why does this happen when braking at
over 80 kph. had pads and front rotor
changed recently. car is 1989 300E.

Check the Rotors
 

Greetings,

I would check the rotors again with the car off the ground, to see if there is a high or warped spot on the new rotors as you spin the hub. They can and do warp because of improper metal content, regardless of age. I think if you don't find that to be the problem and the car stops in a straight line, I'd be checking wheel balance as well as slipped steel belts in my tires. They can do that when checking for balance. If the car seems to pull to one side when applying the brakes I'd check the opposite side for air in the braking caliper.


Charles

I do suspect its the rotors too.

Were the rotors OEM?

yes, they are oem rotors and pads!!
quite puzzling, could there be other explanation
for this behavior?

Maybe the rotor alignment bolt was not tightened properly?

Did they use the air drill to wrench the bolts back on or did they torque them to spec by hand?

Check tire blanacing, and for warped rotors.

Water on a hot disc can warp it.

Perhaps your ABS sensors are dirty and are kicking int he abs.

Check the rear brakes, and also check for any bad suspension bushings.

I hope that helps, I'm not a tech, but that list shoudl just about cover it.

Alon

thanks alon. i will check all of the above. cheers!!

Shudder when braking
 

Also, make sure that the brake caliper bolts are tight.
I had once a situation like that.
Other possibilties is Warped Rotors
Good Luck

Car shudders while braking...

This can be caused by:
1) the braking system,
2) improper balanced wheels
3) damaged tires

The rotors are attached to the car with one alignment bolt. The rotor itself is in contact with the cars' axle by a cones shaped edge all around the center. If there is rust between this contact surface (not cleaned properly during the installation of the new rotors), it will cause some shuddering when braking.
The rotors can be warped (production fault or caused by water when hot). The caliper bolt(s) can be loose (a little).

The complete wheel can be damaged (not round) or just improper balanced. The tire can be damaged.

...just some thoughts...greetingz,

You may have developed hard spots on the pad surfaces. This is usually caused by excessive heat before the pads have properly seated on the rotors. If the rotors look OK and you may have to check them for runout. (new doesn't always mean fixed), then remove the pads, examine the contact surface and if they look glazed, you may have to sand all of the glaze off to get them to seat properly. This can also cause squealing as well.

Has it rained since you got the car back from the brake change? If you went thru a puddle of water. Washing the wheels right after the car was just driven causes, this problem also. It can cause your rotors to warp like, someone suggested. Don't worry, I think I recently got this problem.

Lets assume the rotors and pads are fine.

I would then think you might have to check the lower arms, joint and bushes (is that how you spell it, coz thats how I would pronounce it).

I suspect could be the lower arm or the rod thats needs to be checked.

Then again, perhaps you hit something or went through a huge potbelly .. ops.. pothole and knocked something in the front undercarraige?

thank y'all for those replies.
I value the camaraderie.