Davis D100 Backhoe Repair and Subframe for Kubota L285

tprothma · Jan 4, 2015

Bought a Davis or Case D100 4pt Backhoe off Craigslist for $800. It needed minor hydraulic repairs, but at the time I didn't know how much repair work would be needed. Later found it was just minor control valve leaks and the left/right ram had a leak. The minor repairs took some time but was very cheap and all I needed to do was to design and build a subframe to attach it to the Kubota L285.

For the hydraulics I had to repair the left/right ram which had a bad nick from sitting for years. It's a split ram design with a huge gear in the middle. I repaired the ram rod by soldering the nick and then carefully sanding (removing little to no chrome). I researched industrial epoxies, but the cost was prohibitive and I could not buy small quantities. This repair will last longer than most of the other rams and will protect the new seals. Needed to use a propane torch to get the ram hot enough. I replaced the o-ring and backing ring with a single C-cup seal (NOK 70mm ID, 80mm OD, 8mm thick or N86XX, IDI 70 80 8). This is an unloaded seal (meaning it has no spring liner). These can be obtained at most hydraulic repair places. The C-cup expands when pressurized and does a great job even on the repaired side. The wiper seal is National 310841 2.75" ID, 3.125" OD, 3/16" thick. I was able to read the numbers off the old wiper seal and it was an easy match.

For the control valve, I replaced the top seals and bottom o-ring of each control piston. The top seal is P125-.625 (5/8X7/8X1/8 inches loaded c-cup). The oring at the bottom is a 114. If doing this repair yourself make sure you buy at least 12 of each (2x) because you will destroy some trying to install- they are just tough to get into position.

In all the whole cost of the backhoe attachment is $1000 including the steel remnants. I also paid about $1500 for the tractor from the government because it needed some of the hydraulic lines replaced. They were quoted $100/line for 12 lines. I replaced the lines for about $100 with off the shelf parts from tractor supply.
So the whole deal is about $2500.

Stay tuned for details of the subframe.

[EDIT] Ram before soldering, will post pic after soldering in next update

Backhoe attached

buffdan · Jan 4, 2015

Thanks for the post..
I'd say you got quite a good deal..

I too have a D100 backhoe, came with my Davis TF500 trencher..
It worked ok on the trencher, but the swing arm cylinder leaks badly, and the piston rod has a number of pits.
I only dug small hole to test..

I bought the seals, o-rings from Colemans. Havent installed yet..
Thought about replacing the swing arm rod, and have someone re-weld the gear rack.. Not sure if its feasible or cost effective.
I need to remove it first..Maybe soldering is the way to go..

The other cylinders need new rods.. pitted... Plus the boom arm cylinder bleeds down..
I have the seals on order, and just fabricated a gland nut spanner..

I only have $700 or so into the hoe , so I done mind putting a bit more into it.

I also would like to mount this to my Kubota B3030.. Subframe mount.
According to trencher manual, the hoe weighs 900lbs, plus I weighed it with out bucket, and my Chatillion scale showed 850lbs.

This has some good sized cylinders for a small backhoe, the bucket breakout shows 10k lbs according to trencher manual..
At 2000 PSI hydraulic pressure.. Should have a lot of digging power..

What solder did you use?

Very anxious to see you post more..

Dan - Buffalo NY

tprothma · Jan 4, 2015

Hi Dan,
I just realized that I only had a picture of the swing ram before soldering (after cleaning and prepped). So I updated the caption above in the original post.

I believe the 10k breakout. I've never actually weighed the unit, but the same guy who told me 10k breakout also told me 1600lbs, so at least he was half right. It is very heavy, and that's for certain. If you know where I can get a copy of the trencher manual I'd appreciate it.

Yes I could have replaced the swing arm ram piston, but think it's a simple repair and I think it will outlast the other rams. It's a 70mm dia rod about 1/4" thick- which is standard material that a hydraulics shop would have or be able to order. You'd have to weld on the gear rack and there is also an alignment bar opposite the gear rack (you can see it in the picture I posted above). In addition you'd need to weld in a end cap and cushion valve on one end of the piston, the other end of the piston remains hollow. The valve slows the movement near the end of the swing and I made up the name cushion valve, it probably has a proper name.

I definitely recommend using the unloaded C-cup seal I mentioned above for the swing ram and you may consider letting a hydraulics shop install them as they can get them in better than a DIY'er and I can tell you that it's a lot harder than putting in an o-ring and backing washer.

For repairing the nicks which will tear through a new seal if left alone, I actually started with a Silver (lead free solder). But the ram is so big and I could not get a good braze on it with a propane torch so I settled for Eutectic Pb/Sn solder which does have a lower stiffness, but still harder than the epoxies that are often used. The cold method of repair such as an epoxy would have been preferred and if they sold Belzona at a reasonable price in an ounce container for instance it would have been great. I talked to the local Belzona sales guy and let him know they were missing a potential market.

I have some surplus rams which would nearly be an exact fit for the 3 rams on the arm that I got for $30 each, but I want to get some work out of it before I dive that deep and would need to re-plumb the whole thing at that time. I may get around to replacing all the rams one day, but not in the near future. I considered building my own backhoe because of the cost, and was happy to find one cheap that I did not have to spend a lot of time building. It was hard enough to adapt it to the tractor in a sturdy way.

Tim in El Dodado- Northern Cal

tprothma · Jan 4, 2015

The ROPS cross member was too high, so I moved it down and integrated it into the design to be used as a place to put the seat and attach the struts. Then it can be moved back up to its original position to enable full upward swing of the 3pt when removed.

Welded 3/4" nuts onto the cap of the cross member

Welded the end caps to the cross member

After griding the edges of the end cap, the cross member is installed.
The bolt sticking out is used for the strut which connects to the upper attach points of the 4 pnt.

More to come...

buffdan · Jan 4, 2015

Tim,
I'll mail you a copy of the manual.. Private message me your address..

I have attached photos of my cylinders.. You can see how bad the boom one is, and pits on the swing arm cylinder..
Also picture of scale showing weight of D100, and scan of specs from manual.

Dan

tprothma · Jan 5, 2015

Hi Dan,
Thanks... will PM you for the manual.

Looks like the weather in upstate NY has not been kind to the rams. Pitting is what will cause the leaks, mine are near their end of life, but other than the swing arm ram which has been repaired, there is no actual pitting and everything is just superficial.

On yours it's hard to tell from the pictures as to the extent of pitting as I go by sense of feel anyway. But I suspect they're fairly rough and you'd be soon replacing the seals again.

For the boom for instance, there are 3 routes:
1) DIY rebuild- I priced out the raw materials from Bailey (Bailey International | Mobile Hydraulic Solutions) 1.5" Chrome Rod, $2.04/inch. I don't know if they would need to be threaded on the inside or if they can be welded. Threading would add some cost at a machine shop.
2) Hydraulic shop- It would take a couple of hundred per ram to have a hydraulic shop replace the cylinder and seals. I never asked for a quote because I knew it was above my budget. Also re-chroming is actually more costly than replacing the rod because they have to grind and polish to get it back to the original dimensions after rechroming.
3) Find some surplus rams.... I got lucky. The ones I found have the right basic dimensions, but may be 1" too long which I can either live with or make some minor tweaks including shortening which is cheaper than a new ram. It looks like you may be needing to do some plumbing repairs so if you focus on the dimensions of the rams and ignore the fittings and hoses you may find it cheaper to re-do some of the plumbing than to try for an exact fit.

I'll take some pictures of my rams including the solder repair.

Tim

pabble · Jan 5, 2015

Hi...I have a thread going here about trying to fit a case d100 backhoe to my ford 335 industrial tractor. Your method of attachment appears quite different than others I've seen - could you add more detail and also step by step on how you attach and remove it? how has it worked out in practice - anything you would do differently? thanks......

tprothma · Jan 5, 2015

Hi Pabble,
Thanks for your interest. The design is very robust and it lacks a few finishing touches such as paint and a finishing the length cuts on rear struts. I designed it very close to the rear wheels and designed it to co-exist with the 3pt (without removing the subframe). I also wanted to make it fast and easy to install without sacrificing the rigidity.

The design concept is simple. It wraps around the axle and is not merely attached to the bottom of the axle. The wrap around design transfers the load to the subframe between the tractor axles in the subframe. The tilting action of the hoe forces the rear strut to pull on the front strut transferring the load to the middle of the tractor. This could also be done without the ROPS by just connecting the front and rear struts to each other, but the ROPS was there and I used it for convenience.

Alternate view of struts. 1/2" thick 3" wide.

Up Members with first collar (later will be cut to accept a 1" bolt during initial alignment)

Up Member welded to subframe

Subframe is bolted to the bottom of the axle along with the ROPS, then a clamp is used to hold the subframe to the ROPS (belt and suspenders approach)

Bolted up at the bottom showing the up member. Note that during installation only the top bolt of the bottom attach point is installed and it slips into the collar of the up member. Also note that 3/4" nuts are welded to the head of the 1" bolts so only 1 socket (and 1 wrench to hold) is needed to do the installation.