W126 front end/braking - PeachParts Mercedes-Benz Forum

JohninFla · #1 01-19-2005, 03:23 PM

Good afternoon. Car is a 1989 560SEL, 175K miles. Car has been in the shop for the third time in 3 weeks. Problem is a strong vibration in the front end, experienced during braking from 45 - 50 mph. The entire front of the car shakes and wobbles, but only during braking. The upper ball joint assembly, including the bushings and lower ball joints were replaced, and the problem remains. All four rotors and pads all around were replaced 50 miles ago.

Mechanic now reports the drivers side brake rotor is blue, and he has changed the passenger side caliper with a "used but good" caliper he had in his shop.

I was wondering if this could be related to the anti lock brake system malfunctioning? Does anyone have any ideas?

I am out about $1,000 USD so far, and I am quickly losing confidence in my mechanic's ability to diagnose the problem.

Thanks for the help. I am at the end of my rope, and my checkbook.

MFG
John

Brian Carlton · #2 01-19-2005, 03:33 PM

Does this vibration seem to come from one side of the vehicle?

Does the vehicle pull one way or the other when braking?

Does the vibration occur when you brake at 70 mph? Is it worse or better?

Does the vibration occur on light braking or on heavy braking or both?

Does the vibration go away if you do very heavy braking?

Is there any vibration at 70 mph without braking?

JohninFla · #3 01-19-2005, 03:37 PM

Vehicle does not pull to either side, and the vibration seems to come from the passenger side.

I will not drive 70mph when I have problems braking. 45-50 mph is even too fast.

Vibration is slight at lower speeds, and seems to be more pronounced during harder braking at higher speeds.

There is not any vibration without braking, at any speeds.

Brian Carlton · #4 01-19-2005, 03:40 PM

Be very careful with the answer to this question:

Was the problem there before the pads were changed?

JohninFla · #5 01-19-2005, 03:50 PM

The problem existed before the rotors and pads were changed. No change in symptoms was experienced when the pads and rotors were changed, as with replacing the upper and lower ball joints.

Brian Carlton · #6 01-19-2005, 04:03 PM

I definitely feel that these symptoms are brake/rotor related. The ball joints could never have caused the vibration that you are referring to on braking.

If any one of the suspension components, on one side, has failed, the vehicle would pull. So, I am leaning away from any of the suspension bushings.

Have the mechanic setup a dial indicator (he ought to have one) and measure the runout of the face of both brake rotors. To do this, remove the wheel, setup the indicator on the face of the rotor, and rotate the rotor.
The runout should be about .001 or less. You will probably see numbers at .005 or above for the symptoms you are describing, if this is the culprit.

Now, if you get a high value, it does NOT mean the rotor is bad. The mounting face for the rotor might be dirty or rusted and the mechanic simply slapped a brand new rotor in place. These vehicles are very sensitive to runout in the rotors, no matter how it occurs. Such a condition can also occur if the wheel bearing is damaged (unlikely, but possible).

The aforementioned test is very inexpensive and valuable.

Consider additional suggestions from others. However, do NOT spend any more money throwing parts at it. The problem that you are experiencing can be diagnosed with the proper knowledge and measuring equipment.

JohninFla · #7 01-19-2005, 04:15 PM

I can appreciate that dirt or debris behind the rotor would cause a problem, but how would this happen BEFORE the rotors were replaced?

I did ask to have the runout of the rotors measured during my last phone call. I agree with this advice and inspection.

Brian Carlton · #8 01-19-2005, 05:15 PM

Quote:

Originally Posted by JohninFla

I can appreciate that dirt or debris behind the rotor would cause a problem, but how would this happen BEFORE the rotors were replaced?

Probably would not. Therefore, with the change of rotors, the problem would have to be in the bearing/spindle. Less likely culprits.

But, I'm out of suggestions because of the lack of any pulling.

Let's see what the runout indicator shows. Make sure he does both sides.

BTW, do you feel any pulsation in the brake pedal when this vibration occurs?

samiam4 · #9 01-19-2005, 06:22 PM

Your mech should be doing the diagnosis!

I can imagine suspension parts being loose or bad giving a shimmy-. Sounds like the suspension is tight- a bad caliper wouldn't give a vibration. Are the guide mounts good? Steering dampener? Did he set the wheel brgs with a dial indicator or just "wing it?".

Michael

newr · #10 01-19-2005, 06:45 PM

I can't give you any mechanical advice about the problem, but I can advise to you find another mechanic. Obviously this guy is diagnosing the problem by trials and errors at your expenses.

brooktre · #11 01-19-2005, 06:53 PM

Had a similar problem w/ 83 W126. It was brake related. I replaced pads, rotors AND BRAKE LINES. I heard or read that the problem can be related to any of those and all were changed. If your lines weren't changed, I'd think about changing them.

Brian Carlton · #12 01-19-2005, 08:22 PM

Quote:

Originally Posted by samiam4

Your mech should be doing the diagnosis!

Why do you think he is here???

wbain5280 · #13 01-20-2005, 12:42 AM

I've got the same problem, and I replaced mine early last year. It's clunking and I have to replace it again.

Brian Carlton · #14 01-20-2005, 12:47 AM

Warren,

Regarding the guide rod mounts:

Did you notice any vibration/shimmy when the brakes are applied at 45-50 mph, without any pull?

My thought is that a guide rod mount that has failed badly enough to cause this vibration will present a serious pull to that side.

It would be amazing if both guide rod mounts failed in similar fashion so that both front wheels are moving rearward the same amount when the brakes are applied.

Any additional thoughts on guide rods? More discussion please (tomorrow).

wbain5280 · #15 01-20-2005, 03:45 AM

A W126 owner doesn't have to worry about brake induced pull because the suspension has zero offset. That's because the spindle centerline and tire contact center meet on the road surface. Viola, no torque is produced.

Check the small rubber boots for breaks. (no pun intended).

When was the last time these were changed, or are the original?

Be careful when installing the new ones. The old ones are most likely rusted and there will be a lot of rusty stuff on the housing walls. I think my problem is caused by incorrectly installing them. When the weather warms up, I'll take the old one out and install the new one using slip joint pliars to fit it in the hold. I used a shop press and probably stretched it out of shape.