1984 5 ton m923

[topshot]

I just got this very clean AM general with the Cummins motor and Allison trans does not have a turbo there is a loud knock if I could send a video to anybody if they can determine if this is okay or its got a problem
I live in Michigan by Port Huron
The truck runs great starts right up and has good oil pressure, it has lot of power and runs down the road fine

Thanks guys

 

[elkhtr]

Post a short video for all to see.
If its the rapping on a coconut sound while rolling down the road, that is nhc 250 normal.

 

[swbradley1]

Could be stuck injector or a head gasket leak. If it were a rod it would probably be more pronounced.

White smoke with antifreeze smell - head gasket.
Put a infrared thermometer on each cylinder and if you have a cold one - possible injector.
Drop the pan and look for a rod loose.


But if it rattles like a tin can with rocks in it then you are good to go.

 

[Floridianson]

When does the knock start. When at idle or when you hit a hill or put a good load on the motor running through the gears.

 

[wheelspinner]

Also the air compressor can make a very pronounced knock. Does it go away when full air is there?

 

[topshot]

I just got this very clean AM general with the Cummings motor and Allison trans does not have a turbo there is a loud knock if I could send a video to anybody if they can determine if this is okay or its got a problem
I live in Michigan by Port Huron
The truck runs great starts right up and has good oil pressure, it has lot of power and runs down the road fine

Thanks guys

Can't load a video

 

[topshot]

At all times I can send you a video through email

 

[dmetalmiki]

Sounds like the typical Cummins 250 to us.

 

[wreckerman893]

The M900 trucks with the 250 made a weird sound when going down the road. I never figured out exactly what caused it but it is common. If the knock increases and decreases under load then you may have a problem.
I would find an old school Cummins mechanic in your area and have him check it out.....worth a few bucks for the peace of mind.

 

[topshot]

Thanks guys
I think everyone is right its a load B@$%h lol

 

[davo727]

Cummins engine right? Not Cummings

 

[R Racing]

When they are under load they sound like dancing coconuts LOL Which is normal if that's the case.

 

[acme66]

Not that it answers your question about if your knock is bad (video it and post it) I can say the coconut noise description is very apt. My 925 is MUCH louder in the cab than the 923 was and it is that dang nut noise. Very disconcerting but they tell me it is normal. If you ever find a solution to it let me know, the 925 is so loud in the cab as to be rather unpleasant to drive w/o hearing protection.

Ken

 

[topshot]

Thanks ken I tried every way to load a video but no luck

 

[acme66]

Thanks ken I tried every way to load a video but no luck

Load the video to youtube then post a link to it, that is what I do.

Ken

 

[turnkey]

Sounds like a n250 alright...But better to have it checked out by a top mech....Best of luck.

 

[Rmtaunton]

Not that it answers your question about if your knock is bad (video it and post it) I can say the coconut noise description is very apt. My 925 is MUCH louder in the cab than the 923 was and it is that dang nut noise. Very disconcerting but they tell me it is normal. If you ever find a solution to it let me know, the 925 is so loud in the cab as to be rather unpleasant to drive w/o hearing protection.

Ken

Have you ever been in a deuce ? Ha I think the A1's are relaxing compared to

 

[juanprado]

my cab is not unpleasant with the noise level. I will tell you that I did blow out the muffler on the recovery as it was probably internally rusted by water sitting up as it had no rain cap. I used an almost new take off muffler and that made a lot of difference. I also have a hard top. I now have a rain cap.

Check the condition of your muffler?

 

[cwc]

The M900 trucks with the 250 made a weird sound when going down the road. I never figured out exactly what caused it but it is common. If the knock increases and decreases under load then you may have a problem.
I would find an old school Cummins mechanic in your area and have him check it out.....worth a few bucks for the peace of mind.

When they are under load they sound like dancing coconuts LOL Which is normal if that's the case.

So how does a "normal" amount of knocking coconut sound correspond to load? My 1984 M925 has more "coconut" effect than my 1986 M925A1, and it increases with load. It is not really present at all when coasting. I had a career army truck mechanic ride in it and he said it is completely normal, no cause for concern, they all do it, etc., but it is more noticeable in the one truck than the other. I'll do the dual fuel line mod if I can ever get caught up a bit.

 

[Swamp Donkey]

I agree with Juan. I had the Hawaiian dance team with coconut bikinis riding with me before I replaced my muffler. Mine had rusted out at the bottom. I replaced it with a NOS surplus muffler (correct muffler but a variation) and it sounds like a real truck now. It still has a unique tone to it compared to other big trucks, civilian and military, but there is far less cab noise and the cocounts are gone. This tells me that most of the coconuts are in the muffler.