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Hisun 550 750 Stuck In Rear Diff Lock

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  • 1 month later...

With wheels blocked, motor off but key on, use a volt meter and see if you actually have 12 volts at your splice - hot lead from meter on your splice other lead on a clean metal part of the frame - have a helper activate and deactivate the switch for the differential lock while you are watching the meter - if you have the correct voltage, look for a bad ground wire - if no voltage (and you are sure this is the hot wire to the differential solenoid) - undo your splice,  make a jumper from the battery positive terminal and momentarily touch it to the hot wire on the side going to the differential - you should hear the solenoid click - if no click check the ground from solenoid again - last hope at that point is turn off the switch and connect  an ohm meter  to the hot wire and ground of the differential lock - an open - (no reading on the vom) means a wire broken beyond the splice, or no ground or a burned out solenoid on the differential lock - a 0.00 ohms reading means that you might have a shorted or burned coil inside of the solenoid - try reading at the lowest (smallest) ohms setting on the meter - manuals for your buggy are available in several places online - they tell you what ohm reading is allowed for many parts of the vehicle - search this forum for links to the service  manual - did I mention to check the ground again - lol - that would be a subconscious accident of 40 plus years of experience (bad experiences - grin) 

Edited by etimc
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  • 11 months later...

I bought a slightly used (15 hrs) HiSun 550 UTV  from Rural King that had been returned by a customer.  It was running rough and couldn't get the gear shifter to operate correctly.  I bought it at a discounted price and have fixed the rough running and gear shift problems; new fuel injector and in-line filter, and idle air control valve.   Part of the gear shifting problem was because of rough and fast idle, and when I recalibrated the engine for the injector, the idle speed was smooth at about 1100 RPM. 
But now I notice that the rear differential stays in the locked mode all the time, 4 wheel drive or 2 wheel drive.  I don't think this is normal because it is hard to turn and the wheels dig out dirt and scoot when making a sharp turn.  Does anyone have a clue about how the rear differential is supposed to engage the locking mode?  

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Not all Hisun 550 models (mostly 2016+ models) do not have a rear differential. They are a "spooler" type axles with a solid center  section--I.e. equal power to both wheels at all times.

OP (older thread, one post newbie has probably moved on but I'll try to help) , what model Hisun 550 doe you have, is it an "HS" series,  a "Sector", "Vector" or "Strike"? What model year is it?

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Okay, I contacted the factory technical person about the rear differential "problem", and he said that the model I have doesn't really have a regular differential.  It is a "positrac" type that has both rear axles locked together all of the time.   So, I really don't have a problem other than I don't like that feature because it makes it hard to turn a sharp radius and tears up the ground pretty bad.


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4 hours ago, Daniel P said:

Okay, I contacted the factory technical person about the rear differential "problem", and he said that the model I have doesn't really have a regular differential.  It is a "positrac" type that has both rear axles locked together all of the time.   So, I really don't have a problem other than I don't like that feature because it makes it hard to turn a sharp radius and tears up the ground pretty bad.

Their stating it"...doesn't really have a regular differential." is correct--however to call it "...a 'positrac' type..." is not. Posii Trac is GMs  trade name for their clutch-pack type limited slip differential, which is a differential with a stack of alternate composite-faced  and bare steel plates, the composite plates are splined to the carrier, the bare plates to the axle (or 'tother way round). In operation when one wheel slips the lateral force generated by the driven wheel's side gear clamps the clutches, locking the wheels together. However It is a real differential and behaves as such when he force needed to spin the wheels at differing speeds exceeds the clamping force of the clutch pack--I.e. it is "limited slip" in straight-line travel.

Ford call s it Trac Lok.

Our vehicles do not have a differential at he rear, but rather what is usually and correctly called a 'Rear Reducer" or "Rear Bridge (Reducer)" that uses  a solid "spool" connection between the axles; there is no possibility of the wheels rotating ate differing speeds, or with differing power. Both axles connect directly to the reduction unit's ring gear

HS550 rear reducer:

The downsides to this are, as you stated tearing up soft surfaces in tight turns, and tire wear. The upside is very  much improved traction in straight-line and modest turns without the cost and complexity of a limited-slip, or open but "lockable" differential¹ (there are other types in addition to the clutch-pack variety)--his is not a benefit to be overlooked. 

¹- Some pre-2016 Hisun 550 models did have open, but lockable (solenoid operated it appears), rear differentials--my understanding is they were troublesome and did not drive the vehicle especially well off road when not locked;  so they were generally kept locked which of course lead to "unlocking'" problems as the miles piled up.




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