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    Technical Data Section - Electrical Tips

    This page initiated 06-06-03, upgraded 07-07-03, upgraded 02-26-05, upgraded 06-14-08

    To view other pages in the Technical Library, such as the Detroit Diesel Publication, scroll to the bottom of this page, click the Navigation Bar for your choice

    NOTE: COPYRIGHT 2006 Tejas Coach Works
    This information is open for anyone to read, but is not intended to be copied.
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    Currently Back Logged to the End of October!

    Special Bulletin! 09/08/09

    Is the Oil Pressure in your Turbo Engine TOO LOW??

    Engines that are turbo charged absorb a hefty percentage of the oil to lubricate the turbo.
    I have seen some that will not maintain 30 to 35 psi at max rpm after warm up.

    Delo 100 is also available in 50 WT. It will give a tired engine some more compression and bring up the Oil Pressure. The heavier viscosity oil will boost the oil pressure and at the same time it could increase your compression in turn helping the engine run cooler and possibly smoke a little less.

    This is not as good as an overhaul by any means, but It is a way to extend the life of an old engine, especially if you do not have the big bucks it takes today to overhaul. I stumbled on to this talking to a West Coast operator who indicated he had been using it for years and he was getting it from an Authorized Genuine Detroit Dealer. I have not attempted to purchase it through the Dealers, but did find some locally at an independent oil distributor.

    NOTE 1: If your engine is maintaining 60 psi at 70 mph and 15 to 20 psi at idle with a warmed up engine, you do not need this weight oil!

    NOTE 2: If you have a non turbo engine that has low oil pressure this will also work in it.

    Special Bulletin!
    Scarcity of Availability
    Straight 40 WT. Oils
    Information is now posted in NEW page Helpful Tips & Oil Information

    Instructions where to find Locations with MAP & PHONE links.

    Sulfated Ash Rate Comparison Chart Updated 08/30/06

    Electrical Troubleshooting

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    Delco 50dn 220 to 300 Amp Alternator

    Trouble Shooting

    Problem: Not Charging!

    To test it to see if it is working you can bypass the regulator and all the switches. You will need a Volt Meter (digital would be best) and a Jumper Wire, preferably a larger gauge such as a 16, 14, or 12 would be safer (If you use a very light jumper such as a 18 gauge or smaller it might get hot in a short time and burn as you hold it to the terminals especially if it there is an internal short in the alternator). There are two major differences on the types of this alternator, some are Air Cooled, such as on most all the older Eagle buses, and a few were on some of the early GMs and the early MCIs. The housing on the opposite end of the belt drive or gear drive (depending on which vehicle you are working on) the housing will have the heavy NEG and POS posts located on the side of the round housing. The NEG will usually have a strap connected from the post to the case. The POS will be insulated and not grounded. On an Oil Cooled alternator, such as is on the MOST (but not all) of the old GM and MCI buses, the POS post is located on a step out hump on the back end of the alternator. (IF you have any doubts about which cable is which, use a volt meter to verify which one is the POS. Carefully put a jumper wire direct FROM the large 12v (or 24v) POS (big as your thumb cable) TO the FIELD terminal momentarily with the engine running. MAKE SURE that you do not jump to the GND or the RELAY terminals. What you should see is a "Soft Spark" and at the same time you will hear the engine slow down from the "LOAD" you have just put on the alternator.

    CAUTION: This is only a momentary test!!
    If you leave it on too long it can burn up the alternator by heating up the bearings, diodes, stator, and the field coil inside the alternator and overcharge the batteries possibly causing a the batteries to explode. What you are doing is making the alternator put out about 18 or more volts(on a 12 volt system or 27 to 32 volts on a 24 volt system). It SHOULD not harm it for a very SHORT momentary test.
    SOFT SPARK with HIGH Voltage
    IF you hear the engine slow down under the load, and have a soft spark (Blue or light yellow but NOT a hot loud crack) and you get a voltage reading above 16 volts (on a 12 volt system or 27 volts on a 24 volt system) the problem is more than likely the Voltage Regulator, a Relay, a faulty ground, a Circuit Breaker or loss of continuity in a wire loom. To isolate the Voltage Regulator from the possibility of being the problem, it has 3 wires going to it. The center post is the FIELD. Of the outer 2 post, one will be the GND, the opposite one will be the POSITIVE. Depending on how you are viewing the regulator, IF it is orientated in the vertical position (Tall) and the Hole with a HEX HEAD cover cap for the ADJUSTING SCREW is above the terminals, then the left outside terminal will be the GND, and the opposing outside terminal on the right will be the POS. If there is any doubt, test with your meter to insure which one is POS. You can jump across the FIELD (center) to the POS. If the system starts charging, the problem is NOT the REGULATOR but one of the 3 circuits has a fault.
    SOFT SPARK with LOW Voltage
    IF you hear the engine slow down under the load, and have a soft spark (Blue or light yellow but NOT a hot loud crack) and you get a voltage reading below 16 volts (on a 12 volt system or 27 volts on a 24 volt system) BUT you do get a noticeable increase in volts, the problem is more than likely 1 (one) or more of the 6 Diodes are blown.
    SOFT SPARK with NO Voltage deviation
    IF you do not hear the engine slow down under a load, and you do not get an indication of higher output on the volt meter, then the problem could be a bad Rotor.
    This could be caused by a direct short from a internal jumper wire shorted due to faulty insulation or it could a blown or shorted diode or a shorted out Stator.
    IF no spark then a lack of continuity, a bad Field Coil, a bad Stator, burned out BUSS BAR, several Diodes blown or some other problem.

    A faulty alternator should be repaired only by a repair facility that has experience in working on the 50dn series. IF THEY DO NOT HAVE THE Manual or have not worked on one they can do serious damage that could break some parts of the housings, bus bars, insulators that are not readily available with out incurring some overnight air freight charges causing an expensive delay in repairs. Case in point, a customer dropped on his Neihoff alternator to a repair facility NOT familiar with the unit to replace the bearings. When the customer went back to get his alternator, the repair person made the following statement: There is something wrong inside this alternator that can no longer be repaired. After bringing the unit to us, when the unit was inspected, the entire inside of the housing had been destroyed by the repair facility that was not familiar with the unit when they had attempted to press out the bearings with out totally disassembling all that was necessary prior to pressing on the bearings. The particular alternator common to the later Eagles cost approximately $3000.00. And as sad as it is, the repairman was correct in his statement.

    Preventive Maintenance

    To test the bearings you can use a long (24 inch more or less) stick, iron rod, broom handle, long screw driver or what have you. With the engine running at idle, wrap your fingers around one end of the stick with about 1 inch of the stick exposed on the end where your thumb is and cover the end with your thumb with the knuckle bent as tight as you can comfortably holding pressure against the stick with the thumb. (You can purchase a stethoscope for automotive diagnosis or a electronic listing device with ear phones to perform this test also) CAREFULLY place the opposite end of the stick on the end of the housing close to the pulley and place your ear on the knuckle of the thumb. You should hear a whine or a fine smooth noise as the alternator is spinning. You can go to the middle of the housing and perform the same test. It will be difficult to distinguish between the two bearings, but it may be possible. If the noise that you hear sounds ROUGH, or has a clicking with a odd rhythm, you should have the alternator checked out by a trusted repair facility to confirm your diagnosis.
    This would also be a good time to check the bearings in the Pillow Block under the Alternator. It has two bearings in it also.

    Do not allow the stick to get into any rotating shafts, blades, belts.
    You can do a further test by shutting off the engine, loosen and remove the fan belts and carefully rotating (KEEP your fingers out of the cooling blades on the pulley) and listen to the bearing again with the sounding rod. It should be easier to determine if it is in the alternator with the engine not running while you make this test. While the belts are loose, check them for gaps on the inside surface of the belt. A gap of the rubber on a belt could be a source of an unusual noise while listening on the stick during the engine on portion of the above test and it also should be replaced prior to reinstallation.


    Alternator Belts
    If you are away from a source for belts and you are using the 3 or 4 belt system to turn you alternator, and you notice one of the belts is much looser or is about to break soon, remove it from the system. When it breaks it usually will get under one or more of the remaining belts and cause them to break. Do not throw the loose one away until you have got a new full set for replacement. ALWAYS carry a set of spares, and if you replace them and can not locate a new full set for your next replacement, do not discard the old ones until you do.

    Alternator Belts Replacement
    When you replace belts, try to do it when you will have time to use the vehicle for about 2 hours under load. New belts will stretch just a little after initial installation causing them to loosen. Check the tension on the belts to see if you need to adjust the tension tighter. If you over tighten the belts you could ruin the bearings, but if you do not get them tight enough they can slip. It is a good practice to keep a closer watch on the belts for the first 25 hours of service.

    I have seen belts that were installed and did fine for the first 2 runs of approximately 2 hours each. The belts were not checked before the next run of 6 hours but everything appeared to be normal to the driver. On the return 6 hour run the vehicle was parked and a visual inspection was performed in the but the tension on the belts was not checked. During the trip the Alternator was under heavy demand and the belts got just enough slack to cause them to slip, which in turn caused the pulley to overheat. The following morning a driver started the bus and the belts were smoking and the alternator was not turning. The belts had melted from the heat and welded themselves to the pulley at the alternator. The drive pulley turned and the belts burned off before he could get the engine to shut off.

    It is a good practice to see if you can spin the alternator before starting the engine with a wrench on the shaft nut. If you can spin it, the belts are too loose and/or possibly the pulley shivs are worn out and needs replaced or machined. It is not unusual for the older Eagles (05s and early 10s using the 3 belt system on the Delco Alternator) to have worn out pulleys on the alternators which do not fit the belts good. The pulleys are not easy to locate and after several million miles of use they can be almost razor sharp. You can have them machined on a lathe to the original pitch angle and flatten the edges back to a safe surface. Great care will have to be taken to insure that all 3 shivs are exactly the same so that the belts will all have the same tension. Width, Angle and depth are all critical. If they differ, not only will one be tighter than the other it will also be trying to travel at a different speed then the others causing it over heat. This will reduce the circumference and in effect increase the speed of the unit which should not cause any major problems unless you are one of those who like to turn you engine up to the 2750 rpm range and run full throttle.

    NOTE: COPYRIGHT 2006 Tejas Coach Works
    This information is open for anyone to read, but is not intended to be copied.
    Instead, please feel free to invite others to view it
    here at

    Helpful Tips & Oil Information DDC OIL TEJAS OIL TIRES ELECTRIC
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