Rear drivetrain clunk, what’s worn? (Video) (1 Viewer)

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Nov 8, 2007
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Location
Baton Rouge, LA
I’ve read over nearly every reverse to drive clunk thread and can’t seem to figure out my issue. First off, it’s nothing front end related as I have the front driveshaft removed and the center diff locked.

I’ve removed the rear DS, cleaned the ujoints, regreased, cleaned the slip joint splines and removed old grease, regreased, all of those feel tight with no play. I seem to be having play at the input shaft to the rear diff or possibly where the input shaft goes into the transfer case (if that’s possible).

Here is a video of shifting from R-D-R a few times. You can see the amount of rotational play in the shaft before I start moving forward or backwards. If the vehicle is in park with the ebrake on, I can grab the shaft and get a similar amount of rotational play as well.

Any ideas on what could be worn and causing this?!? (Reuploading with sound)


AE9AD4E1-0850-4480-B881-42E013EC412C.jpeg
 
With the miles, you get little extra backlash in pinion and ring gear. You can continue with it and if it is annoying you will need to pull the diff and get it reset to proper backlash. Also, notice the splines on drive gears inside the diff and half shafts can have some play too. It is very difficulty to get rid of all the play without getting new drive gears and half shafts. I did all OEM front bushings and OEM CV axles with OEM flanges and I still experience some clunk on the front diff. Non of this clunk is an issue with a manual transmission, so I bought My 21 Taco with a Manual trans. I seriously hate automatics primarily due to this clunk!
 
Here's my guess. 3 splined locations and the rear diff gear mesh/backlash. Any one of those could do it. They're all probably contributing a little.

Splines at the diff input are probably pretty straightforward to replace if desired. Rear diff gear slop is not cheap or easy to fix. Rear axle splines at the wheels is the final link in that chain that I'd investigate. I know I have some play in mine. You can feel it if you lift just one wheel in the air and rotate the wheel.

Your t-case joint may also be worn, but if the rear 4 I circled are solid, they would disallow the shaft movement, even if the joint at the T-case had slop.

1613509573743.png
 
your control arm bushings look to be worn and are exhibiting some axle wrap.

add that to worn splines, some wear in the diff gear mesh... that's my bet.
Gears are 4.88 nitro that have about ~30k miles on them.
 
With the miles, you get little extra backlash in pinion and ring gear. You can continue with it and if it is annoying you will need to pull the diff and get it reset to proper backlash. Also, notice the splines on drive gears inside the diff and half shafts can have some play too. It is very difficulty to get rid of all the play without getting new drive gears and half shafts. I did all OEM front bushings and OEM CV axles with OEM flanges and I still experience some clunk on the front diff. Non of this clunk is an issue with a manual transmission, so I bought My 21 Taco with a Manual trans. I seriously hate automatics primarily due to this clunk!
The truck was regeared about 30k miles ago to 4.88. The same play before and after from what I remember.
 
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Here's my guess. 3 splined locations and the rear diff gear mesh/backlash. Any one of those could do it. They're all probably contributing a little.

Splines at the diff input are probably pretty straightforward to replace if desired. Rear diff gear slop is not cheap or easy to fix. Rear axle splines at the wheels is the final link in that chain that I'd investigate. I know I have some play in mine. You can feel it if you lift just one wheel in the air and rotate the wheel.

Your t-case joint may also be worn, but if the rear 4 I circled are solid, they would disallow the shaft movement, even if the joint at the T-case had slop.

View attachment 2587252
The spots at the hubs, are those pressed on? As in if those are slightly worn can those be semi easily replaced like the front drive flanges? Or does that require removing the pumpkin and removing the shafts?
Also thanks for making a sweet product. Snagged one of these right when you started making them.
EFDC28F4-7328-466B-8967-D3E08B04C23B.jpeg
 
The truck was regeared about 30k miles ago to 4.88. The same play before and after from what I remember.

Nix those then.

I'm still seeing axle wrap in the video though. Set your camera up to watch the joints and add a witness mark, my money is on more play in those bushings than you'd expect.
 
Nix those then.

I'm still seeing axle wrap in the video though. Set your camera up to watch the joints and add a witness mark, my money is on more play in those bushings than you'd expect.
I zoomed in on those suckers while watching from my phone and yup, there seems to be some play in that poly bushing. That’ll be next on the list to replace as soon as I can figure out what size they are.

Thank you for spotting that by the way!
 
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The spots at the hubs, are those pressed on? As in if those are slightly worn can those be semi easily replaced like the front drive flanges? Or does that require removing the pumpkin and removing the shafts?
Also thanks for making a sweet product. Snagged one of these right when you started making them.
View attachment 2587289
Looks like it's located at the output of the pumpkin. Not sure how much disassembly that requires on a 100, but I'm guessing a lot - haven't tackled it myself yet. I need to tear into my rear axle soon as I have a leak in a seal or two. Not a job I'm looking forward to.
View attachment 2587291

Also agreed that if your rear diff is newish, that's unlikely the problem. Bushings are always good to check and replace as needed. I'm thinking the companion flange might be a good low effort thing to replace if you're desperate to give something a try. I did that on my 99. Can't recall how big the difference was.

View attachment 2587297

Thanks for the compliments on the key! That's a really old one, judging by the front face. Glad to see it's holding up well! :)


*Edit, just remembered that I did the FRONT companion flange on my 99. Similar deal in the rear I believe. You'll probably have to be thoughtful of how you disassemble and reassemble. I recall there being a "single-use only" part inside the diff behind that flange. You can re-use it (so says I) if you carefully attempt to measure the previous torque value and then exceed that value upon install of the new one. That might not be worth the effort, haha.
 
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Looks like it's located at the output of the pumpkin. Not sure how much disassembly that requires on a 100, but I'm guessing a lot - haven't tackled it myself yet. I need to tear into my rear axle soon as I have a leak in a seal or two. Not a job I'm looking forward to.
View attachment 2587291

Also agreed that if your rear diff is newish, that's unlikely the problem. Bushings are always good to check and replace as needed. I'm thinking the companion flange might be a good low effort thing to replace if you're desperate to give something a try. I did that on my 99. Can't recall how big the difference was.

View attachment 2587297

Thanks for the compliments on the key! That's a really old one, judging by the front face. Glad to see it's holding up well! :)


Correct, no splines at the outboard ends of the rear axle shafts. The rear axle doesn't work the same way the front does (no drive hub flange with splines engaging the shaft. it's all keyed at splines within the pumpkin.) As long as the gear oil was never replaced with mud, those inner splines should stay happy... they don't see any considerable sliding like the drive hub flange and the drive shaft splines see.

I had my rear axles out to replace those inner seals a few weeks ago, it wasn't nearly as bad as you'd think (if you are seeing leaks, check that your breather isn't clogged). It does get really nasty if you decide to dig into the rear wheel bearings though, that is a pretty big ordeal to get those bearings off and get everything (including the ABS tone ring) back together correctly. My bearings were in in great shape... so I opted for the easier route and left that whole assembly together.
 
Correct, no splines at the outboard ends of the rear axle shafts. The rear axle doesn't work the same way the front does (no drive hub flange with splines engaging the shaft. it's all keyed at splines within the pumpkin.) As long as the gear oil was never replaced with mud, those inner splines should stay happy... they don't see any considerable sliding like the drive hub flange and the drive shaft splines see.

I had my rear axles out to replace those inner seals a few weeks ago, it wasn't nearly as bad as you'd think (if you are seeing leaks, check that your breather isn't clogged). It does get really nasty if you decide to dig into the rear wheel bearings though, that is a pretty big ordeal to get those bearings off and get everything (including the ABS tone ring) back together correctly. My bearings were in in great shape... so I opted for the easier route and left that whole assembly together.
I'd love to make that job simple. Were you able to get to the oil seal? I recall there being an oil seal deep within the assembly and then an outer grease seal and the culprit of leaking oil is maybe the inner seal?
 
I don’t see anything out of the ordinary in that video other than the control arm bushings that @Somebodyelse5 noted. IIRC, the FSM states something like 1.5” rotational play in the driveshaft as being factory spec.
 
I'd love to make that job simple. Were you able to get to the oil seal? I recall there being an oil seal deep within the assembly and then an outer grease seal and the culprit of leaking oil is maybe the inner seal?
I didn't take many pictures when I did it, but there is only one seal per side (no inner seal, only the outer seal). It's only like 3" deep inside the tube. This is the part number:

9031058002
1613527326813.png


There is also a big oring you'll need but I wasn't able to track that part number down and the parts guy I know couldn't seem to find it either so I cleaned and reused the ones I had.
This picture has the oring sitting on top of the backing plate, gotta look close though.
1613527915272.png

per @JunkCrzr89 "Them there tubes are full of erl" :flipoff2: :moon:
 
Worn bushes are a separate concern that will definitely lead to a driveline clunk but completely unrelated to the amount of driveline lash initially posted. I think the lash looks pretty normal to me, but with worn bushes the feeling of engagement in the driveline becomes more pronounced.

If you have poly bushes in your rear link arms, the black poly bushes tend to compress and loose memory so they allow the sleeve to move around creating a greater amount of slop once worn. Mine were done at 30-35,000 miles.
 

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