USA Standard Gear (ZG GM8.5-373) Ring & Pinion Gear Set for GM 8.5 Differential
Condition: New
$140.00
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Availability:
In Stock.
Arrives
Friday, Nov 6
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At a glance
- Condition
- New
- Style
- GM 8.5" 3.73 Ratio
- Model
- ZG GM8.5-373
- Dimensions
- 16 x 12 x 6 in
- Weight
- 17.67 lb
- Exterior
- Machined
- OEM Part Number
- FDHDZG GM8.5-373
Features 5
- USA Standard ring and pinion sets are the right choice to add confidence to your install
- USA Standard Gear offers a full line of ring and pinion sets for a variety of common and hard to find applications
- USA standard gear offers a standard one year against defects on their ring and pinion sets
- This product is used in a 3. 73 axle ratio
- 12 Ring Gear Bolts
Description
Ring and Pinion Gear Sets from USA Standard offer enhanced strength while maintaining affordability, making them ideal for your next repair, rebuild or regear project.
Specs 9
| Manufacturer | USA Standard Gear |
|---|---|
| Brand | USA Standard Gear |
| Model | USA Standard Gear (ZG GM8.5-373) Ring & Pinion Gear Set for GM 8.5 Differential |
| Item Weight | 17.67 pounds |
| Product Dimensions | 16 x 12 x 6 inches |
| Item model number | ZG GM8.5-373 |
| Exterior | Machined |
| Manufacturer Part Number | ZG GM8.5-373 |
| OEM Part Number | FDHDZG GM8.5-373 |
No specs match.
Frequently asked questions
If you place your order now, the estimated arrival date for this product is:
Friday, Nov 6
Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
To initiate a return, please visit our Returns Center.
View our full returns policy here.
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Top Amazon Reviews
Works for me
Style: GM 9.5 3.73 Ratio
Setup was uneventful using Trutrac carrier. Six months and 2000 mi, quiet no issues. I'm happy.
Reviewed in the United States on May 11, 2026 by Old Jimmy
Notice for GM 12 bolt C10 diff install
Style: GM 12-Bolt Truck 3.73 Ratio
These gears appear to be good quality and the wear pattern looks the best I've ever seen after adjustment. I have a 12 bolt 8.875 GM truck rear in my '67 C10. All 3 of my C10's, '67, '68, '69 2wd trucks had 3.08 factory installed gears. I guess because of only a 3 speed auto trans in my '67 and '68, it was better on the highway. My '69 is a 3 speed manual. I decided that since I built a 383 stroker small block and installed a 3000 rpm stall converter in the TH400, due to the cam profile, I would replace the 3.08 geared, one wheel peel with a 3.73 gear and a Spartan "lunch box" locker. I'm just about to fire this thing up in a week or two. Just waiting on the machine shop to do the final piston fit honing and it ready to assemble, stab it in, hook everything up, start it up, and hold onto my hat. But I digress. Sorry, lost track. Anyhow, changing the gears from 3.08 to 3.73 I obviously had to re-shim my carrier to move it to the left. The factory shims were just about equal from one side to the other. Left being a .230 and right being a .243 thickness. I had to bring my left side to .445 and the right only has .024 gap in order to get my .006-.010 backlash needed for a good pattern. I even had to shim my pinion an additional .030 just to get it right. It's not quite a tight fit as factory, but I don't have a housing spreader and the 3 very thin .008 shims were giving a fit without trying to fold over on me. I don't think .004" is going to give me any trouble. Especially with the Moser girdled diff cover I'm using. Okay, here's the issue I ran into. Being that I needed to shift the carrier over almost a quarter inch, the right side of the carrier was hitting the area just outside and to the front of the bore for the carrier bearing. So, I removed the carrier and used a dremel tool to slightly grind the carrier housing on the four 'corners' where the bearing is pressed on. I took off about .100" on each edge and it then fit like a glove. I got my backlash to .008". Installed the yoke with a new crush sleeve and torqued the pinion nut to 11 in.lbs. Re-installed my carrier and torqued the caps to 60 ft.lbs. and installed the diff girdle cover. Hint to the next guy that decides to rebuild a differential. Purchase some cheap new pinion bearings in addition to the bearings that you are going to install. Grind the inner race of the cheap bearings so they slide over the pinion without being pressed on. This will save a bunch of time and frustration when adjusting or shimming the pinion depth. When it's all clocked in, just remove the dummy bearings and press the final good bearings onto the pinion. Oh, btw, the spartan locker is a pain in the butt to install with the diff housing in the vehicle. If possible, remove it and set it on a bench or jack stands with the yoke facing the floor. It's much easier to articulate the c-clips this way as long as you hold your tongue right. Good luck
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Reviewed in the United States on August 3, 2019 by Rascal The Rat
great daily driver equipment
Style: Chrysler 9.25" 3.55 Ratio
have used USA Standard Gear ring/pinion sets for years now. always a good value for daily driver level use. My first set ordered from amazon arrived beat to hell with broken teeth etc. easily got a replacement that arrived in perfect condition. Glad it was 'sold and shipped by Amazon' item not a secondary seller on Amazon. Anyway, got the gear set installed. works great!
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Reviewed in the United States on December 26, 2024 by REEK
Setup but still a little noisy.
Style: GM 8.5" 3.73 Ratio
Good quality. Pinion gear has a slightly shorter gear face then the factory ones and I suspect that adds to the slightly noticeable noise. Not bad but not the best set I've installed. I would use as a daily driver set but NOT a performance set.
Reviewed in the United States on April 2, 2026 by Your Mechanic
Just get it
Style: GM 14-Bolt Truck 10.5" 3.73 Ratio
Installed these into my 87 square body and had no issues! Was able to get the pattern on the first try and have had no issues with the rear end since the rebuild!
Reviewed in the United States on November 6, 2025 by Shelly
Well placed inside the fence
Style: GM 8.25" Reverse Rotation IFS 4.11 Ratio
Well placed inside the fence
Reviewed in the United States on June 25, 2026 by Jeremiah Crumm
FORD 7.5 USA GEAR 4:56 RATIO CROSS PIN LOCK ISSUE
Style: Ford 7.5" 4.56 Ratio
Well I’ve worked at Ford as a Ase Master for 22 years. My Old ford ranger has 331,000mi on it and the ring and pinion failed. I previously installed a 3.73 USA Gear for a customer and had no issues except spent 2 days trying get paint wear correct. Had to grind my own shims. I ordered the 4:56 for a little more torque for my 4cyl Manual Trans to pull the boat out on the ramps. Everything installed fine but had to preheat the ring to expand slightly to get onto spool. The problem I ran into is this particular set (4:56) the teeth cover over half the hole. No correctly notched cross pin exists for this ring on a factory carrier. I did make it work by tophatting the gear teeth by the hole and also removing 1/8 in from the original notched crosspin. Removing too much from either the ring or cross pin will result in failure. Truck drives wonderful with th 4cyl manual trans and 4:56. Truck runs about 75 at 3000rpms. But at 65 I am at 2000rpm in overdrive. Would I do again? Likely not too much play and adjusting this set along with modifications. Also I still worry my C clips will slip out since shaving pin 1/16. It is unlikely, but as a Ford Tech I wouldn’t do this to a customers car.
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Reviewed in the United States on February 20, 2019 by Bdamon
Decent quality, price, and customer service
Style: Dana 60 Reverse Rotation 5.13 Ratio
Bought these for price and probably should have known better. You usually get what ya pay for. They came with setup paint on them and appear to have been ran for a while; the machining marks are gone from the coast and drive sides of both the ring and pinion gears. We'll see if the seller makes it right, and I'll post an update. UPDATE: after talking with a few friends, they all felt the paint and markings were just to lap the gears together, essentially negating the break-in period. The gears appear to be un damaged and in good shape, and they even set up pretty well. I've never seen a set of gears that were lapped like this before, so I'll update again, once I've ran them for a while. Also, the seller responded to me in less than a day, on a Sunday, which I did not expect. So good on them and their customer service. Good experience all around.
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Reviewed in the United States on December 9, 2018 by kurt braschler