Rumble When Braking 1990 300ce

[Markus]

So braking from highway speeds to about 45mph car rumbles under braking, appears to be coming from the front. New rotors, pads, and rebuilt all 4 calipers 2 years ago, last year new front lower control arms. No shudder or rumble at lower speeds that would indicate warped rotor. From high speed the harder I brake the louder the rumble.
Suspecting front wheel bearings? All quiet coasting, or going around corners.
Thoughts?

[speednjay]

Take the wheel off and have a look. I’ve had a caliper bolt fall out before making a rumble sound

[Markus]

Nope, caliper bolts were tight, bearings are out installing new ones tomorrow. Inners were original car has 125,000 miles. Engine mounts replaced 5 years ago.

[Ferdman]

Markus, take a look at the condition of the driveshaft flex discs. It's a long shot, but they could be worn and need replacement … especially if they are the original ones.

[Markus]

OK so I replaced the front wheel bearings it has made no difference, still rumbles when braking from highway speeds.
- Flex discs (looked OK no cracks)
- transmission mount
- engine mounts
-rebuilt prop shaft and center bearing
All replaced 7 years ago when I had the transmission rebuilt.


Since I had the car up on the Jacks yesterday and during test drive noticed that now a slight rumble exists when the car is in gear at idle intermittently.

Failed engine or transmission mount already? I only use Lemforder or OEM suppliers for any rubber parts where available, never Uro.

While under the car checked the rear suspension and know already that I need to plan for new control arms, links, and subframe mounts while I'm at it. Placed a jack under the diff and lifted, one of the diff mounts moved about 2mm, so those too.

[ILUVMILS]

The complaint description sounds exactly like warped rotors.....

[Markus]

That’s what I thought initially as well but ruled it out since new front rotors were put on three years ago and 13,300 miles ago. New rotor measures 22 mm thickness currently 21.4 This car is not abused and more like granny driven. If the minimum rotor thickness is 19 mm doing the math with the current wear rate should yield at least 60,000 miles. That might be optimistic but 45;000 miles be easily achieved. I’ll put a dial indicator on it tomorrow and measure run out, just to make sure rotors are not warped.

[speednjay]

Probably just the tread of your tires mashing into the asphalt

[URO Parts Support]

Originally Posted by Markus

So braking from highway speeds to about 45mph car rumbles under braking, appears to be coming from the front. No shudder or rumble at lower speeds that would indicate warped rotor. From high speed the harder I brake the louder the rumble.

It's only a rumbling noise, or can you also feel a shudder or vibration while braking from 65 to 45?

[Markus]

Okay, so I put a dial indicator on both front rotors needle stays right at the zeroed position so I think I can rule out warped front rotors. Further inspection of the rear has yielded right rear, front sub-frame separation, right outer lower control arm bushing knackered. This weekend longer highway drive in crosswinds resulted in rear end squirreliness/wandering. Maybe after I rebuild the rear sub-frame, diff bushings and install all new links, and wheel bearings perhaps that will solve the rumble under braking. Transmitting through chassis?
No shudder or vibration under braking but definate rumbling, like something is moving and making contact with the chassis.

[Markus]

Okay so I dropped and completely rebuilt the rear sub-frame assembly. Sub frame mounts, all links, bushings, wheel bearings, spring pads, shocks, rotors 1/2 shaft boots and painted everything! Amazing difference in feel and the car has yet to be aligned. No clunks going over bumps.

What I learned in addition to all the DIY tips here:

1) On the lower spring link inner bushing replacement, DO NOT press them out they are very tight and you will destroy the link.
DO: drill out the center aluminum bushing pass your hacksaw blade through and cut through the remaining rubber and outer steel sleeve until you can collapse and chisel out remainder. Freeze and press in new bushings.

2) The hub carrier bearing can be removed and reinstalled using 3/8" thread stock utilizing an assortment of sockets, old washers and bearing races. No need to purchase the the $270 special tool.

3) Freezing sub frame mounts overnight, coat with NAPA cylglide (silicone paste) and they can be persuaded to the seated position using a rubber mallet or wooden block and hammer.

4) Shim the brake backing plate before pressing out the wheel bearing from the hub carrier or you will bend it beyond recognition.

5) Freeze wheel bearings overnight before pressing them into the hub, using the old bearing on the outer race ONLY, correctly shim the brake backing plate or you will bend it beyond repair.

6) Take your time.



That being said I still have the original problem! Decelerating from highway speed under assertive braking still have a groaning noise coming from the front, and it is definitely from the front somewhere.

[RobertFini]

Please don't be offended by this simple suggestion, but have you tried swapping the wheels/tires either front-to-back or from a different vehicle? A bent wheel or separating tread will produce a very similar kind of rumble under braking as a warped rotor; you might also be able to feel it side-to-side when going around a corner.

Best Regards,
Rob

[Markus]

Corrected front wheel bearing clearance, which helped . Bearings were replaced and not tight enough. The thrust washer barely slipping method to provide bearing preload does not work very well or didnt for me. Used a dial indicator and problem partially solved. Other problem was the exhaust mount at the transmission. Various rubber washers and sleeves eventually fail, transmitting any vibration as the weight shifts under braking or begins slightly when placing car into gear from P or N. New mounting kit around $40.00. All quiet now.
A/C vacuum pods next.

[Roncallo]

Does this car have a steering damper?

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