Is it a thump or a clunk?

I think its more of a thump. I have a 96 explorer xlt v6 4.0l. auto trans, 4wd. I got the truck from an old high school buddy for a few hours work, but it needed a tranny. OK I have a rebuilt tranny installed. Tranny seems fine. I have a thumping noise, wich seems to be coming from the front end or possibly where the xtrans case is. I brought the truck to my regular mechanic to look over the front end, he says it does'nt appear to be anything such as u joints or driveshaft or cv joints, says its in the differential. So I bring it back to the tranny guy. he has the truck for 3 days and finally tells me that the noise is no longer happening. I take the truck and sure enough the noise is still happening. I then bring the truck to my pops mechanic who is very good, he tells me its the transfer case motor.to save money I do the motor myself 100 bucks from the junky and 3 hours of work, nope no good noise still happening. So now I dont know what to do? I do'nt know how long this noise may have been happening for because I got the truck with a blown tranny, could'nt test drive. My buddy tells me his girlfriend had been using the truck for the past several months, so I do'nt know much about the noise. What I do know is the noise does'nt seem to happen when the truck is cold. It needs to be driven for 15- 30 minutes. It happens most when I accelerate fast to about 30mph and take my foot of the gas. As soon as I take my foot of the gas I get the thump , thump, thump until the truck slows to about under 20.The noise will still happen if I put it in nuetral while the thumping is evident. I get the thumping when I have the tranny in 1st, 2nd, and 3rd gears manually.The noise does'nt happen when I put it in 4w auto only in 2wd. sometimes the noise is louder then other times. sometimes it may thump only 2 or 3 times other times it may bang for as long as the truck will coast down until about 15 mph. If the noise is evident and I re accelerate the noise will go away. The noise does'nt seem to happen above 40 mph.If I press on the brake the noise will generally go away. Well I have written more then most, hopefully I can get some usefull feedback. I want to do some basic changes like a tire rotation to eliminate that and I want to change the gear oil in the front differential. Does anyone know what weight oil to use?

Thanks much
BILL.

When the thumping is occurring, does turning the steering seem to have any effect? Your description kind of sounds like an issue with a CV joint. When loaded, the noise is not apparent, but when unloaded, the noise is there.

If steering doesn't seem to play a role in the noise, then I'd have to suggest you focus on the auto-locking hub set up.

Changing the front differential fluid is a good idea, as you suggested you are planning to do.

-Rod

I have'nt noticed if the steering has an effect on making the noise dissapear. The steering is not causing the noise, I mean I do'nt have to be making a turn for the noise to happen. If it were a cv joint would'nt the noise be happening in 4wd? Would you know what wheels are in use in 2wd front or rear?Does the 96 employ the limited slip differential?

In 2wd, the rear wheels are driven. My thinking is that possibly the noise goes away in 4WD because the front halfshafts are being driven and so there will be torque applied to them rather than them freewheeling. Maybe when torque is applied, the wear points are enough different that the noise is no longer evident. Same theory for the locking hub system. This concept can also be applied to turning the steering, the wear points of the outer CV joint is different from going straight down the road.

-Rod

I rotated the tires today too rule them out. The steering also does'nt seem to have an effect on the noise appearing or disappearing. I want to change the differential fluid, just did'nt have time today. What weight gear oil should I use? The fact that the noise disappears when in 4wd should rule out the cv joints and the axleshaft universals , Right? Thanks for your info rod. I see you respond to many post here. It nice to know there are still some people out there willing to help others. Thanks.

The factory service manual recommends 80W90 QL Thermally Stable 4x4 Axle Lubricant.

I wouldn't say that since the noise disappears in 4WD rules out the CV joints. I tried to explain my reasoning for that in my previous post (torque being applied).

-Rod

Changed oil in differential today........... No luck. Still have the noise.I guess at this point its trial and error. I was wondering if I can take out the driveshaft connecting the front differential and the transfer case and still be able to use the vehicle?

With AWD it's a bad idea, but since yours has 4WD, I'm not sure it's bad. You may end up with a nasty fluid leak though.

-Rod

I have the truck back at the tranny guy. He's looking it over to try and find where the noise is coming from. He said he spoke to someone who is very knoledgeable about 4x4s and transfer case, he says that by disconecting the wiring harness to the transfercase you can determine if it is electrical or mechanical?They did, and the noise is still evident. They told me they had the front driveshaft out and that the noise dissapeared so they think its in the transfer case. They have'nt said that it is the transfer case just that they are leaning that way. I'm not sure if removing the drive shaft actually eliminates any one aspect except for maybe the cvjoints or the front axleshaft universals? What do you think rod? I am very good mechanically and contemplating putting in a junkyard transfercase. Is it the type of job I can do in my driveway?

My suggestion/thaught would be to engage the 4x4 when the CV shaft is out. Reason...The CV spins parts in the transfer case possibly causing the noise. Removing the CV possibly means these parts in the transfer case aren't moving anymore. If you engage the 4x4 those parts should be moving again even if the CV isn't there....Make sense?!?!?!!:dunno:

Good luck!

I agree with denisb. I'm not sure that I'd be ready to condemn the transfer case over something in the front axle assembly if the noise is not present with the shaft between the front axle and transfer case remove and the case set to 4WD.

As for changing the transfer case in your driveway, that depends on the weather, your threshhold for frustration, and tools. I've never personally changed one, but the job appears to be pretty straight-forward.

-Rod

transmission guy says its the transfer case. He looked it over, he pulled out the front drive shaft as well. I had the truck back for a few days now and I have done some checks too. I took out the rear driveshaft and drove the vehicle in 4wd, well I tried to drive it. It made a similar noise and I could only go about 5 mph and the truck was kinda bucking. I chocked the front wheels and with my friend watching the front driveshaft he could see that the front driveshaft was not always turning, so we think its the transfer case slipping. thats what the 1 mechanic said, although he thought it was the transfer case motor. The transmission guy says its the transfer case, so thats what I'm going to sttart with. I got one from a junky for 300. I have a friend who is real good with cars and so am I so I am going to do it in my driveway. I have one question though, What type of fluid is in the transfer case? Is it gear oil? Or is it Tranny fluid? I have heard that some makes combine the tranny and transfer case fluid as one system? Thanks for all your input guys.

SUCCESS..... I think. I changed out the transfer case and sure enough the noise is gone. I hope. I drove it for about 45 minutes or so with no noise. All seems well. Thanks guys for all your input.