3720 MFWD issues

[JasonMac]

That's the thrust nut. What does that do exactly?

 

[chin]

That's the thrust nut. What does that do exactly?

well if its not tight, the front axle goes back and forth causing a knocking sound which can sometimes be felt

 

[Winmac]

I ran into the same issue but with a larger tractor, coupling was fine but pinion spline was worn to 1/4 of it's thickness. Were were tearing down axle to rebuild the king pin bearings and replace u-joints anyway so i removed the center diff and welded up the pinion splines and hand fitted them. even Reused the orignal coupling, with one modification, i installed a greese fitting 90* from the split pin, no need to pull the shaft to grease them. We have since put 2000 hr on that repair with zero issues, even pulled the coupling back to check for wear once.

 

[AKfish]

I ran into the same issue but with a larger tractor, coupling was fine but pinion spline was worn to 1/4 of it's thickness. Were were tearing down axle to rebuild the king pin bearings and replace u-joints anyway so i removed the center diff and welded up the pinion splines and hand fitted them. even Reused the orignal coupling, with one modification, i installed a greese fitting 90* from the split pin, no need to pull the shaft to grease them. We have since put 2000 hr on that repair with zero issues, even pulled the coupling back to check for wear once.

You have a drill press with a milling/machining platform? Pretty hard to cleanly weld those splines and then have a finished/balanced shaft that fits the spline coupler -- unless you can machine it.

AKfish

 

[AKfish]

OK I had to take it apart as it started jumping splines again. The frontmost coupling splines are severely worn as are the pinion splines as well. The others are just fine. For the moment I flipped the coupling iuntil I can get a new one. The roll pin is just in the coupling and used to limit floating.

My advice to all is to pull this shaft down and grease the splines before it makes a mess.

Pop the roll pin out of the rear coupler and slide it rearward. then slide the front coupler all the way forward and the shaft will fall on your head. Thankfully it's light and my head/ear are tough...

OK... this is an older post - I know. But... how did the front roll pin disappear? Without that pin - the spline coupler - will slip back and forth on the shaft. And; from KennedyDiesel's discription - pop off or jump splines. I'm wondering if the pin was ever installed at the factory? Thanks.

AKfish

 

[Winmac]

You have a drill press with a milling/machining platform? Pretty hard to cleanly weld those splines and then have a finished/balanced shaft that fits the spline coupler -- unless you can machine it.

AKfish

I know it seems far fetched but this is the type of work i do and It worked out better than even i expected, i laid in a nice tight mig bead along the remaining half of the spline, adding weld just back to the worn edge . Knocked of the high spots with a grinder and hand files, tacked the low spots and reworked them. i did one at a time fitting the coupling to each before welding up the next. No it was not perfect but it was "good enough for the farmer"

I actually have a bridgeport mill but i would need to buy the spline cutter or grind a form tool and just the set up might have taken as long as my manual repair.


If the front axle has excessive end thrust in the center pivot or is set incorrectly, the drive shaft will carry the thrust (when reversing) and destroy the split pins.

 

[AKfish]

I know it seems far fetched but this is the type of work i do and It worked out better than even i expected, i laid in a nice tight mig bead along the remaining half of the spline, adding weld just back to the worn edge . Knocked of the high spots with a grinder and hand files, tacked the low spots and reworked them. i did one at a time fitting the coupling to each before welding up the next. No it was not perfect but it was "good enough for the farmer"

I actually have a bridgeport mill but i would need to buy the spline cutter or grind a form tool and just the set up might have taken as long as my manual repair.


If the front axle has excessive end thrust in the center pivot or is set incorrectly, the drive shaft will carry the thrust (when reversing) and destroy the split pins.

Well... that's some pretty good welding "for a farmer"! :laughing: So, if I understand correctly; if the center pivot is adjusted rearward (towards the driveline and transmission) too closely it will "load up" the driveline and wreck the split pins.

I have always figured that the pivot adjustment would likely be too loose and need to have the "slop" taken out with tightening the pivot adjustment. Never considered that it might actually be too tight!

AKfish

 

[KennedyDiesel]

Revisiting this once again. Clunk is back, front splined coupler is dry and rusty again. Pinion stub and intermediate shaft have some wear, but with a new coupler should be OK. Old coupler is pretty bad now. I could have swore I bought new coupler(s) back when I first did this, but I may have skipped it.

Rear coupler and joint stayed well greased.