FD 4.88 Problem
 

Hello Everyone!
I have recently decided to swap my final drive to 4.88 for my Subaru BRZ. After install I was contacted by the installer telling me that if my car is supposed to have a whine to it when driving. I told them no and ends up the new Ring and Pinion Gear Set are causing a whine on both Accel and Coast. Next day I am called and told that my gear set is faulty and that is causing the issue, even though they told me the gear set looks in great condition and is perfect (Literally said perfect when they installed it) After having a second opinion from another differential specialist they told me that the ring and pinion is worn out after it being driven for 40km (25miles).

Just wondering if anyone has experience with differentials and if the issue could have been caused by faulty installation. Funnily enough, the owner of the company that installed my gear set is in Hospital, and the Installer is in Hospital too and I wouldn't be able to talk to them for 2 weeks.

https://imgur.com/a/ns704BZ (Photos of the ring and pinion after being driven for 40km (25 miles)

Did they run that thing dry? I don't see a hint of oil anywhere.

If it was a brand new part, manufactured to tolerance, and worn out that quickly, then it MUST be install error. Otherwise, it was defective (out of tolerance) to begin with. It might have looked perfect, but still measured wrong. I dunno if they measured your new parts before install. I doubt gears wear that quickly on top fuel dragsters

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I drained the oil before sending it for second opinion. There were mushy metal shavings on the drainplug. They used 75-85 Oil.

The fact it would have worn out that quick suprises myself. You would think they would measure and look at the gear set before installing?
These are Weir Performance Gear Sets. I didn't see anyone else complaining about Weir Performance having such extreme faulty gears.

what brand gear is it?
It is actually common for some brands to be more whiney. I know MFactory has this reported about them a lot.

Did they verify the correct backlashing, bearing preload, shimming etc?
Did you provide a new set of shims?
and a new crush sleeve?

The Brand is Weir Performance.
The differential was rebuilded with new Pinion Bearings, Carrier Bearings, Pinion Seal, Shims/Spacers and Washers.

I spoke to Spence Weir from Weir Performance. His a great guy and one of the best customer service I have ever recieved. He told me the issue is caused by 1) incorrect pinion depth 2) No pinion bearing preload (loose pinion) 3) No carrier bearing preload (loose carrier)


I'll be getting the differential stripped to inspect all those things and making sure it's all up to spec.

Did you send the pictures to Spence at Weir or just describe what you are seeing over the phone?

Because, I don't see any breaking, chipping, or burning. Machining marks are still visible. Although, the wear pattern does suggest the pinion is a touch deep; I'd get some grease and do pattern test to be sure. But overall, the ring gear in those pictures is in nicer condition than the starting condition of the last gear-set I put in my Mustang (they were used and I didn't care because I was experimenting with gear ratio impact on turbo spool, I ended up running the gears for 4 years).

"Traditional" wisdom said anything steeper than like 3.73 was going to whine. At 4.88 I'd expect it to hear it.

You said you have only 25 miles on the gears, did you do a proper break-in where you drove it easy for 20 miles and then parked and let everything cool down? This needs to be done 2-3 times and new gears should only see light duty, "low" speed, short distance use for the first ~500 miles.

By all means, have a shop double-check pattern, lash, pre-load, etc., but also don't be surprised if you just have a whiny gearset., it's a 4.88 after all.

If you had wear like that, that quick, I can only assume it is not installed correctly. Setting these diffs up correctly is a major project if you do not have experience/a crap load of shims on hand.

We built my diff using parts from Weir, no issues. I did have a increase in noise in the 75-85mph range with that diff, but after taking it apart a second time after 2000 miles, we found nothing wrong with it and talking to spence we determined it was probably just a change in chassis harmonics to the diff, or a bushing etc, as it was at a specific speed vs accel/decel sound

I talked to Spence over the phone and then I also sent him the same photos of the wear. He told me that there is cleary “significant stuffing in the contact area” and wasnt installed correctly. I'm aware of people saying a gear ratio like 4.88 can have some whine and I was prepared for that but it would begin whining over 12mph and howl on decel at certain speeds.
I made sure to drive slowly and break in the gears as recommended.

I had a 4.88 in my '57 chevy which made no noise. I have a 5.12 in my BRZ and it makes no noise. I previously had a 4.56 rear in my BRZ which was noisy on drive side and quiet on coast side. Make sure to use a shop that does rear ends regularly.

I just realized I had the brightness of my monitor turned down.... so yeah, there is more wear than I could see earlier, but they still do not look worn out to me (and I'd still say they're better than the set that went into my Mustang).

From what I'm seeing, I'd re-shim the install, inspect/clean/replace the bearings, (maybe) hand polish the faces, and call it good.

I'll be taking the diff back to the installer in a few coming days after arguing with him on the phone. It makes it a headache because he cannot tell me what is wrong with the gears when he is being insistent that the issue is the gear set. It would make sense if there were irregularities in the pattern or different backlash measurements every quarter turn. But when there are no irregularities, backlash is consistent and it is still grinding against each other then it just automatically makes me believe its not the gear set.

I thought maybe I have to let it break in more than just the 25 miles so it can smoothen out more, but then again. I don't have much knowledge on Differentials/Ring and Pinion setups.

I've setup a couple of these diffs but my experience is only with oem Toyota gearsets so I can't speak about weir or mfactory. When it comes to the Toyota gears I've found that the pinion shim that came with original gears almost always gives the best pattern even with the new gears. Unfortunately, unlike with some domestic differentials that have tools you can use to actually measure your pinion depth, theres nothing like that for these diffs and nothing called out in the service manual except to set to a specific backlash and check the pattern. There's also a couple of other things that need to be checked such as pinion bearing preload, side bearing preload, backlash in multiple locations of the gear, and overall runout. Your pattern doesn't look horrible but could possibly be better with a thinner pinion shim. The other big question is did you install stiffer differential bushings/inserts when you reinstalled everything. Also for future reference, this page provides all the part numbers necessary for installing oem toyota gearsets ranging from 3.58 all the way up to 5.125 incase anyone else will ever need this info. http://www.a-t-s.co.jp/19new_item/in...owfinallsd.php