w108 weird grinding sound at initial acceleration on uphills?

[Jazzenco]

Hi everybody,

I have w108 280SE 3.5 and recently experienced with some weird sound which comes out somewhere from rear bottom side of engine or from automatic transmission. Metallic, grinding sound occurs at initial acceleration on uphills for few seconds then finishes. Sound looks like smth rotating metal bracket contacts with some other surface. I checked but did not find any suggestions? Can it be starter or exhaust leaks?

Thank you very much in advance.

Kutluhan

[JMela]

You're confident that problem is motor-based and not something else?

Wheel bearings would be an easy one to check, if you haven't already.

[Frank Reiner]

Jazz:

First suspect: drive shaft center bearing.
Second suspect: A drive shaft component (flex disc) contacting the floor of the car. This could be caused by a separated left engine mount, or a separated transmission mount.

[Jazzenco]

Thank you very much Mr. Frank and JMela.

First of all I'm sure that this sound is not coming with wheels or wheel bearings, because sounds occurs when I push on accelaration pedal at the initial acceleration and it looks like sorry but roughly 'tiny cııııırt sound'. I checked it comes from center bottom. It' more when going uphill more than normal.

About drive shaft central bearing, in fact I had problems with balance because there was noticeable vibration and I brought shaft rear(long one) for balancing to specific shaft balacing shop. I guess they already checked central shaft bearing for play any other problem.

But you mentioned me;
''to check A drive shaft component (flex disc) contacting the floor of the car. This could be caused by a separated left engine mount, or a separated transmission mount.''

I will check this flex disc but do you think it can contact with car bottom floor during initial acceleration and can cause such grinding sound?

Engine mounts were good condition therefore I could not replaced with new ones. What I can check about engine mounts? How they damage? Rubber cracks or broken over time?

Also I installed new transmission mount when I place engine with transmission on car. I had competed full restoration which took 3 years and finished previous summer.




Thank you

Kutluhan

[280EZRider]

Originally Posted by Jazzenco

About drive shaft central bearing, in fact I had problems with balance because there was noticeable vibration and I brought shaft rear(long one) for balancing to specific shaft balacing shop. I guess they already checked central shaft bearing for play any other problem.

To effectly balance the driveshaft, it should be balanced as a complete unit (both halves together with center carrier bearing on), although this is probably not the cause of your grinding sound.

To determine motor mount collapse (usually rubber deterioration), look for space difference between top and lower sides of the cooling fan in relation to the fan schroud (if you have one) and for contact between metal sides of the motor mounts with the metal supports extending from the motor that connect to the mounts.

[97 SL320]

Apply the parking brake.

Apply the foot brake.

Select drive.

Apply no more than 1/2 throttle for no longer than 5 seconds.

If you get the same noise look at the left motor mount, it may be broken allowing the engine to lift and contact the body. Look at the right motor mount for it being collapsed. Also look at the exhaust, it may be contacting the body as the engine lifts even with good mounts.

[Jazzenco]

Thank you very much 280EZRider and 97 SL320 for your suggestions. I will check for motor mounts first than exhaust for contacting body. I also did not check yet shaft flex disc contact with body..