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M813 Clunk..

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MikeGuti

New member
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Location
Albuquerque, NM
I need some help..The truck will bang loud and fierce when driving. It does this on the sand and on the pavement but not all the time. Recently replaced the transfer case and opened up both differentials there didn't appear to be any problems in the differentials. So at this point I'm pretty confused. it feels like the noise and the popping is coming from either the rear differentials or the rear drive lines. The truck does have lockers in it.

Mike
 
R

R Racing

Active member
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St. Leonard, MD
Lockers generally make big bangs that's normal ! They unlock in turns and when they relock it makes a lot of noise. Also the walker beam suspension the rear axles walk out as 4 inches on either side of the rear. When they do in climbing and going around corners it makes a lot of noise as well.
 
M

MikeGuti

New member
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Albuquerque, NM
R Racing said:
Lockers generally make big bangs that's normal ! They unlock in turns and when they relock it makes a lot of noise. Also the walker beam suspension the rear axles walk out as 4 inches on either side of the rear. When they do in climbing and going around corners it makes a lot of noise as well.
Click to expand...
It is happening when driving straight. The whole truck shakes when it pops.
 
Mercunimog404

Mercunimog404

Banned
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Carson City/Nevada
My vfd had an m44 that had a sprag case. It would clunk real bad. We found out it is required to go from reverse to first. Otherwise the sprag would bind up and a loud bang would result. Doesn't the 800 series have a sprag? Maybe this is the cause.
 
dilligaf13

dilligaf13

Active member
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south, florida
You hear the pop and feel it shake, when driving straight. Is this after coming out of a turn? After it shakes and pops does it ride normal, for the duration of your straightaway driving?
 
M

MikeGuti

New member
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Albuquerque, NM
No its not out of a turn and no it doesn't stop once it starts but there is not a set time frame between the pops. Sometinew is is every 3 or seconds sometimes a minute.
 
Squirt-Truck

Squirt-Truck

Master Chief
Steel Soldiers Supporter
1,180
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Marietta, Georgia
No you do not have to go reverse to first, the air valve operates off the first reverse shift rail, but shifts just coming our of reverse to neutral.
BUT, be sure it moves (the sprag clutch ring in the transfer.)
Simple way to check all the front drive is to remove the front propeller shaft, if the pop goes away you have a front drive issue, if not, remove the intermediate rear propeller shaft and then check. Does sound like missing teeth.
 
Autocar

Autocar

Member
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Location
California
Sounds like the sprags in the transfer case to me. There are air valves on the trans shifter that operate a 2 way air cylinder on the transfer case. The cylinder has to be fully in one position or the other to engage the forward or reverse sprag. When the trans is in neutral or forward gear, one sprag is applied. When in reverse, the other sprag is applied. It sounds to me like the cylinder is not working and the transfer case thinks it's in reverse. You are hurting the sprag big time right now. Go from neutral to reverse and back and see if the cylinder is shifting at the transfer case. If you drop the front drive shaft and the problem goes away, then it is the sprag because the front axle quits fighting the rear axles(binding). There was a discussion about the sprags a year or two ago in this forum I think. I explained the operation of the transfer case.
 
sandcobra164

sandcobra164

Well-known member
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Leesburg, GA
I recovered an M818 for a guy and it would do the same thing. I mean it would almost feel like a driveshaft broke out from under the truck. I read the advice on this site and rebuilt the sprag selector on the transfer case. Still not fixed, I took the transmission tunnel apart and found a bolt installed where the vent for the selector on the transmission is. This truck didn't have the usual "pssst" upon shifting from reverse to neutral and that was certainly why. It sounded and acted normal after removing the bolt and spraying some PB Blaster in all the lines.
 
Autocar

Autocar

Member
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Location
California
Best to start at the beginning of the thread that my link points to. The link was my explanation of how the 5 ton transfer case works. What you are experiencing is the reverse sprag being engaged instead of the forward sprag while moving forward. The axles are winding up so tightly that they are overpowering the holding force of the sprag. The bang and shudder you feel is the sprag elements snapping free. Do it very many times and you have a broken sprag.
 
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