643 weak and slow lift and tilt - Aux hydraulic pressure ~2000PSI

[ByggareBobby]

Hi friends,

Continuing the renovation of my Bobcat 643. Next challenge is to fix the slow and weak lift (ant tilt) on the machine. I hooked up a hydraulic pressure gauge to the Aux port to check the gear pump and rule out the seals in the lift and tilt cylinders. Not too surprised the pressure is way below what I have read is normal. At idle the gauge read ~200PSI, at half throttle ~840PSI and full throttle only delivered ~1900PSI. The engine runs fine and revs as it should. Drive/hydrostat works like a charm.

So what's my next step in troubleshooting and fixing the problem? A direct gear pump pressure measurement? (I'm a bit reluctant to do this as I've got quite a bit of respect for the pressure these pumps produces) Check/renovate the main relief valve? Remove and inspect/renovate/buy a new gear pump?

Any comments, ideas and suggestions are more than welcome!

Cheers and keep safe out there!

Regards /Stefan : )

 

[ByggareBobby]

Do you need to empty the hydraulic tank before pulling the main relief valve? (ref. gear pump w. part number 6662894)

 

[ByggareBobby]

Is it really correct that the gear/vane pump on a 643 only produces 2250-2400 psi? (see below from the manual). According to some Youtube videos I've seen measurements of ~3500 psi but maybe this is what newer machines deliver...?!