the center of the 6 o’clock position stud. This will give you your bolt circle. If it is a 5 lug then a little math is involved. The simplest way is to measure from the center of the 1st stud skipping the 2nd stud and going to the center of the 3rd. You will then add a 1/4 inch to this and it will give you the bolt pattern. For example if the 1st to 3rd length going center of stud to center of stud is 4 1/2 inches you would then add 1/4 inch to this for 4.5 + .25 = 4.75 or 4 3/4 Chevy pattern. A typlical Ford 5 lug would measure 1st to 3rd at 4.25 inches so 4.25+.25= 4.5 or 4 1/2 Ford pattern. Measuring center of 1st to outside of 3rd doesn’t always work especially with a larger stud diameter like 5/8″ studs.

What gear oil do I use?

Your rear end fluid choice is predicated on what “carrier” you are using.  Moser Engineering manufactured items can be used with any mineral or synthetic based oils, we do recommend a GL-5 or higher rating.  These items include; Axles, Bearings, Cases, Mini-Spools, Pinion Supports and Spools.   Aftermarket gear manufactures, “Motive Gear” and “Richmond Gear” both promote synthetic oils for their Ring & Pinions.  To assist you in selecting the correct oil we have attached direct quotes from some of the leading differential manufactures websites below;


What kind of oil and additive should be used with an Auburn Performance Differential?It is important when installing
an Auburn High Performance, Pro Series or ECTED® LOCKER that a high quality non-synthetic 80W90 GL-5 gear oil
be used. Treat the oil with Auburn Gear, GM or Ford friction additive. Three ounces of additive treats one quart of oil.
Friction additive part numbers:
 Auburn Gear: 504102
 GM: 1052358                                                                                                                                                             
 Ford: C8A219B546A


Detroit Locker

What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?
A quality petroleum/mineral based oil works best in the Detroit Locker units. We do not recommend synthetic oil. Friction additive/modifier is not required.

Eaton Posi

What kind of oil should I use? Can I use synthetics? Do I need a friction additive/modifier?
Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance.


What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?
A quality petroleum/mineral based oil works best in the Truetrac units. We do not recommend synthetic oil. Friction additive/modifier is not required.



Your new Wavetrac® differential is incredibly durable and will withstand the harshest environments… as long as suitable oil is used.
Many customers ask what oil we recommend for use with the Wavetrac® differential.
We feel the best answer is:
Use the “factory fill.”

In other words, use the gear oil spec that your car manufacturer recommends for your car. The Wavetrac® is compatible with virtually all factory-installed gear oils used today.
If you are racing your vehicle, and wish to upgrade the gear oil to improve performance or durability in racing conditions, choose the oil carefully: be aware that some gear oils have additives that are not recommended for use with your Wavetrac®.
Some have friction modifiers designed for limited slip differentials. These modifiers generally increase slipperiness and are intended to reduce clutch disc chatter in conventional clutch-type LSDs.
Some gear oils such as Red Line Oil’s Shockproof® type have microscopic solid particles in immersion in order to “cushion” transmission components, acting as an extreme pressure agent.
The Wavetrac®, and all helical gear differentials in general, operate using friction. The friction generated between its internal gears and its housing are what allow this type of differential to function.
Gear oil additives that drastically reduce friction will actually reduce the performance of gear differentials. The internals of the diff get too slick to generate adequate friction – reducing the differential’s effectiveness – reducing its ability to drive both wheels.

In conclusion, when using a Wavetrac®:
• Use factory spec oils for your car
• Use factory-compatible high performance oils if you wish to upgrade the oil.

Please consult Autotech Driveline for recommendations.
• Do NOT use gear oils with friction modifiers or limited slip additives.
• Do NOT use Shockproof®1 or similar gear oils designed to reduce friction.

Please note that you will void the Wavetrac® Limited Lifetime Warranty if incorrect
gear oil is used.

1 Red Line Oil offers many, high quality, high performance gear oils that are compatible with Wavetrac® differentials.Only the Shockproof® types should not be used with the Wavetrac®.


How can I determine if my axles can be cut and resplined?

A. The axle shaft has to be the same size or bigger as the original spline OD where you need it cut.(They can NOT be smaller )

B. On the original axles you need to be taking off at least 3 1/2″ to get past the original spline area. 

Is a C-Clip axle race legal?

 No a C-Clip axle is not a race legal axle.

Can I reuse my stock GM drum brakes with a press-on axle bearing?

A. To reuse your stock drum brakes, you can use are GM 10/12 Bolt Housings Ends for press-on axle bearings like the 7900 Moser housing ends. 

B. They are made to work with a big ford axle bearing that uses a 3.150 OD .

C. You have to open up the center hole on your backing plate to at least 3.200 OD so it will slide over the press-on bearing that is on the axle.
Can I use c-clip eliminators for street use?

 A. We do NOT recommend using C-Clip Eliminators for street use; a C-Clip Eliminator is made for drag race only ( As a safety issue so you do not loose an axle, if it breaks ).C-Clip Eliminators are made for the straight shot down the strip. If you use C-Clip Eliminators on the street the aluminum block will eventually flex from cornering or just going around curves causing the C-Clip Eliminator to leak Rearend fluid.

What do you need if I want to have a housing narrowed?
A. You would need to send the housing to us clean and bare. (Totally Disassembled — no internal parts, brakes or axles) along with instructions on what you need done to the housing. We will also need a return address and a day time phone number where we can call if we need more information. Housings when disassembled can ship UPS.

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