M1008 Engine Vibration

[pvkj454]

I have a part throttle low rpm vibration that I can't figure out. The truck feels like it has solid motor mounts or an exhaust pipe touching the frame. I replaced the motor and transmission mounts. There is no metal contact anywhere that I can find. The motor idles and revs very smooth. Has anyone else experienced this.
Thanks, Perry.

 

[Recovry4x4]

This may or may not be related but consider changing out harmonic balancer. They are known to SLIGHTLY fail and commence a slight vibration that eventually snaps a crankshaft. I've hear lots of horror stories about this but only fell victim once. Now its at the top of the list on all 6.2L diesels that come my way.

 

[dilvoy]

Hey Perry, I read in a military repair bulletin about the CUCV's having a problem with the left alternator bracket getting loose and at certain speeds putting up a pretty big houl. The problem had a name like "altenator bracket houl" I'm not joking about this" The bulliten said that the left bracket can come loose or crack and the vibration causes the noise. Check your bracket carefully. Since you have not found the cause for the vibration at the obvious places, you may have the dreaded alternator bracket houl. Does your vebration occur in and out of four wheel drive and with the hubs locked and unlocked. I'm thinking that the detroit joint or U joing may be contributing. Also make sure if it is actually freewheeling while in two wheel drive and with the hubs unlocked. George

 

[Txstruck]

Does it happen while just idling or when it is also moving? I know on some Chevy 4x4's, the frame is known to crack where the steering box mounts to the frame. I know it wasnt an issue on the 1 tons due to the frame being thicker.

 

[pvkj454]

The left alternator bracket is tight and I see no cracks. I am not running an alternator on the left side now. The vibration is from the engine and is rpm related, not the drivetrain. It vibrates in neautral or any gear, truck moving or not. The harmonic balancer looks as good as new, no cracked or buldging rubber. I may replace it to be safe. The odometer shows 45,000 now but it appears that the engine has been replaced at one time. The oil pan gasket was leaking so I removed the pan to reseal it. The cylinders had a heavy crosshatch pattern so it looks like a very low mile engine. Nothing I have done has changed the vibration. I installed a set of 6.5 turbo injectors and turned the fuel screw up 1/4 turn. I have a GM5 turbo from a 6.5 and a Duramax intercooler that I will install over the summer, I need to correct the vibration first. One thing that is odd, from the appearance of the bolts, it appears the engine mounting frame brackets have been changed to small block brackets. When I replaced the motor mounts, the 6.2 mounts would not fit. I had to use small block mounts. I wonder if the extra weight of the 6.2 causes metal to metal contact inside the rubber mount.
Thanks.

 

[MV Trucker]

I had a fan clutch go off center, causing vibration in my M1008. The innards kind of came apart from my constant running at highway speeds. Luckily, the assembly did not come completely apart and fly into the radiator.

 

[m1010]

[No message]

 

[mouse]

here is a long shot from a rookie, check fly wheel for cracks by the bolts. first hand knowledge of this( first you get the vibration then later it will sound like a rod knock)as the cracks get larger, the flex plate will move in & out with excelleration