my hydraulic trailer will not raise unassisted, and will not hold once raised???

Hello desireedog2:

These are just thought and suggestions OK?

Check the bearing on the side which acts as the hinge. The bearing may be dodgy which may account for the bed not going down when empty.

As has been said, there must still be a leak but on the inside. It means you are not at full pressure and hence the symptom. The leak on the inside, depending on the pistons can be leaking into the piston itself and something will fail if it is left. I am assuming you have just one pump?...........

Fixed and not replaced. What does that mean? I think you may have used a filler or tape round the leaking area to temporarily stop the leak.

For your safety and every one else's, I suggest you should replace all the rings and seals, like NOW!It is a relatively small job on a vehicle with a single pump.

Good luck, and get working, with no 'short-cuts'! There is an awful lot of pressure in those pipes when it is working as it should, it will hurt if it suddenly blows!

Take care.............

As stated by another reader please for SAFETY sake REPLACE not "fix". You could have a bypass of the piston seal in the cylinder.It could also be that your "fix" could have led to something being sucked into the control valve or a relief valve.

the answer is in these two bits of info

'after that i raised the bed and it went all the way up but would not go back down'

what did you do while fixing that would cause the sticking?

'i finally got it to go down'

consider how you did that. that info would help you troubleshoot.

if all else fails, take everything appart and inspect, then put it back together. if nothing else, it will be quite instructing.

I was going to suggest that desireedog2 generate a hydraulic schematic but you did this verbally. I have dealt with hydraulic systems but never a dump bed specifically. I was wondering if this system may have separate safety hold valves or ones that would be build into other devices in the system. That way the bed could not go down (or maybe even up) without a specific hydraulic signal.

A malfunctioning hold valve could cause confusing up/down problems.

An accurate hydraulic schematic is always the first step of diagnosing an odd hydraulic issue.

I made the assumption that the system used a manually controlled spool valve. It might have relays and solenoids to allow the use of electric controls. Good point on your part. Now that you mention it I have seen a couple trailers with a remote pendant control. They might be more common than I am aware of.

great reply to the post.

after reading the original enquiry i went back to basics as presented in the hydraulic circuits shown in my john deere repair manuals, and to look at some designs of offshore (aka t-i won) sourced hydraulic pressure pumps.these things came out of the search

one the seats of the check valves for the up down lever may not be smooth or the pressure of the open close spool valve springs may not be strong enough to allow the ball bearing to seat properly.

two apparently the springs in the offfshore sourced products have been designed for other applications but are used in the pumps as well

three the body of the pump itself may have a cavity which when pressure is applied leaks through the castings wall and into the internal cavity void or as suggested in the post right through the castings wall

four the suggestion duck tape or similar glue or actual fabric etc being sucked in and jamming the return valve cannot be avoided

five the hydraulic jack buiklt into the 5 ton cab over of the international was known as a hazard i think that is why the truck maker started putting in internal supports that kept the cab up whie the top part of the engine e.g. alternator waws worked on.

as stated VERY GOOD response

'da ber

These are some very good posts and I believe your answer is in them. I would like to add some personal experience about the safety when dealing with any type of hydraulics. I had a buddy that drove a cab over diesel truck several years ago. These older type trucks had a lever behind the seat that worked a valve to lift the cab up to gain access to the motor area. While he was lifting the cab a high pressure hose burst and injected hydraulic fluid into his thumb. After several weeks of trying to save his thumb they finally had to amputate it. it was a very strange and misfortune accident. I have found over the years it is way better and safer to replace things that seal rather than to fix them and hope for the best especially on the high pressure hydraulics systems. Please be careful!

pipewelder

Another safety note.

Never stick your head or any part of your body between the raised bed and the frame without safety blocks or pins in place. Should the bed drop you will not likely react in time. Lots of needless injuries by not following this simple rule.

I just completed a major refurbish/retrofit on a dump truck a friend of mine bought. The first thing I did was to add a steel brace and pin to lock the bed up before doing any work underneath it. This is a basic rule I follow before working on any dump in my shop. If a truck does not have a bed lock system I will refuse to work on it unless the customer agrees to pay for me to add one. I have seen where people slide a large wood or metal beam under the bed to have a stop to block the bed from being able to come all the way down but I have also seen a bed fall because of bursting seals and push these stops all the way up or shear the wooden ones off to where they would not have done much good. Thank god no one was under the bed at the time!

pipewelder

Hi,

I wrote a long post about the dangers of working on hydraulics if one is not trained in the hazards. But then I decided it would sound like a typical internet flame post, and would be easy to dismiss. But I do want to seriously raise the issue that hydraulics is a hazardous field, and can surprise you and injure you.

I recommend you go to this link first, then consider whether you want to go ahead:

http://www.fluidpowersafety.com/fpsi_alerts_enter.html

You will have to log in (it's free) and then you can read the safety alerts. Please do so for your safety and to make sure you come home intact and healthy to your loved ones.

Best wishes,

safetyguy

You said you fixed a leak , did you bleed the system after repairing the leak ? Usually if fluid is leaking it is being replaced by air . If there is air in the system , the air will compress in a hydraulic system and give many odd effects . If the fluid is airated ( tiny bubbles ) it can take time to compress that air and give the inching down impression much like the brakes on your car that need bleeding , spongy . Also may give the effect of " not enough pressure " as the pump will be compressing the air as it pumps fluid .

From your description my first thought was their maybe air in the cylinder; you may need bleed or purge the air out.