Cummins serpentine belt issues

[Merv]

My 1999 Monaco Diplomat Cummins 5.9 ISB 275 hp. recently experienced a serpintine belt failure. I managed to shut it down before any overheating. I installed a new belt and found that when I switched on the heater or head lights the voltage dropped from just under 14v to 12.5-13v. I figured that the belt must be slipping so changed out the tension arm and idler assembly. Same problem. The fan and alternator both spin easily by hand and very smooth. The water pump does not spin quite as easily but does not feel at all rough. I'm trying to decide if I should change out the water pump. Anyone had any similar experience?

Thanks in advance,

Merv

[beejay25]

Merv The first thing I would check it the routing of the belt. The belt is in contact with the water pump pulley for about one half of the pulley or it will slip. Hope this helps.

[luckyd]

2002 windsor
Left campground early and put headlights on. Later noticed the
temp. guage was close to 200. Shut headlights off, and temp returned
to normal. All guages jumped up when lights turned on
and dropped back with lights off.

[palehorse89]

Originally Posted by luckyd

2002 windsor
Left campground early and put headlights on. Later noticed the
temp. guage was close to 200. Shut headlights off, and temp returned
to normal. All guages jumped up when lights turned on
and dropped back with lights off.

Sounds like you might have a little ground issue.....

[hillboy]

AS noted your problem may be a ground, but just for back round don't assume that the belt that was on it when you got it was the right one. You can measure to check.

[flamebuster]

When you lost the serpentine belt did any strands of the belt get wrapped around the shaft of one or more of the pulleys, such as the water pump or alt.? I have had this happen and it can really put a drag on things especially as it heats up and gets more rubbery..Also what is the condition of the pulleys as far as wear. Might also look for damaged wires that the shredded belt may have hit..
Bad water pumps usually leak out of the weep hole when they are close to failure so I don't think yours is bad..Just guessing to possible causes. I would suspect the alt. first, you may want to pull it and have it bench tested.. I had one on a spray rig do that and it was the rear bearing of the alt. was bad...causing charging issues...Just some ideas of possibly where to look...

[palehorse89]

Post #3 here http://www.irv2.com/forums/f123/driv...ly-139474.html , looks right?

[Merv]

Thanks guys for the suggestions.

The belt routing is correct.

I don't think I have a grounding problem.

I will check for belt length although the belt came from Cummins and they checked against the serial number.

I will check for belt debris jamming a pulley.

When I turn on the head lights the voltage drops very little. It is when I turn on the heater/air condition switch that the voltage drops below 13v and the headlights dim. I think there is an electric compressor which starts when heater damper settings require to be altered?? Will check that out in morning.

Thanks again and will keep you informed.

[CJScepter]

I'm not much a fan of the voltmeter that Monaco uses, I would prefer an amp meter. I believe the 1999 Monaco I had, and my current coach do about the same thing, voltage drops alittle when you turn more equiptment on. I'm not sure where they read that voltage for the dash meter. If it starts at 14 volts and low is 12.5 volts seems ok to me. If it goes below 12 volts then it's not charging for sure. My alternator went out on my 1999 Monaco and gauge showed 12 volts, less with heater fan and radio on, my VOM meter agreed. You might check voltage with VOM at batteries with engine running and compare the dash meter.
By the way, when the alternator went I ran some jumper cables from the house batteries to the chassis batteries, started generator and finished the 200 miles to home.
John G.

[nymoment]

Had the same problem with my 07 300 hp isb. had belt squeel replaced belt and had the same problem . Problem turned out to be belt tensioner was bad would not put the proper tension on the belt .Replace the tensioner problem gone. Gary

[Merv]

Thanks all who responded. As per John G's suggestion I checked the voltage at the batteries and compared to the dash volt meter. The voltage remained relatively constant at the batteries so I can assume that the dash volt meter is not accurate.

Heading for Az. next week to get out of the grey British Columbian weather and feel confident that all is in order under the hood! Thanks again.

Merv

[Parkerco]

Just replaced the serpentine belt on my 2000 5.9 ISB and had a hard time figuring out the routing because the way the picture shows in the previous post will not work on my engine. The belt is too short and it is the same length as the old one. By rerouting from crank to water pump to fan to alt to tensioner the belt fits perfectly so I assume it is correct even though it is different from the posted pic. The water pump still rotates ccw while the rest of the pulleys run cw so I am thinking the routing is OK. Any thoughts from anyone would be appreciated.
Harv

[charles tuit]

I'm going by memory but some years back I read about the generator adjustment bracket was installed incorrectly on some Freightliner chassis. It affected the belt tension.

[Merv]

I'm not sure which diagram you referred to, but I have a 1999 5.9 Cummins in my Monaco and the diagram posted by Palehorse89 is the correct routing for my belt. That is crank to fan to water pump to alternator to tensioner.

Merv