Hey forum

I'm gradually getting my 1978 nonturbo 300D in the condition I want it. To give you the most recent history, there was a squeal from the drive belt region when I got it, which was diagnosed as a problem with the idler pulley. The local benz diesel specialist replaced this, along with a new belt around the AC and idler pulley.

Squeal gone---great. However, there is now a quite different, intermittent squeal from the belt slipping on the AC---only occurring when the compressor clutch is engaged, of course. The slipping more or less disappears above idling speeds.

I'm not keen to send it back to the same garage at the moment, as (a) they thought the second squeal was because the belt was *too* tight, which doesn't make any sense to me and (b) when the guy loosened the belt a little and the slipping became continuous, rather than intermittent, he said my ac was seizing. (Add that to the fact that it went in for an oil and filter change along with the idler pulley replacement but came back with dangerously low oil levels, and also that he put the belt on incorrectly to begin with, causing it to break immediately I drove it out of the garage and necessitating the new belt. That wasn't done by the main mechanic in this place, but bad enough.)

Anyway, it seems to me like the new belt may be just not tensioned high enough. It displaces almost an inch with moderate pressure downward in the center between ac and idler pulley. With the belt on, the part of the ac with the belt around it turns OK---some resistance I assume because I am sliding the belt around the main drive wheel, and I expect everything would turn easily if I took the belt off. Also, the smaller wheel, on the front of the AC (on the nearside of the AC to me as I stand over the engine), which is I assume what is actually connected to the bearings inside the ac, turns very easily indeed.

Also, the AC was working fine before I took it in, apart from the (quite different) squeal from the idler pulley. I don't know if the mechanic's diagnosis of seizing does make sense to you guys, but it seems at least worth a try just tightening the belt, right?

Is the best way just to undo the single pivot bolt offset from the back of the idler pulley, push the idler pulley up to make the belt tighter, and then re-tighten the pivot bolt?

It's the pivoting action that determines belt tension. If the pully on the a/c compressor turns freely when the compressor clutch is not engaged, that is how it should be.

When you hear the belt squealing, where is the squeal coming from, the crank pully or the a/c compressor? Does the A/C compressor pully stop spinning when the squeal begins?

The belt tension you describe sounds about right.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

I believe the York compressor is quite robust, at least I haven't really heard of seizing problems? Is it possible the tech put the belt on correctly, but the bad compressor caused it to break? I would take the belt off, engage the clutch, and gauge how difficult the compressor is to turn. I don't know exactly how easily it should turn, but perhaps others with this compressor can give you an idea.
In any case, the it sounds like your mechanic doesn't know the box end of an endwrench. I think I would look elsewhere for help.

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For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel

Hi Bajaman

I don't think the compressor caused the belt to break. THe main mechanic (not the guy who'd actually done the work) looked at it straight after it'd broken, and said it looked like the other guy'd tried to wind one belt around multiple components! Maybe he thought it was a serpentine, who knows....

This is borne out by the fact that when it did break, about 100yards from the garage, not only did AC go, but more noticeably the power steering and cooling system went. By the time I'd driven around the one-way system to get back the car was overheating. So I'm pretty sure it wasn't *just* that the belt around the AC was put on properly, and then broke due to compressor. But difficult to know *exactly* what happened.

I'll take the belt off and engage the clutch to check ease movement of the whole compressor unit, definitively. By the way, isn't it kind of enough that the smaller, front wheel on the compressor turns freely, without it engaging the pulley? I would think it is this wheel that is connected internally to the compressor pump, right?



Hi rrgrassi

Yes, when the squeal happens, the AC stops spinning. I think what happens is that the belt slips at that moment, causing the squeal, then eventually the belt grips the ac and stops for a moment. Then everything starts moving again. I'm in work but going to look at it again later to try and work out the exact order in which things stop/start/squeal, but does that sound like what I'd expect with a loose belt, or more like seizing?

If I do just need to adjust tension...with the pivoting of the idler pulley, there is just one bolt to loosen, right? Then I pivot the pulley by hand or with some leverage, and retighten?

Thanks both of you for your help!
-J

That sounds right on tightening, but my car has the R-4 on the lower driver side, not the York on the upper passenger side.

If it is that it just squeals when the clutch first engages, then every thing begins to spin, that points to either a loose, worn out, or wrong size belt.

Either way, remove the belt first, engage the compressor clutch and see if you can spin it, or if it feels like it locked up, then moves.

The York does have reed valves that like to break. Older Dodge and Fords used them also. When the work, they are good at what they are supposed to do. I know of wrecking yard guys that take old Yorks and make air compressors out of them so they can run impact wrenches for junk car dissasembly.

Are you still using R-12?

R-134 does operate at higher pressure, and makes it harder for the engine to spin the compressor.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

hi

It squeals intermittently while the compressor clutch is engaged, not just at the start. I'll try this evening with the belt off how easy it is to move the compressor wheel. If it turns I'll try rotating the idler pulley pivot to tighten the belt and see if it helps.

I didn't realise that other w123s had the ac in a different position. They changed that for later models, did they?

Thanks again for the help
-J

...and when you say `spin it', you don't mean it'll actually spin/free-wheel, do you? I mean, I'm expecting that with the clutch engaged it should turn easily as I rotate it, and then stop as soon as I stop turning.

I just thought I'd check as I'm not sure how easily it *should* turn....

Well, for what it's worth, I've been thru most of the same on a 1992 500SL,,
Idler Pulley, Belt , Tension.. Etc. Now beginning to suspect the Intermittent
Noise is from the Old Water Pump which sits above some of the Pulleys..
It shows signs of water stains there, and I'm about to replace all the Parts
there... Pump, Thermo, Hoses.... ( BTW, even went thru the Hyd.Steer Pump)

Will get back later on to let you know what transpired.. It was All Due, Anyhow..!

Not Mercedes related, but....

I used to own a 79 Caddy with a 429 that had a belt squeal on the power steering pump.

After replacing the pump, I eventually discovered the root cause was an incorrect belt cross-section.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Be aware that engaging the A/C puts a load on all the belts, so look closely at the alternator belt as being the loose one. With the engine off, try to rotate the alternator pulley against normal rotation by hand. If it rotates at all, the belt's too loose and glazed which requires replacement. The alternator belt tension is critical on this era of MB and finding it loose is not uncommon. Belt deflection should be close to a 1/2 inch on any engine belt. Also list year and type of MB in your signature profile. Keeps us from having to scroll up 3 to 5 posts just to confirm what you own.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Hi again

I did the adjustment this evening. I tightened the compressort belt as much as I could by pivoting the idler pulley upward, and it made a difference. The intermittent squealing is still there, but less frequent. Probably still not usable, though.

Maybe if it were tighter still, the result would be better. What method/tools do people use to adjust the position of the idler pulley? I just tried to lever the idler pulley upward with one wrench, while tightening the pivot bolt with another. Considering it's also pretty essential to nudge the rubber coolant pipe out of the way to tighten the pivot bolt, I didn't feel I was applying force optimally to the idler pulley! Maybe I need more/stronger hands.

On the other hand, maybe the main mechanic at the garage was right. The compressor wheel didn't turn all *that* easily with belts off. And I realised that the squealing is actually coming from the main drive wheel---the belt, the idler pulley and the compressor wheel all stop momentarily, and the belt rubs against the main wheel, causing the squeal. It could still be a lack of tension in the belt, but I'm not sure---maybe the compressor wheel really is getting stuck intermittently. Does that sound plausible?

Any way to gauge how freely it should turn, if it's not beginning to seize?

-J
PS model year should now appear in my sig.

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1978 300D non-turbo 383k (Claudia)