Hello everyone, im new to this forum and hopefully I can sort a problem I have with my Bobcat 631. Here we go: After a few years of rebuilding this machine over my spare weekends I have completed it!!. I finally started it three weeks ago and she was working fine. The machine was pretty smooth to operate as I have renewed all control bushes, fluids and top end engine rebuild. My problem came when the hydraulic pipe from the reservoir to the hyd pump was resting on the rotating universal joint going from engine to pump! ouch!! Hence from the above, it made quite a hole in the hydraulic hose and obviously most of the Super Universal Tractor Oil in the reservoir drained out!. I had a new pipe made the next day but was not able to get the same oil that was originally in the rest of the pump, motors etc. I bought HV46 hydraulic fluid (blue in colour) and refilled the reservoir. When it started the machine up it creeps forward slowly which it never used to and when levers are moved forward it drives fine, but when reversing and turning the whole thing "Bucks or Jerks" violently! its pretty frightening... I have read several threads and a lot of people say it could be the pintle levers are worn etc which mine are slightly but what I cant work out is why it was not like this before the hose leak???? Im assuming its something else since I have refilled the system or mixing oils, air in the system etc? if anyone has any ideas it would be greatly appreciated.
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ancomcabs
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I don't know much about the hydraulic fluid you mention but I'm positive that the 630-631-632 called for 10w30 motor oil in the hydraulic resevoir, could be related
Many thanks for your quick reply, the original oil I put in the machine was 10w 30 but the extra top-up oil HV46 was much thinner..... but what I cant understand is why it goes forward ok and not reverse or turn, surely if it was a problem with the oil it would do this going forward too....
Before anything else I would block it up with all wheels off the ground and run it at medium speed both forward and reverse for several minutes. Your problem is probably due to air in the system and it is not good for air bubbles to go through the motors and pumps while under load. Check the reservoir to for foamy fluid. The 10-30 is the right oil but cant see what you have in there as causing the problem right now.
Hi, yes I have jacked it up and run it forwards and backwards for a few minutes and the wheels all seem to moving smoothly, maybe when on load is the main cause and there is air in the system still, but why doesn't it do it in forward direction if this was an air problem?.. . In cant really see if fluids foamy as there are the old spill to fill holes, but I noticed that the oil that comes out of the spill to fill do have large bubbles now and then. Is there a common valve that could have dirt etc in it that would cause the wheels to keep creeping forward when controls are in neutral?
ancomcabs
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When the hose got chewed up could pieces of it have made it into the system?
I'd check the port block filter, i'd doubt it is the problem but it never hurts to check it.
I guess it could be the shuttle valve in the drive motors too.
I'd like to think that the oil is just foamy from the eating of the hose. Generally the air bleeds out pretty fast.
hi thanks for the last two replies, I was wondering about bits of the hose getting into the system which could be a possibility... I have checked the port block filter and there was a lot of dirt which it looks like its been there for years but couldn't see and bits of rubber/metal etc so its doing its job as inside the filter was immaculate. Whats the chances of two of the motors having problems starting the same time straight away and allow creeping forward? would a relief valve give this problem if had muck in it? Is there a common valve supplying both motors at the same time, whats the small pipe going onto the hydraulic motors that tees off from a central small block for, does anyone know? selector valve...? im running out of ideas and what makes it worse is its fine forward and was happening before a changed fluid and pipe lol Many thanks for everyones help so far.
Hello Steve, The small (3rd) line from the drive motors will be your case drain, this is the return line back to your low pressure side of your hydraulic system (someone correct me if I'm wrong) but should be around 125 to 250psi. I believe there are a couple of case drain filter assemblies inline with this either #4 or #6 hose. This oil returns to your reservoir via a port block with low pressure relief valve and eventually ends up getting filtered and put back into your main hyd oil tank. I hope I got that circuit right! JLM
Steve, I just reread your last post. If you have any dirt anywhere.. my suggestion is a complete hyd oil system drain & flush. You will be money ahead! Dirt, silicone rubber(gasket material) are no-no's in a hydraulic system. I would also suggest you install the recommended oil (usually spec'd by the mfr of the hydro-stat pump) and not rely on a Bobcat dealer. Most hydraulic systems use oil that pretty close to automatic transmission fluid (don't use that though). The oil should have a ISO VG AW32 specification or standard similar to that. Best of luck to you! JLM
Many thanks Jlmoon, I think I will have to bite the bullet and do a complete flush. many thanks I will keep you posted when completed. regards steveo631
