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Strange sound coming from rear end

o1951

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If you have experience, you can feel .020. I'd be prying a bit with a long screwdriver or rod to put a little pressure on them.

I did not have fancy equipment. I found vibrations by first bringing engine up to highway speed in neutral. If no vibration, then the engine, flywheel, damper pulley and accessories were probably OK.

Next step was to jack up the vehicle and solidly support it on suspension as close to the wheels as possible, so the suspension was as close as possible to normal ride height. I would quickly bring the drive train up to speed and then take my foot off, reversing the loadings. That would tell me if the vibration was caused by worn U joints, a bad pinion bearing, or out of balance tire or bent wheel.

If I did not find anything, I would remove wheels, put lug nuts on backwards to secure brake drums or rotors and try again. That would tell me if a drive shaft, or half shaft was out of balance.
 

INFChief

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Let’s revive this but add a twist.

Haven’t been driving the truck much but It started noticing a “thump” like you would get driving over the expansion joints on a concrete slab highway. Today the truck has a noticeable “quick shimmy / bounce” at the same time.

I recently greased all fittings and noticed 2 broken off in the intermediate drive shaft (nearest the diff pinion). I also noticed a ding & scuffing in the drive shaft. Several weeks ago while I was underneath checking things out I noticed that it looked like it has a new transmission. I also checked and changed both diff oils. There was sludge on the drain plugs but no pieces or chunks. I have no reason at the moment to suspect the differentials or hubs.

Between the new tranny and the dinged drive shaft I reckon something gave way - who knows what caused what but that’s not important. It does make me suspect a bent drive shaft - but this only started 2 short trips ago.

I looked at the torque rods and shocks and they look fine. I’ve got the more aggressive tires on it and I suppose one of those could be causing the thump, and now vibration.

I called a driveline company close by and they can check, repair, and balance. I will be removing the shaft and taking it down next week.

What I’m looking for from this group are some insights & pointers of what else might be causing this?

TIA
 

GeneralDisorder

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The driveshafts turn at a pretty high rate - remember with the 2:1 reduction hubs the driveshafts are spinning at twice the speed of a normal truck with 3.90 gears. So given that statement - do you believe the thump/shimmy/bounce is at the frequency of the drivelines, or at the frequency of the tires?

By "more aggressive" do you mean the Michelin XML or the Goodyear MVT?

The MVT is significantly better all-around. Thus why the military switched to them.
 

Wingnut13

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I’ve got the very same issue with a vibration, which seems to be on the front end. Not much noise until you unload the driveline at around 35-40. Everything greased, u joints seem ok, haven’t had the driveline balanced yet. But when I first got the truck the front driveshaft was out of phase.
 

GeneralDisorder

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I’ve got the very same issue with a vibration, which seems to be on the front end. Not much noise until you unload the driveline at around 35-40. Everything greased, u joints seem ok, haven’t had the driveline balanced yet. But when I first got the truck the front driveshaft was out of phase.
I would absolutely address this - S&S/BAE had to put nord-lock washers on everything (A1+) attached to the engine to prevent "normal" vibration from causing every bolt to back out. If there is any question about driveline balance I would pull them and have them completely serviced.
 

INFChief

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The driveshafts turn at a pretty high rate - remember with the 2:1 reduction hubs the driveshafts are spinning at twice the speed of a normal truck with 3.90 gears. So given that statement - do you believe the thump/shimmy/bounce is at the frequency of the drivelines, or at the frequency of the tires?

By "more aggressive" do you mean the Michelin XML or the Goodyear MVT?

The MVT is significantly better all-around. Thus why the military switched to them.
I first put this truck on the road a few weeks ago & have only gone on very short trips. This happened rather suddenly & coincidentally occurred right after I changed diff oil and greased up the U-joints. I’ve worked in a variety of vehicles over the years and am pretty mechanically inclined - but am a complete newbie to FMTV’s. That said, anything that suddenly pops up normally isn’t a coincidence.

I have the Michelin XML’s on it right now. Good point about driveshaft speed. It seems to ‘bounce’ with tire rotation versus drive shaft. The bounce is almost like the truck is being lifted up - which made me think I had a tire issue. But again, can these tires cause a sudden bounce onset?

I’ll also double check the phasing of the drive shaft; I most likely only glanced at it. I’ll also check the torque rods on the left side and look at that wishbone torque rod thing above the rear axles. I suppose the issue could be on the left side and transmits to the right. Kind of like noises and leaks.

Thanks for the insight - I’ll try to keep everyone posted in hopes that any new info I provide will help narrow down the culprit (s).
 

INFChief

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I’ve got the very same issue with a vibration, which seems to be on the front end. Not much noise until you unload the driveline at around 35-40. Everything greased, u joints seem ok, haven’t had the driveline balanced yet. But when I first got the truck the front driveshaft was out of phase.
I’ll certainly take a closer look at the drive shafts. Other than greasing them I only gave them a passing glance.
 

INFChief

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Location
New York
I would absolutely address this - S&S/BAE had to put nord-lock washers on everything (A1+) attached to the engine to prevent "normal" vibration from causing every bolt to back out. If there is any question about driveline balance I would pull them and have them completely serviced.
What’s a nord-lock; a split lock washer or tabbed lock plates? I’ll trust a Google search might help me there! lol

You recommend I pull the drive shafts and have them serviced? I have seen several posts about getting them balanced but up until now I didn’t latch on to that. I figured since there was no issue I would work through more pressing maintenance items and do that after I swap out all 6 wheels / tires to the less aggressive tread.

TomTime lives fairly close and he and I talk fairly regularly. I believe he said he had all of his drive shafts checked & balanced and one repaired. Tom has put a LOT of time in to researching and checking various common maintenance issues that people have encountered. I’ve seen his truck; it looks spectacular! For my truck, it looks like the drive shafts & tires have become an immediate maintenance item and the next thing for me to tackle.

Thank you for the tips. I’ll try to share anything else I find in hopes those bits might be better clues to what’s going on.
 

o1951

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You said
" I recently greased all fittings and noticed 2 broken off in the intermediate drive shaft (nearest the diff pinion). I also noticed a ding & scuffing in the drive shaft. I noticed that it looked like it has a new transmission. "

I would be looking at driveshaft. Best would be to pull them and take to shop. May only be busted needles in a dry U joint .

Perhaps there was an impact that tore bottom of trans, busted grease fittings and dented/ scuffed driveshaft. Op does not know lube is gone, and keeps going until trans is FUBAR. Most expedient repair is to swap in another trans and sell truck.
 

INFChief

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Location
New York
You said
" I recently greased all fittings and noticed 2 broken off in the intermediate drive shaft (nearest the diff pinion). I also noticed a ding & scuffing in the drive shaft. I noticed that it looked like it has a new transmission. "

I would be looking at driveshaft. Best would be to pull them and take to shop. May only be busted needles in a dry U joint .

Perhaps there was an impact that tore bottom of trans, busted grease fittings and dented/ scuffed driveshaft. Op does not know lube is gone, and keeps going until trans is FUBAR. Most expedient repair is to swap in another trans and sell truck.
My gut was telling me that but I was second-guessing. Turns out the drive shaft IS out of phase. Going to pull the drive shaft & take it in.

You’re right about everything! Thanks for the input, much appreciated!
 

GeneralDisorder

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They are used all over the engine accessories, brackets, etc. The support bracket for the compressor/power steering pump, the alternator - in fact the long pivot bolt on the bottom of the alt - they used a Nord-Lock under the head of the bolt AND under the nut on the opposite side.

Seen a truck where PVT Snuffy changed alt three times due to the upper mounting bolt backing out because the Nord-Lock was lost and the bolt worked loose and wrecked the threads on two alternators. Of course the Army just orders another alt - no one orders the correct washer because no one in Motorpool understands what's happening or how to fix it - or for that matter how to do a thread repair and not have to replace the $2,600 alternator. 🤦‍♂️
 

INFChief

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Location
New York

They are used all over the engine accessories, brackets, etc. The support bracket for the compressor/power steering pump, the alternator - in fact the long pivot bolt on the bottom of the alt - they used a Nord-Lock under the head of the bolt AND under the nut on the opposite side.

Seen a truck where PVT Snuffy changed alt three times due to the upper mounting bolt backing out because the Nord-Lock was lost and the bolt worked loose and wrecked the threads on two alternators. Of course the Army just orders another alt - no one orders the correct washer because no one in Motorpool understands what's happening or how to fix it - or for that matter how to do a thread repair and not have to replace the $2,600 alternator. 🤦‍♂️
I Googled them. Pretty nifty.
 

INFChief

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Location
New York
The drive shaft is out of phase. See pictures. You can also see the damage that occurred way back and for whatever reason. The new scars are from me trying to jockey it around to get access to remove the u-joints.

I don’t have any-joint puller and I don’t like the idea of using a Jack. So I improvised and used a 2 jaw puller. Since the u-joint is getting replaced anyway I removed the 2 retainer bolts then knocked off the security cap off. Put the puller on it and pushed it clear.

The front u-joint caps slid out without any serious effort.

The two pictures that have the larger scars are on the same end just 180 degrees opposite.

Off to the drive shaft shop they are open.
 

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INFChief

Well-known member
721
1,344
93
Location
New York
The drive shaft is out of phase. See pictures. You can also see the damage that occurred way back and for whatever reason. The new scars are from me trying to jockey it around to get access to remove the u-joints.

I don’t have any-joint puller and I don’t like the idea of using a Jack. So I improvised and used a 2 jaw puller. Since the u-joint is getting replaced anyway I removed the 2 retainer bolts then knocked off the security cap off. Put the puller on it and pushed it clear.

The front u-joint caps slid out without any serious effort.

The two pictures that have the larger scars are on the same end just 180 degrees opposite.

Off to the drive shaft shop they are open.
This picture didn’t make it in the previous post. It shows how far out the u-joints are from being in phase.
 

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INFChief

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Location
New York
Got the driveshaft balanced with 2 new u-joints; no change. Will be getting the other 2 balanced.

My wife drove it home from a parade we participated in and I followed in my truck. I could not see anything happening.

I told TomTime that the ABS light recently started coming on. It goes out after I stop the truck and shut the engine off then restart it. That got me wondering if a brake shoe or brake shoe adjuster or a brake shoe anchor / guide might be getting hung up some how.

I’ll get the other 2 shafts balanced and in the very near future pull the brake drums (starting at the right rear) and begin to remove, inspect, clean, and re-lube the brake adjusters.

Like most of you I’ve got too many projects going on. I need to get the siding finished on the rear of my house done!
 

MrMikey4026

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The maximum working angle for a ujoint should not exceed 4 degrees. When I measured mine they are easily double that. Because of the excessive angles on the ujoints, as the drive line rotates the drive line minutely speeds up and down twice per revolution. The opposing angle on the opposite ujoints is supposed to help cancel out the speed changes. They really cannot cope with angles this severe.
The speed changes on the drive lines cause the gears to rattle, they all have to have an operating clearance. It is less noticeable when cold because the gear oil is much thicker when cold. This will never be completely solved unless all of the driveline angles are corrected. Some of this was cured with the A1R trucks, at least on the rear axle. Can someone that has one post a picture of the 4x4 axle?
The 6x6 has much improved angles also. All suffer from bad driveline angles on the front shaft.
 

INFChief

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Location
New York
The maximum working angle for a ujoint should not exceed 4 degrees. When I measured mine they are easily double that. Because of the excessive angles on the ujoints, as the drive line rotates the drive line minutely speeds up and down twice per revolution. The opposing angle on the opposite ujoints is supposed to help cancel out the speed changes. They really cannot cope with angles this severe.
The speed changes on the drive lines cause the gears to rattle, they all have to have an operating clearance. It is less noticeable when cold because the gear oil is much thicker when cold. This will never be completely solved unless all of the driveline angles are corrected. Some of this was cured with the A1R trucks, at least on the rear axle. Can someone that has one post a picture of the 4x4 axle?
The 6x6 has much improved angles also. All suffer from bad driveline angles on the front shaft.
Do you know the process for correcting the DL angle - if it’s off?
 

coachgeo

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North of Cincy OH
The maximum working angle for a ujoint should not exceed 4 degrees. When I measured mine they are easily double that. Because of the excessive angles on the ujoints, as the drive line rotates the drive line minutely speeds up and down twice per revolution. The opposing angle on the opposite ujoints is supposed to help cancel out the speed changes. They really cannot cope with angles this severe.
The speed changes on the drive lines cause the gears to rattle, they all have to have an operating clearance. It is less noticeable when cold because the gear oil is much thicker when cold. This will never be completely solved unless all of the driveline angles are corrected. Some of this was cured with the A1R trucks, at least on the rear axle. Can someone that has one post a picture of the 4x4 axle?
The 6x6 has much improved angles also. All suffer from bad driveline angles on the front shaft.
A1r 4x4 axle looks just like front pair of the 6x6 axle but with leaf spring perch. They just put dummy stuff in the power divider box that would have been outputs to the rear if it was used as a 6x6 axle
 

MrMikey4026

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Do you know the process for correcting the DL angle - if it’s off?
These trucks were designed with extreme driveline angles, it is important to remember these trucks were to be operated at 30 mph, although they will go much faster. There are no good solutions for the front axle, the rear axle driveline angles can be corrected by installing the A1R axle assembly. Just installing the A1R drop in becomes a problem as the bolt pattern is reversed, it would fit fine if it could be installed upside down. The A0 and A1 housing has been reworked and the power divider modified to fit and work at great cost.
Double Cardan and Rezeppa ujoints have been tried with poor results. The extreme angles and high speeds resulted in overheating and failure in short order. The best and most affordable options are to have new drivelines made by a high quality builder with the best quality components.
 

o1951

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Got the driveshaft balanced with 2 new u-joints; no change. Will be getting the other 2 balanced.

I’ll get the other 2 shafts balanced and in the very near future pull the brake drums (starting at the right rear) and begin to remove, inspect, clean, and re-lube the brake adjusters.
New U-joints- Good! A U-joint failing at speed can really ruin your day, and maybe someone else's too.
 
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