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Interpreting rear-end noise

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I have zero experience working on rear ends - never had an issue to repair- but I think I’m about to learn, and was hoping you folks might have some advice based on what I’m seeing and hearing, to get me started in the right direction.

I’m getting a relatively loud thrumming out of the rear end at any speed above about 20 mph. It doesn’t sound like the even roar or a wheel bearing, and definitely has a beat.

When I’m accelerating or climbing, it has one tone. When I am decelerating or coming down hill, it has a very different tone. The tempo of the beat (at a given speed) is the same either way, but the pitch or tone is different. When I’m on flat ground and maintaining speed, I can find a spot in the throttle where the sound goes away altogether.

When I started working on it again, after sitting for 10 years, I saw that the pinion seal had puked on the floor. When I topped it up, it only took about 3 oz of gear oil, so it didn’t leak a lot, but there is at least a slow leak at the pinion. Also, I have not greased the u-joints yet either.

I’m thinking it’s probably the pinion gear floating in place, but don’t know rear ends enough to be sure. I’m thinking my first step is to grease the u-joints, drop the rear of the driveshaft, and learn how to replace that pinion gear and reset its tension.

Thought/inputs/cautions?
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Discussion Starter · #22 ·
Did you take the copper sealing washers off the studs?
Assuming the copper washers are out, put a floor jack under the pinion of the diff and pump just a
bit. Should pop free.
Perfect. Thanks, gents. Five of the 10 bolts had the copper washers on them (bottom 4 and top center). They were a bit of a PITA to get off. Once I did, I put four nuts back on the studs, one short pump of the floor jack broke it loose. I was able to give the yolk a shake and it pulled forward to the nuts and is draining now.

Appreciate the help.
 

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Discussion Starter · #23 ·
I haven’t pulled anything down further yet. So far, I have noticed two almost identical chips on the ring gear. No damage on the pinion gear teeth that I can see.
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Backlash is currently .004”.

I’m pretty sure I do have a bad bearing in the assembly. When I was turning the pinion by hand, I would occasionally find a hitch. It wasn’t hard to roll past it, but it was there. Not in the same place on each rotation, and sometimes I could go 10 or 12 rotations before I would feel it.

Really hoping I don’t need to replace the ring gear right now. Lost my main job on Friday, so I’ve put myself in a temporary car spending pause. Also, I’m assuming I’ll need/want to regear the rearend once I figure out what I’m doing with the rest of the drivetrain, so I’d hate to buy new right now and get it wrong.

The rebuild kit I have coming has new Timken bearings for the diff and a new pinion crush sleeve. I’m really hoping I can get it back together and working decent with just that.
 

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Man, I feel for you. I know you don't want to hear it, but I don't think I would feel comfortable re-using that gear set with damage like that. It seems something got in the gears and caused that tooth to come apart, but who knows. I am thinking you will find damage on your pinion as well. I suppose if you had to dress it up and put those gears back in, they would probably work, but who knows what kind of noise they would produce or how long they would last without further damage, producing grit, etc.?
You are going to have to disassemble everything to check out all of the bearings, I am relatively sure you will find damage there a well.
I will say this, everybody has their preference but I like Richmond gears. They come with a run in dimension etched on the gears from the factory, and when you set up your gears, it is a great help to have a target dimension to shoot for.
I see some Richmond (Excel) gears on Amazon for half the price of the regular Richmond gear. I looked on the Richmond gear site and the warranty is 1/2 of the standard gearset, but the price is half too, so that may be an option for you for a short term gear.
Keep us posted for any damage you find.
Where are you located?
 

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Discussion Starter · #25 ·
Man, I feel for you. I know you don't want to hear it, but I don't think I would feel comfortable re-using that gear set with damage like that. It seems something got in the gears and caused that tooth to come apart, but who knows. I am thinking you will find damage on your pinion as well. I suppose if you had to dress it up and put those gears back in, they would probably work, but who knows what kind of noise they would produce or how long they would last without further damage, producing grit, etc.?
You are going to have to disassemble everything to check out all of the bearings, I am relatively sure you will find damage there a well.
I will say this, everybody has their preference but I like Richmond gears. They come with a run in dimension etched on the gears from the factory, and when you set up your gears, it is a great help to have a target dimension to shoot for.
I see some Richmond (Excel) gears on Amazon for half the price of the regular Richmond gear. I looked on the Richmond gear site and the warranty is 1/2 of the standard gearset, but the price is half too, so that may be an option for you for a short term gear.
Keep us posted for any damage you find.
Where are you located?
No worries. I’m not broke or anything. I’m just hoping not to have to buy new gears because I (1) know how these things have a way of ballooning into me deciding that I need to go with a top-quality LSD or 600 HP locker, or (2)that I’m going to want to do that eventually and would hate to buy parts twice- especially right now.

I’m going to see what else I find in there. If it’s a definitely bad bearing, I think I’m going to finish the rebuild and dress those two teeth and see what I get. If the noise was actually those teeth, and not the bearing, then yes I’ve wasted $80 on bearings. If there isn’t a bad bearing, then I’ll probably break down and add a couple hundred bucks to a new gear set, trying to keep myself from going full wish-list and just put a serviceable set of gears in it for now.

I appreciate the thoughts/advice, even if they’re not exactly what I want to hear at any given moment. At the end of the day, I’m a big boy and have to make my own decisions, so bad news is just news until I decide what to do with it.

I’ll follow up with what else I find in there.
 

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Motive gears! They're not expensive, I think I just paid $250 for a set of 3:40's . Now is a good time to make the change. An LSD Tracloc is roughly $700 to build, an Eaton Trutrac is right at $1.1k. That's bearings, carrier, gears, rebuild kit, beer, and a weekend to do it. Love my Eatons.
 

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I haven’t pulled anything down further yet. So far, I have noticed two almost identical chips on the ring gear. No damage on the pinion gear teeth that I can see.
View attachment 868238

Backlash is currently .004”.

I’m pretty sure I do have a bad bearing in the assembly. When I was turning the pinion by hand, I would occasionally find a hitch. It wasn’t hard to roll past it, but it was there. Not in the same place on each rotation, and sometimes I could go 10 or 12 rotations before I would feel it.

Really hoping I don’t need to replace the ring gear right now. Lost my main job on Friday, so I’ve put myself in a temporary car spending pause. Also, I’m assuming I’ll need/want to regear the rearend once I figure out what I’m doing with the rest of the drivetrain, so I’d hate to buy new right now and get it wrong.

The rebuild kit I have coming has new Timken bearings for the diff and a new pinion crush sleeve. I’m really hoping I can get it back together and working decent with just that.
I can relate. A few years ago I needed to replace my rear springs, the old ones were causing funny driving characteristics. I was planning on buying Eaton springs but I also was about to be laid off from work so that pretty much shut things down. Luckily another member had a basically set of brand new Scott Drake’s he didn’t want and sold them to me for a great price I couldn’t refuse. There’s no shame in taking a slightly different route at this time. Maybe you can find just a good used 8” to stick in for the time being?
 

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Discussion Starter · #28 ·
So, I’ve decided that I’m OK with buying a new ring and pinion if I need it. As I look examples of the correct contact pattern, I’m not convinced that these two chips are even going to contact the pinion, though. If I do end up going with a new gear, I think I’m going to take the opportunity to change the gearing a little. It’s currently a 2.80.

What would you recommend for a low HP 302 on a C4? My stepdad confirmed that he still has the original 289 from it, which I plan to go get soon to put on a stand for a later build. My goal for the drivetrain is to build the engine to 250-275HP max, and stick with the original C4. There’s a chance I could eventually get around to putting a T5 in it, but I don’t expect to do that any time in the next couple-few years.


A couple notes on what I’ve found so far:

The carrier bearings and races are not the problem. They’re in great shape and feel perfect. I’m nearly certain that the issue is in one of the pinion bearings. The pinion itself has no viable damage and, once I pulled the carrier out, and spun the yolk by hand, I can feel a bearing rattle that (I know this probably sounds stupid) sounds/feels like exactly the same tone of the noise I was hearing while driving it.

The one thing I haven’t gotten to look at was the spider gears. Until I’m fully committed, with ring gear in hand, I’m avoiding pulling the carrier bearings.

Is there any way to test the spider gears without disassembling the carrier? Any indication of a problem in there without pulling it apart?

I’ve got a press, but stopped short of pulling the pinion just yet. I’m planning to do that today or tomorrow to see if I can put eyes on a pinion bearing problem like I suspect.
 

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Discussion Starter · #29 ·
I’m making progress.
I did a contact pattern before I took it apart, and it doesn’t look like the two chipped ends will ever contact the pinion gear. Also, I filtered and ran magnets through the fluid and sludge and didn’t come up with enough metal to account for even a tenth of one of them, and there was no glitter to the fluid, so I don’t think it’s been chewing on them.

I do, however, think I’ve found the source of the noise: there was absolutely no preload on the pinion bearings.

I’m fairly good at estimating torque in in/lbs, at least on a screwdriver. I’ve turned so many thousands of in/lb screws and bolts in my gunsmithing career that I have a pretty good feel for it. When I pulled the pinion assembly out, I didn’t feel much resistance, but I assumed that was because I had the leverage of the yolk and the target was so low- also, I could feel/hear some metallic wobble.

When I pulled it apart, I did find some pitting in one of the pinion bearings and race, and in the pilot bearing. I replaced the bearings and races, and put it back together with a new seal and crush sleeve, and torqued it all down to 175 ft/lb, and I still had end shake so I thought I was doing something wrong.

I probably spent a collective three hours taking it back apart and putting it back together, trying to figure out why I had end shake, and just decided to torque it to 175 one more time, and then put the impact to it. I got about 3/8 more turn on the nut, discovered the end-shake was gone, went to spin the pinion and freaked out that I’d put too much preload on it. There was definitely a resistance there that I didn’t have before I took it apart.

I put my gauge on it and it was only at 5 in/lb. My in/lb torque gauge is a damned good one, and spec for a new seal and bearings is 17-32 in/lb, so I knew I had plenty more to put on it before it was right.

Within a couple cycles of watching the impact wrench and checking the pre-load, I realized I could pretty reliably dial it into within 1-2 in/lb so, instead of aiming to just get within in the range, I decided to shoot for dead in the middle at 24-26 in/lb.

I’d read in a thread here or on another forum about whacking the front and rear of the pinion and rechecking the pre-load until the pre-load didn’t drop anymore, and that proved to be true. I worked through three of those cycles until the preload didn’t drop, and ended up right at 24-25 all the way around in both directions.

All said and done, I’m now sure I had no pre-load to speak of, and probably had a tiny amount of end-shake in the pinion.

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I still have to swap out the carrier bearings, and think I’m going to crack it open to at least put eyes on the spider gears while I’m in there, but I do feel pretty confident that I found the source of some noise, if not THE noise, in those two pinion bearings and the lack of pre-load.
 

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I’d say you found the problem. In the mid 80’s I had a 77 Econoline E150. I remember the differential would start making noise and time to tighten the pinion nut. The truck was a POS and on borrowed time so I never worried about setting actual preload, just enough to make sure the yoke didn’t fall off.
 

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Discussion Starter · #31 ·
I need some help/tips.

How in the heck do you open the carrier? I’ve removed the ring gear, and the manual says to remove the differential pinion, so I did that, but then it just says “separate the two halves” or something to that effect.

My diff pinion has just enough wear on it that I really want to take a good look at its gears before I start putting it back together, but I can’t, for the life of me, figure out how to get purchase on the two halves to either press them or beat them apart.

The circumference of one of the two is slightly larger than the other, but it’s got a beveled edge and, even if it was square, I’m not sure how you’d get it to press.

Thoughts?
 

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Discussion Starter · #32 ·
Here’s the pinion shaft. The bore of both of the spider gears look good, so I’m guessing the shaft is the wear part. I’m going to get a replacement in order, but would really feel better if I could put eyes on the gears. I have a good bore scope, but I don’t think that’s going to let me see everything well enough to call it good.
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Discussion Starter · #33 · (Edited)
Disregard. I got it. I noticed these two blind holes and figured they had to be there for a reason (of course, that reason could be factory fixturing and I just winged it), so I put a beating roller in each one, put the ring gear on it, and used its screws to press the bearing rollers. That popped it apart.

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Edit: now that I think it through, that shouldn’t have worked. I guess is just flexed the diff housing enough to break it loose. Once it popped loose and gave me enough room to get a wedge in it, I backed the bolts out and worked it the rest of the way apart with the wedge.

It’s back together now, and I have just under 0.001” runout, so nothing got damaged, but I think I got lucky.
Don’t do that.
 
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