Backhoe subframe mounted to rear axle case

[KeithG]

So I was putting the backhoe back on my B2710 and I noticed a loose bolt by the right rear wheel that connects the backhoe subframe to the rear axle case. When I attempted to tighten the bolt it would not tighten and just spun. I turned the bolt with my hand and realized that he bolt had snapped inside the axle case. So I took the bolt out and inspected the rest of the bolts on the tractor and noticed that the left side had a broken bolt also, in the exact same spot on the opposite side.

Looking at the bolts there is some rust on them and I am concerned that the broken pieces might be rusted solid in the axle case. My questions are:
1) What would be the easiest way to remove the broken bolt pieces if using one of those "drill out" tools does not work (i.e. you put the drill in reverse and the bit is designed to bite into the bolt pieces in the opposite direction causing it to spin out)?
2) If the threads are damaged due to the rust issue, can the threads be re-tapped to clean them up?

The pictures below show the broken bolts, location on the subframe where the bolts go, and the rear axle case from the Kubota parts manual.

Thanks,
-Keith

 

[rbargeron]

Hi Keith,
The bolts look fishy to me. Are they metric thread? The tapped holes in Kubota iron parts are usually metric, and are often the more coarse of the metric pitches for the size. The fractures look like ductile torque failures, like they were damaged (yielded) when they were installed - like a mismatched thread forced in with an impact wrench. Getting the broken off end(s) out may be a project. My guess is the ends are really seized and "easy-out" type tools may not work. With the tire out of the way there may be decent access for carefully drilling them out, working your way up to a near-tap-size drill and digging out what's left of the bolt with machinist's picks. Could be looking at a project.

Any chance the backhoe subframe was originally installed by a nearby dealer? If so maybe their shop foreman would have some suggestions on fixing it.

 

[KeithG]

Thanks for the quick reply. The subframe was installed at my local (i.e. an hour away) dealer about 12 years ago. I doubt anyone would recall the install.

I did check the size of the bolts and compared them with new ones and the best I can figure is that they are M12 bolts with a 1.75 pitch and 8.8 grade rating. When I called the parts department at the dealer he seemed to think the bolts might be 60mm in length because of the non-threaded shoulder length.

I am going to be taking the rear tires off this weekend to see if I can replace the broken bolts (doing one side at a time that is).

 

[100 td]

First up, get some PB blaster or similar onto the broken bolts from both ends if possible. You never know they may come out easily! One key problem with using thread extractors of any type is getting the pilot hole in the center. If you can get a double cut carbide burr in and square the end of the broken bolt off first, it makes things a bit easier. The one linked may be a bit wide, I didn't look for different sizes. https://www.ebay.com/itm/381468525734
Then get a drift/pin punch of 3/8 or biggest that will fit and give them a decent whack. This shock load may crack the corrosion between the the bolt and the housing and allow easier removal. (Other options, heat/cold etc)
Then get a center punch and very lightly pop the center of the bolt. Lightly, so if after you do it you realize it's a tiny bit off, you can pop again and get it right. After you have it truly center, then pop it harder making a proper start for your first pilot drill so that it can't run off. As previously noted, then go up sizes to at least 8mm before using an extractor. If you are still absolutely center you can, and are best to go bigger. (No bigger than 3/8, 9.5mm allowing for a tiny runoff)
Personally I would look at replacing all the bolts holding the subframe to the tractor and torque them up to spec with some loctite or similar.
You can buy a 12mm bottom tap to clean up the housing threads before replacement.

 

[BAP]

Get some left handed drill bits. Sometimes you get lucky and as you are drilling with the drill in reverse and it will spin the bolt out. The least it does is keep from tightening the bolt anymore.

 

[Tunaslayer]

I have been there, and I feel for you.. sheared bolts suck. I have seen a 100 percent success rate with using a welder, and welding a sacrificial socket/extension on and going for an impact gun. I know it's extreme, but sometimes you do more damage resulting in galling. You can get lucky tho. It's worth a little poke to see. Good luck, and may the force be with you.


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[OrangeColoredTractor]

Also, keep in mind, once the end broke off, there is no torque on the bolts, they should come out easily, exception, rust over the years. Its not unusual to see rust from a bolt that was loose also. Try the left handed bits after the PB blaster is in place, start with a pilot hole dead center. This is critical. Then slowing just increase drill size will the bolt it gone, threads left behind and pick them out. Chase it with a tap to clean it up.

 

[JeffL]

Follow the tips outlined by 100 td in an earlier post. Most likely the bolt holes are blind so drill thru the remaining bolt and then fill with PB Blaster. Let this soak for as long as you can before starting the extraction process. Best if you can soak for several days. Reapply PB Blaster every day during the soak. Go slow and think about every step, that way you will not need to repair or replace the case!

 

[shooter56]

I have been lucky getting broken bolts out with several heat and cool cycles ,it seems to help break the threads loose. Like others have said get the center of the bolt punched. I drill bolts and use a left hand tap then thread a left hand bolt in to get the broken piece out. ( It was a bonus working at the aircraft.)

 

[lugbolt]

Couple things for consideration.

First you need to know what you're dealing with. If the remainder of the bolt is loose, lots of times you can center punch the outer part of it lightly and it will turn. Keep doing it and it will back out. If that's not an option read on.

If it is in fact loose in the threaded hole, and you can't budge it with a center punch, screwdriver, whatever, you will have to grab your drill motor and contemplate. Left hand drill. Start with the smallest bit, even though it might be a 14mm bolt, start small. Center punch the bolt dead center. If you get it offcenter, you will fight yourself from beginning to end and often times end up repairing the threaded hole. Once punched dead center, use your left hand drill and get after it. Make sure you go in straight, or again you'll fight against yourself and make a 10 minute job turn into a 10 hour job. Trust me. If the bolt is loose enough, the smallest bit will grab the bolt and spin it as you are drilling, which will back it out of it's threads. If not, move up a size and try again. Keep doing this and watch closely, which also means you have to clear the chips often so you can see where you're drillling and where your hole is going. Sometimes during drilling the bit will "walk" off center, and you have to tilt your drill motor to re-center the bit. But again, it is imperative to keep it dead center. 90% of the time they will back out if they're loose, with nothing more than a left hand drill bit. If it's in there tight-as if it may have been cross threaded, you have no other choice but to go further....

If it's real tight (cross threaded or otherwise thread damaged), you will have to drill all the way to the thread's minor diameter. This is where you will appreciate having the drilled hole dead centered. If you're off, you create problems. So it won't back out with the left hand drill, so you will have to look at your drill bit/tap drill size chart to choose what final drill bit size you will have to use. Once you drill in with that bit, all that is left is the threads, and at that point you can just run a GOOD tap into the threads and it will break the threads out of the hole, leaving you with the original threaded hole.

Rusted, a lot of times just whacking it a few times with a center punch will bust it loose from the rust. Again, punch it dead center-just in case you have to fully drill and tap it.

Easy out (or "eze out")-they are junk. If you have one, throw it in the scrap pile. They cost me so much time at work that I am getting to the point where if someone calls me telling me they broke an easy out in a broken hole, I tell them to take it elsewhere. Nobody wants to pay the hourly rate to remove them, and when they get the bill they are shocked. Nobody wins, so I just refuse them from the get-go anymore. The ONLY time they actually work is when the remainder of the broken bolt is loose enough to unscrew it-which is about 5% of the time in my case dealing with turbochargers.

The best option is EDM machine. My dad used to run one at the railroad rebuilding turbo's and it is a neat setup. Burns the bolt out without hurting the surrounding soft aluminum or cast steel. But that costs a pretty penny unless you know someone who has a machine and doesn't mind doing it for you in exchange for his favorite case of cold beverages. Or maybe warm if he or she is German.

 

[KeithG]

So project update, after struggling with it for 3 hours, drilling through the stuck bolt piece, trying a square tap tool, an easy out tool that looks like a reverse auger and finally a lot of heat, the bugger finally came out. It was only about 5/8" long!

I was ready to kick the tires and ship it off to my Kubota dealer to have them deal with it when my friend noticed that they did not use lock washers, did not put anything on the bolts like anti-sieze and used standard bolts instead of grade bolts. So I probably would have had the problem again later. So now I am off to buy 4 grade 8 bolts with 4 lock washers and some anti-sieze (not sure if that is the spelling).

Will work on the second bolt tomorrow.... If only things were done correctly the first time...

Thanks,
-Keith

 

[100 td]

One down, one to go, good luck. What grade were the bolts, I thought you mentioned they were 8.8?

 

[D2Cat]

If you have difficulty finding the hard metric bolts of the correct length, Fastenal is a good place to find them.

 

[FrankBaggs1]

If you have difficulty finding the hard metric bolts of the correct length, Fastenal is a good place to find them.

Yes sir...as D2Cat stated!
I have a Fastenal just about 3 blocks away from me and they carry most all standard and metric hardened bolts, nuts and lock washers!

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[KeithG]

One down, one to go, good luck. What grade were the bolts, I thought you mentioned they were 8.8?

Yes, they are 8.8 which I believe is similar to grade 5. I was going to upgrade the bolts and replace them all to 10.8 (i.e. grade 8) and my friend said that they would be stronger but also a lot more difficult to drill out if they fail. So I guess I am going to replace them with 8.8 bolts.

 

[KeithG]

Project update two: The second bolt piece was tougher to drill through and required using 1/8, 5/32, 7/32 and finally 1/4 inch bits. The way the bolt broke left a high point on the surface that would cause the bits to want to wander off center. Once the bolt piece was drilled, put the easy out auger through the hole and it came right out.

The entire time spent working this piece was about 20 minutes! Very pleased with the results and even offered to pay my friend because of the aggravation he saved me. He would not take any money because he says he has borrowed my tractor enough that he feels he still owes me...

He is one of the few friends I trust with my tractor.

Now off to get replacement bolts and a replacement nut for the tire lug as it seems to have gotten damaged when I took it off. Don't have any real tractor place near by and tractor supply had nothing so going to try Home Depot...

 

[KeithG]

Just found a Fastenal in NH and they are practically across the street from Home Depot! Too bad they are closed today or I could have finished putting the tractor back together and put the snowblower on it...

 

[JeffL]

Upgrading to a higher grade is almost never a good idea. Most cases the material you are screwing the bolt into is not strong enough to take the clamp load of the higher grade bolt. If you torque a high grade bolt to a lower grade spec it will not stay tight. A bolt needs to stretch to develop clamp load. You can upgrade if you are bolting thru and using a matching grade nut, washers, and lock washers. Jeff