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3400 hyd losing prime

Zane are you here?

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08-20-1999 19:22:40

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Just rebuilt hydraulic pump, replaced hydraulic
oil, and installed new lift kit. After priming, lift works just has a little chatter as it is coming up, but will lift up the back end of a pick-up truck. When you shut it off for 3 or 4 hours, and come back to it, it has lost prime and
will only work when re-primed. Any suggestions?

Thanks in advance,

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08-20-1999 22:56:02

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 Re: 3400 hyd losing prime - Zane are you here? in reply to John, 08-20-1999 19:22:40  
Check for possible air leak on the suction side of the pump. Did you replace the o-ring on the manifold or inlet tube? Since you say you rebuilt the pump, I'm assuming you replaced the driveshaft seal as well. A leak here can cause the pump to suck air.

Also, did you remove and clean the pump inlet screen in the bottom of the center housing when you had the lift off? More often than not these are pretty plugged, and this will definitely cause a pump to not want to prime very well. Shouldn't really make it loose prime, but it can't help the situation either.

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08-21-1999 03:56:30

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 Re: Re: 3400 hyd losing prime - Zane are you here? in reply to Bern, 08-20-1999 22:56:02  
Exellent advice! I might add that if the pump shaf is worn much where the seal makes contact it will cause it to suck in air. Also where the needle side thrust bearing runs will sometimes wear into the shaft on one side. If this has happeded the shaft will either have to be replaced or built up and machined back down to a mirror finish.

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08-21-1999 14:51:24

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 Re: Re: Re: 3400 hyd losing prime - Zane are you here? in reply to ZANE, 08-21-1999 03:56:30  
Bern and Zane,

Thanks for the advice. I did tear the pump back down and replaced the needle bearings and put in another new seal. It has held prime for 3 hours so far. But still has a chatter as the lift comes up. Chatter meaning small jerks as it raises.
But can live with that. I'm hoping that it is just some air trapped in the system. Thanks,

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08-21-1999 20:10:08

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 Re: Re: Re: Re: 3400 hyd losing prime - Zane are you here? in reply to John, 08-21-1999 14:51:24  
John, is your inlet screen in the rear axle clean? Also, it is normal for these things to take a while for all the air to get out of the system. Some I have to run a half hour or so to get all the chatter out of the system. Why it takes so long I really don't know. Piston pumps are not real good about priming themselves though, and a plugged inlet screen will only compound this problem.

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