Vacuum Loss, Firm Brake Pedal, Screeching Noise - PeachParts Mercedes-Benz Forum

GoldenEagle · #1 12-02-2016, 10:05 PM

Working through the bugs on a 1983 300CD that I bought earlier this week.

Two nights ago I took it around the block just as a test run and it ran pretty well until about 3 miles into our journey when suddenly the brake pedal got rock hard. The brakes still worked but not very well and I had to stand on them to get a response. I suspected vacuum and sure enough when I got home and got parked it would not turn off with the key (it previously had turned off with the key without any issues). I shut it off with the stop lever under the hood and called it a night.

Yesterday I fired it back up and the brake pedal was still too firm and it would not shut off with the key. While the car was running, I put a vacuum gauge on the two nipples attached to the main vacuum feed from the vacuum pump to the brake booster and sure enough I got a zero reading. I turned the car off and disconnected the main vacuum line from the vacuum pump and restarted the car. Suddenly there was full vacuum coming from the pump. I reassembled everything and now I have good brakes and the car turns off with the key as expected.

Driving around the block last night and initially the brakes worked fine. After a couple miles, the brakes got rock hard again but this time the car sputtered and died. I jumped it and it started back up, but died again about 100 feet down the road. I jumped it a second time and this time after about 100 feet, it started to chirp/screech extremely loudly and then died. I gave up and dragged it the rest of the way home behind my truck.

I was immediately thinking alternator with the fact that it keeps draining the battery and figured the screeching was the bearing going out in the alternator. So i took it off and had it tested at the auto parts store and their machine claims it is still good. Spinning the pulley sounds a little gritty but not horrible.

Any ideas?

Also, there are two grooves in the alternator pulley but only one belt. Is this correct or should there be two belts?

Thanks. I know there is a lot going on in this thread but I appreciate any feedback.

sixto · #2 12-02-2016, 10:35 PM

Might be a sticky check valve on the pump outlet.

There should be 2 belts.

Sixto
83 300SD

GoldenEagle · #3 12-02-2016, 10:42 PM

Quote:

Originally Posted by sixto

Might be a sticky check valve on the pump outlet.

There should be 2 belts.

Sixto
83 300SD

Thank you. Thoughts on the repeatedly dying engine but seemingly good alternator?

Diseasel300 · #4 12-02-2016, 11:00 PM

Check the vacuum pump. If it has failed, it can cause catastrophic damage (timing chain and worse). Alternator should have no effect on a diesel once it's running. Everything important for the engine to run is 100% mechanical. You could remove the battery and alternator entirely and it should still continue to run.

GoldenEagle · #5 12-02-2016, 11:58 PM

Quote:

Originally Posted by Diseasel300

Check the vacuum pump. If it has failed, it can cause catastrophic damage (timing chain and worse). Alternator should have no effect on a diesel once it's running. Everything important for the engine to run is 100% mechanical. You could remove the battery and alternator entirely and it should still continue to run.

I agree with your assessment that the diesel engine should be a pseudo-perpetual motion machine once set in motion (obviously with the energy input in the form of diesel fuel). However, something was pulling on the battery causing it to stall shortly after it got a mini-boost via a jump from my truck. I didn't put a voltmeter on the battery, but there is no doubt that it would restart with jumper cables and die within seconds after they were removed.

Diseasel300 · #6 12-03-2016, 12:18 AM

About the only thing that's going to drag the alternator/battery down hard enough to even attempt to stall the engine is a short circuit somewhere. If you were under way and the alternator loaded up, I'd expect the engine to have enough power to snap the belt or at least smoke it without stalling out. Easy enough to test - Remove the alternator belt and see if the engine still squeals and stalls.

Given the rag shown in the other thread, I'd be inclined to suspect oil starvation. With all the fluff and debris that came from that rag, I'd suspect you've got a clogged oil pump intake strainer at the very least. It would be very surprising to have that in there and not have some sort of major side effect, especially considering that the valve train split the rag between 2 lobes.

GoldenEagle · #7 12-03-2016, 06:47 PM

Well I got the battery and alternator tested today and the battery tested bad but the alternator tested good. The alternator bearings sounded pretty gritty so I just replaced it anyway just to be safe.

I also bought new alternator v-belts. Any tips on getting the new belts on or do I have to remove/loosen all the other components with belts blocking the v-grooves I need to get to install the alternator belts?

I also drained all the oil but no one had a oil pan gasket in stock locally so I'm waiting to pull the oil pan to see what is stuck to the pick up.