More and more “do it yourself” home mechanics are replacing the front struts on their BMWs. But which BMW strut spring compression tool is the correct one to get the job done?
There is a substantial cost savings in replacing the front struts on your BMW; not only in labor but in parts. For the savvy home mechanic, removing the front strut assemblies from the vehicle is easy. The nerve racking part of the repair is compressing the spring so it can be transferred over to the new strut. It is very important to choose the correct spring compression tool to accomplish this part of the repair.
When disassembling the front struts on your BMW, the springs must be compressed with a tool to relieve the pressure on the strut mount so the top lock nut can be removed (see image below). Removing the lock nut allows the strut to be disassembled so all of the parts, including the spring, can be transfer over to the new strut. The tricky part for the home mechanic is compressing the spring. A BMW strut spring is a large steel coil under a tremendous amount of force. It can become a dangerous projectile if it snaps or slips off of the tool during compression. Front strut spring compression can cause a lot of anxiety in the DIY mechanic…and rightly so.
Choosing the best compression tool
If you run a Google search on “strut spring compression tools”, you will be returned a myriad of different options to choose from. Unless you are planning on investing in an expensive floor unit (like the ones found at most commercial repair shops), the home mechanic only has two choices to pick from; the hook or the plate (also know as the “fork”) “screw” style compression tool. Both the hook and the plate style compression tools use a threaded rod (hence the name “screw”) to compress the spring. Most brands cost under $100 and are therefore the first choice for the home mechanic…who will most likely only use it once. But the question still remains…which one is the better choice?
Hook style compression tool
We are not going to waste any time here and just “cut to the chase”; the hook style spring compression tool does not work when performing a BMW strut replacement, and is basically a waste of money. We will tell you why after briefly explaining how it works.
The hook style compressor works by using two threaded rods with grooved blocks of steel on each end (the hooks).
The hooks are placed on the spring coils, and as the threaded rods are tightened they slowly compress the spring. The hooks have safety pins that keep them from slipping off of the coils while being retracted.
The problem with the hook style compression tool is that it cannot compress the spring far enough to install the new strut. Due to the thickness of the hooks and their placement on the spring helix, you will never be able to retract them far enough to get the strut mount and lock nut on the new strut. It’s as simple as that.
Plate (or “fork”) style compression tool
The correct tool for performing a BMW front strut replacement is the plate, or “fork”, style compression tool. Unlike the hook style tool, the plate compressor uses only one threaded rod to retract two plates that “squeeze” the spring from top to bottom.
The steel plates are actually pitched so they conform perfectly to the slope of the spring’s helix to prevent any type of slippage. The pitch also allows the plates to be slid further up the helix allowing for a more complete compression of the spring.
Unlike the hook style tool, a more complete and uniform compression allows the strut mount and lock nut to be installed.
The plate style tool also creates a “safer” environment when compressing a strut spring. It is a much more robust tool than the hook style, and it does not give the user the feeling that it could slip off or break causing injury.
The BMW Repair Guide only recommends the use of a plate style compressor to the home DIY mechanic interested in servicing their own front struts. It is more expensive than the hook style tool, but the extra money spent is more than compensated by the savings achieved by “doing it yourself”.