220D vibration on braking. Help! - PeachParts Mercedes-Benz Forum

BluEyes · #1 03-24-2007, 12:44 PM

I've had a vibration problem on my '71 220D for awhile now. Pretty much every time I hit the brakes the car is filled with a loud throbbing noise. No, it is NOT warped rotors, there is none of the pulsation that goes along with that. The vibration is engine related as the tone and frequency will change if I change the engine RPM while braking. The vibration appears to be sensitive to brake force, and actually the direction of braking on the front wheels. It only seems to occur when the front brakes are working to try and stop the car from rolling forwards.

Here is what I have tested so far:

Normal braking on flat ground: vibration
Braking on a downhill: worse vibration
Holding car stopped with brakes on a downhill: vibration
Holding car stopped with only parking brake on a downhill: no vibration

Braking while backing up: no vibration
Holding car stopped with brakes on an uphill: no vibration

I had thought it was maybe a problem with the engine mounts untill I discovered that using the parking brake to hold the car on a downhill made the problem go away. Now I am thinking that the problem may be in the rubber mounts that hold the front axle subframe to the cars body? Does anyone have any experience with a problem like this? It is really interfering with enjoying driving my Benz!

nhdoc · #2 03-24-2007, 01:45 PM

I had this on a W115 240D (1974) and it was caused by bad motor mounts. In that car the A/C compressor would make contact with the body of the car during certain braking conditions and caused a severe vibration. New mounts cured it. I'm guessing you don't have A/C but maybe something else is hitting. When the mounts fail the engine just does not sit right. I'd suggest trying that as it is an easy and cheap fix.

BluEyes · #3 03-25-2007, 06:24 PM

I've looked and felt around the engine and nothing seems too close. The thing is, the motor mounts don't explain how switching to using the parking brake to hold the car stopped on a downhill makes it go away.
Of course, I don't know that the motor mounts have ever been replaced in 36 years. Is there any way to inspect them?

300SDog · #4 03-25-2007, 08:25 PM

Family owned but no service records and nobody knows how the car's been maintained? Motor and tranny mounts should be primary suspect and replaced as matter of course assuming they're at least 100k miles old. And what do flex discs look like? Has center support driveshaft bearing (chronic prob on 114/115's) ever been replaced? Nevermind subframe bushings crumbled to smitherines that keep the car rocking and swaying all over the place.

Blue Eyes, it's got nothing to do with the braking system. Everytime you touch the pedal you're shifting stress innertia points on the car. No doubt what you've got is vibration/movement in engine & drivetrain, thats what's going on. Heck if motor/tranny mounts and flex discs are blown then even the driveshaft itself is probly rocking and back'n forth. But if you replace the items mentioned above, routine maintenance items for 220D, then all vibration from differential to driveshaft to tranny bell housing, engine and suspension will definitely disappear - no matter how hard you step on the brakes.

(edit: Or if all this sounds like more repair work than you can manage then talk to me offlist and I will consider trading my excellent running '83 240D 4-spd German Import model for your '71 220D, assuming your car is otherwise in decent running condition and includes sunroof option.

gatorblue92 · #5 03-26-2007, 08:14 AM

sounds just like my 240D when i had a bad driveshaft support bearing... put the car on some ramps and try to give the driveshaft a good shake... if there is more than just a little free play then thats your problem

#6 03-27-2007, 07:24 AM

Check or change the motor mounts.

Diesel Dan · #7 03-27-2007, 09:37 AM

I don't mean to hijack the thread, but...

I have a similar condition on my '87 300D. But it's not a vibration, so much as a noise that occurs during hard braking. It's a "tacka-tacka-tacka" kind of noise, and if I really stand on the brakes, I get a "tacka-tacka-tacka-faWUMP!". Once I hear the "faWUMP", I won't hear the "tacka-tacka" again for a while; only "faWUMP"s. I feel nothing unusual in the pedal. The frequency of the sound is not affected by the speed of the vehicle, but it will get louder as I stand harder on the brakes.

My mechanic gave the front end/brakes a quick look and didn't see anything unusual. I just had my motor mounts replaced, and lower ball joints, just because they needed to be done. This did not change the noise.

I had never considered the possibility of the problem being non-brake system related, but now I wonder if my cooling fan is contacting the radiator and making the noise. My radiator is all chewed up due to contact with the cooling fan, and yet the fan spins freely without contacting the radiator when I am looking at it. I've always been baffled by this. I wonder if during heavy braking, the engine pitches forward, and the fan hits the radiator. I suppose I should try hard braking in reverse to see if I can replicate the noise.

Does anyone know how I can increase the clearance between my fan and my radiator?

wbredin · #8 09-15-2007, 10:32 AM

Quote:

Originally Posted by Diesel Dan

I don't mean to hijack the thread, but...

I have a similar condition on my '87 300D. But it's not a vibration, so much as a noise that occurs during hard braking. It's a "tacka-tacka-tacka" kind of noise, and if I really stand on the brakes, I get a "tacka-tacka-tacka-faWUMP!". Once I hear the "faWUMP", I won't hear the "tacka-tacka" again for a while; only "faWUMP"s. I feel nothing unusual in the pedal. The
Does anyone know how I can increase the clearance between my fan and my radiator?

I have exactly the same problem!! I know exactly what you mean with that noise....what did you do? I just replaced the radiator with a brand new one and ever since then, the noise has been there under hard braking. I think I might have killed my radiator, but i'm not sure....it sure doesn't seem to be the fan that is hitting b/c when the car is just ideling the spacing is just fine. did you ever figure it out????Thanks!

Diesel Dan · #9 09-16-2007, 12:21 AM

Try driving in reverse and then slamming on the brakes. I'll bet you don't hear the noise. Turns out, when I was braking, the fan was hitting either the radiator and/or the radiator shroud. The engine was pitching forward during braking, which is why there appears to be clearance when at a standstill. Problem is worse as you brake harder? Is your radiator or shroud or fan all torn up? I ended up using sheet metal shears to clip off the tips of my fan (which is plastic), and that was enough to solve the problem.

Good luck!