Crown FC-4000:
slow traction , zero coasting...please help!!

I am an in house tech for a food company and I really need some advice on this particular truck. The truck speed is very low as if the brakes were locked or the parking brake engaged, if you let go the accel pedal while driving it will come to a sudden stop it will not coast. I can hear the high speed contactor coming in as I press the pedal so I dont think theres any electrical issue also there is no error codes at all!!

I suspect the open differential is the culprit and I'll explain how I got to the conclusion: I jacked up the truck by the front end and left both wheels suspended and when I pressed the accelerator pedal both wheels started spinning in low speed instead of just one wheel spinning? I then did the same test to another identical truck and only one wheel spun and it did at high speed.

I then got into the faulty truck and drove it with the steering locked all the way to the left and pressed the accel pedal like driving in circles... to my surprise it reached top speed as if there were no issues... same result obtained when I locked the steering fully to the right...full speed!!

I might be wrong but this tells me there is no issues with the parking brake or service brakes being locked up or dragging, I can also see the parking brake engaging and releasing normally as requested.

Please help me out and if there's anyone with experience in this type of differentials let me know what should I do!! Thanks!!
  • Posted 5 Jun 2015 08:59
  • Discussion started by cubapnea
  • Florida, United States
Showing items 1 - 3 of 3 results.
As I promised to update on this matter here it comes!!. I had ordered two new hub adjusting nuts because the ones in there looked damaged by being tightened with a punch and hammer and I also ordered a special spanner wrench or ''socket'' to remove and replace those bearing hubs, I then proceeded to torque them to 235 ft pounds then rotate them clock and counter clock wise a few times then back to 95 ft pounds..the issue is still present.

After further investigation I was told that drive unit had been dropped and rebuild twice by the same tech , I was told after rebuild the truck speed was significantly decreased by half. I contacted the tech who performed the job and he sounded like he did not pay attention to detail at the service manual and use the right torque on the job.

My next step is to try to reach those two adjustment cups ( differential and second reduction gear and properly seat them , I think I can get to them without dropping the whole assembly...I will post when this gets done!!
  • Posted 25 Jun 2015 07:12
  • Reply by cubapnea
  • Florida, United States
Crownie the truck works in a dry environment and mast and brake switch are electrical issues or codes...I took out both axles only to find out the adjusting hub nuts are way too loose....looks like..somebody tighten them with a hammer and punch they need about 90 pounds of torque. I order the spanner wrench and new nuts and will update results...wish me luck so I don't have to drop that pumpkin. Thanks for your help greatly appreciatted.
  • Posted 11 Jun 2015 00:37
  • Reply by cubapnea
  • Florida, United States
If it ain't know...
the fc4000 does not use a steer position sensor
the brake pedal switch will reduce speed
the mast staging switch will reduce speed
i suspect your brake switch
if your truck works in water the left front wheel sprays water into the distribution board located under left step
when the board corodes you get many strange faults
try placing blocks under mast so both drive wheels are off of ground, drive unit and observe drive wheels
when releasing accelerator pedal observe if both wheels stop suddenly or if speed winds down
  • Posted 10 Jun 2015 12:23
  • Modified 10 Jun 2015 12:26 by poster
  • Reply by crownie
  • Victoria, Australia

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