Strange sound coming from rear end

[coachgeo]

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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.

not that it matters much.... if I recall right the study on this showed the double cardan worked marginally better than original.. not worth the expense level of marginal though.. and the Rezeppa really worked fairly well....... problem is...... the particular Rezeppa used in the study was custom made. Reality though is no Rezeppas as huge as is needed for vehicles ths size is commercially available..... and govt. requires the parts (sorta kinda) have to be commercially available so military could not choose to go that route. And far as I know.... no Rezeppa's that size have come to market since the study either.

but maybe Im recalling the study info incorrectly....

 

[MrMikey4026]

not that it matters much.... if I recall right the study on this showed the double cardan worked marginally better than original.. not worth the expense level of marginal though.. and the Rezeppa really worked fairly well....... problem is...... the particular Rezeppa used in the study was custom made. Reality though is no Rezeppas as huge as is needed for vehicles ths size is commercially available..... and govt. requires the parts (sorta kinda) have to be commercially available so military could not choose to go that route. And far as I know.... no Rezeppa's that size have come to market since the study either.

but maybe Im recalling the study info incorrectly....

No, I think you have the study correct. There really was not a good solution.

 

[mccullek]

I'm a new owner of a M1078 A0 and mine runs and drives great. I have mostly only driven it for a few short miles here and there so far, but today I took it for a longer drive and I noticed when I'm running around 35 to 40 mph and let off the gas, I can hear a roaring noise coming from just behind the motor. It's hard to describe but something between grinding and roaring. As soon as you give it gas, it stops, but then when you let off the gas and coast, the noise comes back. It only happens at this one speed. If I'm going slower or faster, I do not hear the noise, and I only hear it when I let of the gas and coast a bit. Maybe it's a normal noise, but I don't have enough experience driving these things to know. Fluids are all good and I will grease it today and see if that changes anything.

 

[Mullaney]

I'm a new owner of a M1078 A0 and mine runs and drives great. I have mostly only driven it for a few short miles here and there so far, but today I took it for a longer drive and I noticed when I'm running around 35 to 40 mph and let off the gas, I can hear a roaring noise coming from just behind the motor. It's hard to describe but something between grinding and roaring. As soon as you give it gas, it stops, but then when you let off the gas and coast, the noise comes back. It only happens at this one speed. If I'm going slower or faster, I do not hear the noise, and I only hear it when I let of the gas and coast a bit. Maybe it's a normal noise, but I don't have enough experience driving these things to know. Fluids are all good and I will grease it today and see if that changes anything.

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Grease for sure.

I would start with the drive shafts. Push and wiggle them too - searching for "play" in the joints and slip yoke before you hit them with a grease gun... Have you thought about (read about) getting the shafts on your new truck balanced? That is a big deal. Also, cheap and easy - what about "indexing" or making sure that the drive shafts are indexed prpoperly?

 

[mccullek]

.
Grease for sure.

I would start with the drive shafts. Push and wiggle them too - searching for "play" in the joints and slip yoke before you hit them with a grease gun... Have you thought about (read about) getting the shafts on your new truck balanced? That is a big deal. Also, cheap and easy - what about "indexing" or making sure that the drive shafts are indexed prpoperly?

I will look into these suggestions. Im aware of what balancing a shaft consists of, but what is indexing, as I am not familiar with that one?

 

[Guruman]

I will look into these suggestions. Im aware of what balancing a shaft consists of, but what is indexing, as I am not familiar with that one?

The u-joints of each end of a driveshaft assembly need to line up. If Sargent Snuffy took the driveshaft apart at the splines, then re-assembled it a few splines off, it will be out-of-phase with the other end.

 

[Mullaney]

I will look into these suggestions. Im aware of what balancing a shaft consists of, but what is indexing, as I am not familiar with that one?

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Like @Guruman mentioned, aligning the yolks is the same as "Indexing". I was a little lazy and snagged an image off the web rather than crawling under a truck to take a picture. ANYHOW, picture below is what we are talking about. Align the joints is another way of saying "index your drive shafts".

Back in the 40's, 50's, and 60's there was a "fat spline" that made it impossible to index the slip joint incorrectly. I guess these days that "feature" was dropped since it cost more money to make...