Front End "bucking" hard when 4x4 is engaged

Had a pretty bad snow storm last week in CO. Threw the truck in 4hi and the front end started "bucking" really hard! (Bounced my coffee out of the cup holder and all over the passenger seat) 4x4 engages and disengages just fine but it feels like the gears are just bouncing instead of seating together. Does anybody have any input as to what the problems could be? Tcase? Hubs? Front Diff? I can't imagine it would be the front diff because the front diff is still in use even when the truck is in 2hi and there are no problems. The front drive shaft seems to be all good as well. My clutch has been acting a little finicky lately as well.. Pretty sure it is going out, but could that possibly be the issue?

Anything helps.

Thanks
D

 

Clutch slippage could definitely cause bucking. Any difference in size between front/rear tires? Truck ever been regeared?

 

Change the diff fluid and see if there are any metal chunks. I would also wonder if the rear had been regeared and not the front. How long have you had the truck and have you ever had it in 4wd before?

 

Tires are the same size on front and back.. I did put in a new rear diff about 2 months ago. Never had an issue with 4wheel prior to that change. Had a guy I know who works at the dealership do it for me. I would assume he geared it correctly..

 

Were you turning when this bucking occured ?

 

I have had the truck for close to 3 years.. Lived in Colorado the whole time so I use 4x4 pretty regularly during the winter. Plus do a good bit of off roading stuff. I put in a new rear diff a couple months ago. Could that be geared differently causing the bucking?

 

Its pretty much all the time. If i get it over 5 mph in 4wd it starts bouncing hard

 

I would be looking at the new gears as primary suspect as this started after the swap, triple check gear ratios, even if it means pulling the new third member to check, I think they have some kind of tab with a number or gear info you can check, hopefully saving a yank...

 

Where would I find that info? That is why I had the dealership do it b/c I have very little knowledge with diffs and gearing ratios and what not.

 

Check your bolts for the front diff drop bracket. I had the same thing happen on my old truck could not figure it out till the bolt disappeared and took out the CV and shock with it.

 

Should be able to jack up the rear and count the rotations of the drive shaft per wheel rotation. 4 1/2 rotations is roughly 4.56 gearing, a little over 4 spins is 4.10. That's the simple way to check. Should work for the front as well.

 

Went digging through the glove box and found old paper work for when the previous owner had the 6" fabtec lift put in.. He had it regeared to 4.56. When I had the dealership put in the new rear diff. the instaled a 4.10 which is the stock gearing. So thanks for the tips guys. Now I get to go fight with the dealership to fix it!

 

Dang that sucks.

 

You might lose that fight. They assumed stock gears and had no reason to assume anything else. Hopefully, if they take pity on you, they might just charge for labor to install proper diff, to keep your business.

On second thought, the tech should have noticed the 6" lift, and asked you if it had been re-geared. Were the tires bigger than stock?

 

The only way to find out is go in with a smile and start a discussion, maybe have the gearing information at the top of glove box so when opened it is the first thing you see...if you had bigger tires and a lift, that should have set alarms bells off for gearing, first thing is they should have verified what was in there to begin with, and, just to make it more their fault, all they had to do was examine the one that came out FIRST, very simple, it would have been obvious before anything went back in...


good luck, I hope you win this one...

 

Clearly they never test drove it either.