4WD quit on my 2011 4520R

[bernardcuziillo]

I was doing various operations when I noticed that I had lost torque on my front wheels. With the front axle off the ground using the FEL, with rear wheel spinning, the front wheels have no spin. I don't hear any funny noises. The MFWD shifter feels normal. I've looked at the service manual and it seems like it's one of three areas: 1) 4WD gear in transmission, 2) prop shaft, or 3) front axle. If any of you had this happen, what caused it?

It's also an interesting safety hazard as I discovered while toting a boulder in the bucket down a muddy road. The brakes only work through the transmission, so with a fully loaded bucket the rear wheels don't have enough road friction to stop. Luckily I was able to ski down the road to a stop without dumping the boulder, sending it careening into a neighbor's truck.

Thanks!

 

[ptsg]

I see you put the year of your tractor as well as the model, and if I remember correctly from older threads, the older 20 series had an overload protection on the front axle. Basically, on the prop shaft, on the front axle end, there is a hub with 6 ball bearings. If the axle is overloaded, these balls will pop out and disengage the front axle, to protect it from breaking stuff.

Now it's a matter of putting it back together and it should be good to go.

On the newer stuff, I would say 2014 and on, they just use a splined coupler on both ends of the prop shaft. The coupler stays in place with a roll pin on the middle that prevents it from sliding on way or the other and disengaging the front axle. It's no uncommon to hear that the roll pin broke and the couple just slide on way or the other.

 

[bernardcuziillo]

Thank you ptsg. I found the old thread: Branson 4WD They say both front and rear of the prop shaft have torque fuses.

Now I'll go have a look.

 

[ptsg]

Good call on checking old threads. Keep us updated and hopefully it's something simple and easy to fix.

 

[bernardcuziillo]

All fixed, and not exactly what the threads said. Yes, it was the prop shaft, but no, there are no balls and no roll pins, and nothing else to act as a torque breaker. Both ends of the prop shaft and both the tranny and front axle are all male splines, mated with female spline couplings. During removal, the snap rings and couplings are slid up the prop shaft. When reinstalling, the couplings are slid onto the tranny and front axle, then the snap rings are placed in the grooves to prevent the couplings from backing out. Apparently someone was in their before me and stretched out one of the snap rings so that it didn't stay seated in its groove on the shaft. This allowed the front coupling to move forward when I came down a short, steep slope and bottomed out on my bucket lip, causing a fast deceleration in addition to gravity, knocking the front snap ring out of the groove. Further work on up slopes caused the front coupling to slide up the prop shaft and out of mesh with the front axle. I re-bent the snap ring and put it back together. If you needed a new snap ring, it looks like it's McMaster p/n 98541A440 in packs of 25 for less than nine bucks. Here are some photos. The snap ring is bent and shows a pattern of uneven contact with the shaft groove shoulder. On one end of the prop shaft, the splines were chipped. These chips are a mystery because the couplings can't slide too far onto either the tranny or the front axle, as both have limited length, so the prop shaft could never get barely engaged with a coupling. The the two ends of the prop shaft itself appear to be identical, so it doesn't matter which way you re-install it. I can't imagine using a non-4WD tractor. Thanks again to ptsg and the thread writers!

 

[ptsg]

Looking at the damage on the end of the shaft, looks like it happened before and in a more violent way than it did with you. At least it was an easy fix. Thanks for the update and conclusion of the issue.

 

[ericm979]

I'd replace the snap ring with a new one. Once bent it'll bend back easier. Besides being bent the old one looks like it's worn on the bent side. The ring has a sharp and a rounded side. The pic looks like the sharp side except it looks beveled on the bent end. When installed the sharp side should face away from where the force comes from.

 

[bernardcuziillo]

@ericm979: True. Next time this happens I'll have 25 new snap rings from McMaster in stock!