BMW Preventive Maintenance – Inspecting The Rear Of The Car
1. Check the exhaust. Visually inspect the muffler can, exhaust piping and catalytic converter for signs of heavy rusting or cracks (Fig. 5). Look for cracks at the points where the piping enters or exits the converter, resonator and muffler housings. Inspect all of the connection points for leakage. If there are cracks or other leaks, there will likely be some evidence of exhaust leakage such as, black carbon at the point of leakage. Inspect welded-on hanger points and brackets for cracking. Inspect the rubber isolation hanger donuts or blocks. Excessively stretched or cracking hangers should be replaced. Finally, start the engine and place a folded-up rag over the exhaust tip(s) in order to restrict the exhaust flow. Check the exhaust piping and assemblies. Any small exhaust leaks will be apparent at this point, due to the increase in pressure in the exhaust system. Any leakage will require that the Muffler Assembly or the Catalytic Converter be replaced.
2. Check the wheel bearings. Typically, rear wheel bearings will make a lot of noise when you’re driving long before they will show any physical looseness. Thus, if there has been no rear-end driving noise, the rear wheel bearings are likely in good shape. (Keep in mind, this is typical but certainly not “cast in stone.”) However, since you do have the vehicle up on jack stands, grasp the tire at the 12-o’clock and 6-o’clock positions. Alternately, push and pull the tire/wheel assembly. Repeat at 3-o’clock and 9-o’clock. You should detect no movement or wobble. If any movement is detected, inspect to see if the movement is between the wheel/tire assembly and the trailing arm/hub (indicating a wheel bearing) or if the trailing arm/hub is moving with the wheel/tire (indicating worn suspension bushings).
3. Check brake calipers. For this test, the rear wheels must be free to rotate. Check for sticking brake calipers by stepping hard on the brake pedal, then releasing it. Now spin each rear wheel. They should turn fairly freely. If either will not turn freely, or one has more resistance than the other (and the pads are more worn – see step 7), you may have a sticking brake caliper due to corrosion between the caliper’s hydraulic piston and its cylinder bore. This would require either replacement calipers or that the calipers be rebuilt. (Note: we now offer remanufactured calipers )
4. Check your tires. Remove the tire/wheel assembly. (If you did not loosen the lug bolts earlier, or if they are not cooperating, have a helper step on the brakes so you can apply pressure to the lug bolts without spinning the wheel). Inspect the inner and outer sidewalls for cracking or bulging. Either condition is cause for replacement due to the possibility of a blowout. Inspect the tire tread: it should exhibit smooth and even wear from the inside tread blocks to the outside blocks. There should be no cracking in the valleys between the raised tread blocks. The tread depth should be consistent across the tread face (tread depth gauges can accurately and consistently read the tread depth). There should be none of the molded-in wear indicator bars showing between the tread blocks. If the wear bars are showing at the tread block height, the tires are legally worn out (they will be far more susceptible to hydroplaning in wet conditions) and should be replaced. Rub your hand across the tread blocks, in various directions. You should feel no sharp edges to the tread blocks (feathered edging). Finally, view the tread surface from different angles: do you see any uneven wear areas that are worn more than the surrounding area (cupping)? (Fig. 6).
Other signs to look for:
-Inner and outer tread blocks have less depth than the center tread blocks. This indicates a history of under-inflation.
-Center tread blocks have less tread depth than the inner and outer blocks. This indicates a history of over-inflation.
-Inner tread blocks have less tread depth than outer tread blocks. This is an indicator of excessive negative camber. Note that this is somewhat common on BMWs (and very common if the car is lowered). If the vehicle has not been lowered, but camber wear is excessive, we offer special suspension modifications (upper strut mounts and rear control arm bushings) that allow the camber to be reduced. Lowered cars typically require the installation of Camber adjustable upper strut mounts and rear control arm bushings.
-Feathered edging. This is typically an indicator of an improper toe-in/toe-out alignment.
-Cupping. This is typically due to worn out suspension and/or steering components.
5. Inspect the valve stems. If they are rubber, gently bend them and inspect for cracking. If cracks are found, the valve stems should be replaced. Note that models with Tire Pressure Monitoring systems have unique valve stem assemblies.
6. Inspect your wheels.Look for heavy rusting or cracking. Cracked wheels should be replaced. Heavily rusted wheels should be replaced or de-rusted, inspected and re-painted if no cracks are found.
7. Check your brakes. You should have already tested for a sticking caliper in step 3. Now inspect the brake rotor for: heavy rusting at the outer edges and circumference; heavy scoring on the brake pad wear surface; and a heavy ridge at the outer edge of the pad wear surface (Fig. 7).
Any of these conditions warrants replacement of the rotor. Inspect the thickness of the brake pad friction material by looking through the inspection port in the middle of the caliper (Fig. 8).
Both pads (inner and outer) should be worn evenly. If the outer pad is worn more than the inner pad, this is an indicator that the caliper guide bolts are sticking in the bushings. Remove the guide bolts, clean the bolts and the bushings and lubricate with Liqui-Moly Anti-Seize or Sta-Lube synthetic brake caliper grease. Alternately, you can replace the guide bolts and bushings with new ones (Fig. 9).
If the pad material is 1/8” thick or less, you should plan on replacing the brake pads as soon as it is convenient, taking note of the rotor condition as well. If the rotor is at all suspect, you might as well replace it at the same time you replace the brake pads and save yourself some time and money. Inspect the rubber brake fluid hose that runs from the chassis to the caliper (Fig. 10). Any signs of cracking or leakage indicate a need for immediate replacement.
8. Check your shocks and springs. Inspect the shock housing for oil leakage from the upper shaft seal. Leakage indicates a need for replacement of the shock absorber (Fig. 11).
Inspect the upper and lower ends of the coil spring (Fig. 12) for broken ends. This is especially important on the 3 series 84 thru 05.
The last upper or lower coil on the springs, for these models, have a habit of breaking (Fig. 12a), altering the suspension geometry and giving you a less than optimal ride. Inspect the dust protection boot and compression bumper (on the shock upper rod) for deterioration.
9. Inspect sway bar links. Look at the links that connect the ends of the sway bar to the control arm, swing arm or trailing arm (Fig. 13). The links will either have rubber bushings in each end or small ball joints. The rubber bushing ends should not be excessively deformed or pushed out of the link’s eyelet ends. Test the ball joint ends for play or deteriorated boots. A common source for a “clunking” noise is worn out sway bar links. Replace the sway bar links if you find loose or worn ends.
10. Check the suspension arms. Depending on the model BMW or MINI that you are inspecting, there will be various combinations of swing arms, trailing arms and/or control arms. All of these components have various types of bushings at the attachment points to the chassis, suspension carrier and wheel hubs. You should inspect all of the bushings for cracks or deterioration and gently pry on the bushing points to test for play or overly soft rubber in the bushings (Figs. 14, 15, 16, 17 & 18).
11. Inspect the suspension carrier bushings.Check the bushings that connect the rear suspension carrier (or subframe) to the vehicle’s chassis. Look for deteriorated rubber and/or obviously pulled-apart bushings (Figs. 14-18). Additionally, inspect the vehicle chassis sheet metal in the area of the bushing mounting points. Some BMW chassis have a propensity to develop cracks in these areas.
12. Check the axle assemblies. Inspect the inner and outer axle constant velocity (CV) joint boots for cracks, deterioration or tears (Fig. 19).
A hole in the CV boot will allow the grease to leak out and dirt and water to enter. This will destroy the CV joint, in short order. If the boot has not been damaged for too long, and the CV joint is not showing signs of wear/damage (noise, clunking, etc), the boot can be replaced and the CV joint re-greased. Refer to Fig. 20: notice the caked grease on the ball-joint, tie-rod end and brake backing plate… AND the new CV boot (Note: the photo is of a front axle on a 325xi; the rear axle will look similar).
13. Look for fluid leaks. When inspecting for leaking fluids (transmission oil, differential oil and fuel), we must note that, on a BMW, a dry underside is not a common occurrence. Most BMWs will have a variety of fluid leaks. In this step you are searching for the sources of the leaks and trying to determine if they are in need of immediate repair (active dripping from the component or a spot where the fluid is collecting). We encourage you to correct all leaks that are found, but some leaks will be imperative to repair (e.g. ANY fuel leak). In searching out the source of a wet spot or obvious leak, sometimes you can simply follow the trail of wet fluid to the source. Other times, the underside may be so coated with fluids that you cannot tell where the starting points are, or there is so much machinery jammed into the area you simply can’t see the point of origin. In these cases, it helps to get the area as clean as possible so that you can take note of fresh fluid as it leaks out and down. A spray can of Wurth brake parts cleaner works quite well for cleaning up a fluid-soaked underside (purchase a few cans). It will, however, make a mess as it drips down. We like to use the oil absorbent Pig Mat to keep the dripping mess in-check. You can also place the Pig Mats under the vehicle so that you can see exactly where a fresh drip is coming from, making it easier to trace upward to find the source.
For leaks where the source is difucult to locate, you can use the Leak Detection Kit. This DIY kit includes flourescent dyes for lubricants (oils), coolant and A/C systems. The dye is poured or injected into the system and as the fluid leaks, the dye will also leak. You then use the included UV light and UV enhancing goggles to follow the leaking fluid to the source of the leak.