Hyster E40BS:
Low Hydraulic Pressure

Hi..New to forum.
I just bought an older (1977) Hyster electric 4000#.
When I bought it 2 months ago forks would go all the way up but it would not lift a heavy load. Now (2 months later) it will not go past the first cylinder on lift and wont lift more than a few hundred pounds. The tilt is also very weak.
Thus far I have changed fluid and filter and had pump checked - all ok. A gauge on the port shows only 200 psi.
Is there a bypass valve or a check valve that can be causing such low pressure. Thanks for any help.
  • Posted 8 Nov 2011 05:43
  • Discussion started by run_rock
  • Texas, United States
Showing items 1 - 10 of 10 results.
OK, my email is in my profile. The board automatically deletes all links and email addresses inside posts.
  • Posted 23 Nov 2011 15:41
  • Reply by lumberjack
  • Maryland, United States
my email is [email address removed]
i took some pics of the machine today- i will send to you via email.
  • Posted 23 Nov 2011 12:47
  • Reply by run_rock
  • Texas, United States
Put your email in your profile or in a post written out like "person AT blahblah DOT com" so I can send you a picture of a similar valve. That way we'll be sure to be talking about the same things.

The relief valve should be an allen headed screw (usually with an acorn cap nut on top) in the same spool that the pressure line goes into. Some older trucks also had a relief valve in the pump. (I can't remember if old Hysters had them or not)

If the relief valve on the control valve is the problem, you may be able to feel the oil rushing through the return line from control valve back to the sump.

If you're careful you should be able to remove and inspect the relief valve parts without a problem.

By the way, do NOT hook the pressure line directly into a gauge. This "dead heads" the pump and blows it up instantly.
  • Posted 22 Nov 2011 08:27
  • Reply by lumberjack
  • Maryland, United States
Thanks Lumberjack. I will check the relief valve below the flow control valve more carefully. How do i know if there is another bypass valve on the machine? There is a big dual in/ dual out valve (block?) on the mast - could that have a bypass inside?
  • Posted 22 Nov 2011 04:04
  • Reply by run_rock
  • Texas, United States
Ha it censored me. A collapsed hose could cause you to s u c k in air.
Like you do with a straw. Or how you start a siphon. It's the word used to describe Michael Moore's movies.
  • Posted 19 Nov 2011 09:35
  • Reply by lumberjack
  • Maryland, United States
The relief valve may have a broken spring. Unscrew it completely and the spring and ball will fall out, or can be gotten out with a magnet. Be prepared for a little oil as well. Everything needs to be kept clean for reassembly. There is also the chance that a bit of dirt or debris got trapped in the valve. It's probably worthwhile to inspect the port with mirrors and a flashlight.

The only other thoughts I had: Check that the supply hose from the sump to the pump isn't collapsing when the pump is operated. This starves the pump for oil and could cause you to be *** in air. The other thing - check to make sure you only have one relief valve. If there's more than one, you want the one closest to the pressure supply hose.

Good luck with it.
  • Posted 19 Nov 2011 09:30
  • Reply by lumberjack
  • Maryland, United States
Thank you for the reply. I adjusted the relief valve screw all the way one direction then all the way the other. No change in the pressure reading during and after.
Where is the bypass located? is it possible this is stuck open?
Battery is strong and at full charge.
  • Posted 10 Nov 2011 09:12
  • Reply by run_rock
  • Texas, United States
Your relief valve screw is way out of adjustment. You may have proper flow but if the pressure on the spring isn't set correctly than the bypass will open and dump back to tank.

Put a gauge in the test port hold over relief and slowly adjust pressure to spec.

Of course if your battery is shot than this is all pointless
  • Posted 8 Nov 2011 16:14
  • Reply by VAN_CEN
  • British Columbia, Canada
batterys were recently tested - all ok. full charge.
that is the reading with the lever at full pull.
  • Posted 8 Nov 2011 12:17
  • Reply by run_rock
  • Texas, United States
how is the battery?
is that 200 PSI with the tilt lever pulled back to "stall"
  • Posted 8 Nov 2011 06:34
  • Reply by edward_t
  • South Carolina, United States
"it's not rocket surgery"

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