MF drivetrain bang when 4wd disengages

[Rookieerror]

Have a 2010 5470 with suspended font axle, that does this bang when 4wd disengages - not sure if it’s coming from front axle, rear diff or somewhere else.

Feels like massive torque wind-up in the drivetrain and worse when a load on / at speed and in 2wd then brake (4wd comes on) lift foot off brake, then 4wd disengages and sounds like someone hitting drivetrain with a sledgehammer - it’s that loud and that much of a thump. When just on light work and at slow speeds it’s less of a bang but does it every time. If turning & on loader work when lift foot off brake it can make the whole machine jump a tad. Sometimes bang seems to come from under the seat, other times seems to come from front axle. Been doing if for years, makes me feel a bit sick when does it as it can’t be good for anything?! It was milder a few years ago but think it’s got bit worse. Excellent freelance MF mechanic has tried / tested:

- stripped 4wd clutch, replaced all plates
- stripped driveshafts, checked splines, bushes, replaced bearings
- stripped front axle to inspect for play
- checked all guards are tight
- changed tyres - all new BKT’s all round, correct size and tried combinations of worn fronts / rears
- changed tyre pressure combinations
- dropped rear oil to check if rear diff - mechanic said it was the cleanest back-end oil he’d ever seen so diff should be fine
- checked alternator running right voltage (incase a tardy switch somewhere)

Any ideas what else to look at next? Must be something happening somewhere! Seems like massive torque wind-up… would not have done this when new so something has changed over time. Seems that others have had this issue with other MF’s on other threads… anyone managed to cure it? Not keen on a switch to turn off 4wd braking when in 2wd…

Such a cracker of a tractor just a shame this is happening and concerned one day something major will break as a result. As an interim I try not to use the brakes too much when in 2wd… and 4wd for slow / yard work to save engage / disengaging 4wd - but not ideal…

Thanks all

 

[24/7 farming]

On a tractor of that age/spec should there be anything computer controlled that is supposed to prevent it from happening (e.g. not allow disengagement until wheels are near straight?... always assumed that newer tractors would use something like a steering angle sensor to control something like that) I only have experience of 300, 3000 and a bit of 4000 series I think a certain amount of that was always normal in those models, have a switch on 300 series and 4WD braking always off for yard work due to the bang (and having a load on the front loader can make it feel even worse!), all is perfectly smooth if disengaged when wheels are straight, but the bang is not nice when disengaging with a decent bit of turn on the front wheels, worse again if disengages when in reverse with a turn on the wheels!, been told its normal, caused by load on front axle LSD being released?!?
Have learned to live with it, there are two ways to approach our farm and one has a turn off at the bottom of a pretty steep hill, if loaded I will have the switch on coming down the hill but will come to a near stop on the road in a straight line and flick the switch off before turning in, if turn in and still breaking and release the bang is painful!

 

[Dave6170]

@dee

 

[Spud]

What size tyres are you running?
The circumference ratio will need to be iro 1.2-1.3 sounds like yours is 1.4+

 

[goldeneagle]

Not that its any consolation but my NH digger does the exact same. It doesn't do it in reverse so when disengaging 4wd always reverse the thing and don't use the 4wd braking either.

 

[Rookieerror]

What size tyres are you running?
The circumference ratio will need to be iro 1.2-1.3 sounds like yours is 1.4+

460 x85 R38
380 x85 R28
BKT's - would have been Michelin originally and checked they are same size as fitted with when out the factory.
Daft question - do different tyre makers have slightly different sizes / circumferences?

 

[Rookieerror]

On a tractor of that age/spec should there be anything computer controlled that is supposed to prevent it from happening (e.g. not allow disengagement until wheels are near straight?... always assumed that newer tractors would use something like a steering angle sensor to control something like that) I only have experience of 300, 3000 and a bit of 4000 series I think a certain amount of that was always normal in those models, have a switch on 300 series and 4WD braking always off for yard work due to the bang (and having a load on the front loader can make it feel even worse!), all is perfectly smooth if disengaged when wheels are straight, but the bang is not nice when disengaging with a decent bit of turn on the front wheels, worse again if disengages when in reverse with a turn on the wheels!, been told its normal, caused by load on front axle LSD being released?!?
Have learned to live with it, there are two ways to approach our farm and one has a turn off at the bottom of a pretty steep hill, if loaded I will have the switch on coming down the hill but will come to a near stop on the road in a straight line and flick the switch off before turning in, if turn in and still breaking and release the bang is painful!

Don't think there's anything computer controlled on mine that does that. Mine bangs when wheels straight or turned...

 

[DrDunc]

460 x85 R38
380 x85 R28
BKT's - would have been Michelin originally and checked they are same size as fitted with when out the factory.
Daft question - do different tyre makers have slightly different sizes / circumferences?

Not a daft question, because different tyres DO have different rolling circumferences

BKT are usually smaller than others. However the ratio of the differences should be the same as the original Michelin, so they shouldn't cause the wind up

That said, did it bang out of 4wd before the bkt were fitted?

 

[Rookieerror]

Not a daft question, because different tyres DO have different rolling circumferences

BKT are usually smaller than others. However the ratio of the differences should be the same as the original Michelin, so they shouldn't cause the wind up

That said, did it bang out of 4wd before the bkt were fitted?

When it was new to me it had Michelins on back (fairly worn) and newer BKT's on the front. Did bang when 4wd disengaged then too - but maybe not quite as bad as now. Changed the full set at same time when worn out to new BKT's - hoped it might improve it but didn't...

 

[David Bliss]

I know the old Fords once the newness was off with the 4 Wheel Braking to do the same, every time you take your foot off the brakes especially just turning round in a yard there was a loud crack, it was a dog clutch type and when new would stay locked until the load on the driveshaft was very little so as it unlocked was silent, but once it had slight wear it made a loud crack as it disengaged under heavy load, and when you think about it could do that many times in a few minutes and soon get the rice crispy sound. The simplest thing to stop it happening was to disconnect a single wire under dash, manual 4WD still worked. agents wont tell you the simple fix as its a H&S E issue as you wouldn't get 4 wheel braking unless you engage it manually.

 

[Universe]

Not a solution, but on roadwork you do soon remember to scrub off most of the speed with the brakes while in a straight line, just before turning in without the brake pedal pressed down...

 

[dee]

Are you able to get your hands on another set of wheels to fit on the tractor to rule out the tyres causing the issue.

Another thing test the transmission accumulator to see if it's got the right pressure.
It might mean nothing but if it was low or burst it could cause the supply going to the 4wd to spike

 

[DrDunc]

I think the rear tyres may be slightly too small

Looking at adverts for 5470s, they seem to shod with 520/70r38 420/70r28, or similar?

Checking bkt rolling circumference (RC) figures gives:

520/70r38 RC5300mm
420/70r28 RC4020mm

460/85r38 RC5161mm
380/85r38 RC4015mm

Not much difference to be fair, but might be enough to cause the wind up

Try running the fronts soft at 10psi and rears hard at 28psi. If it's the lead ratio this might help identify the culprit. Ok for an experiment, but NOT recommended for long distance road travel!

 

[Rookieerror]

Are you able to get your hands on another set of wheels to fit on the tractor to rule out the tyres causing the issue.

Another thing test the transmission accumulator to see if it's got the right pressure.
It might mean nothing but if it was low or burst it could cause the supply going to the 4wd to spike

Another set have been tried but can't remember if it was to compare worn / newer of same size. Thanks re accumulator - will look into that

 

[Rookieerror]

I think the rear tyres may be slightly too small

Looking at adverts for 5470s, they seem to shod with 520/70r38 420/70r28, or similar?

Checking bkt rolling circumference (RC) figures gives:

520/70r38 RC5300mm
420/70r28 RC4020mm

460/85r38 RC5161mm
380/85r38 RC4015mm

Not much difference to be fair, but might be enough to cause the wind up

Try running the fronts soft at 10psi and rears hard at 28psi. If it's the lead ratio this might help identify the culprit. Ok for an experiment, but NOT recommended for long distance road travel!

Thanks for this, interesting re the RC figs and rears being too small, good idea checking other ads (hadn't thought of that!) Apparently what it's on now is an approved OEM size but it makes sense that even slightly out would cause the wind up. I'll try changing the tyre pressures as you suggest as a test and report back, might be a few days as finally stopped raining...

 

[glasshouse]

My case 125 does the same

 

[Spud]

Try blowing the front tyres up to 25 ish and let the rears down to half that and have a test drive, I think your ratio is a bit keen at 1.29

Your easiest swap would be 16.9r28 on the front, which would reduce the ratio to 1.22 which would help reduce windup

 

[Old apprentice]

You naught it second hand and it did it at start but got werse? May be some one has been in it before you naught and put something different in it ?

 

[Rookieerror]

Finally got round to tyre pressure experiments as suggested above so thought better update the thread. Thank you for all the comments and advice back in April, really appreciate it.

Initially tried blowing the fronts up 25 and dropping the rears down to 10 but it made no difference, if not made it worse.

Then blew the rears up to 35 and dropped fronts to 10... and with testing the banging seemed to stop! Set them back to normal pressure and back it came again...

So although the current tyre combo are correct according to the book, local tyre fitter is going to see if can get slightly smaller fronts (cheaper option!) and if not then larger rears to try as suggested by DrDunc. Got a loader on so options for smaller fronts might be a bit limited.

Will update the thread after next stage for anyone interested and incase it helps anyone else with similar issues. Thanks all

 

[Steevo]

Finally got round to tyre pressure experiments as suggested above so thought better update the thread. Thank you for all the comments and advice back in April, really appreciate it.

Initially tried blowing the fronts up 25 and dropping the rears down to 10 but it made no difference, if not made it worse.

Then blew the rears up to 35 and dropped fronts to 10... and with testing the banging seemed to stop! Set them back to normal pressure and back it came again...

So although the current tyre combo are correct according to the book, local tyre fitter is going to see if can get slightly smaller fronts (cheaper option!) and if not then larger rears to try as suggested by DrDunc. Got a loader on so options for smaller fronts might be a bit limited.

Will update the thread after next stage for anyone interested and incase it helps anyone else with similar issues. Thanks all

Thank you.

I have a 6290 with a loader which also bangs as yours does. Really appreciate you updating this.