Hi:

Any guidance would be appreciated.

My 79 300td has just started producing a loud screeching noise (not unlike the noise a loose/worn out alternator belt makes). It's been very occasional, but almost every time I've heard it I've been coasting in gear, and as soon as I press on the accellerator (sometimes very gently) the noise starts. If I release the pedal and then press again, it usually doesn't recur.

The weather's been hot, and it seems to happen late in a given drive.

The alt. belt and the power steering belt are in good shape and seem tight.

My transmission is not too happy lately, as my vacuum system is not working properly. Some hard shifts and occasional early or late shifts, but it hasn't been too bad in my opinion, and I've been limping along until I can figure out a plan for getting vacuum again. I've driven over a thousand miles like this, if I can call that limping.

Trans fluid and crankcase oil levels check out fine.

Thanks in advance,

Bradley

could be the water pump or alternator bearing going out

What about the a/c belt.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

"coasting in gear" doesn't give us much to work with... please explain in detail.

how fast are you going? is the a/c on? are you going down a hill? what's running in the car? how hot is it? what's the engine temp? how old are the belts? is the a/c belt connected to the compressor? does the a/c compressor work?
the more details the better.
coasting on the highway down a hill, the engine fan could be freewheeling, and accelerating could cause a load on it... alt bearings, a/c bearings, glazed belts...
the list goes on...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Good ideas all, thank you. I've never heard bearing noise, though, and it's very intermittent, confounding diagnosis. Where do I go from here, do you think?

Not the A/C belt though; I purged it a few months ago.

Bradley

Sorry, you're right re: detail.

First of all, it hasn't happened on the highway. I also haven't been on the highway since the initial instance. And I THINK that I can rule out glazed belts, because 1) I have experience with the noise/behaviour of the alternator belt slipping, and this sounds/feels different. The new alternator belt is 1500 miles/ three months old. THere's no A/C belt. The power steering belt is old but doesn't look bad.

Hills aren't a factor. Speed was anywhere between 10 mph and 35. And I'm talking about very mild push on the accelerator (sometimes just because that's the way it happened, and sometimes because I was operating cautiously because the noise had just occured and I didn't want to hear it again.)

COULD THIS NOISE BE COMING FROM MY TRANSMISSION??

Many thanks,

Bradley

Temp guage was at normal operating position. Air temp approx 80 - 85.

where does the noise "appear" to be coming from? front? center? rear?

the driveshaft has a center bearing that could be making a whine...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I'll have to get back to you on that question -- I haven't really formed an impression. "Whine," though, doesn't describe this noise terribly well...

Bradley

.

does you car shakes bit more than usually when warmed up and then on idle?

.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

Yes, it does seem to be shaking a little bit more than I remember...

in that case (but you have to be aware that I ain't no expert whatsoever )
I would not go for tranny,... rather possible air in fuel or fuel system itself...

.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

If it WERE transmission noise, what might it be?

Bradley

OK, I just went for a long drive, the car's first time at highway speed since I first heard the noise. It wasn't very revealing, but I'll report in anyhow: Relatively cold, the squealing sounded once during a slow, smooth acceleration, at approx. 20 mph. It didn't occur at all during the remainder of the 25 mile drive.

Puzzling.

If you can hear it at low speed and not high speeds, I personally would suspect the bearings in the alternator or the water pump, once everything gets louder you probably cant hear either. See if you can spin the pulley's and check if they operate smooth...free??

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