- 03/23/2014
- 2 Min Read
- By: Gareth Foley
JT Designs vs. OEM Rear Shock Mounts, the Differences
The History
For those of you who do not know, BMW E30, E36, and E46 models are notorious for having the rear shock mounts fail (RSM for short). For one, they're not very heavy duty from the factory. The mount base is a stamped/molded piece of aluminum which has a rubber bushing pressed into it. It's very basic and more or less does the job until it fails. Now keep in mind the rear suspension on these cars was basically the same from the E30 up to the E46 and the RSM's pretty much stayed the same. The issue with the factory style mount is the bushing needs to endure vertical force from the shaft of the shock. As the rear of the car articulates bumps and dips in the road, the rear trailing arm travels up and down.
As the trailing arm travels it also applies horizontal forces to the rear shock mount. The vertical and horizontal forces basically twist the rubber bushing inside the mount causing it to separate, tear, and eventually fail. A failed rear shock mount will be pretty noticeable as the rear shocks are no longer connected to the car. The forces mentioned above are exacerbated by vehicles with modified suspensions or vehicles that travel on particularly poor roads. It's not uncommon for the RSM to be replaced multiple times before the shock needs to be replaced. What is JT Designs? JT Designs is a company that makes performance products for BMW's. They specialize in engine, suspension, and drivetrain components. They are essentially an enthusiast company who redesigns OE parts as they would build them. They are most notable for the E30, E36, E46 RSM's. Comparing JT Designs RSM's to OE Sachs RSM's Here's the fun part, comparing the OE parts to these specialized replacements. There are two different versions of the JT Designs RSM's:
Sachs OEM RSM:
Just by looking at the OE version of the RSM you can already tell that it is designed to meet strict NVH standards. For those of you who don't know what NVH is it stands for noise, vibration, harshness. Every manufacturer strives to meet these standards and to maximize ride comfort. Sometime ride comfort is prioritized over durability. The OE design is effective on cutting down noise and vibration but not effective for performance or durability. If you're looking to maintain the stock character of your car or not looking to spend a lot of money the Sachs or Meyle RSM's are recommended. Meyle makes an HD version of this mount for the E36 and E46 and they improved durability by adding some internal reinforcement to the bushing. If you're worried about the durability of this part have a look at the Meyle HD version as it will maintain the NVH standard of your vehicles.
JT Designs heavy Duty RSM:
Pictured above is the HD RSM made by JT Designs. It is a pretty simply piece and while it looks pretty similar to the standard Sachs version there are a few differences. For one, the bushing is replaceable if need be. Secondly, the bushing is made from polyurethane which is much stronger than a standard rubber bushing. The centering sleeve which you can see installed in the mount secures the two halves of this bushing together making it even stronger. The price of this piece is very close to that of the Meyle HD and Sachs version but is much more durable and will help improve stiffness of the rear end. If you are upgrading your shocks to something other than OEM I would advise using these mounts. Also consider the OE BMW RSM reinforcement plates when using these HD versions.
JT Designs Billet Aluminum RSM:
Pictured above is quite possible the most durable RSM you could ever install on an E30, E36, or E46. For one, the body is made of billet aluminum. For those of you who do now know billet aluminum parts are machined from a solid block of aluminum. This makes the part significantly stronger that a stamped or cast piece, it also makes it more expensive. JT Designs also only sells these mounts in pairs. The price is negligible once you consider all of the advantages of this RSM over anything on the market. As mentioned, the body is billet aluminum making it super strong. In addition to being billet, the body of the mount is solid all the way through. OE versions and the JT HD version are all thin in comparison. Out of the box, these comes with gaskets, nylock nuts, and washers. The most impressive part about these mounts is the bushing is 100% servicable and replaceable with the mount installed on the car. The shuttle (blue piece) can be removed with a 36mm socket. The poly bushing is held in place and supported by the shuttle. One the shuttle is removed the bushing can be easily removed, a replacement can be installed, and the shuttle can be tightened again. This is a major advantage because it makes an otherwise cumbersome repair job (normally the shock would have to come out for the RSM to be replaced) and makes it extremely easy with only basic tools being required. If you are replacing a lowering spring, Bilstein HD or Sport shock, coilovers, or any other suspension upgrade also consider these. In addition to being ultra durable they are also nice to look at, easy to maintain, and offer the most reliable service life.
All RSM's available from FCP Euro:
BMW Shock Mount Rear (E36 E46) - Sachs 33521092362
BMW Shock Mount Rear (E36 E46) - Meyle HD 33521092362
BMW Heavy Duty Shock Mount Rear (E36 E46) - JT Design 33521092362
BMW Heavy Duty Billet Shock Mount Set Rear (E30 E36 E46) - JT Design 884024550
Kits:
BMW Shock Mount Kit Rear (E36 E46) - Meyle HD E36E46MOUNTKIT
BMW Heavy Duty Billet Shock Mount Set Rear (E30 E36 E46) - JT Design 884024550
About the Author: Gareth Foley
Gareth runs the BMW catalog at FCP Euro, he can be reached at gareth@fcpeuro.com
