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Mack MP8 Fan Clutch Harness

Hunter013

Hunter013

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Joined
Oct 4, 2021
Messages
165
Location
Wisconsin
Occupation
Head Floor Sweeper
2018 Mack GU813 MP8

The fan belt blew up a few weeks ago and took out the fan clutch harness. Asked Mack if I could just get the harness and they said no. We replaced the fan clutch and everything ran fine till yesterday. Fan belt blew up again and took out the fan clutch harness again. Fan clutch P/N: 24437931. My 2 questions:

1. Is it possible to just get the fan clutch harness rather than dropping another $1,600 for a fan clutch?

2. What would cause the belt to blow again? Tensioner has good tension and no play, idlers/pulleys roll fine and don't have any play either. A sister truck to this one had a problem with the alternator belt blowing every other day which ended up being bad motor mounts. This trucks motor mounts look fine. What else should I look at?
 
Hunter013

Hunter013

Well-Known Member
Joined
Oct 4, 2021
Messages
165
Location
Wisconsin
Occupation
Head Floor Sweeper
Truck Shop said:
Crank Damper.
Click to expand...
I did watch the damper while it was running and it seemed like it had a slight wobble to it, but I thought it was more of my eyes playing tricks on me. Is that a pretty common thing to fail?
 
Junkyard

Junkyard

Senior Member
Joined
Jun 5, 2016
Messages
3,636
Location
Claremore, OK
Occupation
Field Mechanic
I just repaired similar issue on an MP8 with alternator belt shredding and getting balled up behind damper and taking crank seal out. The tensioner for the alternator belt had lost a bit of its spring so it was bouncing a bit, you could watch the belt jump a rib on the pulley. It would be out of the groove a rib, then jump back in about every other revolution. Can’t say I had seen that before.

I noticed those pulleys are kinda soft and would be easy to ding. Are there any bad spots? Tensioner bouncing a bit? Even with that big belt it’s asking a lot to run that fan at full rpm if the tensioner isn’t doing its job. The way the ECM controls the fan speed doesn’t help in my humble opinion.
 
Hunter013

Hunter013

Well-Known Member
Joined
Oct 4, 2021
Messages
165
Location
Wisconsin
Occupation
Head Floor Sweeper
Junkyard said:
I noticed those pulleys are kinda soft and would be easy to ding. Are there any bad spots? Tensioner bouncing a bit? Even with that big belt it’s asking a lot to run that fan at full rpm if the tensioner isn’t doing its job. The way the ECM controls the fan speed doesn’t help in my humble opinion.
Click to expand...
I will look a little more extensively, but I couldn't see any bad spots on the pulleys or tensioner. The belt wasn't jumping tension wise and I watched it for awhile and I didn't see it jump between ribs at all.
 
Hunter013

Hunter013

Well-Known Member
Joined
Oct 4, 2021
Messages
165
Location
Wisconsin
Occupation
Head Floor Sweeper
I found the harness part number. 23481456

Could a failing thrust bearing cause the crank pulley to want to pull the belt in a certain direction?
 
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