Squealing/Screeching noise. - PeachParts Mercedes-Benz Forum

Graham · #1 10-20-2009, 06:17 PM

Beautiful Fall day here today. Went for ride. Stopped to get some lunch. When I went to restart car, it makes a kind of squealing/screeching sound. ( I had heard this briefly on start up at home in last few days, but it was very brief.

Open hood but it is hard to tell where it is coming from - Sounds like more toward rear than front even although, to me, it is kind of sound that could be a slipping belt or a bearing without enough oil! Increases in frequency as engine speed increases. Check under car - seems louder, but still hard to pinpoint.

Drove slowly to nearby parts store just in case low oil was problem. But fluids are OK.

Drove slowly in direction of home but noise was still there, so pulled into a repair shop that always has a few old MBs outside. Owner came and listened - He did not think noise was from engine, but could not pinpoint it. Said it should be OK to drive home! At cruising speed I don't hear noise. Just at idle and slow speed. Sometimes if I hear it, a quick pump on pedal and it goes away. As is normal, when I try and check it, it goes away altogether.

So what to do?

I tried using a stethoscope to locate source of noise, but either it stops making the noise or it I can hear it but not through the stethoscope.

This one has me very puzzled!

Mike D · #2 10-20-2009, 06:30 PM

Automatic or manual transmission?

Graham · #3 10-20-2009, 07:12 PM

Quote:

Originally Posted by Mike D

Automatic or manual transmission?

1972 350SL 4.5L with 3-spd transmission.

PS: The question got me thinking! I believe I may have a bad torque converter.

Pooka · #4 10-20-2009, 08:59 PM

Use the steth on the distributor. It could be the bearing inside of it is going out. Or it could be a cam bearing.

Graham · #5 10-20-2009, 09:17 PM

Quote:

Originally Posted by Pooka

Use the steth on the distributor. It could be the bearing inside of it is going out. Or it could be a cam bearing.

I could not pick up the sound on any of the usual suspects in the engine bay. It was just everywhere.

I was able to reproduce it by putting shift in D then shifting to N. After one or two such shifts it stopped doing it. But if I waited a little while and repeated the same shifts, it would squeal again.

Seems like starting/stopping converter produces the sound.

meltedpanda · #6 10-21-2009, 08:39 PM

not a heat shield or metal on metal - exhaust? not fuel pump?
other than things in engine bay , only thing left is tranny and flex discs?

Graham · #7 10-21-2009, 08:49 PM

Quote:

Originally Posted by meltedpanda

not a heat shield or metal on metal - exhaust? not fuel pump?
other than things in engine bay , only thing left is tranny and flex discs?

It at first made the loudest sounds at IDLE , so could not be anything beyond the torque converter. But today, I hear nothing at idle but just on mild acceleration. Still a little squeak as it goes from D to N.

I did have engine mounts changed a few weeks ago. Wondering if they are not properly torqued and it's they who are chirping. I did not do trans mount at same time. I am getting a vibration that was not there before. Problems may be related.

Will install new belts just in case this is the problem. They are due anyway.

There is some heat shield vibration noise. But, I recognize that - Been driving sheetmetal screws up through floor! Had to grind off the points!

Going to Trans shop tomorrow for a quick look-see.

meltedpanda · #8 10-21-2009, 09:14 PM

ahh sound like you have your bases covered. Drive to neutral changes torque on mounts , so you may be onto something there. Check your drive train - flex discs, rear dif mount

GGR · #9 10-22-2009, 09:21 PM

Alternator bearing? It may go away when rpm changes, which is the case when you shift from neutral to drive. As you want to change the bets, try to run the engine without the accessories (including water pump) and try to add them one by one.

Graham · #10 10-22-2009, 10:12 PM

Quote:

Originally Posted by GGR

Alternator bearing? It may go away when rpm changes, which is the case when you shift from neutral to drive. As you want to change the bets, try to run the engine without the accessories (including water pump) and try to add them one by one.

Gael,

I did think about alt & PS bearings and put stethoscope on them one of the times the noise cooperated and allowed me to do some checking. But it was not coming from there. I did not think about the water pump bearing at the time. The noise from there might not be as easy to check - might dissipate through block. May be able to tell something when I have belts off? No sign of leakage.

Was at transmission shop today. They don't think it is the TC or transmission. Only thing we saw, was a loose bolt on the transmission support. While there, only noise I could create was a small chirp as I moved from D --> N . Seems it could be the new mounts squeaking or maybe the engine shocks. Perhaps if the tranny mount is loose, it is allowing more engine movement?

I am at a bit of a loss. There was originally a LOT of noise. I was afraid to drive car. Now, it has almost gone away - but I still hear it when I do a mild acceleration while under way. What I do have, is a vibration through the drivetrain when the engine loads up - For example when accelerating up a rise when the tranny should shift down but has not (this happens on these 3-speeds!)

Thanks for input!

GGR · #11 10-23-2009, 07:06 AM

Re the vibration: You may first check all engine, trans, diff, front and rear subframe mounts as well prop shaft flex-discs and center bearing. If all is OK, you should then make sure the trans output flange and diff input flange rotate in parrallel plans, even if not perfectly aligned. If you have a doubt, while the car is on the lift, you may take the driveshaft out, bolt two metal bars (L or square shaped) to the flanges so that they are vertical going downwards? You then measure the distance between the bars at flange level and once more one meter down. The distances should be the same. You repeat the operation with the bars as close as horizontal as thay can go, on both sides. If distances are not the same, you should adjust the position of the engine/trans or diff so that the two bars become parallel in all three positions.

Graham · #12 10-23-2009, 12:18 PM

Quote:

Originally Posted by GGR

Re the vibration: You may first check all engine, trans, diff, front and rear subframe mounts as well prop shaft flex-discs and center bearing. If all is OK, you should then make sure the trans output flange and diff input flange rotate in parrallel plans, even if not perfectly aligned. If you have a doubt, while the car is on the lift, you may take the driveshaft out, bolt two metal bars (L or square shaped) to the flanges so that they are vertical going downwards? You then measure the distance between the bars at flange level and once more one meter down. The distances should be the same. You repeat the operation with the bars as close as horizontal as thay can go, on both sides. If distances are not the same, you should adjust the position of the engine/trans or diff so that the two bars become parallel in all three positions.

Shop did rear seal on tranny last year, but it is leaking again. They want car overnight, so I am going to let them install new Transmission and Diff mounts. Despite the leak, they are a good shop and should know how to get things aligned. Without a hoist and having bad back, I don't want to even try!

They had the transmission out a year ago and it never vibrated after that. But I did have another shop put new engine mounts in about a month ago. Could doing that have thrown the alignment out at the rear of the transmission?

The transmission shop found a loose bolt on the transmission mount - They would fix that when they put the mount in. But it could perhaps be part of problem.

I also noticed front right engine shock seems to be more extended than it used to be. Shaft has rust on it. It may be squeaking as it vibrates. I am going to squirt some WD-40 on it and see if that helps.

Thanks for input.

Pooka · #13 10-23-2009, 04:42 PM

Another longshot, but one that is easy to check if they have the car on a lift...

The center driveshaft bearing, also properly known as the carrier bearing. You mentioned the vibration when starting up driving and that is a classic sign of one of these going out. Really the bearing starts to go and it tears up the rubber carrier that bolts to the car. As it gets moe torn up it vibrates worse and worse until you know something is really wrong.

The only good thing about it is that it is easy to check and easy to repair. You just have to know to check it. As I said, if the car is up on a lift it is as easy to check as a rubber muffler hanger, so you might ask them to take a look at it.

Graham · #14 10-23-2009, 07:26 PM

Quote:

Originally Posted by Pooka

Another longshot, but one that is easy to check if they have the car on a lift...

The center driveshaft bearing, also properly known as the carrier bearing. You mentioned the vibration when starting up driving and that is a classic sign of one of these going out. Really the bearing starts to go and it tears up the rubber carrier that bolts to the car. As it gets moe torn up it vibrates worse and worse until you know something is really wrong.

The only good thing about it is that it is easy to check and easy to repair. You just have to know to check it. As I said, if the car is up on a lift it is as easy to check as a rubber muffler hanger, so you might ask them to take a look at it.

The center bearing can't be the cause of the noise (it happened at idle), but could be cause of vibration. It is on my list of things to check. First we are doing the tranny & diff mounts. Will inspect flex disks and bearing while doing that.

Drove car today. No noise at idle. Just occasional noise when accelerating once car has warmed up a bit. Noise seems to be getting less frequent. It would be a lot easier if it would just do it all the time

Won't get belts until Monday. Will probably just tighten old ones on weekend.

I did lube the engine shock shaft (the one I can find!). The other one is hiding back under drivers side manifold somewhere!

Graham · #15 10-24-2009, 09:49 PM

Quote:

Originally Posted by Pooka

Use the steth on the distributor. It could be the bearing inside of it is going out. Or it could be a cam bearing.

Switched to a spare distributor today. I did not drive car very far, but I think I may have noise still. It now only comes when I accelerate mildly at relatively low speed. But it is same louder noise that I originally heard at idle too.

I found that coolant level was lower that it should be. Filled it. I thought that maybe there was air in system from when I pulled AAV a week or so ago. Again. no conclusive test.

Belts are quite tight, but I thought I would tighten more and see if I could make noise happen again at idle. But, Alt adjuster is tight - soaking it overnight with Release-It.

Not sure how I would check cam bearings?