3720 MFWD issues

[KennedyDiesel]

Today my 3720 started making clunking noises when changing directions. It only does it in 4wd and only seems to do it when the initial load is applied. The front wheels do appear to drive. I looked at the front driveshaft (unimpressive to say the least) but couldn't see any glaring issues. The dry splines and floating/roll pinned collars on the shaft have me scratching my head.

At any rate has anybody had any diff/driveshaft issues?

I should add that the sound seems to border on a clunk and a pop and seems to change where it is coming from. Some times it seems to be up under the front diff and other times it sounds like it's midship.

 

[Glen Watkins]

Make sure your wheels lugs are all tight!

 

[KennedyDiesel]

Well I think it's the driveshaft splines. I did not get a chance to study thoroughly, but it's not very impressive. There are at least 2 short splined couplings. The rearward one is pinned with a roll pin. The front one slides free or at least mine does. All I did was slide it around a bunch trying to see what movement was allowed. These splines really should be lubed in my opinion.

Anyhow, I went to do a different task and tried it and it worked fine.

I have to say, the front PTO shaft setup on my 455 is more robust that this spindly little thing...

 

[KennedyDiesel]

What I have learned so far is that both of these splined couplers are supposed to be pinned. My forward one is not. probably won't get to lok at this for a week or so, but I have a coupler and pins coming. from what I see i would highly recommend disassembly and greasing on these with a super good moly grease like Cenpeco Mega Moly.

 

[AKfish]

For what it's worth - the front driveline on my 110TLB is pretty "spindly", too! And the front collar joint is pinned with a roll-pin as well.

Have never heard of anyone twisting or breaking the collared joints, though.

Since the shaft does not slide back and forth with any up and down motion - the front axle and transmission are solidly fixed - and the distance does not change; grease would only help to deter corrosion.

I would be more concerned with possible damage to the front axle hub.

AKfish

 

[toolbox5]

did you try checking your front axel thrust bolt, my tractor did that and once i retorqued it and it stoped specs are in owners manual , might help

 

[KennedyDiesel]

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...

 

[JasonMac]

I'm having the same issues right now. I'm hoping it isn't the cable that controls the movement of the shaft with the lever.

I can put the shaft into 4WD mode by hand, but it won't stay in 4wd mode. The shaft jostles free after using it for a few seconds.

I am really puzzled, because it looks like the roll pins are in place on both couplers.

Any ideas?

It doesn't look like my splines are worn too badly.

 

[JasonMac]

I would send it to dealer, but I'm afraid once it is there, It will snow, and I'll have nothing to use.

 

[chin]

I dont remeber the torque spec but it is in the manual. These bolts seem to be very loose on all machines from the factory. Check it out.

 

[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.