Rear End Whine on Acceleration and Deceleration

[Thyme]

I've had my rear rebuilt twice now by the same shop. The first time I had them put in a new diff (Eaton True-Trac) along with 3.55 gears. I leave the shop, and still hear the whine on accel and decel that prompted me to get it rebuilt in the first place. I take it back, they claim its the u-joints and/or trans. I put in new u-joints and get another T-45 rebuild and put it in. Whine still exists. I have them rebuild it again, and they refuse to warranty their work from the first time because I provided the bearings and that "they can't make my bearings go bad". They stated that specifically a carrier bearing went bad. So now they've rebuilt it with their own bearings, still using the same gears and diff. Exact same whine still exists, right down to the pitch of it. Now, they claimed I was full of shit about the noise and still blamed the trans. Finally got another mechanic at the shop to give it a drive and he thinks its the pinion bearings. He also said that if it isn't them messing up the build, or me beating on the rear too hard, that the front of the bell housing could be warped but they wouldn't be able to tell that. Going in for round 3 this week this time free of charge, so I'd like to get some opinions on what could be shitting the bed here.
Some things to note as of this most recent rebuild:
When slipping the clutch in first and reverse, the driveshaft shakes pretty violently and makes a fairly loud noise. I sadly did not take a video of this when I had the chance.
There seems to be a lot of slop in the rear itself causing this. I've videoed this.

When coasting in neutral, you can hear a very regular but quiet clunking noise from the drivetrain.
Gear pattern looked good after their first rebuild, haven't laid eyes on it as of the 2nd build.

 

[cobrajeff96]

There's a few things that can cause what you're experiencing. Usually clunking is too much backlash or space between ring and pinion teeth. Also, if the carrier bearings don't have enough load on them that'll cause clunking. Whine is either backlash too tight or the pinion bearing too tight or a bit of both. A distant second place for whine could be improper pinion angle which can be easily measured and corrected by shimming the trans up or down, usually down. But you have to measure and get the front and rear u-joints at the same angle somewhere within 1 and 3 degrees max.

They probably just threw shit together and didn't take their time to do it right.

 

[b1pig]

Diffs can be VERY tricky. In my experience, WHINE will come come from the ring and pinion.
ROARing (or a scrub/scrape) will come from axle bearings.
HARMONIC vibrations will come from the driveshaft.

If either the carrier bearings or pinion bearings were worn out or not installed properly, once you start loading the diff on the road, any failure in the installation will become apparent quickly. I have looked recently, and found there is no real specification on pinion "slop". The only measurements critical to the pinion are the installed pinion depth and the rotation resistance in inch pounds, I think.

The first thing I'd look at is the backlash. Pull the cover, put a dial gauge on the ring gear. If the backlash is out of spec, that would be the most likely cause. If backlash is within spec, some gear mesh compound to see the pattern. If the pinion depth is out of spec, that will show in the pattern.
It is also possible that your car has a damaged housing. If you "beat" on it... then it could be a possibility. Not an absolute, though.


About a transmission. I have "heard" of instances where noise confused a mecanic/owner because the whine was transferred in some way by the driveshaft. Only heard it twice, though.... The best way to know the difference is that whine from the Diff will change in pitch with the road speed and may come/go when the clutch is in or youre out of gear. Whine from the transmission will change pitch with nearly EVERY gear you select and will be completely gone when shifter is in neutral.

I have done three separate Dana 35 axles and one Dana 44 myself. The last time, I bought the gear removal tool as I was trying not to be destructive.


What you honestly could be facing is not a mechanic that is incompetent, but simply a mechanic that has encountered a problem above their level of experience. You'll be hard pressed to get a shop to admit when this happens.

 

[07GtS197]

What brand of gears did you get? In the last couple of years, a new tooth cutting process has been used and can cause issues if not set up correctly.

https://www.s197forum.com/threads/f...process-differences-that-affect-setup.139760/

 

[Thyme]

What brand of gears did you get? In the last couple of years, a new tooth cutting process has been used and can cause issues if not set up correctly.

https://www.s197forum.com/threads/f...process-differences-that-affect-setup.139760/

I believe the shop used a gearset from NAPA, and I am assuming the NAPA brand gears themselves were chosen. Based on the info you linked, I think they're the face hobbed variety.

It is also possible that your car has a damaged housing. If you "beat" on it... then it could be a possibility. Not an absolute, though.

Is there any reliable way to determine if the housing is warped? I believe the housing could've overheated when my rear end woes began with this car, but I'm not certain.

I dug up the pictures I took after the 500 mile break in period from the first rebuild they did. To my knowledge this is an alright wear pattern. Keep in mind it was whining the whole time, they'd just told me it "wasn't the diff".

 

[b1pig]

I believe the shop used a gearset from NAPA, and I am assuming the NAPA brand gears themselves were chosen. Based on the info you linked, I think they're the face hobbed variety.


Is there any reliable way to determine if the housing is warped? I believe the housing could've overheated when my rear end woes began with this car, but I'm not certain.

I dug up the pictures I took after the 500 mile break in period from the first rebuild they did. To my knowledge this is an alright wear pattern. Keep in mind it was whining the whole time, they'd just told me it "wasn't the diff".
View attachment 24481View attachment 24482

Man, it's hard to really tell in the photos.... but the only true way to check the pattern is with compound. I would think the parts store would have some. If not, search "gear marking compound" on Amazon.
For comparison.... something like this comes in every gear master set.

https://www.amazon.com/JEGS-612200-Gear-Marking-Compound/dp/B078WJ7GNS/ref=sr_1_3?keywords=gear+pattern+compound&qid=1679270490&sprefix=gear+pattern+comp%2Caps%2C671&sr=8-3

To get an understanding of what you need to be looking at, I STRONGLY recommend going here:

StackPath

Every gear set I have installed in my Jeeps was from Yukon. I installed one set in a Friend's JK that came from US Gear or something. Yukon has given great customer service. I'm sure others do, just speaking from my own experience. The info on their website is very detailed. Even if you have none of the tools to do the work, it is always a good idea for all of us to understand what is going on with our cars when we are forced to have someone else do the work.... also prevents people trying to BS us when they do shoddy work.

 

[cobrajeff96]

One thing also is those shim pack kits. They're ok for setting things up, not so good for the permanent install. It's so much better to use solid shims that are perfectly spaced for the carrier bearings specifically. The best shops will use solid, one-piece shims and not a combination of different thicknesses.

 

[Notthenow]

Ford Racing gear sets are the easiest to install and the quietest. Richmond tend to be louder as the teeth are ground for strength overall at the expense of sound. Ratios 3.73 and down should run without a sound. Pinion gear depth issues can produce accel and decel whine. Easiest start is to check is pattern and backlash. Have to pull axels to check pinion preload.

Trans bearings can whine, driveshafts can transmit that. These are all unlikely if new, unless poorly installed.

 

[Thyme]

Update on the rear: Shop redid the work under warranty, with new gears (3.55), bearings & races, shims, and crush sleeve. I noticed the accel and decel whine immediately upon leaving the shop. Biggest difference was that both noises became apparent at lower speeds than before, and the decel whine is even audible below 20mph. Driveshaft still shakes along its axis of rotation when slipping the clutch in first.
Shop wants to claim the bellhousing is warped in the pinion area. Claimed the preload was set to 25inlbs with 0.011" of backlash. I'm just about ready to say to hell with it and just drive on it as long as it isn't making glitter.

 

[Snorky]

Sounds like the mesh pattern sucks. You will hear a groaning/whirring noise when the pinion/carrier/wheel bearings are compromised. The mesh pattern will cause howling. Howling on deaccel could also be the pinion preload loosening up. More than likely the shop lacks experience in setting up gears.

 

[Notthenow]

Right, the pattern indicates pinion depth. Do they know if there is a shim under the pinion bearing. Pinion depth affects noise as I understand it. If you took a quiet set of gears and loosened the pinion nut, they would become noisy. Never hear of the center section "warping" before.

 

[Notthenow]

Gear pattern with backlash and pinion tension all working together. Also, gears with bad patterns worn in won't become quiet with wear in or if I understand correctly, if set up properly later. I have taken a used gear set with good wear and set it up to run quiet (3.73 GM).

 

[Snorky]

Gear pattern with backlash and pinion tension all working together. Also, gears with bad patterns worn in won't become quiet with wear in or if I understand correctly, if set up properly later. I have taken a used gear set with good wear and set it up to run quiet (3.73 GM).

This is true.

 

[Thyme]

Thanks all for the advice and knowledge, I'm going see about at least checking the pattern with compound this weekend. When checking pinion preload, do only the axles need to be removed, or should the entire differential be pulled leaving only the pinion in the case? This will be my first time actually working on the guts of a rear end, so any tips would be greatly appreciated.

 

[Notthenow]

Unfortunately, to get an accurate pinion bearing pre-load you have to have the carrier out. If you decide to do it you must keep the caps on the correct sides and orientation. The caps are machined in place and are not exchangeable or replaceable without machining.

Keep it slow and observe everything carefully. Take photos. Check pattern first, then backlash (you will need a dial indicator and mag base. Harbor has a decent flexible unit).

Hopefully this isn't a car you need to drive right away.

 

[Thyme]

Hopefully this isn't a car you need to drive right away.

Bad news, its my daily and only car. What I'll likely end up doing is getting another shop to give me a second opinion on the work done after I check the gear pattern. The shop and the tech in particular who's been working on this rear are pretty much trying to tell me that I'm an idiot, so the hope is another shop telling them that they're f'ed up will humble them a bit. Maybe they'll even refund for their screw up without a fight.

 

[Notthenow]

Tough spot to be. I hope it's an obvious error and a basic fix.

Good luck!

 

[b1pig]

Bad news, its my daily and only car. What I'll likely end up doing is getting another shop to give me a second opinion on the work done after I check the gear pattern. The shop and the tech in particular who's been working on this rear are pretty much trying to tell me that I'm an idiot, so the hope is another shop telling them that they're f'ed up will humble them a bit. Maybe they'll even refund for their screw up without a fight.

Honestly, at this rate ... and this is only my personal opinion and you can freely ignore it...

At this stage, I would just hunt for a complete replacement rear axle. Build the replacement axle and then swap in a complete axle assembly. Just a thought. Would also simplify the issue of this being your daily.

The 8.8 was a common swap for Jeep YJ owners (and early TJs), as it made an easy upgrade to rear disks. The 8.8 was considered comparable in strength to the D35. They can bend tubes, spin tubes, crack or bend sections of the diff housing and snap the c-clip axles. Referencing Jeep shenanigans, but there are vids on youtube of Mustangs having damaged 8.8s. Those preload style diff covers are on the market to cut down on issues with weak diffs. Hell, my car had one on it when I bought it.

 

[b1pig]

double post

 

[Notthenow]

I know that the heavy cover is to reinforce the case while in motion, but I haven't heard of a case warping. I mean axles bent, sure, and case distorting under load, but it would stay distorted when unloaded.....