988B hyd problems

[gladiatore]

Thanks a lot guys I changed accumulator and the hose that goes to the double pump, give service to pilot system and change base from valves from controls because was broke, really thank you with all my heart

 

[lantraxco]

Yay!

 

[kshansen]

Thanks a lot guys I changed accumulator and the hose that goes to the double pump, give service to pilot system and change base from valves from controls because was broke, really thank you with all my heart

Is this the base of the small valve up by the control levers?

Might be interesting to take the accumulator apart to see if there is a real problem inside. They are very simple design. Just be sure to vent off all nitrogen pressure before starting! Four bolts take off head and then there is just a piston just like one out of one of the tilt cylinder inside only difference is no hole through it for a ram, seals just like a hydraulic cylinder.

Glade to hear you have it working again:thumbsup:drinkup

Now just waiting for the next phone call from someone with a problem, right?

 

[Bob/Ont]

There is a strap preventing two bolts from coming out until it's removed, it covers a hole that will let out any nitrogen if not drained.
Later Bob

 

[kshansen]

There is a strap preventing two bolts from coming out until it's removed, it covers a hole that will let out any nitrogen if not drained.
Later Bob

That's assuming the strap is still there!

I have no problem dealing with the nitrogen systems myself having worked on the accumulators used in Cats since the 988 87A days and the 769A,B,C,D truck suspension cylinders among others. But at another plant in the company just this last year there was a mechanic doing some work on a front suspension cylinder on a 769 or 773 truck. He was reaching over the front tire and started to remove some bolts on the cover. Do not know if all the warning tags were still in place or if he had any idea of how this cylinders worked. Suffice it to say it was not a good outcome.

 

[Bob/Ont]

That strap I speak of has a seal and covers a hole through the cover of the accumulator, remove the strap and the nitrogen all bleeds out. If someone cut the ends off of it allowing access to the bolts people could die as a result.
Later Bob

 

[gladiatore]

,now I start have other problem hyd oil is becoming hot but when I check tubes that goes to cooler are cold, so I'm going to check the lines.

 

[Nige]

Is there a thermostatic bypass valve somewhere in the system that sends hydraulic oil to the cooler only when it's hot..? I know on larger machines they have a habit of failing closed and causing overheating.

The other possibility as Bob/Ont mentioned before is if the brake pump is not destroking correctly when the accumulators get up to pressure it will cause the oil to overheat.

 

[gladiatore]

Nigel do you know where is located that thermostatic bypass valvle?

 

[Nige]

There doesn't appear to be a thermostatic bypass valve on the 988B but there is a pressure-operated cooler relief valve right next to the cooler itself. It is designed to open and bypass the cooler if the pressure in the cooler lines is too high. If that valve is stuck open and the cooler is permamently bypassing then the hydraulic temperature would be too high.

 

[gladiatore]

Alrady changed and same

 

[Nige]

In that case my suspicion would be on the pump not destroking in response to the accumulator charge valve signal.

 

[Bob/Ont]

Nige that pump is a vane fixed displacement. the problem would be caused by the charge valve spool not directing the flow to the steering when the brake max pressure is reached. However I think cool lines where mentioned if so the oil isn't flowing to the cooler, check that valve again for correct assembly.
Later Bob

In that case my suspicion would be on the pump not destroking in response to the accumulator charge valve signal.

 

[Nige]

Sorry, didn't check. I thought it was a variable displacement pump.

 

[gladiatore]

I already changed
3 acumulators

 

[Bob/Ont]

I already changed
3 acumulators

Accumulator only stores energy like a battery, keeps a reserve of braking oil under pressure. The valve that diverts the oil back and forth between the brake and steering circuits might cause trouble if it is stuck feeding the brakes and not going to the open center steering valve. But if the cooler lines are not as warm as the hyd tank then look for a obstruction in them. Feeling them is the best tool, just touch lightly and don't get burned.
Later Bob

 

[Bob/Ont]

I think the B machines have gear pumps the 87A machines had vane pumps.
Later Bob

Sorry, didn't check. I thought it was a variable displacement pump.

 

[gladiatore]

h

Also light from pilot system illuminates

 

[gladiatore]

Cooler hoses are cold hyd hot like crazy

 

[Nige]

Cooler hoses are cold hyd hot like crazy

Oil isn't going to the cooler for some reason .......... your challenge is to find out why. Maybe you have a blocked hose somewhere.