After shutting down in 4wd and starting in 2wd - Thunk from the front

[Lemarque]

My second post about my new to me 2008 FX4 automatic.

As the title states:

I live on a bumpy dirt road and the final hill to my house I switch to 4wd. After shutting the truck off and turning the switch to 2wd, when I start the truck again in 2wd, there's a 'thunk' that I'm guessing is something disengaging the 4wd.

Is this normal or do I have repairs in my future?

TIA

 

[4.0blue98]

Don't know if it's "normal", but my 98 does this sometimes. I assumed it didn't fully disengage before I shut it off. I try to exercise the tcase every few weeks since I don't use it often.

BTW has the tcase been serviced lately?

 

[Dirtman]

When you switch between 4hi and 2wd without the truck rolling sometimes the front axle can't completely disengage so when you go to move again it will click or clunk as it releases. Try shifting back to 2wd while you are still moving.

 

[Lemarque]

Thanks folks.

I'll do the suggested/ Had my fingers crossed that it wasn't a known failure.

 

[gw33gp]

When you are in 4WD, the transfer case can bind a little or a lot depending on how much traction the tires have. When you shift out of 4WD with the transfer case in a bind it will stay in 4WD until the binding relaxes. You can get a thunk as it disengages. Driving it in a straight line will reduce the binding. I always try to drive in a straight line while in 4WD before shifting out of 4WD and it usually comes right out. Turning while in 4WD cases binding in the transfer case and can damage things if your tires have good traction.

 

[RonD]

Shift from 4WD to 2WD while still moving and before shutting off vehicle

 

[Lemarque]

When you are in 4WD, the transfer case can bind a little or a lot depending on how much traction the tires have. When you shift out of 4WD with the transfer case in a bind it will stay in 4WD until the binding relaxes. You can get a thunk as it disengages. Driving it in a straight line will reduce the binding. I always try to drive in a straight line while in 4WD before shifting out of 4WD and it usually comes right out. Turning while in 4WD cases binding in the transfer case and can damage things if your tires have good traction.

"gw33gp" Have to ask, how to decode your handle ;-) But thanks. Think I got it; if not I'll post back.

 

[gw33gp]

'gw' are my initials, '33' is my race car number and 'gp' is the class I used to race in. The class I race in now is HP but I never changed my handle. Not related to your issue but you asked.

 

[Lemarque]

OIC. So what kinda car?

So, yeah. I have to switch to 2wd and have the wheels pointing straight. A bit tricky 'cause my driveway is windy but no clunk.

 

[gw33gp]

My race car is a 61 Austin Healey Sprite modified to modern racing rules. I raced in SCCA until this year. With so many race cancellations due to the Pandemic, I did not renew my license. I still am able to get my car on the track for some high speed driving though.

As long as your driveway turns are not too sharp, your transfer case should gently relax the bind as you turn back and forth. This should allow it to shift out of 4WD without the clunk..

 

[RonD]

So, yeah. I have to switch to 2wd and have the wheels pointing straight. A bit tricky 'cause my driveway is windy but no clunk.

You have Live Axles in 2008 so no need to have "front wheels straight" when shifting into or out of 4WD, no locking hubs
2WD and 4WD is just done inside the transfer case

 

[Dirtman]

I love you all.

 

[sheep herder]

I love you all.

 

[Lemarque]

My race car is a 61 Austin Healey Sprite modified to modern racing rules. I raced in SCCA until this year. With so many race cancellations due to the Pandemic, I did not renew my license. I still am able to get my car on the track for some high speed driving though.

As long as your driveway turns are not too sharp, your transfer case should gently relax the bind as you turn back and forth. This should allow it to shift out of 4WD without the clunk..

Ah, I was a hairs breadth away from buying a Bugeye many many years ago. Ended up with a TR3 and 4 and then... my buddy and I came across a Twin Cam MGA. We used to take it up to LimeRock . He was going for his license.

 

[Lemarque]

You have Live Axles in 2008 so no need to have "front wheels straight" when shifting into or out of 4WD, no locking hubs
2WD and 4WD is just done inside the transfer case

Yeah but, it seems that switching into 2wd for the final leg eliminates the thunk. I've just started and if it rears its ugly head, I'll post back.