Lots of extra drag when 790 4WD engaged

[1948B]

When I have my 4WD engaged on my 790, and depress the clutch, the tractor stops relatively quickly. It seems l something is creating a lot of drag when the 4WD is engaged. Anyone know what might be the problem. The 4WD oil looks fine -- clean and full. The tractor is stock with a factory front loader (not used heavily) 180 hours. Tractor gets ued mostly for mowing grass and plowing snow.

 

[kennyd]

Welcome to TBN

Are you engaging the 4WD on a hard surface when you are feeling this? The 4WD (or MFWD as JD calls it) should only be used on loose or slippery surfaces because the front wheels actually turn slightly faster than the rear wheels to help "pull" the tractor. This is why it's very important to keep tire sizes the same when replacing tires. I suspect you are feeling this on hard surfaces so the wheels cannot "slip" properly and you are feeling the driveline binding up.

 

[BobT_770]

I notice this from time-to-time on hard surfaces like gravel or dirt. I just figure ANY 4WD system creates more parasitic losses when engaged. I am always sure to only use MFWD when I absolutley need it and am quick to disengage it when no longer needed.

WHY does deere mess with the different wheel speeds ? All normal 4WD vehicles/ATV's etc have the same speeds front/rear to preserve the center differential.

 

[Mech]

When I have my 4WD engaged on my 790, and depress the clutch, the tractor stops relatively quickly. It seems l something is creating a lot of drag when the 4WD is engaged. Anyone know what might be the problem. The 4WD oil looks fine -- clean and full. The tractor is stock with a factory front loader (not used heavily) 180 hours. Tractor gets ued mostly for mowing grass and plowing snow.

The front wheel drive engages/disengage at the transmission, right below the operators platform, so the front wheels, differential, and driveshaft are turning whether the front wheels are engaged or not, so any drag difference when engaged wouldn't be from the front end but from the transmission being engaged with the front wheels. I don't notice a drag diffent on my 790 but then it has never been on anything but dirt up to this point and I don't usually engage the 4WD unless I need it.

 

[RollTideRam]

I notice this from time-to-time on hard surfaces like gravel or dirt. I just figure ANY 4WD system creates more parasitic losses when engaged. I am always sure to only use MFWD when I absolutley need it and am quick to disengage it when no longer needed.

WHY does deere mess with the different wheel speeds ? All normal 4WD vehicles/ATV's etc have the same speeds front/rear to preserve the center differential.

Even on a 4wd truck where gear ratios and tire sizes are the same, you will cause a bind when turning because all wheels are turning at a different speed. JC

 

[Muxster]

He is not talking about drag while moving... but drag while stopped and the clutch disengaged. Sounds like a weird problem to me. When the clutch is depressed there should be no difference in engine load in FWD or 2WD because the drive train is disconnected from the engine. Sounds like maybe a clutch issue. The clutch may not be fully disengaging.

BobT, try putting the hi-low range selector in N and see if that makes any difference in 4 or 2WD.

 

[Muxster]

BobT, try putting the hi-low range selector in N and see if that makes any difference in 4 or 2WD.

I mean 1948B... try this...

 

[kennyd]

He is not talking about drag while moving... but drag while stopped and the clutch disengaged. Sounds like a weird problem to me. When the clutch is depressed there should be no difference in engine load in FWD or 2WD because the drive train is disconnected from the engine. Sounds like maybe a clutch issue. The clutch may not be fully disengaging.

BobT, try putting the hi-low range selector in N and see if that makes any difference in 4 or 2WD.

I disagree, even with the clutch disengaged, the front and rear wheels are still tied together if it's in 4WD, and since the ratio's are different you can can this dragging feeling if on a hard surface.

 

[Jack Squat]

Yes - I also notice the effect you describe in 4WD - MFWD. The forward motion stops sooner than in 2WD. I imagined that the front axle and rear are actively tied together even with the clutch in - couldn't have imagined what else would cause it. I try not to use it unless needed as well - and some of the slopes around the crater (what I call the pond) sure do need it.

 

[bjcsc]

If I brake above a certain speed in 2wd (somewhere around 8mph or so) my MFWD automatically engages to assist in slowing. Maybe they design it that way...