Frequently Asked Questions

Does the cover come with the differential?

We do not include a cover with the differential unless the cover is purchased separately. You can reuse your cover with the new differential and seal it with a proper bead of black RTV gasket maker. Be thorough when applying the bead of RTV to the differential but try to keep as much material from going into the differential when the cover is properly seated as possible.

What is the break in period?

All differentials purchased through Diffsonline LLC require a 1,200-mile break-in period. During this period, you should keep constant vehicle speeds under 80 mph and drive the vehicle moderately. This will allow the gears, bearings and limited slip parts to break in properly and without excessive heat. After 1,200 miles the fluid should be changed in your new differential with the same recommended fluid. After the initial flush, we recommend changing the fluid every 24K miles in a street driven car, or every 12K miles in a car that sees autocross and track day use. For dedicated track cars, you will want to flush the differential after the first full track day and change the fluid with every engine oil change.

What does REM polishing do for me?

REMĀ® Polishing reduces friction, heat, and wear inside your differential. The flash point of where the pinion gear meets the ring gear is where the majority of the heat inside a differential is generated. REM Polishing will reduce these temperatures thus keeping the differential in top working order. Less heat -> longer fluid life -> longer life of clutches -> better performance -> more time between needed rebuilds -> less down time and more time in the seat. Isn't that what we are doing this for in the first place?

What is the warranty policy?

All rebuilt products are covered by our 2 year unlimited mileage warranty against workmanship defects. Exception is all OS Giken products or differentials equipped with an OS Giken product are sold without warranty and are intended for off road use only. There is no warranty on individual part sales. All used differentials are covered by our 30 day warranty. Diffsonline LLC is not responsible for shipping (either way) or any labor charges associated with warranty claims.

What fluid should I be using in my differential?

For all clutch based limited slips, and including the Diffsonline Race carrier, helical carriers, and open differentials, we recommend using Redline 75w110 fluid. For all builds using the M Variable limited slip, you will need to use the OE BMW XJ+FM fluid. For builds using the OS Giken limited slip, you need to use the OS Giken 80w250. For Kaaz limited slips, you need to use the Kaaz fluid.

How often should I change the fluid?

For normal street driven vehicles, we recommend changing the differential fluid every 24k and for mixed street/track vehicles, every 12k. On a dedicated track car, you will want to change the differential fluid every other engine oil change at a minimum. Ideally, every oil change is best. The differential fluid lubricates the ring and pinion gears, which transfer power from the driveshaft to the axles. The limited-slip unit requires fluid to keep all of the internal parts healthy and moving properly. Differential fluid changes areas imperative as changing the oil in the engine, and for the exact same reasons. Metal-to-metal contact wears down surfaces and creates heat from friction, which weakens parts and can lead to failure.

Core Returns

Cores are to be returned within 15 days of receiving the new unit, unless prior arrangements have been made. Please have the name that the differential was sold to and your order number written clearly on the box being shipped back to us to expedite the return being processed. Core Return Slip

How can I avoid the core charge?

You can send your differential into us to get rebuilt to avoid the core charge. Please print our rebuild form and include in the shipment with your contact info and specs you want the differential to be built. You can also email us with the tracking number so we are aware of the shipment and can get you into queue. This method will only prevent you from paying the amount of the core charge. On applications that came with a limited slip from the factory, the core will need to have the same style limited slip to qualify for a full core value. IE, if you send an E36 325 diff that was an open carrier and are buying a differential with a limited slip, you would be responsible for the difference that we show when you would return an open core vs a core with a limited slip. Rebuild Form