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New PTO control valve on 756


7and8and1456

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 I have not been able to keep the adjusting nut tight (for several years) on the PTO control valve stem on 1969 756. I drilled and threaded a small hole into the adjusting nut and installed a set screw in it but the set screw loosens and falls out.   I am replacing adjusting nut and control stem with new. There is difference in length of threaded section of old and new stems. When new stem with longer threaded area is installed, the hole through the stem  is not accessible above the  stem control stop.   The hole is for inserting a punch or a nail into hole to hold the stem stationary while adjusting nut is turned for adjustment of pressure. In looking at parts diagrams on internet I see that early 756 and later 756 had different part numbers for stem and stem control stop. Later part numbers are also same as found in the 66 series tractors. Both later 756 and 66 series parts show a 3/8"-16 hex nut with the adjusting nut. With the longer threaded area on later number stems , is not that extra length for the 3/8-16 hex nut to be used as a jam nut run up against the adjustment nut in order to keep it tight?  It seems like I have seen a tractor with a jam nut on the stem and adjusting nut.

The parts diagrams show different numbers for the stem control stop according to which stem is used. I believe that the stem control stop has to be a thinner piece of bushing stock in order to allow enough of the stem to protrude above it in order to access the hole through the stem. Can someone please take a look at a 66 series tractor and verify that the control stop is indeed a fairly thin piece of material? I estimate that a thinner stop would need to be about 1/4 inch thick. My part is 14.22 mm thick  (equals 0.56 inches). I can ether grind down and make thinner my existing control stop or put a stack of washers in its place in order to gain access to the hole as needed. Pictures below show comparisons of old and new parts.

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PTO parts.jpg

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You need a different seal holder which will recess the seal.  You also need a thinner spacer to go with the new seal holder.  If you don't recess the seal, the adjustment hole of the stem will be in the seal.     A 3/8" nut is installed above the thinner spacer so it can lock against the long engagement nut.  Use the parts diagram for a 66 series to get the correct part numbers.

Red Tech

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11 hours ago, Red Tech said:

You need a different seal holder which will recess the seal.  You also need a thinner spacer to go with the new seal holder.  If you don't recess the seal, the adjustment hole of the stem will be in the seal.     A 3/8" nut is installed above the thinner spacer so it can lock against the long engagement nut.  Use the parts diagram for a 66 series to get the correct part numbers.

Red Tech

Two screen shots below . First 756.  Second 1066. What you call the "seal holder", is #33  "control valve fitting (plug)", 381476R3.  This  number is used for all early and late serial number 56 series tractors, plus the 06, 66 and 86 series. There is no different "seal holder" which will recess the seal. What you call "Spacer," is #32 control valve stem stop, 384876R1, used for early serial 756 tractors and all the prior series 06 tractors. Then 528486R1 for later serial 756 tractors AND all 66 and 86 tractors.  This stem stop is definitely thinner than the earlier ones.

What I need to know is the thickness of the  control valve stem stop, 528486R1. With the 528486R1 at $75.96, I'll make one myself. I know that generally when a machine assembly has a part that needs jam nuts, they are thinner than regular dimension nuts. Fastenal... https://www.fastenal.com/product/details/1136206#

 

 

Screenshot 2023-09-24 756 PTO.jpg

Screenshot 2023-09-24 1066 PTO.jpg

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