Sponsored

Question for switching 2H to 4H with FAD

scinoakville

Member
First Name
SC
Joined
Dec 8, 2021
Threads
4
Messages
20
Reaction score
25
Location
Canada
Vehicle(s)
2023 Rubi Unlimited
When you are on 2H, with the FAD, two axles will spin at opposite direction. Acoording to the owner's mannual, you can switch from 2H to 4H (or 4H auto) at speed upto 45mph. So once 4H is engaged, two axles will be locked together, meaning one axle spinning one way will be forced to spin backward righaway. Although the load is not big (just the axle, differencial and front drive shaft), mechanically the axle won't be happy.
Does this switching make some noise on the axle? Will there be any vibration?

My 2023 Rubi3.6 does not have FAD function, so have no idea whether this switching is smooth or not.
Sponsored

 

GATORB8

Well-Known Member
First Name
Matt
Joined
May 30, 2021
Threads
19
Messages
7,021
Reaction score
9,078
Location
CLT NC
Vehicle(s)
21 JLURe
Did you replace your axle? Wasn't aware of any factory FAD deletes other than the 392.
 
OP
OP
scinoakville

scinoakville

Member
First Name
SC
Joined
Dec 8, 2021
Threads
4
Messages
20
Reaction score
25
Location
Canada
Vehicle(s)
2023 Rubi Unlimited
Jeep deleted the FAD, maybe by mistake or only for Canada.
 

five9dak

Well-Known Member
First Name
Chris
Joined
Feb 26, 2021
Threads
0
Messages
964
Reaction score
1,660
Location
PA
Vehicle(s)
Bikini '20 JL Freedom, '99 Dakota R/T, '97 Boxster
I think your first sentence is wrong or lacking clarification.

The spider gears are turning opposite directions in the front axle when the FAD is disconnected. This means both sides of the two piece axle across the FAD are turning opposite directions. However, when the transfer case engages, the front pinion speed will match the rear pinion speed, and the spider gears will go the same speed and direction. Across the FAD there is now no appreciable differential speed or direction, and it can close.

If you wrangler does not have a FAD, it operates like millions of other Jeeps without this fuel saving feature, the 4wd engagement at speed is smooth, since both the front and rear driveshafts are already spinning at the same speed going down the road. The exception is if you try to engage 4wd DURING rear wheel spin - dont do that.

The 4wd engagment will work fine at 45mph - perhaps maybe even better/smoother than a FAD equipped jeeps. JK and TJ were like this, and you can rip that fun lever all you want at speed. The benefit of using part time 4wd at speeds over 45mph is pretty questionable though. In some scenarios it may be more dangerous than 2wd.
 
OP
OP
scinoakville

scinoakville

Member
First Name
SC
Joined
Dec 8, 2021
Threads
4
Messages
20
Reaction score
25
Location
Canada
Vehicle(s)
2023 Rubi Unlimited
I think your first sentence is wrong or lacking clarification.

The spider gears are turning opposite directions in the front axle when the FAD is disconnected. This means both sides of the two piece axle across the FAD are turning opposite directions. However, when the transfer case engages, the front pinion speed will match the rear pinion speed, and the spider gears will go the same speed and direction. Across the FAD there is now no appreciable differential speed or direction, and it can close.

If you wrangler does not have a FAD, it operates like millions of other Jeeps without this fuel saving feature, the 4wd engagement at speed is smooth, since both the front and rear driveshafts are already spinning at the same speed going down the road. The exception is if you try to engage 4wd DURING rear wheel spin - dont do that.

The 4wd engagment will work fine at 45mph - perhaps maybe even better/smoother than a FAD equipped jeeps. JK and TJ were like this, and you can rip that fun lever all you want at speed. The benefit of using part time 4wd at speeds over 45mph is pretty questionable though. In some scenarios it may be more dangerous than 2wd.
Thanks a lot for your clarification. Didn't think what T case will do first.
 

Sponsored

txj2go

Well-Known Member
Joined
Apr 7, 2020
Threads
34
Messages
1,219
Reaction score
1,244
Location
DFW
Vehicle(s)
CTS-V, 2018 JLU Sport Firecracker Red
The spider gears are turning opposite directions in the front axle when the FAD is disconnected. This means both sides of the two piece axle across the FAD are turning opposite directions. However, when the transfer case engages, the front pinion speed will match the rear pinion speed, and the spider gears will go the same speed and direction. Across the FAD there is now no appreciable differential speed or direction, and it can close.
It looks to me like the slider in the FAD engages the short axle shaft immediately and the short axle, ring gear carrier, pinion and front driveshaft have to very quickly accelerate up to the same speed as the parts in the rear. This should generate very high loads on the slider. If they say it works then I can't argue with them but it looks questionable to me.
 

bjm00se

Well-Known Member
First Name
Steve
Joined
Jan 26, 2021
Threads
7
Messages
1,302
Reaction score
3,109
Location
California
Vehicle(s)
JLUR 6sp ordered 11/3/21, picked up 8/30/22
The transfer case lever is mechanical, so moving it engages the transfer case into 4h.

The FAD is electrical, and is triggered once the lever is thrown. Lights on the dash flash if the electronic FAD sleeve is unable to engage for some reason.

So yes, from personal experience, it engages smoothly. Just did it in the last big snowstorm of the year a couple of weeks ago.
 

CarbonSteel

Well-Known Member
Joined
Jul 21, 2019
Threads
296
Messages
5,268
Reaction score
7,144
Location
Colorado
Vehicle(s)
2023 Ford Bronco Wildtrak
Vehicle Showcase
1
Jeep deleted the FAD, maybe by mistake or only for Canada.
Did they delete it or just block it off? With the housing still there, I suspect the latter.
 
OP
OP
scinoakville

scinoakville

Member
First Name
SC
Joined
Dec 8, 2021
Threads
4
Messages
20
Reaction score
25
Location
Canada
Vehicle(s)
2023 Rubi Unlimited
You are right . I mean they delete the FAD function by putting a plate there (should have piece of metal fork on the plate to lock two axles)
Sponsored

 
 



Top