a "buck" in the rear end?

[CRUISERMEDIC]

i got a 97 expl. xlt v6 4wd that every now and then i get a slight bucking feeling in the rear end. the best way for me to describe it is its almost like you run over a crack in the road....but there aint no crack. this problem doesnt happen on a regular basis hot cold wet dry it dont matter. just happend once in a while and one bump and thats it. no shudder or shakes. ive taken it in afew times and no one can find any thing wron...no slop in u-joints or drive shaft. tranny shifts great through all gears and engine runs smooth as can be...121,000 mile on her. ive only had this truck about a month and the previouse owner was a well to do guy and he never did any of his own up keep and had service records that show great care was given and the condition of the vehi9cle leads me to believe it was definetly not neglected. any way im stumped, any ideas you guys can toss in to me are great.....im gonna get under there this weekend and start changing all fluids for starters....does the rear end have a drain or do i need to pull the diff. cover?

 

[CRUISERMEDIC]

bump......i really did search!

 

[95exploderboy]

I'd put the rear on jack stands and pull the diff cover. There isn't a drain plug, just loosen all the bolts, free the cover with a dead blow hammer and let the oil drain for a little before you remove all the bolts and the cover. Have some brake cleaner handy so you can clean off the carrier and inspect the teeth. Look for any chips or odd wear patterns. Also pay attention when the oil is draining out, and see if there are any metal shavings or debris.

 

[daffy]

Look for posts on slip-joints, see if the problems they describe are what you're experiencing.

 

[CRUISERMEDIC]

thanks for the info....i did find a post about a "slip joint" that needed grease and fixed his problem. i guess im not to sure what this is. most my mechanic skills are not in suspension and steering although ive changed alot of tie rods and ball joints, which i have to do on this truck soon. i guess ill do that and pull the shaft and check the u joints my self........what exctly am i looking for in them? excessive wear? thanks for the help

 

[daffy]

The slip joint is not the same as a U-joint. Simply put, it's a section of the drive shaft that expands and contracts, the outer boot looks like a shock boot, inside is a splined shaft, and it's counter-part (I have no idea what it's called, the female part of a splined shaft), the gist is, take the boot off, clean the old crap out, put in fresh grease, replace boot. Much easier done out of the vehicle. I'm looking to do this to mine, just haven't had the time when the weather is decent.

 

[Fastonion]

I had the same problem when I bought my 2000 Ex back in 03. The truck wasn't driven much for 9 months before I bought it. It would only do it on the highway and not very often. I took it to Ford, they changed the fuel filter and it never did it again. Go figure.

 

[CRUISERMEDIC]

update for all who responded with tips.......4405 t-case problems. it is engaing 4wd even with all elec stuff unplugged up on a lift. is this a repairable problem or just look for a used t-case? any one got one for sale in the lansing michigan area?