thedivinemisse

Hi all! I just bought my first truck and I'm concerned it may have a transmission issue. It is an 04 F150 XLT with the 5.4L Triton engine and a 3.73 limit slip axel. What it does:

at speeds under 30mph when accelerating, the truck makes a "thunk" noise from the rear. It's the same feel and sound you get when there is something heavy rolling around in the bed. Accelerate...thunk....accelerate...thunk. It shifts into gear fine though. The RPMs don't go nuts. Occasionally it will make a double thunk. We took the spare tire off because it was loose, so we thought maybe that was what was making the thunk. Nope, still does it.

Any ideas? It's at a dealership now waiting for a diagnostic test, but I thought I would seek some advice here as well and see if it's a normal thing or if I need to be concerned and prepared to take it back to the dealership where I bought it for repair or return.

Thanks!

thedivinemisse

Update:

Ok the dealership thinks (without opening up the truck) that I need a new Ring & Pinion set and Clutch Set. I have read a couple of places about people getting the slip yoke lubed and that fixes the issue. The dealer says they hadn't heard of that being an issue??

Any ideas? It's $250 just to have them open it up and look at it. *sigh* If it's the problem they say it is, the repair costs $1600.

thedivinemisse

Problem solved. I told the dealership to lubricate the slip joint. They giggled at me, but did it anyhow. No more thunk! A $42 fix. I need to learn to do this stuff myself.

wde3477

First, congratulations on investigating the problem further rather than blindly accepting the dealer's guess. Looks like you took care of the problem in short order before anyone here could help you out. I would suspect the big dollars were a powerful motivator. :-)

Good grief - it's been a while since I've had a vehicle worked on at a dealership - what's a good number for the going shop hourly rate? $250 to drain, open, inspect, close, and refill a diffey seems pretty pricey. Not to mention the $1600 for what sounds like a complete replacement. Ouch.

Keep an eye, er, ear on this for a while. I'm just a little suspicious of grease solving a clunking problem, may just mask it for a while. But hey - if it does, it does and chalk your experience up as a great diagnosis. If not, at least you know where to focus your attention when it returns.

wde3477

ah - one more thing - thanks for the updates. It's good to know what the solution to the problem turned out to be.

ajaxn

Hello WDE 3477,do you know why my truck will not down shift to third,from OD,this happens when acellerating onto interstate,my truck is 91 f 150,5.0 E4OD transmission.i put a new neutral safety switch on last weekend but didnt fix the problem,.........not sure what to do ¿