i've noticed this for a long time on my 93 f150 extended 4x4 and always chalked it up to a slightly worn u-joint. i finally got around to putting in a new u-joint and greased up the slip joint into the trasnfer case and it didnot cure the thump. actually its nothing you can hear but you can feel it in the truck and it happens just after youstart to roll. every thing seems tight and the slop in the rear pinion seems normal. the truck just rolled 99,000 and it has not been abused just need some input for some new places to look.

 

Check your wheel lug nuts, front wheel bearing play, tires. Does the thump increase with speed? Check the CV joints in the front axle. Does the thump occur with the hubs unlocked? Look at the front rotors for cracks or warpage. one of these is likely to be your problem. Does it do this forward and reverse, in all gears? Auto or manual?

 

Mine is starting to do the same thing, I'm going to check the tranny and motor mounts.

 

i just repacked the wheel bearings installed new u-joints in the front axle, rotors look fairly new it makes no difference if the hubs are unlocked or locked. it only happens when accelerating from a stop just after you start rolling if you go real easy on the gas it wont make the thump. i rotated the tires resently and it made no difference, but i will check the lug nuts again today. i actually lost a rear wheel on my 88 ranger 5.0 4x4 at about 45 mph no fun and causes alot of body damage plus its all kinds of ammunition for your friends to rib you.

 

i never noticed it in reverse and it is a automatic E4OD. i'll try to look at the mounts today. if i thought i could safely do it, it would be interesting to have someone brake torque the motor and see what the engine and tranny mounts were doing under load

 

Mine is making a similar noise also on acceleration from a stop. I am begining to wonder if the front radius arm bushings are bad on my truck. When accererating from a dead stop, there is a definate feeling of slop, of something shifting slightly. Mine is a 2WD and I don't know if your 4X4 is set up the same or not with the radius arm. Mine is going to the front end shop for it's first alighment since I bought it soon. I will have him check into this when it is there. But I hope it is something simplier (read cheaper!) to fix as I think I have read elsewhere that replacing these bushings is not easy or cheap. Charles

 

i have a 95 f150 ext cab 4x4 that does the same thing it thumps when i take off, mine seems to be from the front suspension unloading, i had someone get in it and power it up against the brakes in 4 wheeldrive and i checked the motor mounts and trans mount they didnt move at all. my radius arm bushings look ok.

 

Radius arm bushings do take a while to change but do not cost much and aren't as hard as they seem. I just remove the front springs and break loose the bolt holding the I-beam to radius arm. Then I remove the radius arm bushing nut and pull everything forward to get the radius arm out. It may be different on 4x4 because all my 4x4s until recently were leaf spring F250. They are easier for me anyway to change than the ball joints but I don't mind them either if I have time. If the truck only did it on moderate to hard acceleration, I'd definitely look at motor mounts. Normally you can operate the throttle by hand at the engine and see if the engine lifts too much. Radius arm bushing wear will show up more on rough road or offroad than acceleration, as will bad shocks or loose caliper. I hate the float pins in pre95 F series calipers. I've changed several and installed new calipers to no avail. I finally just bought post 95 F series. That's not your problem though. I don't fully understand the transfer case but the drive chain sometimes stretches and can rub on the housing. I wouldn't expect it to do this at 90K though, I've had trucks go over 300K before it went out. And I don't think the chain moves in 2wd but may be some other thing to consider if some one else knows more about it. Transmission mounts could cause the problem but you should see it. Or you could slightly lift trans/Transfer case with a jack and check for movement. You shouldn't have a carrier bearing either on 4x4 so I'm out of ideas for now. Again, good luck.

 

I have the same dump in my 1996 150 SuperCab 4x4. When I wiggle the bed sideways, there is a clonking sound in the rearaxle, 8.8. Did the same on my 82-250 Dana 60 axle- no clonk.My theory; can the axleshafts move out or inwards in the axle and that slight move make the sound when power goes thru the differentialgears? I also want to know, it is very irritating.

 

Have red some artiles about this noise and a common reason for this seems to be lack of grease in the splines of the slipyoke, in my case the transfercase. Greased the splines and no more "clonk".

 

well i heard that too and when i replaced the rear u-joint 1 month ago i anti seized the slip were the splines are and were the seal rides with no luck.

 

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I have the same feeling in my 4x4 and a good mechanic told me that it was the rear leaf springs wrapping up and hitting themselves when they get a little worn in, He said that most fords have this problem.
If you think about it it makes sense ,As you brake to a stop your rear end gets pulled nose down ,and when you accelerate the rear end wants to twist nose up ,and once those little pads on the end of your leafs start to wear out (thump).
Makes sense?

 

If that's the case, I'd also check the tie bolt that goes through the center of the leafs and holds them tight together (in the middle, not ends). They are easy enough to replace and cheap. Normally you have to buy a longer bolt and grind it off once you get it tight. I've had to replace a few on my work trucks from the woods. The worn bolts show up when the leafs start to fan out laterally and will let the axle walk sideways. This may not be a problem for you but certainly worth checking into.

 

Look at your leaf spring bushings. I had this same problem, drove me crazy. Replaced U joints, bearings, greased the slip yoke, you name it, I did it. Finally got a friend to do a few starts and stops while I laid on the ground a few yards away with a pair of binoculars staring at the rear suspension.
Every time the weight transferred from front to rear, I could see the springs shift at the rear of the truck. Got some poly bushings for the springs, no more clunk.