Lift slow and eventually stops as machine warms up

I've been trying to diagnose this one for a while... Bobcat 753G

I now have a pressure valve on a tee on the retraction side of the lift boom - lowering the boom with the bucket on the ground gives me:

(With the machine cold), I get 2100 PSI at idle and 2500 PSI full throttle
(With the machine warm), I get around 1100 PSI at idle and 1500 PSI at full throttle - when the machine is warm it isn't able to lift the boom except for small jerks when I press and release the pedal

Tilt seems okay through out this process

I've tried capping off each lift cylinder extension hose and attempted to retract the lift (with the bucket down) to check for fluid bypass but there was none - I then capped off both extension hoses and tried lifting to check for load on the engine (per Willies suggestion) but the engine did not seem to bog down

Could the port relief valve be the culprit? If so, what should I be looking for when taking it apart?
Could it be the spool valve leaking? Any way to narrow it down to this?
Could it be the gear pump itself? I wouldn't think so, because the tilt is working okay, but maybe the tilt doesn't require as much power?

Any advice on what I should do next to diagnose would be greatly appreciated

"Could the port relief valve be the culprit? If so, what should I be looking for when taking it apart?"
yes, I'd look for broken spring, o rings, scratches, debris in the way, and check for smooth operation, and the seat is intact.

"Could it be the spool valve leaking? Any way to narrow it down to this? "
Not as likely unless the housing is cracked.

"Could it be the gear pump itself? I wouldn't think so, because the tilt is working okay, but maybe the tilt doesn't require as much power?"
Again, not as likely. You could test the pressure on the tilt function, or swap hoses with the lift to test the pump and the spool valve.

My first thought with those low pressures would make me think the pump is worn -- bucket function doesn't take much pressure to move ---try that with a full bucket of wet dirt--see if it lacks power or tee your gauge into a bucket line. I don't know how accessible the pump is but almost may be easier to take it off and inspect. That pressure is low to begin with and the difference between high and low speed makes me think the pump is feeding an internal leak-- and more than likely the "leak" is inside of the gear pump.

Delmer said:

I'd look for broken spring, o rings, scratches, debris in the way, and check for smooth operation, and the seat is intact.

Click to expand...

I've got the port relief valve off and I can't see any debris or broken orings, I can't actually push the spring in to see if it operates smoothly - should I be able to? My understanding was that doing so would require a lot of pressure

I'll see if I can tee my gauge into any of the other connections to get a reading on the tilt but I think its a slightly different size to what I currently have

I've got my main relief valve out, a few things seem missing, I have no 18 or 20 in the picture below

I know what 18 is because I've got one on the port relief, but what is a "CLYD RING" and whereabouts should it sit on the relief valve?

Could the fact that the CLYD RING is missing be causing my issue?

Also, I was able to easily operate the (poppet) spring in the main relief valve, I guess that means my port relief valve is buggered? I'll post a picture when my other half gets home as my camera isn't very good

[QUOTE = "catmanjan, gönderi: 906904, üye: 82715"] Bir süredir bunu teşhis etmeye çalışıyorum ... Bobcat 753G
Hidrolik pump
Artık kaldırma bomunun geri çekilme tarafındaki bir tişört üzerinde bir basınç valfim var - bomu kepçe yerdeyken indirmek bana şunu veriyor:

(Makine soğukken), rölantide 2100 PSI ve tam gaz 2500 PSI alıyorum
(Makine sıcakken), rölantide yaklaşık 1100 PSI ve tam gazda 1500 PSI alıyorum - makine sıcakken, pedala basıp bıraktığımda küçük sarsıntılar dışında bomu kaldıramıyor

Bu süreç boyunca eğim iyi görünüyor

I've tried capping off each lift cylinder extension hose and attempted to retract the lift (with the bucket down) to check for fluid bypass but there was none - I then capped off both extension hoses and tried lifting to check for load on the engine (per Willies suggestion) but the engine did not seem to bog down

Could the port relief valve be the culprit? If so, what should I be looking for when taking it apart?
Could it be the spool valve leaking? Any way to narrow it down to this?
Could it be the gear pump itself? I wouldn't think so, because the tilt is working okay, but maybe the tilt doesn't require as much power?

Any advice on what I should do next to diagnose would be greatly appreciated[/QUOTE]

I wouldn't worry too much about the missing parts on the main relief. the backup ring is to keep the o ring from squeezing through gap, if the o ring is ok, then you're fine. Don't know what a clyd ring glide is, maybe cyld ring guide? If the bucket works fine though, i'd stick with the other port relief for now.

Can you get it apart? The spool has to move easily to function, that's with the spring pressure backed off. Maybe you'll find your clyd ring?

Thanks Delmer, I've ordered an o-ring kit for the main relief anyway

The port relief valve looks to be factory sealed - not adjustable and it doesn't disassemble

I'm wondering if anyone has a Bobcat port relief valve and can check whether they can move the poppet by hand, I asked at Bobcat and the guy wasn't sure... Might call another dealer and ask them

Wipe it off and blow through it, you should be able to figure out the function of it, and it shouldn't leak without a lot more pressure than blowing through it.