[dirthead1]

I've searched high and low on four different sites already...

I have a thumping noise/vibration coming from my drivetrain and can't really isolate what is causing it. The sound is not metal to metal, but literally is a "thump, thump, thump, thump". It starts around 30 mph and gets progressively louder and faster as the speed increases and never goes away. The noise is worst when coasting at speed and moderates under heavy acceleration. It sounds like it's coming from the rear, but I can only hear the sound inside the cab and nothing while driving alongside a road barrier or whatever.

I have recently put Deaver 8 leafs in the back and Donahoes in the front, which only increased the "thumping". I have removed the rear drive shaft and drove around in 4, but the problem remained. Any ideas? What does it sound like when the transfer case is going out? I just don't want to start replacing stuff without a plan. The truck really sounds like it is going to break. Unfortunately, the driveline shops in the area just want to start replacing parts to isolate the problem and I know throwing cash at it is not going to fix it.

Should I remove the front shaft and try that too?

 

[Bear]

I've searched high and low on four different sites already...

I have a thumping noise/vibration coming from my drivetrain and can't really isolate what is causing it. The sound is not metal to metal, but literally is a "thump, thump, thump, thump". It starts around 30 mph and gets progressively louder and faster as the speed increases and never goes away. The noise is worst when coasting at speed and moderates under heavy acceleration. It sounds like it's coming from the rear, but I can only hear the sound inside the cab and nothing while driving alongside a road barrier or whatever.

I have recently put Deaver 8 leafs in the back and Donahoes in the front, which only increased the "thumping". I have removed the rear drive shaft and drove around in 4, but the problem remained. Any ideas? What does it sound like when the transfer case is going out? I just don't want to start replacing stuff without a plan. The truck really sounds like it is going to break. Unfortunately, the driveline shops in the area just want to start replacing parts to isolate the problem and I know throwing cash at it is not going to fix it.

Should I remove the front shaft and try that too?

You say it sounds as though it is coming from the rear of the truck? could it be that is sounds like it is behind you as you sit in the seat but not necessarily behind the cab?

Also more truck model information might help. I read your post twice to make sure you were not an older pick up or SAS. (that could be my fault though, due to pain meds )

A thumping under accelleration could be a symptom of a failing carrier bearing or ujoint. a thumping under coasting or the truck coming to rest could signify axle wrap. I can't think of anything at present that would cause the front to effect either situation.

A severe way to test things is to put the truck on jackstands and have a buddy carefully operate the throttle while you are outside the truck to see if you can pin point the noise. But you need to use extreme caution when doing this type of test. But this procedure has helped me pin point which ujoint was going out on my truck.

I agree though, better to find the exact area of noise before throwing buckets of money at the vehicle.

I don't have the answer for you, but maybe with basic information such as mentioned above, I can help you find a starting point, at least until someone with a better solution chimes in.

If you think the noise in the rear, wait to pull the front shaft until you eliminate everything from the t-case back. Don't do double the work if you don't have to.

Another idea just came to me as I proofed for typos. Do you have a body lift by chance? I have had loose body bolts really cause fear causing me to think I had a drive line issue when all it was happened to be a loose bed or cab hitting.

 

[dirthead1]

Thanks for the response. Sorry about the lack of model information. My bad.

Here goes: 1998 Tacoma Xtra cab 4x4 about 110,000 miles on it.

Definitely sounds just behind me. It's very low toned, but loud. Does that make sense? Not a tinny metallic but more like bass. If I lean forward, I'm not really hearing it. I can kind of feel pulsing if I put my hand on the floor. The problem started after prerunning parts of the San Felipe 250. I didn't really beat on it that race, but coming home I could hear it. Let me mention that I have an overly sensitive ear from years as an automotive machinist and motorcycle mechanic. This thing has me baffled.

 

[Bear]

Thanks for the response. Sorry about the lack of model information. My bad.

Here goes: 1998 Tacoma Xtra cab 4x4 about 110,000 miles on it.

which engine? 3.4 (blown or natural) or a 4 banger? The reason I ask is, with the bigger engine and custom leafs, you may be more prone to axle wrap.

What about the body lift? yah or nah?

I once had a bolt so loose that my truck looked like the rear axle had shifted. Another time I thought I had a blown front strut because the thumping was right at my feet and the cab was bouncing against the frame.

 

[dirthead1]

3.4 no blower no body lift.

Thanks for your help.

 

[Bear]

3.4 no blower no body lift.

Thanks for your help.

Okay that already eliminates one thing I thought it could be, no loose body bolts.

Some people have gotten axle wrap with stock 3.4's with custom leafs. ( I don't have that set up so I can't personally comment on that, but it is still something to look at.

But it does sound to you as the noise is from a rotation? By that I mean can you tell if it sounds like the noise is rotating as the drive shaft rotates?

Before you put the truck on jack stands. With the truck in gear but not running, grab the driveshaft near the rear ujoint, if you can move it then replace the ujoint (it is a cheap part) Also while you are there, look really close at all the ujoints to make sure you did not pick up a rock in any of them.

While I am thinking about it, when did the noise/thump start? have you been wheeling lately? I have picked up rocks on the trail or while crossing rivers/creeks and they seem to find the most unique places to hide yet create interesting noises at the same time. I once had sand grit lodge itself between the rear brake drum and the shoes and it sounded like my rear axle was about to fall off. It caused a rotating grinding noise like I had a chipped tooth or something in the rear diff.

What I am trying to do is find an easy or overlooked idea/solution for you before you have to really start tearing into the truck. Sometimes the "minor fixes" are the hardest to find as well as the easiest to overlook by a concerned owner.

 

[Oppositeboy]

I was gonna say you got a squirrel caught up in your driveline... but I won't.

When did this start? Do you remember driving over anything like a shop rag or hand towel or something that may have gotten caught up in there? I am wondering if it could be a u-joint or an out of balance driveshaft? Never heard of one making a thumping sound though.

 

[Bear]

I was gonna say you got a squirrel caught up in your driveline... but I won't.

When did this start? Do you remember driving over anything like a shop rag or hand towel or something that may have gotten caught up in there? I am wondering if it could be a u-joint or an out of balance driveshaft? Never heard of one making a thumping sound though.

Brian, sounds like you and I are on the same line of thinking here, hopefully with his drive line exam he will find the solution.

I have also seen the balancing weights of the drive shaft fly completely off. Yet rare, it can happen.

 

[dirthead1]

As mentioned, I already took the rear driveshaft out and drove it in 4 wheel and the problem remained. So it's not the driveline from the trans back to the third.

I'll look into some of the other things mentioned here. It sounds really bad at 50 on up.

 

[Bear]

See my post to Brian, look for any evidence of the driveshaft balancing weight.

All driveshafts have some counter balance weights on them, if you have one (nomarally there is only one) missing you should see signs of it but a "cleaner" rectanglur area on your driveshaft.

If I remember right it will be close to the carrier bearing, but not always the case. It may take a few rotations of the driveshaft to actually find it.

 

[Bear]

I already took the rear driveshaft out and drove it in 4 wheel and the problem remained.

I'll look into some of the other things mentioned here. It sounds really bad at 50 on up.

along with the thumping, is there any evidence of grinding at all (slight or otherwise)?

 

[dirthead1]

No grinding at all.

 

[Oppositeboy]

Did you hear a pop or something before you started hearing the thumping?

 

[dirthead1]

Nope. Just drove around all weekend in the dirt and going home on the road, I noticed the sound. After lifting it last weekend, the sound is worse now.

 

[Bear]

No grinding at all.

Well if the noise presist without the rear driveshaft that also removes the idea that rear ujoint is bad or an out of balance shaft to the rear. Unless the split shaft between the t-case and carrier bearing is having issues (took me a while to realize that…like I said I am on some good drugs right now)

when you removed the rear shaft, did you just remove it going up to the carrier bearing? I guess I need to know also if you have a regular cab, extended or double cab. If you have a regular cab, then you won't have a carrier bearing. (damn meds are keeping from thinking completely through the problem so bear with me, I think after this I won't need to ask any more questions concerning model type etc.)

You do have function or able to drive the truck with only the front correct? that eliminates you having a broke drive chain in the t-case.

When was the last time you changed fluids in the tranny or t-case? Also did you mention if you had a 5speed or automatic?

If you had a broken tooth in the T-case you maybe able to see evidence of it when examining the oil after draining it.

 

[Bear]

Nope. Just drove around all weekend in the dirt and going home on the road, I noticed the sound. After lifting it last weekend, the sound is worse now.

when you raise the truck by jacking up the frame, do you notice any binding in the rear leaf packs or shackles? you may notice something when you try to fully droop your springs.

If you over tightened the shackle bolts you may have them binding up.

I am sorry it seems like I am sending you on all these wild goose chases, but there really is a lot of factors that could be causing this

 

[dirthead1]

Thank you all for your suggestions. It is the driver's side wheel bearing. Thing is close to grenading. Wow!