Common Questions

Our products are exclusively sold via Amazon and are Prime eligible.  Click here to browse on Amazon.

As a small, part-time, web-based business, we do not have a retail storefront.  Our business model allows us to deliver the best value possible to our enthusiast customers.

Our specialty is providing both European service facilities and DIY enthusiasts with the proper parts for their specific projects.  We do not offer in-house labor services as we've found most customers are best served by purchasing the correct parts from us and then engaging a local enthusiast service facility for installation.

Amazon now ships internationally!  Our entire product line is available here: https://www.amazon.com/s/field-keywords=Thayer+Motorsports

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Our go to gear oil selection for many years is AmSOIL Severe Gear 75W140 - high quality and moderate price makes it a great choice for enthusiasts. In addition, our serious track and endurance racing customers typically choose to run Motul Gear FF Competition 75W140. We do not recommend using Redline products due to a high observed correlation to both bearing and clutch failure.

For units with original friction discs and used for ordinary street driving, clutches typically have a useful life between 60,000 and 80,000 miles before becoming sub-standard.  With the age of these differentials, all should be refreshed to bring back to optimal condition.  As expected, motorsport activity decreases this life span.  Top performing racers refresh annually or after each endurance race.  Our clutches, which offer significantly thicker friction material than stock, are the longest lasting available without sacrifice.

In general, adding additional static lockup to any differential is not desirable.  We've seen our fair share of poorly executed "custom" setups.

The highly desirable setup is low or moderate amount of static lockup and a high amount of dynamic lockup.  For street cars, this results in a smooth driving experience without embarrassing differential chatter.  For performance applications, this results in faster lap times, a faster turn radius, drive line neutral stability through corners, and the ability to apply throttle earlier on corner exit.

We only sell the new and refurbished parts listed on our website.  To find used or core parts, we recommend Facebook, Craigslist or eBay.

Our specialty is providing both European service facilities and DIY enthusiasts with the proper parts for their specific projects.  We do not offer in-house labor services as we've found most customers are best served by purchasing the correct parts from us and engaging a local gear shop for installation.  This saves our customers hundreds of dollars in shipping expense.  Additionally it benefits the community network by expanding the number of facilities able to service BMW differentials.

Upgrading the limited slip unit with one of our kits does not change tolerances associated with differential noise.  Additionally, our kits are specifically engineered with the proper amount of preload to avoid noise during turning.

This is a complicated area, especially if it is your first attempt.  The biggest item is to take your time and be patient!  Properly setting up a differential is something that cannot be rushed.

Gear Pattern

Getting the correct gear pattern is critical to a quiet, properly operating differential.  Using marking paste, it is very important to be happy with the pattern before reinstalling.  There are a lot of resources on the web today about setting up differentials (especially on 4x4 sites) but we've found the following chart to be simplistic and easy for newcomers to understand:

Pinion Depth

The best advice offered for the starting of pinion depth is to use the spacer that is matched with the case and adjust from that starting point based on proper gear pattern setup.  There are many slight variances of case dimensions over the years that all different measuring techniques are slightly problematic.

Bearing Preload / Rolling Resistance Specifications

We've found the following targets to be most beneficial when setting up units:

188mm (Standard) Carrier Rolling Resistance: 20 in.lb. +/- 3 in.lb.

188mm (Standard) Pinion Rolling Resistance: 23 in.lb. +/- 3 in.lb

210mm (Standard) Carrier Rolling Resistance: 25 in.lb. +/- 3 in.lb.

210mm (Standard) Pinion Rolling Resistance: 28 in.lb. +/- 3 in.lb

Ring Gear Torque Specifications

M12: 74 lb.ft. + 50 degrees (~195 lb.ft. total)

M14: 74 lb.ft. + 30 degrees (~225 lb.ft. total)

We recommend checking eBay for used shim assortments.

We are commonly asked what's the best kit for individual needs. It's easy to choose the best kit for your needs using two simple steps.

Street v. Performance:
* Select the street option if your vehicle primary use is on the street. The street option best serves most of our customers. Our street kits are an excellent upgrade for your stock or modified street car. These kit versions offer similar preload (static lockup) and driving characteristics as a stock differential. By keeping excessive preload at bay, normal driveability is maintained even when adding additional clutches.
* Select the performance option if your vehicle spends a good majority of time on racetracks, autocross courses or similar. Our performance kits are aimed specifically at customers who spend a good amount of time at the track or autocross course. The performance kit versions reduce preload (static lockup) for better in-turn performance during driveline neutral events. A small disadvantage to less preload is that the clutches will wear slightly faster due to being able to breakaway more easily.

Number of Clutches:
* Select two clutches if you must conform to class rules (racing, autocross, etc.) or have an absolute desire to keep your differential in stock configuration. NOTE: Most enthusiasts are best served purchasing a three clutch upgrade kit.
* Select three clutches if you want a significant upgrade without sacrifice. The three clutch kits are our most popular products and are the best choice for the majority of our customers.
* Select four clutches if you want the most traction available out of your differential. For forced induction setups, this is a must. This kit is also highly preferred by HPDE enthusiasts as it is a balanced with gobs of traction when needed.

Installation instructions can be found at the following links:
188mm (Standard) 2-Clutch BMW Differential Upgrade Kit
188mm (Standard) 3-Clutch BMW Differential Upgrade Kit
188mm (Standard) 4-Clutch BMW Differential Upgrade Kit

There are a few different factory combinations that are out of the ordinary.  This is not meant to be an exhaustive list, rather a working information page.

Z3M / Z3 Motorsport

What is this setup?

* A non-preloaded, 4-clutch setup with asymmetrical 50 / 65 degree ramps.

* Found in some early Z3 variants and some Z3Ms.

* Typically always are a 3.15 or 3.23 ratio.  3.23 ratio is more common.

How do I identify this differential?

* The code S40 / S25 is stamped after the serial number on the limited slip carrier inside the differential.

* These setups ALWAYS have oval openings on the LSD unit, but having an oval opening is only part of identifying the unit (e.g. there are standard setups with oval openings).

* The ramp nearest the ring gear will have a machined groove around the diameter (see: https://www.bimmerdiffs.com/collections/differential-188mm-standard/products/188mm-standard-bmw-differential-50-65-motorsport-pressure-ramps).

* The ramp angles will not form a v-shape like standard 45 / 45 degree ramps rather be a smoother transition (compare: https://www.bimmerdiffs.com/collections/differential-188mm-standard/products/188mm-standard-bmw-differential-45-45-standard-pressure-ramps to https://www.bimmerdiffs.com/collections/differential-188mm-standard/products/188mm-standard-bmw-differential-50-65-motorsport-pressure-ramps).

In the past, we were able to link another site that provided instructions, but they foolishly asked us to quit linking their site.  Their loss!

So we did one better and partnered with Speed Academy to create a video demonstrating the process.  Sure, it's for their Honda K-Swap 240SX, but the process is the same.

Video here:  https://www.youtube.com/watch?v=FmIX46lBN9U

Stock eccentric bolts are retained during installation.  This allows for installers to rough set camber by adjusting the length the arm and fine tune on the alignment rack using the stock adjusters.  It’s recommended that when installing to set the factory eccentric bolts in the neutral (middle) position to allow for the easiest time and most adjusabiity during the alignment process.

The end-links included with our rear correction arms are PTFE lined (self lubricating). They are to be utilized dry without grease. In the event of necessary replacement due to wear, we can provide information to purchase individual replacement components.

While the end-links provided with our suspension arms are long lasting, environmental conditions may require them to be replaced.  One-off end links are just not cost effective for us to stock and ship, so we recommend purchasing replacement end-links from directly from Summit Racing.

Large End Links (Used On Camber Arms):

https://www.summitracing.com/parts/qa1-xmr14

Small End Links (Used On Toe Arms):

https://www.summitracing.com/parts/qa1-xmr10

https://www.summitracing.com/parts/qa1-xml10

While the bushings provided with our suspension arms are long lasting, environmental conditions may require them to be replaced.  One-off bushings are just not cost effective for us to stock and ship, so we recommend purchasing replacement bushings from directly from Summit Racing.

Bushings (Used On Camber Arms):

https://www.summitracing.com/parts/ens-9-9489g

NOTE:  Some control arm designs require bushings to be shortened via a lathe to fit correctly.

Installation instructions can be found at the following link:
Z3 BMW Seat Mod Seat Tilt Kit