Rpm

[Unimog66]

I have a m1084 and I was wondering if when I am driving if it is normal for the rpm to be around 2300

 

[NDT]

At 55 mph yes unfortunately. ECO hubs is the solution to this.

 

[GeneralDisorder]

I have a m1084 and I was wondering if when I am driving if it is normal for the rpm to be around 2300

Yes. 7.8:1 final drive with the hub reductions. And it destroys the engines, transmissions, drivelines, etc. All that junk is turning 120 mph equivalent at 60 mph road speed. That's why the military's testing showed a MTBF of ~35,000 miles. And they are perfectly OK with that. If you aren't I suggest you get some ECO hubs and cut the RPM in half. Drivetrain longevity reduction is not linear with RPM - it's exponential.

 

[MatthewWBailey]

I had 12,767 miles on the truck before the ECO. Midwest put "Highway gears" (3.07) in there at 9,300 miles which is when I bought it. I'm at 14,600 now. Good thing I did this big overhaul bc the rear U joints have visible movement when you shake them. I'd not have caught that without all the discussion here about driveline wear. The rear ujoint easily has > 1/16" of play that I can see, real loose. Only the front one at the transmission is tight. I'd like to see some examples of driveshaft hoops bc those broken ujoint stories are scary.

 

[GeneralDisorder]

I had 12,767 miles on the truck before the ECO. Midwest put "Highway gears" (3.07) in there at 9,300 miles which is when I bought it. I'm at 14,600 now. Good thing I did this big overhaul bc the rear U joints have visible movement when you shake them. I'd not have caught that without all the discussion here about driveline wear. The rear ujoint easily has > 1/16" of play that I can see, real loose. Only the front one at the transmission is tight. I'd like to see some examples of driveshaft hoops bc those broken ujoint stories are scary.

Yep. If you are keeping the hub reductions (especially the LMTV with the low pinion diff) you need to change the u-joints every 15k miles, and grease them every 3-5k miles. You can probably double that with the ECO hubs but the low pinion 4x4's shouldn't go over 30k even with ECO hubs IMO. The driveline angles are too steep. The front isn't great either but the big issue is that rear low pinion at the diff. Only the MTV and the high pinion LMTV are setup for less pucker factor once you drop the hub reductions. Meritor has lost their damn minds claiming "100,000 mile" greasing interval on the box. Sure - grease them every 100,000 - so long as you replace them every 15,000.

 

[Ronmar]

Yea, at these angles and RPM's the shafts must be perfect, considering a failure typically wipes out the transfer case at the minimum. This is especially true for the rear, as it is at the maximum length of 61" for the type 16 driveshaft, so suffers from maximum longitudinal vibrations already. Eco hubs at least brings them back onto the allowable RPM/angle chart at highway speed...

 

[MatthewWBailey]

This might be a duh, but when I look at that rear axle, my first thought is why isn't there an angle wedge under the leaf stack? Seems like you could add a few degrees of upward angle with very little modification. Is that something that anyone has tried or looked at?

 

[Ronmar]

This might be a duh, but when I look at that rear axle, my first thought is why isn't there an angle wedge under the leaf stack? Seems like you could add a few degrees of upward angle with very little modification. Is that something that anyone has tried or looked at?

running different pinion angles between input and output flanges is considered bad juju...

 

[GeneralDisorder]

This might be a duh, but when I look at that rear axle, my first thought is why isn't there an angle wedge under the leaf stack? Seems like you could add a few degrees of upward angle with very little modification. Is that something that anyone has tried or looked at?

That would actually make it worse. The way u-joints work - at anything other than zero angle they don't rotate with constant velocity (thus the differentiation between a u-joint and any of the "CV" or Constant Velocity joints). As they rotate through 360 degrees they speed up and slow down and the only way to counteract that is to put a CV at one end or if the other end is a u-joint it has to be within a degree or two of being the equal but opposite angle so the differences in velocity line up as they rotate. Otherwise it will tear them apart and you will get horrific vibration.

 

[MatthewWBailey]

That would actually make it worse. The way u-joints work - at anything other than zero angle they don't rotate with constant velocity (thus the differentiation between a u-joint and any of the "CV" or Constant Velocity joints). As they rotate through 360 degrees they speed up and slow down and the only way to counteract that is to put a CV at one end or if the other end is a u-joint it has to be within a degree or two of being the equal but opposite angle so the differences in velocity line up as they rotate. Otherwise it will tear them apart and you will get horrific vibration.

I remember being been told that before at some point. Makes sense as you explain it.