Backhoe A backhoe cautionary tale

[SFish]

I am using my 3320/447 hoe/9" bucket to dig about 4,000 ft of water line trench from a high point where the well and water tanks are to my new house site, mostly on old logging roads. I am digging on a ridge line with stretches of very heavy clay, decomposed sandstone, and lots of roots that make for tough digging, and I have completed about 1,000 ft. One recent downslope was so steep that I had to loosen the surface with the hoe to back up it (R4 tires), and while digging hydraulic oil began spraying out of the back of one of the stabilizer cylinders.

What I found was that the lower pin on the stabilizer had pulled out, shearing one of the 1/4" cotter pins, and this allowed enough torque to be applied to the pin on the back of the cylinder to break the weld on the plug. I think what happened was that the torque on the stabilizer on the steep hill bound the pin and inched it back shearing its cotter pin.

I have had good luck with my dealer with several warranty repairs (mostly hydraulic lines) but they wouldn't cover this one. So I ordered a new cylinder ($690, ouch!), but when I went in to pick it up they looked at the broken one and sent me to a good welding shop. The weld ($40) is good, but I had to pay ~$120 for JDs restocking fee for returning the new cylinder. I could have fought this, but I got off relatively cheap and wanted to keep a good relationship with the service manager.

I solved the pin problem by replacing all four with 3/4" bolts, double nutted. So I suggest that anyone who is digging in a situation that stresses the stabilizers keep an eye on, or replace the pins, and explore repair options before ordering an expensive part.

Steve

[J0be269]

While I don't have a green machine I can give you a bit of advise. Those pivot pins that you replaced (I think that's what you replaced) with 3/4 in bolts are much much harder that the bolts you put in there. I would caution against using the bolts as they will wear with time and when they do it will be the holes that they pass thru that wear next. This will be rather costly to fix when it happens.

I would recommend instead the following fix. You said you lost a cotter or broke one? You may be better served to replace the cotters with bolts. All the pivot pins on my orange tractor are "retained" with 4mm or so bolts, you don't tighten the nuts all the way down against the pin bushing, but leave it a bit loose so it can move a little and use a nylon nut. This will keep the bolts from breaking when under stress, they are going to stand up better than cotter pins, and you will be using your original pivot pins so wear on you machine from the 3/4" bolts will no longer be a concern.

[kennyd]

While I don't have a green machine I can give you a bit of advise. Those pivot pins that you replaced (I think that's what you replaced) with 3/4 in bolts are much much harder that the bolts you put in there. I would caution against using the bolts as they will wear with time and when they do it will be the holes that they pass thru that wear next. This will be rather costly to fix when it happens.

I would recommend instead the following fix. You said you lost a cotter or broke one? You may be better served to replace the cotters with bolts. All the pivot pins on my orange tractor are "retained" with 4mm or so bolts, you don't tighten the nuts all the way down against the pin bushing, but leave it a bit loose so it can move a little and use a nylon nut. This will keep the bolts from breaking when under stress, they are going to stand up better than cotter pins, and you will be using your original pivot pins so wear on you machine from the 3/4" bolts will no longer be a concern.

This is good advice. I also think the bolts will be to soft-worst case would be to bend on in the mount and you would have one he!! of a time getting it out!

Wish you had posted about your cylinder problem before ordering a new one!

[AKfish]

4,000' of water line trench! Now, that's a good sized project even for an excavator! Your 3320/447 will definitely earn it's oats every day.

That's good advice... if you mix different parts that vary in hardness - you will have uneven wear.

And your repair could have unintended consequences.

The small bolt with nylock nut is also a good idea for replacing the cotter pins that can be bent and pushed out by dirt and debris.

A picture of your trenching work would be great!

Best of luck.

AKfish

[pat32rf]

Then again, its easier to replace a worn bolt than rebuild the hole it went thru when it wears..... I have been known to do the same thing but have a source of alloy bolts which are still a bit softer than the hardened pins. Just stay away from the gr2 bolts that you get at the average hardware store

[SFish]

Here are some pictures AK. Thanks all for the tip about bolt hardness. I might have replaced the cotter pins with threaded bolts had I thought about this, but on the other hand I like the idea of cinching down the replacement pins in order to tie together the two flanges to minimize flexing. I will check the bolts and the holes and report back if I begin to see unequal wear. It is just about dry enough to get back to work. Steve