A few questions about "is this normal for a HMMWV"

[Katavic918]

I recently bought a HMMWV. When I went to pick it it was the first time I have ever even touched one. So as you can tell this is a learning experience from the start. It is a 1991 m998 with a 6.2 and th400 trans. I have been in the mechanical\technical field for 15 years and have a pretty good grasp on was right and what's wrong. That being said, I reasonably believe that everything is operating as it should but there are certain things that I would like to know if they are normal.
1. When I start it whether it is cold or warm there is a surging in the charging gauge. It is a repetitive increase and decrease in voltage. This lasts for about a minute and then like a switch is flipped it returns to a steady voltage.
2. Is it normal for a 6.2 to sound like a sack of hammers. No loud knocking or anything like that but it is a clacky sounding motor. 45 psi oil pressure and no smoke.
3. Is it normal for the back tires to lock up in an emergency stop. I test braked a couple times on a dirt road and the rear tires lock first. It feels like the fronts are doing their job but the rears are locked at the same time.

Thanks a lot for any thoughts.

 

[Havok]

I recently bought a HMMWV. When I went to pick it it was the first time I have ever even touched one. So as you can tell this is a learning experience from the start. It is a 1991 m998 with a 6.2 and th400 trans. I have been in the mechanical\technical field for 15 years and have a pretty good grasp on was right and what's wrong. That being said, I reasonably believe that everything is operating as it should but there are certain things that I would like to know if they are normal.
1. When I start it whether it is cold or warm there is a surging in the charging gauge. It is a repetitive increase and decrease in voltage. This lasts for about a minute and then like a switch is flipped it returns to a steady voltage.
2. Is it normal for a 6.2 to sound like a sack of hammers. No loud knocking or anything like that but it is a clacky sounding motor. 45 psi oil pressure and no smoke.
3. Is it normal for the back tires to lock up in an emergency stop. I test braked a couple times on a dirt road and the rear tires lock first. It feels like the fronts are doing their job but the rears are locked at the same time.

Thanks a lot for any thoughts.

I can say for mine
1) I havent noticed so I can comment
2) seems normal for me in cold weather starts. Anything before 50*F and its a rough idle for a minute or two then its perfectly fine.
3) Yes mine do the same. I don't think the trucks have ABS so that's what i attribute it to but that's my 2 cents. Do you have the rear calipher e-brake?

 

[Katavic918]

1. Its kinda hard to notice but I have bad ocd when it comes to mechanical things.
3. Definitely no abs. I would imagine that the brakes were balanced using the rated 2500lb load in the back so that might have something to do with it. Caliper style ebrake.

 

[dilvoy]

Sounds like your truck is working as designed. The glow plugs cycling are causing the voltage drop when started. You might watch for leaks at the geared hubs. These are the most weird thing on this vehicle that most people won't be familiar with, unless they have have worked with farm equipment and other big vehicles. The output seal is where the big leak will be as it is lowest and you might first notice a leak when you see oil on the back side of the wheel rim or that side of the tire. You might actually change out the oil in all four hubs, because they can get water in them. They are a very reliable part, but they need oil. There is a drain plug at the under side of each hub, which can be super difficult to remove so maybe you can open the fill plug and get one of those oil suckers and suck the old oil out.

 

[Cape Coastie]

Don't have one but have worked on several boats with the same engines and the voltage cycling may be the glow plugs completing their cycle then shutting off. Just my 2 cents as to what I have seen in similar set ups.

 

[patracy]

Mine does the afterglow as well, cycling the plugs on and off. 6.2's and 6.5's are a noisy engine. And I've never done a panic stop in mine, but I'd suspect it would lock the rears first. (lightweight on rear)

 

[Katavic918]

Thanks for all the insight from everyone. It seems like everything is in order.

 

[2w091]

[QUOTE3. Is it normal for the back tires to lock up in an emergency stop. I test braked a couple times on a dirt road and the rear tires lock first. It feels like the fronts are doing their job but the rears are locked at the same time.
][/QUOTE]

The answer to that is a very large YES!

I learned via on the job training while driving in the snow and ice, sliding sideways down a hill (in the middle) on a four lane road. Luckily I was the only one on the road while learning this valuable lesson, since the turning radius isn't that great, steering into it just made it more "interesting".

 

[desmodromic]

[QUOTE3. Is it normal for the back tires to lock up in an emergency stop. I test braked a couple times on a dirt road and the rear tires lock first. It feels like the fronts are doing their job but the rears are locked at the same time.
]

The answer to that is a very large YES!

I learned via on the job training while driving in the snow and ice, sliding sideways down a hill (in the middle) on a four lane road. Luckily I was the only one on the road while learning this valuable lesson, since the turning radius isn't that great, steering into it just made it more "interesting". [/QUOTE]

Ha, yah, I will emphatically 2nd the above feedback. I came into a sharp left-hand turn a little to hot on wet conditions and the mv locked right up and the ass end swung around quick. I immediately let off thr brakes, but loss of traction on all four tires continued for some time possibly due to engine breaking. I did my worst Ken Block impression to counter-steer and power-slide through the turn, and I may or may not have used both lanes

As I keep telling my wife, all those years of testing the limits of vehicle in "high school" have "prepared" me for situations like these.

I have read that these things are a handful in the snow/ice. Are the MTRs beterr or worse than the Bajas on road?

 

[2w091]

Yes they are a handful in snow/ice, the main problem is the rear locking up first, even when pumping the brakes to avoid locking the tires up. I'm an LEO and we use ours almost exclusively in bad weather, so I've had plenty of practice. All vehicles suck on ice, the HMMWV is no different, just a bit worse. I can't speak to specific tires, we have the Wrangler MT's, I really don't think it would make much of a difference for our uses. We have a major highway interchange and lots of hills, I spend the majority of time pulling cars/trucks out of the ditch when it snows, they work well for that.

 

[juanprado]

Yes they are a handful in snow/ice, the main problem is the rear locking up first, even when pumping the brakes to avoid locking the tires up. I'm an LEO and we use ours almost exclusively in bad weather, so I've had plenty of practice. All vehicles suck on ice, the HMMWV is no different, just a bit worse. I can't speak to specific tires, we have the Wrangler MT's, I really don't think it would make much of a difference for our uses. We have a major highway interchange and lots of hills, I spend the majority of time pulling cars/trucks out of the ditch when it snows, they work well for that.

Thank you for your service!

 

[bikeman]

Every HMMWV I had, especially in the colder weather, would have the volt meter surge during start up. I always took that as the "walk around, check lights" portion of PMCS. I wouldn't allow my driver, or drive, until the truck had settled, and that was one of the indicators.

 

[Awol]

I have MT/Rs on my F350, and they're not too fun in hard packed snow / ice conditions. I went to make a left hand turn, but the truck kept going straight lol

 

[2w091]

View from the office on snowy days, could be a lot worse places.
Although the heater is modified with "surplus" wife's vacuum cleaner hose for drivers heat.............

 

[snowtrac nome]

yes the brakes are intended for full load, so with no weight expect rear lock up. also don't deaccelerate through high speed corners ,slow down first than lightly accelerate, that was the most common reason for roll overs as the rear wheels tuck in as the rear raises and the front drops with hard breaking.

 

[lindsey97]

I do not own a military hmmwv, nor have I driven one; but I could imagine that if you are braking hard or suddenly, and combined with limited traction or slick road surface, that the rears would lock/slide first, because when you brake hard weight transfer occurs from rear of the vehicle to the front. With almost all vehicles, 80% of your braking capability is on your steer axle, braking systems are designed this way because of the very simple fact that weight transfer occurs when braking.

Exceptions to this would be having cargo in the back over the rear axle, or pulling a trailer matched to your vehicle with the correct amount of tongue weight. My advice would be to temporarily air down your tires during snowy weather, keeping your ground speed slower as to not damage your tires. Or add some weight to the rear of the hmmwv to aid in traction and braking.

Older GM pickups had a proportioning valve installed in the rear brake line, that attached to the rear axle, and limited the amount of brake fluid flow as the rear of the pickup rose up during hard braking. This would keep the rear axle tires from locking up during hard braking, and minimize the possibility of a skidding rear axle, leading to loss of control.