Rattle at highway speed- Engine Governor?

[WildernessJeep]

My 1984 M936 has a terrible rattle at highway speed- but only when the engine is at governor and I go down a slight downhill. At normal cruise it's fine, but when I go to a slight downhill--only enough to put the engine/driveline in a neutral load-- it will rattle like a bunch of bolts in a dryer. If the downhill is steep enough to put negative pressure on the engine, the rattle stops. If I take my foot off the accelerator, the rattle stops. If I do nothing, at the bottom of the hill when the engine resumes a load, the rattle stops. It almost sounds like a bunch of bolts in the torque converter or a driveshaft rattle, from the front or under the cab. I thought it was in the fan belts, but I replaced all those and still have the rattle. I've checked all the driveshafts and u-joints. Anyone got a quick easy fix for me?

Pic for attention. He doesn't even know how to operate that winch (yet).

 

[simp5782]

What is your governor rpm? Or your speed at which this Is happening?

Some pumps are set to 2150, some are 2450, some 2600


Sound like a dieseling sound cause the governor is defueling

 

[WildernessJeep]

What is your governor rpm? Or your speed at which this Is happening?

Some pumps are set to 2150, some are 2450, some 2600.

Governor at 2200, right at 58 mph indicated. I got it up to 61 once and it felt like I was re-entering earth's atmosphere.

Also, re-read my post. I edited to provide more info.

 

[simp5782]

Governor at 2200, right at 58 mph indicated. I got it up to 61 once and it felt like I was re-entering earth's atmosphere.

Also, re-read my post. I edited to provide more info.

On my 816 my front vise rattles the bolts inside the positioning locks when I run it up to speed at times and always on decel.

I have a rattle when the rear PTO is left on and I drive around at speed. I don't ever turn my pto off really it rattles in the rear but it's obvious. Not sure if you have an automatic high idle with your pto or not.

 

[JD4044M]

That sounds like a rod knock to me? The way you describe the noise happening Rods will do that under no load. Lets hope it is not that!!

 

[WildernessJeep]

That sounds like a rod knock to me? The way you describe the noise happening Rods will do that under no load. Lets hope it is not that!!

It sounds too shallow to be that, and I also just had this engine fully rebuilt. It sounds like it is under the cab, not in the engine.

 

[WildernessJeep]

On my 816 my front vise rattles the bolts inside the positioning locks when I run it up to speed at times and always on decel.

I have a rattle when the rear PTO is left on and I drive around at speed. I don't ever turn my pto off really it rattles in the rear but it's obvious. Not sure if you have an automatic high idle with your pto or not.

I do have an automatic high idle with the crane, but I disengaged it at the air piston and control it manually. I drive around with the transfer case on the floor. Never figured out what the upper (above neutral) position does, other than bang my ankle.

 

[charlesmann]

I drive around with the transfer case on the floor. Never figured out what the upper (above neutral) position does, other than bang my ankle.

im betting the tm will say what upper position is. you keep making statements of how, what something is, and 99% can be answered just by reading the tm.

 

[98G]

im betting the tm will say what upper position is. you keep making statements of how, what something is, and 99% can be answered just by reading the tm.

Transfer case lever in the upper position is low range.

Am I missing something?

 

[charlesmann]

Transfer case lever in the upper position is low range.

Am I missing something?

Not missing anything at all.