chevy gear ratio identification
(Accurate identification using the GM RPO code assumes that the rear end has not been previously modified) The prefix is usually F, G or H when referring to Axle Identification. This design was used in all GM rear-drive cars from 1964 through 1972. Typically, 10-bolt carriers are specific to a series of gears. First Gear Second Gear Third Gear Fourth Gear Fifth Gear Sixth Gear; 2008-13 Corvette: 2.66: 1.78: 1.30: 1.00: 0.74: 0.50: 2008-09 Corvette Z51: 2.97: 2.07: 1.43: 1.00: 0.71: 0.57: 2009 Pontiac G8 GXP: 2.97: 2.10: 1.46: 1.00: 0.71: 0.56: 2009-13 Cadillac CTS-V: 2.66: 1.78: 1.30: 1.00: 0.80: 0.63: 2010 Camaro SS: 3.01: 2.07: 1.43: 1.00: 0.84: 0.57: 2012-15 Camaro ZL1: 2.66: 1.78: 1.30: 1.00: 0.80: 0.63: … The next digit is the day it was built, and the last digit is the year it was built. Also, these surfaces run cooler because of their sheer size. Careful identification of the differential you are working on will make sure you get the right parts for the job the first time. These sizes refer to the diameter of the ring gear, and the one you use makes a big difference in the performance potential. These are considered highway gears that are good for top speed, not for off-the-line performance. The code designates the gear ratio. The headset-driven gear is the countergear front gear with a tooth count of 25. To modify this gear ratio, a rear casing and the dimensions of this component are required. In this photo, you clearly see the clutch packs with springs, so indeed these are limited-slip differentials. Once you have identified the housing, you must order the correct parts for the particular axle. For performance vehicles, the 8.2 can typically handle up to 400 hp with street tires, but that’s the limit for this axle. Essentially, the housing is machined to clear the larger gears and carrier, and it’s not a job for the novice. General Motors has been using this axle assembly in cars for 16 years and in 1/2-ton trucks for 30 years. In stock form, the 8.5 can support wheel-standing launches from the turbocharged 6-cylinder. Although the 8.5- and 8.6-inch rear axles are more than capable of handling 400 hp (and with some setups a bit more), the 10-bolt name has a bad reputation due to the inherently weaker 7.5 and 8.2 designs. These are the numbers on my ring gear. Truck 12-bolts have an irregular cover with a ring gear pocket. Buick and Oldsmobile bolt-in axles mount at the bearing flanges on the housing ends. Among the Chevy 10-bolt family of axles, these provide the best performance and durability. These are very high gears, good for top speed, not for off-the-line performance. Because these two sizes are so common in pre-1971 (8.2) and 1975– 2002 (7.5) vehicles, the 8.5 is lumped into the same group. Several differential carriers are offered for the 10-bolt axle assemblies. The axles are retained by a set of C-clips on the inner end of the axle shaft inside the carrier. The two examples at right show you how to decode 10-bolt housings. A small bolt in the center of the carrier retains the crossbar. In the final analysis, this axle is simply too small for high-horsepower cars, and so these axles should be avoided for most muscle cars and certainly any racing applications. General Motors used the in-house Regular Production Option (RPO) code "M15" to identify the three-speed and "M20" for the four-speed. Our experts will help you find the correct ring and pinion set for your particular application. M-21 close ratio 66-70 . It is more difficult to swap these housings from car to car if they do not share the same suspension design. For 1969 and later, the code typically features six to eight digits, including three letters, three numbers, and sometimes an additional number and letter. These are highly sought after, and as such, are hard to find. Chevy 10- and 12-bolt axle assemblies have been standard equipment on GM passenger cars, muscle cars, and trucks for decades. The tooth count is stamped on the head of each pinion for both the pinion and the ring gear. They retain the axle shafts in the event of a failure. To help you identify the 8.2-inch housing, remember that it may have an irregular-shaped cover or a round cover, but it does not have lugs as on the 8.5-inch. Be sure the mesh is correct and that the installed parts are correct so you don’t destroy components. This is suppose to be an S-10 rear end. If your truck has the VIN# on the dash, but … Nothing could be further from the truth. The 3-Series carriers are good for 2.73 and lower gears, so 3.08 and 3.73 gears work well. You can simply clean the area around the casting pad, but a power washer and some hot soapy water can work wonders for 40 years of grime. Considering the challenges of the typical 12-bolt swap for most muscle cars, when the 10-bolt units are often a bolt-in swap, the 8.5 10-bolt starts to look really good. However, only certain gear sets are offered for the carriers, especially if you change gear ratios. 7.5 inch, 8.5 inch, 10.5 inch. Also the 55-62 Corvette standard ratio was 3.70 as the 55-56, probably because of … Ring and Pinion Repair and GM RPO Codes chart. The first and most important step in any differential repair or ratio change is accurate differential identification! Even though it has been used in every major GM rear-wheel-drive platform, the 10-bolt has a bad reputation for being a low-performance unit. The casting numbers for the 12-bolt housings are typically found on the upper rear of the driver’s side of the center section. This reduces the load on the pinion, resulting in less parasitic loss from the friction and load. Aftermarket 12-bolt housings are based on the passenger car design. Figure 3. You can copy and paste this link to share: https://www.chevydiy.com/history-and-identification-of-chevy-10-and-12-bolt-chevy-differentials/. When it comes to GM muscle cars and sports cars, the 12-bolt axle has been the top high-performance axle assembly for decades. Unlike the various 10-bolts, the 12-bolt axle assembly has different components for cars and trucks. The car versions were in production from 1971 to 1987. Axles for high-performance or heavy-duty applications commonly used higher spline-count axles while common passenger car axles use lower spline counts. By decoding the Vehicle Identification Number (VIN), you can also find out what axle ratio your truck has. These numbers are approximately 3 inches from the center section. When too much torque or traction is fed through the axle, it will eventually break the axle. Therefore, the specified pinion and ring gears must be used together. Therefore, the specified pinion and ring gears must be used together. As you can see, 13 is the hypoid gear countfor the pinion and 40 is the ring gear count. The casting numbers are simple to decode. The casting numbers for 10-bolt rear differentials are typically located either on the forward side of the passenger-side axle tube or on the driver’s side. Gears are also “coded” with their teeth count; dividing the number of ring gear teeth by the number of the pinion gear teeth yields the ratio. Call Sierra Gear & Axle at (800)792-2714. You may need to clean the rear housing before you can decode the casting numbers. The 10-bolt can handle just about anything you throw at it, as long as you use the right axle, either the 8.5- or 8.6-inch. Thanks All vehicles have a particular gear ratio at the rear. The truck housings are not as durable as the passenger car housings due to a narrower carrier and a smaller inner pinion bearing. You can see the dramatic difference in not only teeth but in overall diameter. How to Read a Chevrolet Truck Vin Number for the Axle Ratio Step 1 Locate the VIN plate on the Chevrolet Truck. The pinion shaft diameter is 1.625 inches with 28 or 30 splines, which is the same as the GM 12-bolt design. As you can see, the Chevy 12-bolt differential is one stout axle, and it was the rear axle of choice for GM muscle cars and many GM competition cars. Please select a rear end that matches your vehicle below. The Muncie (or Stewart Muncie) division of GM and the New Process division of Chrysler became New Venture and one of the first fruits of this union was the NV4500.The NV4500 was first released in Chevy / GM trucks from 1992 under GM RPO code MT8 and GM part #12346190. As a result, these cars use a specialized axle housing for this suspension, and it’s not easily upgraded. Besides the codes stamped into the axle tubes, some carried ratio and/or posi tags as well as the vehicle having a … This ring-and-pinion gear has suffered catastrophic failure. If you liked this article you will LOVE the full book. GM's goal with the Muncie four-speed was to produce a better shift employing larger synchro cones. A 2-Series carrier holds 2.56:1 and higher gears (numerically lower) such as 2.41. This input shaft can be interchanged with other NV4500 input shafts with this 5.61 1st gear ratio. This means that in the event of an axle break, the wheel stays on the car. Chevrolet Single Speed Rear Axles: Rear Axle Capacity: 18,500 lbs: 23,000 lbs: 30,000 lbs bogie: 34,000 lbs bogie Ratio: 5.57:1: 7.17:1 A full range of pinion gears is offered for the Chevy 10- and 12-bolt axle assemblies so you are able to select the correct gear set for your vehicle, application, and setup. The C-clips are not the strongest method for retaining the axle shafts; many owners convert the Chevy 10- and 12-bolt axles to a flange type, which retains the axle if it fails. The rugged, reliable, and efficient Chevy 12-bolt has established itself as the preeminent rear differential for GM muscle cars since its debut in 1965. The 8.5- and 8.6-inch provide superior performance and have a larger ring and pinion gear surface to handle high horsepower. When you decode these numbers you can conclusively identify your axle. The passenger car 12-bolt has an oval-shaped differential cover, and it measures 1015/16 x 105/8 inches. To remove the axle shafts, you need to remove the four bolts. 1969 Chevelle Rear Axle Identification ... My Chevrolet Parts and Accessories Catalog, circa 1972, only shows the gear ratio service part numbers so it is quite possible one or the other was discontinued in favor of a 'service' part. Engine torque and suspension loads are placed on the rear axle assemblies, which are also subjected to moisture, dirt, and anything the road can throw at it. I couldn't find GMK anywhere. I can't see the pinion to see if there are any numbers on it but if its a 9 tooth l would have a 3:55. There are two super easy ways to tell whether or not the transmission is a 6L80E. M-20 wide ratio 71-74 . These are very high gears, good for top speed, not for off-the-line performance. The differential carriers are also narrower than on the passenger car units, and they do not interchange. Gears of all sizes, limited-slip or Posi-Traction, lockers, and spools are offered. New Venture Gear was the somewhat unlikely merging of the two manual shift design & manufacturing divisions of General Motors and Chrysler Corp. To remove the C-clip, you push the axle in to allow room to snag the C-clip with a pick. GM RPO Codes, or General Motors “Regular Production Option” codes contain lots of valuable information about your GM vehicle. The 8.5 is limited to 30-spline axles, but can withstand 1,000 hp with slicks when properly built. The M-22 is distinguished from an M-21 by the angle of the gear teeth. SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. However, the smaller 10-bolt unfairly gained the reputation as a weak and inadequate rear end for high-performance applications. Using the charts below, you will be able to learn alot about the rear differential in your classic … The Chevy’s rear axle code contains information on the vehicle’s gear ratio, date of manufacture and the rear axle assembly plant. The axles are retained by a set of C-clips on the inner end of the axle shaft inside the carrier. Trucks have a smaller inner pinion shaft (1.438 inches versus 1.675 inches) and bearing, and the pinion rides lower on the ring gear. Identify your GMC or Chevrolet rear end gear ratio by the RPO Codes, usually located on the placard labeled “Service Parts Identification” inside the drivers door panel or glove box. The two lugs on the lower case at the 5 and 7 o’clock positions are also identifying features. Looking up the GT4 code via Google, or any GM reference literature, the code shows your truck has a 3.73 gear ratio. GM / Chevy - Differential Identification Shop by your differential. Ford. In street applications, the 7.5 is good for 350 to 400 hp with street tires and lots of wheel spin. The 2-Series is by far the most common. The 3-Series carriers are good for 2.73 and lower gears, so 3.08 and 3.73 gears work well. These should be square blocks, each with the outer side 90 degrees (vertical) to the road and the bottom-side surface horizontal to the road. Option code list. M-22 close ratio 65-69 . The case has a similar pair of lugs at the base of the center of the housing, which are located at 5 and 7 o’clock. Help me out fellas. The first letter is the month of the year; A is January, B is February, and so on. The types are 2-, 3-, and 4-Series. The front bearing retainer index is 5.60”, and has a … Before you rebuild any axle, you should identify which axle you have. Most 8.5-inch 10-bolts have two lugs on the bottom of the housing at the 5 and 7 o’clock positions. GM RPO Axle Code List | GM Axle Gear Ratio Lookup GM RPO Axle Codes To find the axle … You need to machine the housing to accept a 12-bolt carrier, which also requires custom axles. M-21 close ratio 63-65 . However, the 7.5-inch lugs are smaller, with the outer side running at an angle and the inner side cut with a radius. Of course, this gear ratio can be modified as long as the right size components are available. A Series 2 carrier will work with 2.56 and higher gears (numerically lower) such as 2.41. The countergear has 17 teeth on its first-gear section driving the actual first-speed gear with 36 teeth. Once the C-clip has been removed, the axle slides out of the housing. So now I'm more confused than ever. All GM 12-bolts use C-clip–style axles. Final Gear Ratio Tire Size Engine Rpm Chart Gears Trucks Chart Showing Rear Axles Used In 1973 1987 Chevy Trucks Ring And Pinion Gear Ratio Calculation Chart Quadratec Click the button below and we will send you an exclusive deal on this book. The pinion diameter is 1.438 inches with 25 splines. Most passenger car 12-bolts used a four-bar trailing arm mounting system, with the exception of the Camaro and Nova, which used leaf springs. Chevy Muscle Car Tech Tips, Guides, Articles & How-To. M-21 close ratio 71-74 . Pinion gears and ring gears are not interchangeable because they are designed for the specific (correct) mesh. It consists of a two or three letter prefix representing the gear ratio code, four-digit number for the assembly date in a month/day format and a single letter denoting the manufacturing location. As you can see, 13 is the hypoid gear count for the pinion and 40 is the ring gear count. Monza??? And finally, a Posi-Traction number was used. Identifying the 10-bolt axle is easy. The rear axle identification code consists of a two letter prefix indicating the gear ratio ~ four digits indicating the assembly date as month/day ~ and a single letter suffix indicating the manufacturing location. The smaller 7.5- and 8.2-inch 10-bolt rear axles can’t transmit horsepower loads in excess of 400 hp. The round 10-bolt cover with a bulge for the ring gear identifies this axle assembly as an 8.5-inch 10-bolt. The 6L80E’s gear rations are as follows: Gear. The M-22 was generally installed behind severely powerful (high torque) big-block engines. Ford Rear Axle Assembly Identification Stamped axle codes Ford used a vast array of rear ends over the years. The 55-56 overdrive tag was the same as 57 and later. In addition, the truck 12-bolt has an irregular shape. You can build these for performance, but if you use sticky tires, the superior traction and consequent strain from the grip will kill it quickly on the drag strip. Affordable performance is what the 8.5 is all about. There is some crossover on the trucks, as some earlier trucks had leaves and some later trucks had the trailing arms. Methods to determine the gear ratio of the differential I just wanted to drop these links in somewhere they would be useful....http://www.quadratec.com/jeep_knowledgebase/article-26.htmhttp://www.alloyusa.com/gear-ratio-calculator/ General Motors rear end differentials are referred to by the diameter of the ring gear, i.e. The factory installed the 8.5-inch 10-bolt in the Buick Grand National, and that’s the biggest claim to fame for this OEM axle. Ratio: 1: 4.027: 2: 2.364: 3: 1.532: 4: 1.152: 5: 0.852: 6: 0.0667: Reverse: 3.064: 6L80E Identification. To positively identify the Chevy 10-bolt in the 7.5/7.625-inch size, you need to measure it because it is very similar to the 8.5-inch housing. Products include ring and pinion sets, installation kits and axle shafts for GM, Ford, Chrysler, Jeep, and Toyota vehicles. The aftermarket fully supports the 8.5. It does not have a direct 1:1 ratio like the 4L80E and 4L60E, which is worth noting. Need help with your differential identification? The four bolts that hold the drum back plate on also retain the flange. The large bushings at the top of the differential housing connect to the triangulated four-bar trailing arm system that the Buick used. The distance between the lower cover bolt and either adjacent bolt is 33/4 inches. A variant of this axle assembly was used in 1971–1972 Buick GSs and Skylarks, Oldsmobile Cutlasses, and some 1969–1972 Pontiac Grand Prixs, as well as the 1970–1972 Monte Carlos. On the passenger-side front tube, the stamped axle code designates either 1969-and-earlier units or 1969-and-later builds. Millions of 8.2-inch axle assemblies were built and many can be found in salvage yards. This is specific to the carrier. Give us a call at 800-216-1632 to get started. The first two letters indicate the gear-ratio code, the third letter notes the build plant, and three numbers designate the build day from 001 to 365. Rancho Cordova, CA 95742, Decoding Regular Production Option codes found in GM Vehicles, Copyright © 2019 Sierra Gear & Axle - Web Design by Zenxeon Technologies, Axle Identification – Visual Clues and Tags, Instructions – Differential Installation & Setup, Differential Setup & Torque Specifications, GM RPO Codes – Axle & Ratio Identification, Measurement – Axle Shaft Length & Bolt Circle, Not Open Diff – Positraction / Limited Slip / Typ. Again the 55 and 56 automatic had a round tag that indicated 3.55 ratio. If your 1973 - 1987 body style has a VIN# located on the dashboard, with 17 digits, then it is between 1981 and 1987 model. This example is a 1967 Chevy C10. Sometimes the shift code is stamped, and if the unit has a Posi-Traction, you see a P stamp. Note that this axle has been converted to disc brakes. In this example (Figure 3), GT4 is the axle ratio code. There is very little aftermarket support for this axle assembly because it couldn’t handle high-horsepower loads and therefore its performance potential was marginal. GM trucks from 1961 through 1967 used a two-bar trailing arm mount, while the 1968-up trucks used leaf springs. However, the pinion shaft measures 1.438 inches. The 1969-1976 Camaros, 1964-1976 Chevelles, Malibus and Monte Carlos used an optional quick ratio 12.7:1 unit. Anyone with knowledge of the differences, please contact me so I can share the information with all. Most 8.5 10-bolts are C-clip axles, so a set of C-clips retains the inner end of the axle shaft inside the carrier. The nomenclature actually refers to the number of ring gear bolts. The 1969- and-earlier codes have two letters, then a four-digit number, followed by a letter, and possibly a shift number, for which 1 is the day shift and 2 is the night shift. Camaros, Novas, and 1968 and later trucks used leaf springs like these. The outer cover matches; 10 bolts hold the cover onto the housing. It is driven by the input shaft with 21 teeth. The oval-shaped cover measures 85/16 inches by 109/16 inches. Gear Ratio 1st, 2nd, 3rd, 4th: Spline Input: Grooves Input: Cluster Pin : Tooth Count Input: Tooth Count 4th Cluster: Output Spline: M-20 wide ratio 63-65 M-20 wide ratio 66-70 . The identification code will tell you the gear ratio, if it is a posi, and in some cases what engine and transmission the car is equipped with. These rear axle assemblies can handle up to 400 hp. Sierra Gear & Axle is a premium line of light-duty differential parts. It is located on the right hand side of the case and is composed of two letters. In the world of dirt track racing, some classes require a GM 7.5-inch 10-bolt and because there is no traction on dirt, this rear works very well. They used an independent rear suspension with transverse leaf springs. It was installed on small trucks and vans up to the 2005 model year. First Gear Ratio: Second Gear Ratio: Third Gear Ratio: Fourth Gear/Overdrive: 700R4/4L60: 3.06: 1.63: 1.00: 0.70: 2004R: 2.74: 1.57: 1.00.67: TH-350: 2.52: 1.52: 1.00: N/A: TH-400: 2.48: 1.48: 1.00: N/A: Powerglide: 1.74: 1.00: N/A: N/A And unfortunately, there simply isn’t enough room to install bigger axles, so it isn’t a viable option for a high-performance car. The 8.5- and 8.6-inch 10-bolts have larger ring-and-pinion gears, which makes an important difference. This is the Moser Engineering 12-bolt axle assembly. Try our Differential Gear Calculator. (Photo Courtesy Moser Engineering). When sticky traction bars and/or sticky tires were installed, owners found that 400 hp can quickly turn the 7.5 into shrapnel. As you can see, the Yukon casting is much thicker and so are the springs. The M-20 wide ratio, the M-21 close ratio, and the "Extra heavy duty close ratio" M-22, also known as the "Rock Crusher". Therefore, you need be able to choose the more desirable 8.5- or 8.6-inch and avoid the smaller 7.5/7.625- and 8.2-inch units. The 2010-up Camaro uses a similar design (8.6 10-bolt) in the center section of its independent rear suspension. Compared to the Ford 9-inch, the 12-bolt positions the pinion gear higher on the ring gear. Further Muncie identification 3 Muncie 4 speeds were offered. To support high torque and horsepower loads, the axle shafts need a larger diameter and spline count. General Motors used several different suspension designs in their passenger cars throughout the 1960s and 1970s. You need to be able to accurately identify the GM 10-bolt. In this version, the axles bolt to the housing ends just as on a Ford 8- or 9-inch. Gov-Lock, Axle Rear, 21000 Lbs, Eaton 21065S, Single Speed. Find the application and ratio you need? We carry everything from the 7.25" IFS front end parts, to the large 11.5" rear end parts for 1-ton trucks. The axle may be over or under the leaf, depending on the application. However, the 8.5- and 8.6-inch 10-bolts are extremely stout and effective rear differentials that can transmit up to 1,000 hp to the rear wheels. The 8.5-inch differentials have 103/4-inch hex head bolts with 7/16-20-inch left-hand thread or reverse-thread bolts that hold the ring gear to the carrier. Plug the tooth counts into the above formula and you get a first-gear ratio of 2.52:1. General Motors has a wide range of front and rear ends! Note the thicker head on the bottom axle where the C-clip rides. From 1972-on, General Motors installed its 10-bolt in cars and it remained an option for trucks until 1987. A 2-Series carrier holds 2.56:1 and higher gears (numerically lower) such as 2.41. The spline of the input is 1-1/4” diameter 10 spline and protrudes approximately 7-1/2” from the face of the transmission. The 8.2 was phased out starting in 1971; it was replaced by the 8.5-inch “corporate” 10-bolt, and was installed in everything from Camaros and Chevelles until the mid-1980s. Sierra Gear & Axle parts are designed and engineered to the highest quality specifications for use in street, off-road and performance environments. Identify your GMC or Chevrolet rear end gear ratio by the RPO Codes, usually located on the placard labeled “Service Parts Identification” inside the drivers door panel or glove box. Big-block Chevelles, Camaros, and other GM high-performance vehicles were fitted with the 12-bolt limited-slip axle to maximize torque transfer and traction. But there are several models in the 10-bolt line-up. The pinion nut should measure 11/8 inches, as long as it is the OEM pinion nut. The truck 12-bolt axles are much more affordable than the car units because they are more plentiful but these units have fewer splines so they are not as strong as the axle in the car assemblies. A Yukon aftermarket clutch-type limited-slip differential is on the left; the GM Posi-Traction differential from a 1971 Buick Gran Sport 8.5 10-bolt is on the right. These are two pinion gears for the 8.5-inch 10-bolt. The Series 3 carriers are good for use with 2.73 and lower gears … The 12-bolt carriers also use the same series-specific system as do the 10-bolts; each carrier only works with certain gear sizes. By far, the most common 10-bolt is the 7.5/7.6, and it has been around since 1975. The pinion on the left is part of a 4.11:1 gear set; the one on the right is a 3.08:1 pinion. The rear cover’s shape and the number of bolts are identifying features for GM rear differentials. The early truck 12-bolts had large axle splines with only 12 splines. The 8.2-inch differential does not have these lugs. The distance between the lower center cover bolt and its adjacent bolts is 31/4 inches. The rear housing has a specific size, which also works with a … This 1967 Chevy truck used a trailing-arm design with coil and leaf springs. Written by Jeferson Bryant and Posted with Permission of CarTechBooks. Inside, the ring gear bolts are the same as the 8.5 corporate unit. These axle assemblies had bolt-in axles and were used sporadically in A-Body wagons as well. Location: Main Index » Forum Index » 55-57 Central » 1955-1957 Chevys (Stock / restored / show) » Gear Ratio Identification FusionBB™ Version 2.1 ©2003-2006 InteractivePHP, Inc. If installed on a 400-hp or stronger engine, it often fails. The tooth count is stamped on the head of each pinion for both the pinion and the ring gear. VIN Breakdown Method. That is the great caveat; there are four sizes of 10-bolt GM rear ends: 7.5/7.625-, 8.2-, 8.5-, and 8.6-inch. Pinion gears and ring gears are not interchangeable because they are designed for the specific (correct) mesh. Inside the 8.2, the ring gear bolts have 9/16-inch socket heads with 3/8-24 threads. For example, a 12-bolt axle that was built on March 28, 1967, is C287. From 1973 - 1980 Chevy trucks had a 13 digit VIN#. This is a 1969 Chevelle 12-bolt housing. The GM 10-bolt rear end is quite possibly the most misunderstood and undervalued rear differential ever created. C2 and C3 Corvettes (built from 1963 to 1981) used a non-standard 10-bolt design. In addition, the trucks typically have larger axles and brakes. Most 1972 and newer are located in the left hand (driver's side) dashboard visible from the lower corner of the windshield. The top axle is an 8.5-inch 10-bolt with 30 splines; the bottom axle is an 8.5-inch with 28 splines. 2429 Mercantile Drive Suite A The Chevy 12-bolt axle assemblies for passenger cars feature an oval cover with a diagonal indentation. This code is marked with RED in the location photo above. And like the 7.5 axle, it has a fair amount of aftermarket support but the ring gear is too small and therefore it cannot handle much torque. At just 3/8-inch smaller than the 8.875-inch 12-bolt differential, the 8.5-inch ring gear is strong enough for high-performance applications. It was … Locate a Sierra Gear & Axle Distributor near you. Although gear sets and a locking differential are available, these are only suitable for a mild street engine or possibly a dirt track car. This 8.5-inch 10-bolt came from a 1971 Buick GS. From 1981 - 1987 Chevy Trucks used a 17 digit VIN#. Bolt-in axles include (right to left) the axle, retainer plate, split washer shim, press-on bearing, and housing end. It remained in the 1/2-ton trucks until 1999, when the 8.6 replaced it, using the same basic design. I googeled the 344161 ring gear and it said it was from the H body Chevy. Doing a gear ratio change but not sure what you want? General Motors installed different axles for different applications. We make it easy to verify your He tells us both the M20 wide-ratio and M21 close-ratio transmissions were first offered in 1963. If you take off the center section cover and discover this kind of damage, you need to identify the cause so you don’t repeat this type of failure. You can typically find your RPO code on driver side door panel or glove box.