Tapping sound when braking - PeachParts Mercedes-Benz Forum

MBeige · #1 08-29-2007, 11:34 PM

A bit of background first. The first time I had the front brake pads replaced after a given number of miles I would hear the brakes "tap" when I step on the pedal. So I thought maybe replacing the pads would correct it, which it did, but the pads are still far from worn out maybe just halfway through. That was maybe two years ago, I don't remember, or maybe last year.

Now, it started doing it again. Obviously it's not the pads this time. Do you think the caliper pistons are what's causing the tapping sound, or loose brake pads? Why would the pads become loose, if that's what's happening?

The retaining pins and clips were installed last time (I did it the brakes myself). However I'll admit the brake fluid is in need of replacement. Do you think the bad brake fluid is also causing it?

The brakes work fine except when I repeatedly step on the brake, then it decreases stopping ability. By repeatedly I mean like trying to emulate an ABS response (fast repeated stepping of the brake pedal). This is on my '83 300D by the way, with Bendix calipers on the front.

vstech · #2 08-30-2007, 09:42 AM

repeated stopping loss of power is your booster not getting enough vacuum, or just a bad booster.
tapping? can you be more specific as to when the noise occurs, and describe the tapping better? you could have loose rotors, broken caliper bolts, damaged spindle allowing the caliper to move during braking...
From which side does the noise eminate?

MBeige · #3 08-30-2007, 04:57 PM

The tapping occurs at the front wheels when running and then braking at slow speeds. Often this happens after moderate city driving or repeated braking such as when looking for parking in a parking lot.

Right when you step on the brake there's this "tok" sound or "tick". It's only one tick per brake pedal step so I know it's somewhat related. I know ball joints have a tok-tok-tok sound when going over bumps but mine is when braking only. It occurs on both sides actually. Thanks

300SDog · #4 08-30-2007, 05:57 PM

Ball joints or control arms then is my guess, gettin kicked when you apply the brakes. I'd also replace/repack wheel bearings. At slow speeds with windows rolled down is when these noises become more apparent. I diagnosed bad rear wheel bearings on 114 driving the car walking speed next to a wall to reflect sound with windows rolled down in dead quiet of night. Try this diagnostic procedure with your 300D to better hear the noise.

rrgrassi · #5 08-30-2007, 06:03 PM

If your pads are loose fitting in the caliper, they can do that also, as when the brakes are applied the pads are then thrown against their carrier as the rotor spins.

The pads I replaced on my car were loose fitting, and looked like an AutoZoo special, thanks to the PO.

BlackSheep5 · #6 08-30-2007, 06:10 PM

that happens on my 240 on the front left side, it only happens when i first push down on the brakes at slow speeds, on mine, when the pads start to squeeze the rotor they move forward a little in the caliper and make a "tink" sound.

i just figured i need new calipers because the pads are not worn, it kind of looks like the holes in the pads for the pins are too big and it lets the pads move in the caliper.

MBeige · #7 08-30-2007, 07:21 PM

That adds more mystery because I use ATE pads not the Autozoo specials, and I made sure they're fit and snug when they're installed. Blacksheep I have the same idea that's what I also thought, or maybe sideways movement instead of hitting the caliper as the rotors push it forward when the wheels rotate.

Ball joints have been done already I'm sure it's not them. Otherwise I'd hear the sound whenever I move over bumpy roads, which never happens. It's only during low speed braking with the windows down...

What do you think should I do? Do you think replacing the rotors might help? I'm already on my 2nd set of pads anyhow...and feel some slight pulsation when braking from moderate speeds. Guide/strut rod mounts have been replaced so it's not them, but they were really gone also.

Where do I get new retaining pins by the way? The ones I usually see for my Bendix front calipers are the pads but the retaining wire clips aren't available.

BlackSheep5 · #8 08-30-2007, 09:24 PM

I guess you could get the pins from the dealer, i was just going to get whole new front brakes, rotors, calipers and pads just to know they are good, (ive never touched the front brakes since ive owned the car)

but i do know that the pads move, i had my wife push the brake down while i moved the rotor back and forth, and the pads and the rotor moved as one solid piece together about 1/8 to 1/4 inch front and back.

my brakes work fine i just got use to the clinking noise

MBeige · #9 08-31-2007, 05:23 AM

I noticed that the brake pads have oval/ovoid holes for the retaining pins. The pins, of course, are circular in diameter. Maybe this is what's causing them to move the amount you mentioned especially when around halfway used up.

Wonder how to resolve this? The pins are already hard to punch through the caliper holes.

Ara T. · #10 08-31-2007, 05:39 AM

How about guide rods.

MBeige · #11 08-31-2007, 06:04 AM

Ara, thanks for the suggestion. I just replaced both mounts, but not the guide rods. Why would the rods cause the tapping sound? I know there are two bushings in the LCA where the rods mount to but I don't see how that could cause the sounds. Could you elaborate?

JimFreeh · #12 08-31-2007, 06:38 AM

If it's happening when lightly depressing the pedal, then I would discount the suspension.

How's your play on your wheel bearings? A wobbling rotor can push to pistons back.

Your description suggests that the pads are either getting pushed back frm the rotor when brakes are not applied, or moving slightly in the claiper.

Jim

MBeige · #13 08-31-2007, 06:50 AM

Wheel bearings haven't been done yet so I don't know their actual condition...

It happens when lightly depressing the brake pedal at low speeds like when the transmission is in D and I let my foot off the brakes, then apply them gently. Not always though, it only happens sometimes.

I'll look more into it...what's weird is that replacing the pads last time made the tapping sound disappear. Now I guess the current pads are down to the same level as they were last time when the tapping was first heard. Hmmm...

vstech · #14 08-31-2007, 08:55 AM

Be sure to check the caliper bolts. look around the heads of the bolts to be SURE there are no wear marks that would indicate caliper movement. carefully inspect everyplace the caliper touches the spindle if there is ANY movement of the caliper pull the bolts and verify threads, loc-tite coverage and bolt length. also you can pull the pads and see the back side of them. if the pads are moving the back side of the pads will be worn, most I see the pads are glued to the pistons...