Various M998A1 gremlins

[claptonisgod]

I just had my 1994 M998A1 delivered this morning, after three years of it vacationing with a relative across the country (didn't have the space before now, he did). I'm painfully remembering that it has a range of minor issues, so I was wondering if anyone might be able to help with a general diagnosis so I have an idea of what I'm dealing with when I get in touch with a mechanic/try to tackle things myself.

Issue 1: Lights. The turn signals/hazards/horn only work when the switch is in "stop light" position (except for the left rear, which only comes on as steady burn). The headlights work in "service drive," but the foot switch turns them on and off instead of high beams and the turn signals, hazards, and horn do not work in this mode (indicator light on turn stick doesn't even come on, but the signal lights/tail lights/clearance lights do come on steady). I was driving the truck probably two years ago and the lights all functioned properly, but the light switch broke in the on position and I panicked, afraid I'd not be able to turn the lights off and kill the batteries. Because of my panic, I decided to remove the light switch while they were on before disconnecting the batteries, so I'm guessing I shorted something out. I guess the question here is where would something have shorted out to produce these issues?

Issue 2: When the truck first starts, and I turn the lights on, it surges for about the first minute or so of running. The volt meter moves around in unison, and all of the lights dim, then go back to normal bright, and keep going and it makes some kind of sound that matches this variation. It happens every time I start the truck, no matter if it's been running minutes before. Is this a generator issue? When I had to settle for bringing it to a Chevrolet dealer for basic fluid services, the mechanic said that the generator may be on the way out, so I'm wondering if a bad generator lines up with this issue.

Issue 3: Wipers. They didn't work when I bought the truck, the switch on the motor housing does nothing. I did buy a new one and tried plugging it into the wiring, but I don't think it did anything. Assuming the issue wasn't two bad wiper motors, where would the next place from there be to go look for faults?

Issue 4 (or I'm stupid): Two-part issue here. I was backing the truck into the garage, and the garage has probably a two or three inch height difference with the ground. Obviously it took a little extra gas to get it up and over, but when I was playing with the gas to ease it in, it stalled to a shutoff. Started back up with no issues when I put it in neutral and I got it in, but I've never experienced this before and wonder if I should be concerned. Lastly, after I stalled I figured I should try putting it in low gear, but when the transmission was in neutral the transfer case was grinding when I attempted to shift. Do you have to shut the truck off to change the transfer case? I shut it off and put it in low and started it back up, but unless I messed up the shift and thought I was in a range when I was in neutral (it was late, dark and cold), it wouldn't move in low. Could this be a linkage issue?

I'm sure these are all relatively amateur questions to be asking, but I'm evidently not the most mechanically inclined and want to understand my truck's issues as much as I can. Thanks.

Update edit: I found flasher units online, should my issues be fixed if I replace the truck's? Not sure if this would fix the horn/headlight issues though. Also found that the TM advises shutting engine off before transfer case shift, but not sure this resolves the low not seeming to work issue.

 

[Skinner23]

I’ll be following to see what people say about Issue #2. Mine does the same thing and sometime surges while driving around. I’m currently going through all my connections to make sure I don’t have any loose wires causing grounding issues.


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[claptonisgod]

Glad I'm not alone, my gut says generator but who knows. Also, does anyone have the screw size for soft door handles handy? When I went to close the door after it got off the truck the handle fell apart, I saved everything except the screw I think (I still have both sides of the handle and the spring).

 

[wheelspinner]

Issue #2 sounds like afterglow. Its completely normal. The glowplugs cycle for a minute or two and the lights will dim and the engine surges.

 

[98G]

#2 is likely glow lugs cycling.

edit - I now see that wheelspinner beat me to it

 

[Skinner23]

Mine will surge after letting it warm up and them 10 minutes down the road do it again and then again and then again. I’ve blown multiple tail lights because of it. When I say surge I don’t mean the needle is a little in the red, its pegged in the black!

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[Skinner23]

wheelspinner, does what I described sound like the afterglow you described?
Thanks for the feed back it’s good hearing from you!



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[claptonisgod]

Would replacing the glow plugs fix it? It didn't do it when I first got the truck.

 

[Skinner23]

My glow plugs and controller for them are less than a year old.


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[3jacks]

Your grinding issue:
TM 9-2320-280-10. Paragraph 2-11
Vehicle must be stopped, engine off, and transmission shift lever placed in “N” (Neutral), before transfer case can be shifted. Failure to do this will result in damage to drivetrain.

 

[claptonisgod]

Your grinding issue:
TM 9-2320-280-10. Paragraph 2-11
Vehicle must be stopped, engine off, and transmission shift lever placed in “N” (Neutral), before transfer case can be shifted. Failure to do this will result in damage to drivetrain.

Thanks, I found that shortly after I posted so that's what I'll do from now on. If the low doesn't work, I'll just assume I either have it in the wrong place or the shift connection is bad. Have to say I'm a little surprised and disappointed in AM, as every other manual 4WD I've driven (even my 1947 Willys) will allow you to shift when the trans is in neutral. I was happy to see the ignition has the in-gear safety, since once when I was working on my Willys the ignition circuit somehow got completed while it was parked in first and the starter kept turning and made it buck forward a half a foot slowly into a wall. Got insanely lucky, as I was walking in front of it about twenty seconds before it happened. On a somewhat unrelated transfer/transmission question, is it normal to have a slight clunk between drive and reverse? I stop for a good five seconds in neutral on either way, but still clunks and jumps a bit. I'm guessing this is just a reality of a military transmission, but figured I'd ask. Thanks again.

 

[98G]

wheelspinner, does what I described sound like the afterglow you described?
Thanks for the feed back it’s good hearing from you!

That's not afterglow. That sounds like a voltage regulator failing.

Do you have a grounding kit on your truck?

 

[3jacks]

Thanks, I found that shortly after I posted so that's what I'll do from now on. If the low doesn't work, I'll just assume I either have it in the wrong place or the shift connection is bad. Have to say I'm a little surprised and disappointed in AM, as every other manual 4WD I've driven (even my 1947 Willys) will allow you to shift when the trans is in neutral. I was happy to see the ignition has the in-gear safety, since once when I was working on my Willys the ignition circuit somehow got completed while it was parked in first and the starter kept turning and made it buck forward a half a foot slowly into a wall. Got insanely lucky, as I was walking in front of it about twenty seconds before it happened. On a somewhat unrelated transfer/transmission question, is it normal to have a slight clunk between drive and reverse? I stop for a good five seconds in neutral on either way, but still clunks and jumps a bit. I'm guessing this is just a reality of a military transmission, but figured I'd ask. Thanks again.

I’ve gotten lazy with modern trucks...shifting from rev to D while not fully stopped, flipping I‎t in drive a little carelessly etc. when that spills over to my MV I get a “clunk” but properly operating i don’t get much of it. Is I‎t noticeably different than my daily driver truck? Yup but maybe I’ve just gotten used to I‎t in MV so I’m not noticing I‎t like I‎t was ‘new to me’.

Im quite thankful for the neutral start switch because i often put I‎t in Rev when parked in public. I do this because some idiot might try to steal I‎t and not know to shift down put I‎t in neutral...and i sometimes forget its in Rev and I try to start I‎t.

 

[Bulldogger]

Glad to hear you're back in the saddle...

Issue 1: Sounds like the lighting control panel/switch is malfunctioning. Not an unusual problem, as there are a lot of contacts in there. Many have disassembled and cleaned them with good results. I would recommend you try. Do take care when taking it apart as there are a lot of contacts and some small springs in there. Try not to dump them all out!

Issue 2: This sounds like normal glow plug cycling, with one added unusual condition. The surging is the control box pulsing power to the glow plugs to help get the engine running well quickly. However, you state that it happens all the time, regardless of engine temperature. This should not be the case. Either your control box is malfunctioning, or your temperature sensor is, so the control box doesn't know the engine is hot. I'd check connections to the temp sensor first. New control boxes can be had, and there are some good recent threads about new boxes that are apparently the cat's meow. I'm lucky I haven't had to worry about my box. Disconnect the batteries before fiddling with a control box, it hates to be messed with when power is available. Temp sensor not to finicky.

Issue 3: Most common cause is either the on/off knob itself or the power wires. The wires supplying power run up under the windshield and can get chafed or pinched along the way. The sad part about that it you have to drop the windshield to inspect them. I am glad I never had to do that, though it is not terribly complex to do. Test for power at the wires just under the motor up on the top center of the windshield, using a needle probe or some such to punch straight into the wire if you can't find a disconnect to get into. Since these wires are interior, a small prick shouldn't be a big deal to reliability. You need to find out if power is being supplied. If it is, they dig into the on/off rotary switch next.

Issue 4: Speed stall, crash stall or some such. My truck was doing this; after a surge on the fuel pedal it didn't return to proper idle, but crash stalled instead. In my case this was simply a tired and dirty injection pump, which is one of the most common causes of this behavior. A few tankfuls of Stanadyne Performance blend made an instant change, and after two tanks of fuel my rig has never crash stalled again. Any good diesel injection system cleaner will help, I like the Stanadyne Performance because it contains all other useful additives such as anti-gel and so on. I hope I did not ignite another debate on which one is better... Just get a good fuel system cleaner and drive her hard to get plenty through the system.

Issue 4b: Shifting the transfer case must be done with authority, you can't ease through the settings, give it a good firm push. Don't yank or jerk, but move it with a purpose of moving it. Otherwise yes it will grind. You can cheat and shift with the motor off, I used to until somebody noted to me that it can be switched while running as long as the trans is in neutral. Some shift nicer than others, mine is not nice but I've now shifted many many times without incident, so I believe in it. It is easy to miss the shift points on the T case, and the labels on the shift plate get worn and aren't totally accurate. The correct setting is wherever it works! You have to play with it until you get the feel. It is an unusual action for anyone not used to heavy equipment and shifting transfer cases. I doubt your low gearing is bad, but of course it could be. Practice shifting and so on before allowing suspicions to creep in about the T case itself.

As to the flasher, replacing it might work but first I'd trace the circuit for all the problems. Brake light switches tend to go bad frequently, as do horn buttons and so on. Just start following the wires and trace the 24V positive power to each item. Test switches for continuity when pressed/moved, you will find the problems in due course. A lot of the problems our trucks have is from sitting, once a switch gets dirty or jammed up, it has to be freed before it will work correctly, and then as long as it's driven routinely the problems stay away.

You don't mention your grounding harness or if you've added a supplemental harness. It is strongly recommended and there are a few threads here about it. As a temporary solution, before you go through your wiring harness to trace +24V power to your bad switches and lights, first disconnect the batteries and trace through your ground wires. Loosen, clean and tighten every ground wire. You don't need to check them for continuity, just clean and tighten their fittings. Then reconect the batteries and start walking through your 24V+ circuits. Some of your problems will go away simply due to cleaning up your grounds, it is all but guaranteed that you have a couple of loose grounds in the harness. The grounding issue is a common failing of the design and is why many of us throw together or buy a supplemental harness. Do disconnect the batteries before you work on the grounds, so as to not send on/off power surges through the system.

I hope the above helps. If nothing else it will keep you from wandering the streets for a few hours!


Bulldogger

I just had my 1994 M998A1 delivered this morning, after three years of it vacationing with a relative across the country (didn't have the space before now, he did). I'm painfully remembering that it has a range of minor issues, so I was wondering if anyone might be able to help with a general diagnosis so I have an idea of what I'm dealing with when I get in touch with a mechanic/try to tackle things myself.

Issue 1: Lights. The turn signals/hazards/horn only work when the switch is in "stop light" position (except for the left rear, which only comes on as steady burn). The headlights work in "service drive," but the foot switch turns them on and off instead of high beams and the turn signals, hazards, and horn do not work in this mode (indicator light on turn stick doesn't even come on, but the signal lights/tail lights/clearance lights do come on steady). I was driving the truck probably two years ago and the lights all functioned properly, but the light switch broke in the on position and I panicked, afraid I'd not be able to turn the lights off and kill the batteries. Because of my panic, I decided to remove the light switch while they were on before disconnecting the batteries, so I'm guessing I shorted something out. I guess the question here is where would something have shorted out to produce these issues?

Issue 2: When the truck first starts, and I turn the lights on, it surges for about the first minute or so of running. The volt meter moves around in unison, and all of the lights dim, then go back to normal bright, and keep going and it makes some kind of sound that matches this variation. It happens every time I start the truck, no matter if it's been running minutes before. Is this a generator issue? When I had to settle for bringing it to a Chevrolet dealer for basic fluid services, the mechanic said that the generator may be on the way out, so I'm wondering if a bad generator lines up with this issue.

Issue 3: Wipers. They didn't work when I bought the truck, the switch on the motor housing does nothing. I did buy a new one and tried plugging it into the wiring, but I don't think it did anything. Assuming the issue wasn't two bad wiper motors, where would the next place from there be to go look for faults?

Issue 4 (or I'm stupid): Two-part issue here. I was backing the truck into the garage, and the garage has probably a two or three inch height difference with the ground. Obviously it took a little extra gas to get it up and over, but when I was playing with the gas to ease it in, it stalled to a shutoff. Started back up with no issues when I put it in neutral and I got it in, but I've never experienced this before and wonder if I should be concerned. Lastly, after I stalled I figured I should try putting it in low gear, but when the transmission was in neutral the transfer case was grinding when I attempted to shift. Do you have to shut the truck off to change the transfer case? I shut it off and put it in low and started it back up, but unless I messed up the shift and thought I was in a range when I was in neutral (it was late, dark and cold), it wouldn't move in low. Could this be a linkage issue?

I'm sure these are all relatively amateur questions to be asking, but I'm evidently not the most mechanically inclined and want to understand my truck's issues as much as I can. Thanks.

Update edit: I found flasher units online, should my issues be fixed if I replace the truck's? Not sure if this would fix the horn/headlight issues though. Also found that the TM advises shutting engine off before transfer case shift, but not sure this resolves the low not seeming to work issue.

 

[Skinner23]

That's not afterglow. That sounds like a voltage regulator failing.

Do you have a grounding kit on your truck?

Thanks! Yes I have a grounding kit. Previous owner put it on though. I’ve got one more connection to check and make sure it’s tight and secure. Ran out of time going through it yesterday.


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