loader problems

I recently replaced my two cylinders that tilt the bucket on my d17.  I had a machine shop cut down, weld and repack a set of cylinders that I got with the tractor.  now the loader bucket won't stay in place it keeps creeping down to the dump position.  I can lift the tractor off the ground with the tilt cylinders and it will stay that way for hours with out leaking down, but when I curl the bucket back as soon as I let off the pressure the bucket starts to tilt down?  I tried putting one of the old cylin)ers on (I only have 1 original cylinder) and it did the same thing.  I tried working the lever back and forth for 30-40 minutes in a blizzard this morning to try and work out any air in the lines, but no luck same problem.  any ideas?

Edited by dt1050 - 21 Mar 2018 at 10:03am

hoses are new and I don't see any leaks? 

Edited by dt1050 - 21 Mar 2018 at 10:36am

switched the lines raise and lower to tilt and dump and vice versa got the same results, this time I noticed whe curling the bucket back it never seems to hit a stop that boggs the tractor down?  when a cylinder hits the end of the stroke it will bogg the tractor down when dumping the bucket or raise or lowering it, but now when curling the bucket back?

the cylinders came with the tractor and I sent them off to a machine shop to get shortened. they were about 6 inches to long retracted. they cut them down, welded them and repacked them.

yep all plumbed the same way

Are you using the tractor valve or does the loader have its own valve?

  I talked to the guy who actually reworked the cylinders and he stated that they aren't true dual acting cylinders.  there is a cup in the cylinder and it will only allow pressure in one direction and not both.  he said they could order some parts and machine them so they are dual acting cylinders but is unsure of the price....I aready have $300 in the cylinders.  I would have figured since they knew they were tilt cylinders for a loader they would have told me they wouldn't work!!!

wow, that dont make ya mad at all.. buy a new welder and then they'll ship you the part for $30. 

Could you reverse the cylinders ( change end for end ) so that the good high pressure side keeps the bucket from tipping down, and the leaky side is for tilting bucket down.

Gary

If you had the work done at a real machine shop they should be able to make new pistons that will take standard packing. also since you had them cut them down and they aren't working for you I would think they will help you and give you a break on the price.

well it gets even better, apperntly the cylinders I have are only held in place with a roll pin on the one side, so when back dragging the only thing keeping my piston from fling out is a small roll pin!!! again some handy info to have had before spending the money to have them reworked.  the machine shop suggest getting a new cylinder and the only help they are willing to do is sell me them at cost + shipping.

I'm confused .can you post pics of the cyl they modified? They must have been only one hose connection with a vent on the other and they welded a thread fitting on the vent end?? I know it don't matter at this point but I'm just curious.

I just got a bailies sale book and cylinders are 15% off and free shipping. 18o0 8o0 1810

Okay, so what you've got here...

Your original cylinder was a SINGLE ACTING cylinder... that means it used return force to push back to the other end.  There's obviously a difference in the plumbing, there's also a difference in the piston seal.  The piston of a single-acting acts like the seal in an engine- compression/combustion pressure forces it to seat and seal.  Return stroke though... it doesn't.

on the hydraulic cylinder, a simple 'cup' seal (like what's used in many water wells) seals by pressure, and slides basically 'free' without it. 

And the piston is MADE for the type of seal application.

You've got the wrong piston and seal.

If it were in my garage, I'd take it apart, remove the piston, and find an appropriate piston/seal to put in it's place.  Frequently, the piston head is held to the rod with a large locknut.  Yours is probably serviceable (if they used a removable end packing), and if so, pull one apart, get a good look at the piston. 

DON'T HAVE ONE MADE BY THE MACHINE SHOP!

Look at Bailey's, and other hydraulics supply places... they have standard piston sizes... you can get one with matching seals off their CNC line for substantially less than local machine shop.  You MIGHT hafta have the machine shop bore it to custom-fit your rods, but there's a good chance you'll find a bolt-on solution.

I wouldn't be too sore at the machine shop for doing what you asked... that guy may not have had a clue about hydraulic piston head/seal, or he may have thought you WANTED it that way.  See, there are many machines that use SINGLE ACTING cylinders with TWO HOSES.  Why two hoses?  several reasons:
1: Because they use the volumetric offset to keep reservoir size down
2: Allows the hydraulic system to bleed itself rapidly
3: Allows the cylinder to ACT like a dual, but without having pressure (think gentle handling of a hay bale, or float function of a ground implement) applied on the return stroke.
4:  Allows the cylinder to be used as a variable-rate DAMPER

An excellent example of this function is a cylinder set up for this intentionally on a vertical metal-cutting bandsaw... it will only lower-so-fast.

Don't sweat it- be patient, you'll find a reasonable fix.

Why would a back-hoe not be the same/double cylinder?