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#1
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Just so you know where I'm coming from....
Squeal from Hydraulic Actuator A squealing noise from a hydraulic actuator is typically caused by high-pressure hydraulic fluid passing through a restriction or a malfunctioning component. One common cause is the hydraulic system's pressure relief valve operating, which can occur when the actuator reaches its maximum travel or is under excessive load, forcing fluid to bypass the valve at high velocity. This is often heard as a high-pitched squeal or whine, particularly when lifting heavy loads or when the control lever is near its uppermost position. In some older tractors, this can be a normal characteristic when the lift control is fully raised, entering a "regenerate" mode where the pump continuously releases pressure through the relief valve. Another potential cause is aeration, where air enters the hydraulic fluid, often through leaky couplings, loose fittings, or low fluid levels, leading to a whining or knocking noise that can be erratic in nature. Cavitation, which occurs when fluid pressure drops below its vapor pressure, can also produce a high-pitched whining or screeching sound due to the collapse of vapor bubbles, causing erosion and damage to internal components. This is frequently linked to blocked filters, restricted intake lines, or excessive pump speed. Internal wear or damage within the actuator itself, such as a scored cylinder bore or damaged piston packings, can allow high-pressure fluid to leak through small gaps at high velocity, resulting in a squealing sound. Similarly, a cylinder with a bent rod or worn seals may bind or slip, generating noise during operation. In some cases, a stuck or improperly adjusted relief valve can cause a constant hissing or whistling sound, which may be mistaken for a squeal. Other mechanical issues, such as a damaged or worn pump, faulty directional valve spool, or even a failing clutch throw-out bearing in some tractors, can also contribute to unusual noises that may be perceived as coming from the hydraulic system. It is important to investigate the source promptly, as prolonged operation under these conditions can lead to accelerated wear, component failure, or system damage. 
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#3
09-16-25, 10:26 PM
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Quote:
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#4
09-17-25, 10:16 PM
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Please let us know the resolution to the uplock issue. I once had a squealing noise at altitude above the pressurization setting ..... turned out to be a gasket not sealing on the front inspection covers. Lol, I went through the entire pressurization system.
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#5
09-25-25, 03:09 PM
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uplock actuator
Update:
I had forgotten that the uplock actuator does not have any hoses. Just hard lines. Checked fittings and all tight. Examined lines for cracks, did not find any that can be seen visually. Rechecked all fittings and lines for wetness and all are dry as well as the actuator itself. So decided to do a test flight without reinstalling the rear floor panel and carpet. During gear retraction when the uplocks engaged there was no squeal or squeak. We left our headsets off to make sure we could hear it and there was nothing. Must have had something to do with the homemade hydraulic mule we were using. It is probably putting out more pressure and volume than my engine driven pump but why it would not have caused the uplock actuator to squeal during retraction on previous annual inspection gear swings is still a mystery. Burt
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#6
10-01-25, 02:06 PM
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FYI Bob @ planepartsinc is one of the few places to find the actuator rebuild parts. Verify you get the 337 kit and not the 210 as the actuator itself is same part number. Best to check new parts against parts manual. I just rebuilt mine last week.
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337B Philadelphia PA
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