4WD Front Rear Tire Speeds

[KenJ]

Hi all. Using a B7510HST with FEL and a box scraper to plow out a driveway and horse corral. Ag tires on all four but chains on rear tires only. Everything I've heard or seen here tells me that while in 4WD there is a fixed drive ratio between the front and rear tires. Yesterday I ran into a hard packed drift over ice. Tractor stopped moving, rear tires stopped, HST started whining but front tires kept spinning merrily away. I figured that can't be good for the machine so I backed off quickly, but through the day I noticed that while the tractor speed and rear tire speed varied with the load (as expected), the front tires always seemed to be spinning about the same. The operators manual says not to use 4WD on a hard surface so I assumed it was similar to a standard transfer case, but what I'm seeing is different.
Appreciate any insights, info, thoughts or comments.

 

[jcy110]

Did you have the differential lock lever engaged? Are you sure both rear wheels stopped spinning and just not the one side. One side will stop while the other spins if the rear is not locked............its then a 3 wheel drive.

 

[North Idaho Wolfman]

#1: Check your rear tire pressure, it wouldn't be the first time we have heard of a rim spinning inside a tire.

#2: If the rear wheels, both, are stopping dead and the front is still spinning you have a serious issue with the rear end, like a broken axle gear, broken drive gear, or some other issue with the drive, because the front and rear are tied together via gears, no slippage is possible.

 

[ipz2222]

10 4 to what wolfman said. put a chalk mark ( wifes fingernail polish) on the wheel and tire, both sides. Run awhile and see if the marks move.

 

[KenJ]

Thanks all, rear tire pressures were both low. Pumped them up & problem went away. Still have a question about what pressure to run them at but will start a new thread for it.

 

[85Hokie]

Ken - "tells me that while in 4WD there is a fixed drive ratio between the front and rear tires"

There is ! AND as NIW said - if the rears are not spinning and the fronts are ......not good!

The funny thing about 4wd drive is that is really never is 4wd in a TYPICAL car/truck/tractor. Basically you have 4 wheels - two (f&r) driven at any typical time.

YOU basically have 2 wheels driven - while in 4wd! IF 4wd is engaged - the front and the rear are locked together......due to the standard differential front and rear - the wheel with the least resistance to the ground will turn, because it is the easiest!

I have tried to go up a slight incline on packed snow/ice .....left front spinning, right rear spinning.....ease off - they might switch or might not!!!!

NOW - when you push the diffy lock on the rear - you take the differential out of the equation and BOTH rears will turn at the same rate ......all the time!!!! MAKES steering a little fun! SO - with the diffy lock and 4wd drive engaged .....you will have 3 wd!

Some high end tractors have a system where you can have a locked front too, not sure the computer world has hit the SCUT market yet.

If you have kept up with auto technology - the subaru system of 4wd is a rather unique one. It places power to the wheel that is NOT spinning.

I have a GMC truck with posi-traction , every time I ease out of my driveway (uphill - turning left) both wheel chirp !! Which is nice to know it works!