I have a 1986 bobcat 843. I was cleaning up snow (blizzard of 2013) and it was working great! Used it for about 4 hours without problem. My neighbor came by and asked if I could move a plow pile for him- I had done a bunch already so i drove it down to his place about 800 yards down the road- did the pile- no problem, then I was just dressed things up a bit...real light stuff compared to the plow piles. Then it happened - As I lifted a small pile over head to dump , I tilted the bucket down and as I went to pull back and tilt it back up, the tilt didn't work and the reverse was real noisy. I shut it down immediately it sounded that bad. The bucket was still raised and tilted down. I checked the hydraulic oil and it wasn't even showing on the dip stick. Walked home- got a gallon of Hydraulic oil (not bobcat) and it took 3 quarts to get back within the lines on the dipstick. Started fine and it does move but I have no movement in the tilt and lift cylinders! I was able to let the arms come down via gravity and tilted the bucket back using the the ground and reversing but I have no hydraulic power for lift or tilt- NONE. Even moving doesn't seem right! makes much more noise and it seems to pull to one side! Did i just fry my hydraulics? BTW- fluid and all filters were changed less than 50 hours ago (with bobcat brand). HELP- is there a bleed process or something I can try? Thanks in Advance...feeling dejected.
The pump may be out, but it may not have anything to do with low fluid. Having the bucket up in the air may have caused you to show the machine being low on fluid, a gallon low typically wont cause a problem. Your pump may be out, but I doubt it was due to low oil level.
off the top of my head, is your RH sterring lever pushed off to the cage side of the machine. ie: aux engaged? if the drives are not weak, the coupler between the hyd pump and hydrostat could have broken. if the drive is weak, the pump coupler/ujoint may have stripped or broken :drinkup
I've gone out 3 times to see if perhaps there was an air pocket keeping the pump from priming- no go. To anser some questions- auxiliary hydraulics aren't engaged. I did try it both ways just to be sure and there's no audible difference either way - ie.. no pressure built up. I've been staring at the hydraulic diagram... am I correct in thinking there's 3 pumps? One for each side of the drive wheels and one for the tilt and lift? Also the pressure relief only works for the lift/tilt/aux... correct? I brought the machine home (800 yards) and now I'm really worried... one side isn't driving well at all. Looking at the parts break down, it looks like there's a coupler between the front and rear drive pumps and If that coupler went, it looks like I'd have drive to one side only and depending on how it broke/stripped it might allow the other side to drive if the load was low. And it would also prevent the hydrostatic pump from spinning. Is this likely? How big a job? How the heck could everything have gone so wrong so fast? Everything was literally working perfect one second, then no lift/tilt all all next second PLUS drive problems???
Next step if you have noise and hyd issues is to remove and cut the hyd filter. Cross your fingers it is clean and not full of metal. I would not run it any more until you check the filter condition.
I have 2 filters- hydraulic and hydrostatic. Looks like I'll be cutting both.
I have bugger all experience with bobcat setups but my ASV has three pumps, two for drive and one for the loader arm and aux hyd. Perhaps a relief valve is stuck open?
I think that would explain the lift tilt but not the drive problem (I believe??). I think the relief valve is out of the loop on the drive side. Also- I think is would see some movement on lift tilt eve with the relief valve open? I get nothing, nada, zip... not even a wiggle in a cylinder.
yes there are 3 pumps, all inline rear pump is left side drive, next is right side drive, then (if i recall) a gear pump for hydraulics, what side drive is weak? do you feel a strange "seat of the pants" vibration that wasnt there before? as for why all of a sudden........ unit is 26 years old, nothing lasts forever unfortunately :drinkup BTW the 843 is my least favorite machine to work on.....
thanks for that! I've done so much to it already, about the only thing I hadn't rebuilt was the hydraulics. it's the left side that's weak (my left while sitting in it). Rear pump is the one closest to the engine? Vibration? you could call it that but it's more associated with noise. At full throttle without any hydro demand- there is no vibration. if you move forward or back slowly (half throttle) not much noise- no vibration. Try pivoting or turning (forcing one side to skid) and the noise and vibration are very obvious.
the 1st thing i'd check would be the pump coupler/ujoint, between the engine and pumps... :drinkup
so pull the engine? Aw man! I was hoping for something a little less invasive. if it was the coupler... wouldn't I lose all drive? I still have reasonable drive on one side.
I'm wondering if your gear pump is shot. It provide charge pressure to the hydro pumps. I'm think left was weak to begin with and is more noticeable now with low charge.
that makes sense but I've never seen a pump fail like this. I've seen them get weaker and weaker over time. This one was strong enough to lift a heaping bucket of wet snow one second and then not even be able to budge an empty bucket. It was like something suddenly broke. The inter-pump coupler would make sense if it drove the left wheel pump and gear pump but not if it drives the right wheels (they are still fairly strong) and gear pump (as cheif suggests). Same with the main coupler- I would think if that went, I'd have hardly any drive either and mechanical noises (coupler slip- if it was able to drive low loads). Is there a coupler for the gear pump alone? I don'e see one on the parts diagram. Could a wide open relief valve cause weak charge pressure and absolutely no cylinder movement?
you can check the coupler without pulling the engine.. my thought on the main coupler may be the splines are worn, the engine is turning, but the pump shaft is spinning at a slower speed. but it really sounds like the hyd pump coupler inside the pump broke or stripped it's splines. :drinkup
there should be a splined coupler between the hydrostat and gear pump, without seeing the parts breakdown, it may be show with the gear pump itself, or with the front hydrostat anything is possible with the relief, pull the main relief from the control valve, and see if the orings are blown. :drinkup
First- Thanks for the help guys! It really makes me feel better to be able to bounce idea's off guys in the know. I mostly rebuilt this machine about 50 hours ago including having the engine out for rebuild. The coupler looked really good- no signs of spline wear and the universal joint had no play. It may have failed but I'm pretty good mechanically and the event didn't sound or feel like a what I'd expect if that coupler stripped or the U joint let go. BTW- how the heck do you check that coupler with the engine in? I've been studying the parts diagram and it shows a coupler between the rear (left) drive pump and the front (right) drive pump but it looks like the gear pump is driven directly off the rotating assembly of the front drive pump... I can't see a coupler and if it comes on either the gear pump or the front drive pump, it doesn't look like it can be purchased separately. I'm intrigued by this charge pressure possibility. My gear pump has 2 sections. Section 1 (front most) is the charge pressure side. Section 2 is what creates pressure for the valve block but it also looks like it feeds reservoir oil to the front drive pump (which is the left side drive). I'm going to re-read the oil flow explanation as this seems like this could explain why I have no lift and a week left side drive.
you can get to the coupler, however it's not easy, raise the cab, and lay on top of the pumps, reach around the side of the rear pump mount, inside the blower housing, and it's right there !! i dont have access to parts breakdowns right now, but from what i remember the hydrostat and gear pumps are splined together, most bobcats have a splined adapter coupler at the hyd pump end. i think i'd remove the hyd pump and take a look, something's gotta be broken :drinkup
I can't open the cab in the garage so i'll be doing this outside in lovely New England winter weather. I'll probably order filters and a new relief valve tomorrow then wait for a decent day to pull the pump. I'm pretty sure I'm going to need to check the coupler between the drive pumps too. Any tips? I presume it can all come out from the front under the cab? Not really sure what to look for so I'm hoping the problem is reasonably obvious. With no drain on the oil tank- any tricks for not making a mess when the supply line comes off the gear pump?
pull the suction hose (from the tank to the pump) off at the pump, pull the open end up above the oil level in the tank, you'll loose some oil, but at least you wont have a huge puddle if i recall, and depending on the pump/control configuration, you'll probably have 2 or 3 hoses going in the top, or side of the pump, plus the hose clamped suction hose. 2 bolts and the pump should slide right off. :drinkup
I noticed no one asked if your hyd oil had a lot of foam in it. if so check your seal on the hydro pump. if the seal is bad it will allow the pump to suck in air causing cavitation. just another possibility
Nope - no foam that i could detect on the dip stick (but good thought). And- after I put in 3 quarts, the level is now over full with the arms down and bucket rotated back to level. It seems less likely that I had a low enough oil level to actually run the pump dry. It does seem to point to - something just broke.
Crewchief- I'm rapidly beginning to hate working on the 843! I went to remove pump today since we have another storm coming thursday. Working in the snowy side yard, in the rain- pump removal was going good- too good - until I go for the bottom flange bolt. It's obstructed by inlet T and the inlet line is about 1.5" with no apparent way to drain the oil tank or remove the line without dumping large amounts of hydraulic oil on my lawn! I can't see a way to remove it without suctioning the tank out first. Oh yeah- the tank fill port has a mesh screen which prevents me from suctioning out the tank. What am I missing? The manual is useless! ANY experienced guidance would be appreciated. I'm actually thinking of piercing the hose as a makeshift drain and then replacing the hose but this can't be the appropriate maintenance procedure.
you can use a shop vac to create vacume in your hyd tank so fluid does'nt spill out. put your hose into fill neck and seal it up. take your filter out of your vac. have the hose above hyd tank, so not to suck fluid out. turn on the vac & remove the suction hose. it will keep the oil from comeing out until you can plug the hose.
Everything is a pain in the ass to do on 40 series even in a nice warm shop. I just shake my head when guys go on and on about how easy the old machines are to work on then one of those new ones with all the electronics on them.
Pain in the ass is right. The manual procedure says to first raise the arms.... hard to do if the pumps bad! No thought on flange bolt placement for service either! why not put them at 9 and 3 O'clock instead of 12 and 6 O'clock behind components.
Umm, you are talking about Bobcat...who has been know to place fuel pick-up in tank directly below drive pumps.
*** UPDATE **** After inventing some new swear words, I finally got the pump out. As suspected, the splined shaft was snapped off. Luckily, the splined piece came out of the forward drive pump reasonably easy. I suctioned out about 2 gallons Hydraulic fluid from the sump hose (and lost about a quart) so I'm sure the pump never ran dry. I checked the drive pump shaft and it spins when the engine cranks so I'm pretty sure the damage was contained to the gear pump. Hopefully, restoring charge pressure will also cure the drive noise and flakiness. I don't think the system was contaminated since the shaft broke outside of the pump. Would you guys still cut apart the filters and purge the system?? Seems like a huge pain. I'm pretty sure I'll need to replace the whole pump but it's a shame I can't buy just the shaft and a rebuild kit as the pumps internals seemed strong.
Well it goes back to the old question of what caused the shaft to break ? Does the gear pump spin free or is it bound up? If your getting a new pump quickly blow the old one apart to see its internal condition (just be careful that you can reassemble if it's a core).
good call big ben- the pump is indeed bound up. My understanding is that the pump I can purchase is new (no core required) so I think I will try to disassemble the old and have a look.
Sounds like the shaft in the pump broke or splines are worn. Does it make noise or anything?
yeah- I posted an update. The shaft snapped right where the splines begin (outside of the pump). The splined piece was still in the hydrostat drive pump. I opened up the pump yesterday and found that one of the idler gear shaft bushings was worn and the idler shaft and gear tilted sideways and just dug into the aluminum housing and caused the pump to lock up. There was no debrise inside the pump other than some of the aluminum slivers.
Do you have a clam type bucket?If so ,does it have a crossover relief valve?I am not sure about bobcats system but alot of those skids do not ha ve any circuit relief valves in the aux system.If you run the open clam into a curb or something like that you get a huge (20,000 psi ) pressure spike going back to the gear pump which will stop it very quickly.Then it will either snap the shaft like yours or blow a hole in the side of the pump.
No clam shell bucket- Finally finished it today...almost a grand later and she lives! What a pain! Over $100 for new filters alone! Cut the old ones and they looked decent- i did find a small sliver of aluminum in the hydraulic filter...looks like the same stuff I saw in the failed pump. Lets hope this is a long term fix.
Nice post brother, appreciate the info.