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Rear Brake Pad Replacement
 
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Pelican Technical Article:

Rear Brake Pad Replacement

Tom Morr

Time:

2 hours2 hrs

Tab:

$35 to $70

Talent:

**

Tools:

Floor jack, jack stands, wheel chocks, wood blocks, hammers, punch, flat-blade screwdriver, ratchet, 16mm socket, C-clamps or piston-retraction tool, brush

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

New pads, brake cleaner

Hot Tip:

Using the special piston tool, the calipers can remain in place. Otherwise, they might have to be unbolted from the car.

Performance Gain:

Car stops better

Complementary Modification:

Replace worn rotors, inspect calipers' piston boots for damage, hoses for cracks; replace as necessary

Mercedes-Benz brake pads can often be replaced at home in less time than it takes to drop off and retrieve the car from a shop. Once the vehicle is jacked up and secured and the wheels are off, both sides can be done in under two hours.

Many Mercedes models have pad-wear sensors, particularly in the front. The rear brakes in fixed-caliper four-piston system often have sensors, but two-piston calipers don't in the R170 models. Fortunately, the rear pads don't work as hard as the fronts and consequently don't wear as quickly. Pads with sensors trigger the warning light when about 5mm of friction surface remains. They absolutely must to be replaced when about 2mm of pad material is left.

Ideally, rear pads should be inspected about every 10,000 miles or, immediately any time a brake warning lamp illuminates, or any metal-on-metal grinding sounds coming from the rear. The average lifespan is about 25,000 miles, but that varies depending on the driver and conditions. A perceptible increase in stopping distances is another clue to check the pads.

The penalty for not being proactive: Worn-down pads can groove the rotors necessitating replacement of the rotors, so the job now becomes bigger and more expensive.

Generally, OE-spec pads strike a balance between stopping power, longevity and quietness. Brake pads should always be replaced in pairs -- both calipers on the axle. While changing the pads, inspect for collateral damage: fluid leaks, grooved rotors, torn caliper boots, cracked or bulged hoses. Brake fluid is highly corrosive. It eats paint and is toxic. Inspect pads' wear patterns. Uneven wear can indicate caliper or brake line problems. Release the emergency brake so the rear rotors can spin. New pads' friction material can be more than five times as thick as worn ones. Thus, the pistons need to be backed into the calipers to fit new pads. Pushing the pistons back into their calipers can cause brake fluid to overflow in the master cylinder. Be prepared to suck out some fluid from the master cylinder prior to piston-retraction. Brake fluid is hydroscopic (moisture-absorbing), so always top up the reservoir with new fluid

.

While a special tool is available that allows the pistons to be retracted with the calipers still mounted on the axle it is possible to us a wooden dowel or the plastic handles of your screwdriver to accomplish this. I like to leave the old worn pad in the caliper and use a screwdriver between it and the rotor to push the pistons back in. You want to make sure you do not gouge or tear the pistons' rubber dust seals when pushing the pistons back into the calipers. Alternately, the dual-piston R170's rear calipers can be removed with two 16mm bolts. The pistons can then be retracted using C-clamps. If removing calipers, use wire or zip-ties to secure them temporarily to the car. Never let you calipers hang by the brake lines. Brake hoses aren't designed to support caliper weight.

Clean dust and contaminants off metal parts with brake cleaner. Follow the pad manufacturer's recommendations for squeak-control. Pad shims and/or anti-squeak brake paste or grease on the non-friction surfaces of the pads can reduce vibration and friction between the pads and caliper. Replacing the retaining pins and pad clips can also help minimize squeaks. Once the new pads are in place, depress the brake pedal several times to re-set the caliper's pistons. I recommend following the pad manufacturer's break in procedure. The new pads can take 100-200 miles to "bed," or conform to the rotors' surfaces and pad manufacturers often recommend avoiding unnecessary hard stops if possible during this period.

Use a punch to drive out the retaining pin(s).
Figure 1

Use a punch to drive out the retaining pin(s). Dual piston calipers have a single pin per side; quad-piston systems use two pins per caliper.

If the pistons aren't frozen or damaged, the old pads can be pried out with a flat head screwdriver.
Figure 2

If the pistons aren't frozen or damaged, the old pads can be pried out with a flat head screwdriver.

Retracting the pistons to make room for new, thicker pads will force fluid back into the master cylinder.
Figure 3

Retracting the pistons to make room for new, thicker pads will force fluid back into the master cylinder. Sucking out a little fluid with a clean turkey baster or a siphon is recommended. The old fluid should be properly discarded.

A special tool or sometimes a plastic or wooden handle can be used to push back the piston with the caliper still mounted.
Figure 4

A special tool or sometimes a plastic or wooden handle can be used to push back the piston with the caliper still mounted. The key: not damaging the pistons' dust boots. Alternately, the caliper can be easily removed. The dual-piston fixed caliper is mounted with two 16mm-head bolts (green arrow).

With the caliper suspended from the car so the brake hose isn't overextended, a C-clamp and old brake pad can be used to push the pistons back into the caliper.
Figure 5

With the caliper suspended from the car so the brake hose isn't overextended, a C-clamp and old brake pad can be used to push the pistons back into the caliper.

Brake cleaner can be used to clean pad dust off the rotors, calipers, backing plates, clips and pins.
Figure 6

Brake cleaner can be used to clean pad dust off the rotors, calipers, backing plates, clips and pins. The manual recommends brushing clean the pad-contact areas. Brake paste (anti-seize) can by applied sparingly to the pads' edges to minimize friction as they move in the caliper.

With the caliper bolted back on the car, the replacement pads can be inserted.
Figure 7

With the caliper bolted back on the car, the replacement pads can be inserted. Wear sensors need to be re-installed in quad-pistons systems before the pads are slid into place.

The anti-rattle clip(s) are inserted, then the retaining pin(s) are tapped in until they're fully seated.
Figure 8

The anti-rattle clip(s) are inserted, then the retaining pin(s) are tapped in until they're fully seated.

We re-used existing pads for this demonstration.
Figure 9

We re-used existing pads for this demonstration. We freshened their anti-squeak goop (a little too liberally). Other requirements include a way to retract the pistons (special tool, C-clamps or similar), a flat head screwdriver, a hammer and a punch. A ratchet/socket or combo wrench is required if the caliper needs to be removed. Also, owners might want to minimize squeaks by using brake paste on the back of the pads and replacing the retaining pins and anti-rattle clips in conjunction with the pads.

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Comments and Suggestions:
Sparky Comments: Hi ifound the jacking and rear brake pad replacement excellent but I can't find any information on the front pad replacement.Please can you help ?
Regards Dave.
January 13, 2015
  Followup from the Pelican Staff: I think that article is in the works. Keep an eye here for when it is posted: http://www.pelicanparts.com/techarticles/MBZ_Tech_Index-R170.htm #brakes - Nick at Pelican Parts  

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