I have checked the motor mounts on my 1989 928 S4 (automatic transmission) and they are probably collapsed. The bottom edge of the engine oil pan sits about 1.5cm lower than the front crossmember. From what I have read in this forum both should be at the same height. Right?

With the transmission in P I raised the revs to the same engine speed where the vibration occurs when the car is moving. The vibration is still there and again in the narrow 3,000-3,200 rpm band. But... it is accompanied by a rattling sound coming from underneath the car. At least that is what it sounds like when I sit behind the steering wheel. I repeated the test while standing next to the engine and by moving the throttle linkage at the intake manifold. Again the vibrations and the sound were there, but this time the rattling sound was less pronounced because there were normal noises from the engine and the fans as well.

Any ideas where the rattling sound could be coming from? Could it be linked to the collapsed motor mounts, or does it have another cause. Could the torque tube bearings be on their way out? In any event, the rattling _only_ occurs in the narrow rev band of 3,000-3,200 rpm. Above and below those revs there is absolutely no rattling whatsoever.

Thanks for the feedback,
Rik Gruwez
Brugge, Belgium

 

Dropped low enough, it is possible that the bottom of the oil pan is touching the top of the cross member. Do you remember if you had any space between the oil pan and the crossmember? I am able to get my fingers between the two pieces, when I am under the car........

 

The mounts are gone!!! With the engine running and the hood up, rev the engine a few times abruptly to 4000 and watch for movement . If the engine is stone still, the mounts are bottomed out. My 90 GT had this when I bought it. There was a funny resonance at around 2500 rpm that went away at 2800. Both my mounts were completely collapsed. What a difference the new mounts made!!!!!!!!!!!

 

How many miles on it? You may have both problems......bad mounts and what sounds like a torque tube rattle. While you may narrow it down to one......you might want to replace both.

 

The car has 100,000 miles. Would a torque tube rattle not be present at all engine speeds? Now the rattle is only there at 3,000 - 3,200 rpm.

Another question (and probably a silly one -- bear with me, I'm a newbie)... Where is the torque converter located? Does it sit right behind the engine, with the torque tube between the converter and the transmission? I was just wondering if I do not have a rattly torque converter, or maybe just loose bolts at the flex plate.

Thanks
Rik Gruwez
Brugge, Belgium

 

My 968 torque tube causes a rattle at 2500-2800 and again at 3800-4000. It doesn't rattle when it's cold, but once the grease in those bearings heats up, it makes a metal-on-metal sound. I have replaced my motor mounts. Typically, you will notice engine shake at idle if your mms are bad. With that mileage, you may have both issues. 928 international will sell you a rebuilt tt for about 500 bucks, but you need to take it out yourself and ship it to them or pay a mechanic to remove it. It's a fairly involved process, from what I have read. I'm getting ready to do the job myself, with the help of a seasoned mechanic friend. Read other postings on this site, as well as clarks-garage.com. Someone is in the process of rebuilding a torque tube from a 944 and has posted lots of info.

Terry
new member

 

Thanks for the feedback. I ordered the Ford motor mounts from Anchor and will install them once they get here (from the USA). As to the torque tube, I will be taking the car to a mechanic tomorrow and have him check out the rattling noise. He will be in the pit, I will be in the car playing with the throttle. Maybe that'll reveal more.

In any event, thanks for the feedback.

Regards,
Rik Gruwez
Brugge, Belgium