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  1. #1
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    Default Bobcat s750 high flow-- "Chirping" sound from hydraulics

    Have an S750 high flow.. all the bells and whistles.. and now I have a chirping sound. Sounds like some birds. My tech noticed it and I made an appointment to put it in the shop. They couldn't find anything substantial and said that it was most likely some tubelines touching under pressure.. in other words two lines rubbing just right to create a "chirping" sound. They couldn't stop it but said everything else tested fine.

    Here's what happens. When I have the RPM's about 1900-2200 I can hear it more when I engage hydraulics for example when I open and close my grapple. I can also hear it when I am rolling the bucket back all the way. Basically when the hydro system is under load and the engine noise isn't too great, I can hear it. I tried ignoring it but now it's driving me nuts. Performance is about the same but that chirping is annoying.
    At full RPM it's still there but drowned out from engine noise..

    Anyone ever had this or have any ideas? Machine has about 650 hours.. still under warranty but I don't have time to put it in the shop for a week. Shop agreed to come out and look at it again but I'd like to have an idea of what it could be to help them find it.

    Thx!
    Brush Chipping and Tree Mulching Texas Style!

  2. #2
    Veteran Member SSdoxie's Avatar
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    Bobcat CT225

    Default Re: Bobcat s750 high flow-- "Chirping" sound from hydraulics

    The drive belt can cause this "chirping sound" expecially under load. Check you drive belt adjustment stop. Opeeration Manual explains how to do this, pretty simple.
    Dennis

    CT225 w/7TL QA FEL, 60"tooth dirt bucket, 68" smooth bucket, Pallet Forks, Bale Spear. Hydrualic top llin, QH, 48 RC, 60" tiller, Angle blade, Landscape rake, Carry-all, Post hole auger.

  3. #3
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    Default Re: Bobcat s750 high flow-- "Chirping" sound from hydraulics

    Quote Originally Posted by SSdoxie View Post
    The drive belt can cause this "chirping sound" expecially under load. Check you drive belt adjustment stop. Opeeration Manual explains how to do this, pretty simple.
    Had it in to dealer and they checked the belt and still told me I have two tubelines (somewhere) rubbing together at a high frequency. They said they've seen that before. I only notice it under load and when the machine is warm or I'm trying to do two things at one time. It's very noticeable at low RPM and less noticeable at high rpm.

    Have you heard anything about the pressures or pump increases in the 700 and 800 series machines that are rumored to be in the future for It4 machines?
    Brush Chipping and Tree Mulching Texas Style!

  4. #4
    Veteran Member SSdoxie's Avatar
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    Default Re: Bobcat s750 high flow-- "Chirping" sound from hydraulics

    Yes, The iT4s have a new hydraulic valve that now has 2 relief valves. 1st inline is the main which has been increased to 4000 psi to improve lift and tilt breakout. The a second was added for the front reliefs still set at 3500 psi to protect the attachments (it comes standard on the 850 & 870, is dealer installed option for 600 & 700 models. There was also so internal porting changes made in the tilt (bucket circuit) to allow better bucket function/roll back when the front auxiliary does go into relief.
    Note: this valve is direct interchange with the pre-iT4 machines, can be put on the older M-series and will become the only replacement valve for them.
    Dennis

    CT225 w/7TL QA FEL, 60"tooth dirt bucket, 68" smooth bucket, Pallet Forks, Bale Spear. Hydrualic top llin, QH, 48 RC, 60" tiller, Angle blade, Landscape rake, Carry-all, Post hole auger.

  5. #5
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    Default Re: Bobcat s750 high flow-- "Chirping" sound from hydraulics

    Doxie, you sure know your stuff. Would love to have you around my shop and though I'm not much of a mechanic, I spend a lot of time looking at specs and trying to make the most out of my machines. I've upgraded 12 or 13 times as technology has increased so that I can run my mulcher more efficiently. What I've wanted for a long time is 90 hp machine (92 hp s770 fits that), about 9k lbs for machine, and about 40 gpm at 3800 psi. I don't think that's asking too much from Bobcat with the cooling system but I can't get it. I tried a CAT machine for a few months with 4000 psi and 33 gpm but went back to Bobcat (and lost my butt on the deal).

    I'm considering selling my s750 with 700 hrs and getting into a 770 but I want to pull the counterweight which the shop said is a 10 hr job but doable. I don't need the extra weight on my trailer and debris used to build up in my s300 that had a belly weight. Not sure if they counterweight is the same but my 750 drains a lot better when I wash it out than my s300 did with counterweight in the bottom of keel.
    I'd love to save a ton of money and just put whatever the 770 has for a fuel package on the 750 and get the 92hp but a factory rep I talked to said it's more than just fuel.. ??
    For some reason I don't remember my s330 having that weight? I took off its wheel weights, changed the tilt tatch to an s300 type, and ran the 12x16.5. All that just get more hp to support the pump when mulching which is the most demanding thing I do.

    I'm pretty much committed to Bobcat. Got a lot of attachments, toolcat, and 335 excavator to match the 750 but I feel like I need just a little more hp but don't want anymore weight on my trailer or truck.
    Brush Chipping and Tree Mulching Texas Style!

  6. #6
    Veteran Member SSdoxie's Avatar
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    Default Re: Bobcat s750 high flow-- "Chirping" sound from hydraulics

    Pulling the extra weight out of the 770 should be slightly less time consuming than on the S300. The weights on both are back in around the rear axle tube. The control valve sits on the right side so a lot of hoses and tubelines have to get moved out of the way to get the weight out after it's unbolted. The S300 also had the hydraulic reservoir sitting over the left axle and would have to been removed. On the M-series the reservoir was moved up above the pumps next to the radiator, so 1 less obstical. It can be done, but definitely not a 2 hour job.

    Some of the first iT4 700 models did not get the new control valve, as supply was limited they put them in the 800 models first then did a running change. I believe they are in production on all 700 & 800 models now. The 700s still come with only the main relief and set at 3500 psi. You could add the Auxiliary relief to it up to 4000 psi if you need more lift, but the Auxiliary still calls for 3500 psi. This is because most of the attachments could not withstand higher pressure. The 1 exception is the Forestry Cutter, you could bump it to 3800 psi but only if this is the ONLY attachment you would be running with it. If you did set it higher there is also a relief valve on the Hi-flow pump set at 3500, it would have to be raised as well. Keep in mind 37 gpm @ 3800 psi. is going to require 82 HP leaving only 10 HP of the S770 to move the machine if mulching heavy load and trying to manuver at same time.
    Dennis

    CT225 w/7TL QA FEL, 60"tooth dirt bucket, 68" smooth bucket, Pallet Forks, Bale Spear. Hydrualic top llin, QH, 48 RC, 60" tiller, Angle blade, Landscape rake, Carry-all, Post hole auger.

  7. #7
    Platinum Member
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    Default Re: Bobcat s750 high flow-- "Chirping" sound from hydraulics

    Doxie.. thanks for all your knowledge.. I think I'm going to start trying to get into a 770..
    Brush Chipping and Tree Mulching Texas Style!

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