Old 742 Problems

[3claws]

Hoping I can get a little direction please. I have an old 742 that was somewhat pieced out. I've built the whole thing back together. The problem I can't seem to figure out is hydraulics. Everything works fairly well for the first cold 5-10 minutes. Then it seems like the hydraulic pressure just drops and it won't move, lift stops working and the bucket works very slowly. I have gone through this a handful of times. Rebuilt the drive motors. Rebuilt the hydro-static unit. Nothing was broken or worn. In fact, quite a few of the parts were new which tells me that the original owners couldn't figure it out either. Any help would be really appreciated.
Max

 

[3claws]

Anyone??

 

[brdgbldr]

Anyone??

Are you using the correct weight/type of fluid?
If the fluid is too thin, as soon as the machine warms up it becomes even thinner and can cause a problem like this.

In older machines, I have always had good luck with NAPA AW46 hydraulic oil. Of course the weight of the oil should be dependent on the climate that you use the machine in.

Another issue could be that your control valve needs to be resealed or you have a bad relief valve.

 

[3claws]

I've tried a few different oils and at different temps. I live in colorado so I've been able to try various hydraulic oils in both hot and cold climates. It continued to fail the same with them all.

 

[R.T.E.]

gear pump was it redone, suction hose good and tight , the fitting at the bottom of the hyd tank make sure that's tight, not easy to get to ,i have had that issue and it was the suction hose, hopes this helps

 

[oiu789]

Check charge pressure cold and hot.