380SL Engine Noises - Mercedes-Benz Forum
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#1 (permalink) Old 08-07-2003, 01:26 PM
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380SL Engine Noises

Am experiencing the following two engine noises. Hopefully one of you can help pinpoint the problem(s). This MB was recently purchased and I know next to nothing about it's operation. It has 106,000 miles on the odometer, has had the single to dual timing chain conversion, and the A/C has been rebuilt and converted to 134a.

1. Upon cold start there are noises from the front of the engine which sound like belt noise. Applying belt lube does not resolve the noise. Belts are near new, in good condition. The noise lasts for just about two minutes and then suddenly disappears. During the noise engine RPM is about 900, when the noise stops the RPM drops to about 600. Engine seems very smooth throughout event. It occures to me that maybe the oil is draining from the engine overnight and it takes some time for all the components to receive oil. Or maybe the timing chain tension device?

2. After getting through the above and the engine is warm, at about 1500 I hear and feel a rumble which seems to be coming from the front of the engine. It lasts only through a narrow RPM range, say 1400 to 1600. Above or below that range it disappears. Using a metal rod to various topside engine parts and accessories and holding the RPM at 1500 I can not pinpoint from where the noise is coming.

I posted a question maybe three weeks ago about a high speed whine in the rear end and, just recently started noting what sounds like a significant rumble/vibration which I though was coming from the drive train. But now I have a feeling the above noises, especially #2 which just started recently, could be the problem.

Anyone have suggestions for troubleshooting. I have a Chilton's shop manual but it doesn't address anything like this. Have only had the car about a year and have only driven it 1,000 miles. Kinda afraid to drive it until I resolve the above issues.

Would appreciate your input.

Don


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#2 (permalink) Old 08-09-2003, 02:20 AM
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Not too sure about the 380SL but some of the earlier Mercs have a greasing point on the ...


Not too sure about the 380SL but some of the earlier Mercs have a greasing point on the water pump which will whine if not oiled.

Question two could be a service problem. Try replacing the distributer caps, rotors, leads, plugs etc.

Have you checked the diff oil?


It sounds like a good service will benifit your car. Take it to a good specialist (or DIY) and get all the oil and filters, engine, gearbox and rear diff changed along with the fuel filter and ignition system.
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#3 (permalink) Old 08-09-2003, 10:11 AM
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engine noise

I bet it is the air pump. This runs for a few moments on start up to force more air into the injection system for emissions. They are a pain in the ass. Luckily, you can just take the belt off; why don't you give that a try and see if the noise goes away.
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#4 (permalink) Old 08-09-2003, 10:11 AM
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engine noise

I bet it is the air pump. This runs for a few moments on start up to force more air into the injection system for emissions. They are a pain in the ass. Luckily, you can just take the belt off; why don't you give that a try and see if the noise goes away.
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#5 (permalink) Old 08-11-2003, 01:17 PM
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380SL Engine Noises


No, have been unable to check the diff fluid level because have not been able to remove the fill/check plug. It has apparently siezed. Am looking for a more suitable tool to tackle that again. Looks like I need a 9/16 or 14mm allen wrench with a LONG handle.

Had it on a lift a few days ago to replace the rt. rear axle assembly and bearing, both of which are questionable. Didn't get to finish that because with the fill plug siezed I didn't dare drain the fluid and remove the diff cover to remove the clip holding the axle in place. Have to get back to that when I have the correct tools/oil.

Removed the shield covering the center drive shaft mount. Started the engine and put it in drive and watched. Seems to be excess movement (wobble) in the front end of the driveshaft, as well as in the mount/bearing. Driveshaft was remanufactured/balanced in 1995. Was surprised to find the U-joint was spot welded in place. Don't know if that can be DIY changed but it looks like I need to replace the front shaft bushing, center mount and bearing. I just don't know how much movement one can expect at these points on an MB which does not have the rumble/vibration. That MAY solve part or all the problem, but there still may be a shaft balance or other problem which lead to all this.

Only, that doesn't address the rumble/vibration at about 1500 RPM while in neutral and stationary, which may be translating into the rumble/vibration while driving at certain speeds. That's got to be coming from the engine I would think.

Appreciate your comments.
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#6 (permalink) Old 08-11-2003, 08:26 PM
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Drive shaft and Engine Vibrations


Don

I ended up replacing the entire drive shaft assembly on my 75 450 SL. It is actually two assemblies - front section and rear section. Since I wasn't completely sure whether the vibration was from the bearing assembly or the U-joint, I opted for the entire assembly. I have not had any vibration since; I can also say that where I could physically grab the driveshaft and wiggle it around considerably before replacing the assembly, it is tight now (may relate to the wobble you see with the cover plate off)

Also, I disconnected the air pump on my car (not required due to its age) and many many "mysterious" engine noises disappeared. Worth a try !

Good Luck

Chris Ryan

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#7 (permalink) Old 08-11-2003, 10:19 PM
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Drive Shaft and Engine Vibration

I think you have provided the info I need. Did yu use a new, remanufactured or used shaft? Looking at the parts list for the drive shaft it appears there is a centering bushing at each end. Would assume I would want to change those, the shaft, center mount, bearing, boot - everything. I have several sites bookmarked for parts. Do you have a favorite parts supplier.

I'll do the air pump thing and see if that solves the engine vibration on cold start.

Thanks. I'll let you know how it works out.
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#8 (permalink) Old 08-12-2003, 07:21 AM
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Propeller Shaft Replacement


Don

I replaced the entire assembly. I used a rebuilt unit which a local mechanic got and charged me $775 for the part. I had inquired at MB dealership, who said they sold this as two assemblies - front and rear. (I believe the rear section is the one which has the bearing and U Joint attached to it) MB sells the two assemblies (front and rear) for about $1100. Although I have seen procedures for replacing the center support bearing assembly itself in my service manual, I was told they do not sell this separately, although I think you can buy the components from other parts suppliers. In the end, however, my mechanic convinced me that it was better to put in a complete, matched & balanced asembly rather than replacing only pieces, which I did. I haven't had any trouble since.
I buy parts from MB, as well as from on-line parts suppliers like Performance Products, Benz Bin, K&K,Bud's Benz, World Upholstery, etc.
Good luck ! [:)]

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#9 (permalink) Old 08-12-2003, 07:58 AM
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Propeller Shaft Replacement


Thanks Chris. Your input has been invaluable. Will let you know how it works out.
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#10 (permalink) Old 08-19-2003, 09:27 AM
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380SL Engine Noises and Vibrations


I removed the air pump belt and the noise I was hearing for two minutes after cold start disappeared.

Re the suspected driveshaft vibration, there is only two driveshaft overhaul businesses nearby. One told me they did not have the proper tools to balance the MB two part driveshaft. The oher told me they could overhaul & rebalance this one. Took it to them. It was supposed to be ready the following afternoon. Long story but I picked it up yesterday (three business days later) and they had done nothing. The shop rep told me the rear end was about to fall out, he would be afraid to drive it, and that he did not want to be responsible so he would not do the repairs. I left. (I think I may have torqued him when I questioned why nothing had been done!)

Took it to another shop which has a certified MB mechanic. Although they do not have the equipment to check the balance (it was rebalanced about 30,000 miles ago), they called this AM to bell me they had removed the shaft and see no evidence that a weight has departed or other damage, the bearings and u-joint show no evidence of wear. They also noted the flex disks at each end of the shaft showed signs of wear, they found some bolts loose, and the center mount was badly worn, allowing driveshaft wobble. They recommended replacing some of the rubber mounts the drive train/rear end and changing the oil in the rear end, using MB synthetic oil. That probably will not solve the high speed rear end whine but should help mute it.

If that doesn't fix the rumble I can always go back and change or have the drive shaft shipped somewhere for overhaul.

The nagging doubt in my mind is, if all the components were rebuilt/replaced 30,000 miles ago why am I having this problem? Just sounds like something out of balance causing accelerated wear.
Could that be caused by a bad engine mount?

Sorry I'm so long winded but wanted to give a clear picture of what's happening. I'm a new MB owner, have only driven this car 1,000 miles since purchasing it about one year ago, and am kinda frustrated. Any thoughts?

Don
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