Power beyond problem?

Fred2016

New member

Equipment
Gzd21
Nov 21, 2021
4
0
1
Scotland
Hi all.
Gzd21 zero turn mower. Pto to blades turns then stops. We have fitted a new pto clutch and oil pump. Pressure is good at tipping rams but when testing the PB port the pressure starts at 2 bar quickly dropping to zero. The manual states we should have 10 bar at the PB port. Any ideas?
 

Dave_eng

Well-known member
Lifetime Member

Equipment
M7040, Nuffield 465
Oct 6, 2012
5,108
926
113
Williamstown Ontario Canada
Hi all.
Gzd21 zero turn mower. Pto to blades turns then stops. We have fitted a new pto clutch and oil pump. Pressure is good at tipping rams but when testing the PB port the pressure starts at 2 bar quickly dropping to zero. The manual states we should have 10 bar at the PB port. Any ideas?
I do not know your machine so my comments are general in nature.

Assuming your machine has open center hydraulics, then the only time pressure builds in any out line from a valve or out a PB line is when that out flow is restricted by a cylinder or hydraulic motor. Otherwise the flow is constantly circulating at low pressure from the pump, through a valve(s) and back to the reservoir..

Because you are a new forum member you cannot post photos etc for a while. I will send you my personal email in a private forum conversation. Send me some manual photos and I will post them in your thread.

Dave
 

Fred2016

New member

Equipment
Gzd21
Nov 21, 2021
4
0
1
Scotland
We have now tested the spool valve at which point we have 1800psi. The PB port tests the same when dead headed. When the PB port is T'd to the flow to the pto clutch we get 120psi which we expected however at the clutch operating valve we get 35 psi which rapidly falls to zero. We are now thinking something is seriously wrong inside the casing or the clutch operating valve itself.
 

lugbolt

Well-known member

Equipment
ZG127S-54
Oct 15, 2015
4,808
1,575
113
Mid, South, USA
a leaking pto clutch can do the same thing

remember-pressure is nothing more than the sum of restrictions.
 

Fred2016

New member

Equipment
Gzd21
Nov 21, 2021
4
0
1
Scotland
a leaking pto clutch can do the same thing

remember-pressure is nothing more than the sum of restrictions.
Cheers Lugbolt. That was our first thought and all the symptoms point to that. However we have rebuilt one clutch and then fitted a complete new unit. We took it apart again to check the seal behind the clutch and still the clutch slips. Have you any idea where else or how else the clutch could leak?
 

Fred2016

New member

Equipment
Gzd21
Nov 21, 2021
4
0
1
Scotland
a leaking pto clutch can do the same thing

remember-pressure is nothing more than the sum of restrictions.
We have now removed the PTO valve lever and we're surprised to see three drillings of roughly 4-5mm as expected from the manual drawings. However the hole that looks like the input oil to the PTO is only a tiny hole of maybe just under 1mm. It's as if the hole wasn't completely drilled through and they stopped just as the tip of the drill broke through. Nowhere does the manual mention this. Is it possible someone has previously fitted a faulty part of should it be this way and if so can you explain why?
 
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