My new LMTV is blowing water pumps and loosing alternator brackets!

[Coffey1]

Check drive shaft are clocked right. If somebody removed them and didn't put them back correctly they could be off.

 

[Awesomeness]

Thanks for the feedback! Your comment that the truck has "all that noise and vibration" may be a further clue that you do have some underlying issue unique to your truck (considering your results, my comment is "well duh"!). Other than a little drive-line chatter occasionally, mine is not particularly noisy.

Is there an opportunity for you to ride in another FMTV for comparison?

Awesomeness, where did your engine block break?

By noisy I was basically saying that this isn't like my modern daily commuting vehicle, which is quiet enough to hear every little mechanical change. These trucks are so loud you almost have to wear hearing protection, you have people here on SS installing sound insulation in and under the cab, etc.

I drove these in the Army. I had a buddy who was a light wheeled vehicle mechanic in the Army drive mine. I took mine to a professional shop that even has a former USMC truck mechanic, and he drove it and spent 16 hours going over it trying to figure out the problem. Nobody notices anything obvious, and we can't figure out the problem yet. So it's not like I'm a cherry and am just ignoring the huge clunking, it's something much more subtle and difficult to find.

The engine block cracked from the bolts to the transmission, starting from the second bolt up from the oil pan, and the crack propagated forward and down to the oil pan. This happened on both sides, during a single 25 mile drive on non-highway roads (under max speed). It also broke the starter off at the nose during that drive. Afterward, there was a u-joint cap that was loose, but I had checked it for tightness before, so it's unclear if it got loosened by the vibration, or was the cause of the vibration. (The u-joints are something for the original poster to check, I suppose.) The u-joints are currently tight, and I have a new engine, and yet I still recently broke the alternator off again and cracked a transmission line. I don't know if those are residual issues (maybe the line was fatigued from the previous event or I damaged it while changing the engine, or maybe I didn't install the alternator tightly enough and it wiggled loose and was able to flail around and break off), or the vibration issues persist.

 

[Awesomeness]

Check drive shaft are clocked right. If somebody removed them and didn't put them back correctly they could be off.

Is there a process in the manuals for checking/setting the clocking? I know for a fact the driveshafts have been off, so this sounds like a great place to look. I didn't even know clocking them was a thing.

 

[Coffey1]

We pulled drive shafts on my friends truck and he put them back and realised he put them in wrong.
And had to redo them.
I will get him to chime in and tell what he did.

 

[Andyrv6av8r]

The driveshaft yokes, both front and rear have to be lined up or parallel. There isn't a master spline so they can be put in wrong very easily. The front and rear yoke on each driveshaft have to be aligned as you're looking down them, not 90 degrees or whatever from each other. They were supposed to be marked before removal the first time.

 

[Awesomeness]

The driveshaft yokes, both front and rear have to be lined up or parallel. There isn't a master spline so they can be put in wrong very easily. The front and rear yoke on each driveshaft have to be aligned as you're looking down them, not 90 degrees or whatever from each other. They were supposed to be marked before removal the first time.
View attachment 698572

Thanks, I'll check them.

 

[NDT]

Check drive shaft are clocked right. If somebody removed them and didn't put them back correctly they could be off.

Very likely the problem. I have repaired 2 LMTVs that had out of phase driveshafts. It's easy to miss unless you look for it. Sets up brutal torsional vibrations in the driveline depending on how far out of phase they are.

 

[tennmogger]

Awesomeness, your candor in answering my somewhat insinuating questions is appreciated, and extremely enlightening! What if we (yes, me too, more below) are chasing the wrong cause, not a long term vibration but a recurring but specific event.

Does your transmission occasionally slam into gear? Mine does, and my block has an almost identical crack, present when I bought the truck. In addition, my engine's oil pan will not stay sealed, and had been re-sealed before I got it. Have either of your engines had the oil pan resealed?

The suggestion is that a massive torquing event is taking place when the transmission shifts so hard, twisting the engine block, and breaking the cast iron mounting points of the very heavy accessories attached to the engine.

Your broken cooling lines support that theory. If the transmission twists with respect to the front of the engine, the hard lines would be twisted and could break.

Your second failure on a slow drive over a short distance indicates a catastrophic event, not a long term vibration, IMHO.

Of course if that is correct, this torquing event happens over and over again as we drive. In support of reoccurring event, when I removed my oil pan to seal it, I noticed a wear pattern on some pan bolts indicating relative movement between the pan and the skirt of the block. If the block is twisting, the oil pan has to slip, just like a shoe box being twistable, until the lid is put on.

My transmission shifts hard under one major situation: accelerating down hill. If the transmission 'logic' decides to shift when the drive train has slack in it, then BAM, hard shift. Could that slam be the cause of our problem? Maybe that's when the cast iron reaches yield point?

To avoid that hard shift, as soon as the truck will coast on it's own I punch N for neutral and let it coast. The transmission will keep up. You can feel it shift. After reaching 3rd or 4th, I punch D and resume accelerating. Shifting is much smoother in higher gears.

 

[tennmogger]

Graniteclimber, hope this 'slight' deviation from your original water pump issue is ok. The alternator bracket issue you have is similar to Awesomenesses though so all this could be related. ��

 

[Suprman]

Big clunk could be related to a bad motor or trans mount. Hard to tell visually when the truck is sitting.

 

[Awesomeness]

My truck didn't shift too bad previously, when I broke the block and everything. It shifted hard, but just "standard LMTV hard", and mostly just that 2->3 or 3->2 big ratio jump. Now that I've switched engines it does seem to shift hard often, but I haven't figured that out yet. One suggestion I've been given is changes to throttle position sensor or throttle linkage. I also found the old engine speed sensor was damaged (possibly during engine swap or before), and replaced it with a used one from Suprman - I have no current way to verify that it's good/working, and that the trans isn't just doing goofy stuff because it doesn't know what RPM the engine is at. I've also considered putting the trans into calibration mode (which I just discovered in the manual the other day), and seeing if that helps.

I don't think I have hard shifting issues as bad as yours. Mine seem better described as shifting at inappropriate RPMs. For example, it doesn't shift up to 7th until ~50MPH, while the engine is screaming at max RPM, and then it similarly downshifts to 6th at ~50MPH and the engine has to be wound up fast resulting in a jerk.

I did a quick check of the driveshafts (alignment of the two yokes' clocking) today, and the front one is visibly off 10-15°. That one came off when I had it towed to the shop after breaking the starter off and cracking the block. So I have no evidence if it was incorrect before or not. The rear one looks ok, though I have to really get under there with a long straight something tomorrow, to be sure. Step #1 is now to buy a Tiger Tool and correct the front shaft problem.

Anyone know how much it is to have a driveshaft balanced, while I have it/them off?

 

[Awesomeness]

I got my Tiger Tool, and removed the front shaft. Without doing anything, I took it into the driveline shop, and had them check it. They said both u-joints needed replaced, the u-joint cap holes in the yoke have been wallowed out enough that the caps are no longer press fit, and the shaft has 0.055" runout (tolerance is 0.005"). It's $450 of work to fix and balance it, and replace the u-joints.

For information, just a straighten and balance would have been $90 at this place.

 

[freecr]

Also check the alternator mount bracket and the alternator to make sure they "mate" together. Mine had a similar problem and the mechanic said the mount had a cup to it that caused the alternator to work itself loose. That's where the problem started for me.

 

[Awesomeness]

The backward facing part of my alternator mount had a cup worn in it from the roll pin / spacer on the rear ear of the alternator. I had it machined flat again, and I put a washer in between the alternator mount and the ear of the alternator to take up the space (not a big deal, since the roll pin / spacer can float a little and adjust position to match).

I also had the top face of the alternator mount machined flat again, as it had been beat up when the alternator broke loose. Similarly, I made a spacer from a piece of 1/8"x1" steel flat bar.

I replaced all the alternator bolts, and blue Loctited them in.

 

[Duckworthe]

My alternator bracket was missing two bolts when I bought my truck. I replaced them and drive the truck a bit. Rechecked them and one was missing and one was halfway out and the ear was broken off. I made a new l bracket and also welded a gusset on the new bracket on mine to keep the bracket from braking again. I chased the threads in the block and then used red locktite. Since then I've had no problems with it. I am one of those who drive my truck full throttle down the freeway but have not had the water pump issue. I hope I don't ever! Also wanted to add that I've since placed almost 9000 miles on the truck to date.

 

[Aernan]

Belt started squealing. Bolt missing. What size is it?

Also noticed my water pump is not cat yellow. Has some surface rust. Probably replaced recently. I may have the same problem.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[Aernan]

For the life of me I can't figure out how to upload using chrome or safari. The parts diagram shows a small L bracket the top alternator ear goes into. It lists a locknut and a M8 bolt.
43 PAOZZ 19207 12414308-018 NUT,SELF-LOCKING,EX................. 1
44 PAOZZ 19207 12414307-040 SCREW,CAP,HEXAGON H M8 X 1.25 X 40. 1

Does that sound plausible?

 

[Awesomeness]

The water pumps come from CAT unpainted (for whatever stupid reason). So if someone replaced it previously, and was lazy, you'll have that. The can of CAT yellow paint is like $20... I had to buy it to paint mine (and then wait an extra day to install it until the paint dried).

Yes, M8 sounds right. While you're at it, I would replace all the bolts in the alternator bracket (to the block), and that little L-shaped bracket (to the alternator bracket), too. Blue Loctite 243 them. If the bolts got beat up while things were loose, or stretched, you'll have issues with it all coming apart again.

 

[Aernan]

The water pumps come from CAT unpainted (for whatever stupid reason). So if someone replaced it previously, and was lazy, you'll have that. The can of CAT yellow paint is like $20... I had to buy it to paint mine (and then wait an extra day to install it until the paint dried).

Yes, M8 sounds right. While you're at it, I would replace all the bolts in the alternator bracket (to the block), and that little L-shaped bracket (to the alternator bracket), too. Blue Loctite 243 them. If the bolts got beat up while things were loose, or stretched, you'll have issues with it all coming apart again.

Ok that's great advice. I finally found the parts list in the TM so now I can identify the bolt sizes.

Another thing I am considering is using nord lock washers to keep those fasteners in place.

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[Aernan]

The water pumps come from CAT unpainted (for whatever stupid reason). So if someone replaced it previously, and was lazy, you'll have that. The can of CAT yellow paint is like $20... I had to buy it to paint mine (and then wait an extra day to install it until the paint dried).

Yes, M8 sounds right. While you're at it, I would replace all the bolts in the alternator bracket (to the block), and that little L-shaped bracket (to the alternator bracket), too. Blue Loctite 243 them. If the bolts got beat up while things were loose, or stretched, you'll have issues with it all coming apart again.

Where do I get that magic yellow paint?

Sent from my SAMSUNG-SM-G930A using Tapatalk