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The following is copied from TM 9-2320-209-20-3-1 on sprag adjustment.
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Sprag Adjustment
- Thread starter Recovry4x4
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Is this the reason that sometimes when I am shuttleing my deuse that the truck does not want to move in reverse until I get it moving forward about a foot and then it goes in reverse just fine?
God bless America.
Very Respectfully,
David
God bless America.
Very Respectfully,
David
BFR
Rocket Surgeon
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Is there a way to diagnose a misadjusted linkage vs. damaged sprague?
jasonjc
Well-known member
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Just because you dont have a air switch on the dash does not mead its a spar transfer. At least thats what I found on one of my trucks it has a air shift Tcase but no air going to it. don't know who or when this was done. just goes to show that you have to look at everthing on these old truck or you don't know what you are getting. 
JasonS
Well-known member
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The best way to diagnose a worn out sprag is to take off the front drive cover and measure the dimesions of the sprag segments. There are two sprag clutches. One for forward and one for reverse. All of the forward drive sprag clutches that I have taken apart have been worn out. The rear doesn't wear much because it is only engaged when in reverse.
It is best if you get a manual and try to understand how the linkage works. Contrary to popular opinion, you do not have to shift back through first gear for the forward sprag to engage.
You can also check the sprag by disconnecting the external linkage. A spring in the transfer case will engage one sprag and you can try rotating one front wheel. If it only turns in one direction, great. Have someone push in the rod on the transfer case and try rotating the front wheel. It should rotate the opposite direction only.
It is best if you get a manual and try to understand how the linkage works. Contrary to popular opinion, you do not have to shift back through first gear for the forward sprag to engage.
You can also check the sprag by disconnecting the external linkage. A spring in the transfer case will engage one sprag and you can try rotating one front wheel. If it only turns in one direction, great. Have someone push in the rod on the transfer case and try rotating the front wheel. It should rotate the opposite direction only.
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The operator's manual warns that the shifter should always be moved into (or at last) through first when changing directions. This is so that the proper sprag unit will be selected. While the engine has enough torque to start from second, it is possible that you will be trying to drive forward with the reverse sprag actuated.
And the reverse is also true.....perhaps this is your trouble.
Regards,
David Doyle
And the reverse is also true.....perhaps this is your trouble.
Regards,
David Doyle
JasonS
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That may be what the operator's manual says, but as soon as you pass through neutral, the pressure is released from the linkage. The spring inside the transfer case causes it to move to the forward sprag. However, to most folks who have a malfunctioning sprag, the whole thing is academic.
I have only taken apart three sprag clutches, but in every one the forward sprag was worn out. I forget the TM number but there are two dimensions to check. The length of the sprag segment and the width of the wear pattern on the segment. It needs to be remembered that the sprags are always wearing themselves out. There has to be enough friction that the segments will wedge as soon as rotation is reversed. I could have taken the reverse sprags from two cases and had one good but I opted for the REB kit. If you look on ebay, there is a gasser M35 which appears to have a REB kit. There starting bid was $500 for the whole truck. I have no affiliation with said truck. The sprag is probably reliable when everything is new...
I have only taken apart three sprag clutches, but in every one the forward sprag was worn out. I forget the TM number but there are two dimensions to check. The length of the sprag segment and the width of the wear pattern on the segment. It needs to be remembered that the sprags are always wearing themselves out. There has to be enough friction that the segments will wedge as soon as rotation is reversed. I could have taken the reverse sprags from two cases and had one good but I opted for the REB kit. If you look on ebay, there is a gasser M35 which appears to have a REB kit. There starting bid was $500 for the whole truck. I have no affiliation with said truck. The sprag is probably reliable when everything is new...