When moisture finds its way into a caliper housing, corrosion begins to cause premature pad wear. This article goes over the process of performing an effective slider service in order to fix the issue. Below, you will find pictures along with a step by step guide to complete the process correctly.
Before the Slider Service
Often times, calipers like the one below are given a quick glance and dubbed to be in good condition. In other words, if the dust boot is in one piece and the slider spin moves, then everything is ok. However, this is not the case. In truth, the caliper pictured below could have a number of conditions that would require a service. In addition to inspecting the part, it is important to consider other conditions that might have caused the vehicle to come back prematurely. In this example, the following results were found upon closer inspection:
Slider Pins
As pictured in image 35.2, one of the slider pins had a portion of the anodized coating worn off. (For those that don't know, the anodized coating is important because it prevents corrosion.) As a result, the worn portion is now susceptible to corroding. In this case, industry accepted guidelines suggest that the pin should be replaced.
On the other hand, image 35.3 had not only lost it's anodized coating, but had already begun to corrode as well. Much like a healthy pin, this part still moved as normal.
Caliper Housings
Floating caliper housings utilize casting holes to house the rubber bushings, o-rings or boots. In fact, Moisture intrusion into the caliper housing casting holes results in corrosion in many types of floating calipers.Likewise, as the casting holes corrode the inner diameter of the casting hole is reduced which leads to the rubber bushing, o-ring or boot to be squeezed around the mounting pin. This squeezing results in the caliper housing’s movement being restricted.
Now that we know the conditions that can occur because of moisture intrusion lets discuss how to prevent it or at least slow it down. First, a good dust boot does not mean moisture can‘t effect the pins as shown in Figures 34.2 & 34.3. Both of the dust boots on these pins were intact. Likewise the corroding of the caliper housing where the slider parts reside can‘t be stopped with a good dust boot. The key to preventing these types of problems is in forming moisture barriers. Follow the steps below to form moisture barriers on floating calipers:
Slider Service Steps
1. First, remove all caliper hardware from housing.
2. Second, clean the caliper casting housing holes. When flaking rust has formed tools such as a ball stone hone, wire brush or wheel cylinder hone will not be effective in removing this type of rust. Flaky rust such as that shown in Figure 34.4 will have to be either ground out using a dremel tool or blasted out using an abrasive blaster. The cleaning process should remove the rust but not good material. The end result should look similar to Figure 34.6
3. Third, use a high quality silicone lubricant to place a film in each casting hole as shown in Figure 34.7.
Adding Silicone
4. Coat the portion of the rubber boot that seats against the casting hole with silicone. Using the brush place a light coat of silicone on the inside of the rubber boot making sure to lube the sealing ridges on each end of the boot. See Figures 34.8 & 35.9.
5. Install the rubber boots into each of the casting holes. The silicone on the casting hole should mix with the silicone on the boot to form a protective layer as shown in Figure 35.10. Note: More is not better. Too much lube can cause more problems than it cures. The silicone in the casting hole combines with the silicone on the rubber boot to form an effective moisture barrier.
6. Place a layer of silicone lubricant on the sealing ridge of each pin as shown in Figure 34.11.
7. Install each pin in its rubber boot. The silicone on the sealing lip of the boot will mix with the silicone on the sealing ridge of the pin to form a protective layer (See Figure 35.12)
The steps above cover the process when servicing boot style floating calipers. The steps would be similar when servicing bushing and o-ring style calipers.
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