on our 1990, f450, brush truck with after market 4wd system. 1 of our members was out on a brush fire last week on very dry ground and had it in 4wd. he got back to the station and stated that the axle was popping.

i took it out today and found that if on dry ground, in 4wd with front hubs locked, that there was a popping from the front end, but only when turning.

disengage the transfer case or unlock 1 or both hubs and the popping goes away.

isn't this somewhat normal or should the front diff handle the front wheels turning at different speeds ??

thanks for feedback.

 

IT sounds like it may be a u-joint in one of the axles.

 

this after market axle does not have u-joints. there are large "knuckles" at each wheel hub.

i am not sure if this front axle has limited slip or not, but could it be that it needs the limited slip additive ?

 

unless its gear drive or cv it has a u joint in there.

 

don't know if this help, but this is the front axle.

CARRARO
Made in Italy
Diff Type: Standard
Total Ratio: 5.125/1
Axle Type: HS 6.07
Carraro No: 130981

 

It has to have a flexable joint whether it is a single joint or if it has two regular joints then that makes it a type of constant volocity or a ball type constant volocity.
It may be in the diff but it has to have some kind of flexable joint.

 

Does this thing have a planetary hub?

 

don't know what a planetary hub is or looks like ?

 

The popping noise while turning is probablely due to driveline bind being released
in a tire slipping.4wd should not be used on dry ground unless it was designed for it.
The full time systems have a slipper clutch of some type in the transfer case to allow
for slippage.The popping noise could be caused by damaged locking hubs,you may need to walk beside the truck and see where the noise originates.Hubs are stripped
easily by driveline bind,and will cause a popping or ratcheting noise.

 

Another thought is that it has a limited slip type differential, and is popping in the differential. As stated, the 4wd should not be engaged on dry high friction surfaces, it has to give somehow when turning. Having it locked in doesn't allow it to slip effectively.

 

There are U joints inside the knuckle....that is a lot like the old closed knuckle front axles from back in the 60's on Fords.
There were several other manufacturers that used closed knuckle axles.
The closed knuckle is also very common on equipment axles even today.

Since you have a rather heavy truck there, I bet you have a lockout hub that is getting bad.
But since you can not see the U joint, there is also a good possibility that one needs replaced.

Look at your tire tracks while in a hard left turn.
The right front wheel has to go the longest distance to go around the turn, so it turns fastest.
Ususlly the left front will be between the right and left rear tires, so it turns a little slower than the right front does, but faster than the left rear needs to turn.
The left rear tire travels the shortest distance, so it is the slowest tire of the four.

Since all four tires are tied together in 4x4, it is hard for them to turn 4 different speeds going around a turn.
With enough weight, you could break an axle, driveshaft, or U joint doing a tight turn on bare blacktop or concrete if the lockout hub did not break first.