The Dart we built originally had super stock springs, a pinion snubber ,and cal tracs.It did bend the housing and spring perchs as I said earlier but the car hooked hard enough to pick the wheels a good 4" and ride on the wheelie bars for 60' or so.We think most of the damage was caused because it was a 4 speed car and the 1.40 - 60 ft. times. Rob.
Here's my question with the snubber. Do I need to run one if I am going to have a triangulated 4 link? I am building a coupe will be running a big block and 4 spd. I always ran adj. snubbers on my muscle mopars, but they were with springs. Matt
MM... If you are running a prostreet rear end with about 19-20 inches between links side to side I'd guess you will be ok without it. Our dragsters are about 19-20 inches at the mounts and I can't say I've ever seen a twisted rear end. However we do use anti rotation devices and mounts so effectively we have the pinion solid mounted.....no snubber but no movement possible. For a sprung car if it's heavy and lots of torque with a 4 link I don't know how you would run one as you probably have positive anti-squat so the body/chassis will rise rather than settle toward the pinion. I'd do a stout back brace even though that won't help the twist as noted above. On second thought you are running triangulated links so you probably won't get chassis rise. That being the case I guess if you are going to race occasionally I'd make provision for a snubber to be added at the track. I'd set the chassis right on the pinion for starters. Better safe than sorry.
I found this intersesting tech article on 8 3/4 Mopar rears on the net that some here people may find useful. Enjoy! Mart3406 ================================= http://members.tripod.com/~Mojo_Page/chry875.htm Chrysler 8 3/4 Axle Guide - Adapted from the Mopar Mailing List The following conglomeration of information should help a person be able to locate, identify, and install an 8 3/4 Chrysler rear axle in their AMC product. Many topics are covered, and the text is compiled into one long document in order to speed locating the information you need. The topics covered are as follows: General Where to Find One Axles and Housings Center Section Types Sure Grip Universal Joint Yokes Strength Considerations Service Parts Information Selected Parts Reference Appendix A: 8-3/4 A-body axle upgrade to 4.5" bolt circle Appendix B: How to Put One in a Javelin (or other AMC) General The Chrysler 8-3/4" rear axle assembly was introduced in 1957. It is a banjo-type (Hotchkiss) axle, ie. the differential is contained in a removable carrier assembly which is extracted from the axle housing toward the front of the car. It is retained by 10 nuts on studs in the housing. The differential cover (although permanent) as viewed from the back of the car is smooth and hemispherical; it is welded onto the main housing. The axle tubes are part of the overall housing. The axle has an 8-3/4" diameter ring gear. There are three basic types available distinguished by their drive pinion stem diameter. The 8-3/4" axle was the primary axle assembly used in most Chrysler car lines through 1972. Where To Find One The first thing one needs to know in order to find the right axle for the job is the Chrysler platform code system. With an understanding of the different vehicles involved, you can then determine which one will best suit your application. A-body models include: 1964-76 Plymouth Valiant, 1964-69 Plymouth Barracuda, 1970-76 Plymouth Duster, 1972-76 Plymouth Scamp, 1964-76 Dodge Dart, 1971-72 Dodge Demon, 1973-76 Dodge Dart Sport, 1969-76 Dodge Dart Swinger B-body models include: 1965-70 Plymouth Belvedere, 1965-74 Plymouth Satellite, 1968-74 Plymouth Road Runner, 1970 Plymouth Superbird, 1967-71 Plymouth GTX, 1965-74 Dodge Coronet, 1968-71 Dodge SuperBee, 1966-74 Dodge Charger, 1969 Dodge Charger Daytona C-body models include: All 1965-74 full-size Chrysler models (Newport, New Yorker, Imperial), 1965-74 full size Dodge and Plymouth models (Polara, Monaco, Fury, Sport Fury, etc.) E-body models: 1970-1974 Plymouth Barracuda and 1970-1974 Dodge Challenger Axles and Housings Because the 8-3/4" axle was available in most body lines, there are a variety of housings available. Following are SOME of the passenger car axle dimensions and notations. The 'Perches' dimension is the distance center to center between the spring mount perches. Dimensions are in inches. <tt> Body line Track Perches Notes</tt> <tt>------------------------</tt> <tt>A-body, 65-72 55.6 43.0 4" lug bolt circle,</tt> <tt> offered in heavy duty apps.</tt> <tt>B-body, 62-70 59.2 44.0</tt> <tt>B-body, 71-72 62.0 47.3</tt> <tt>B-body, 71-72 63.4 47.3 station wagon</tt> <tt>C-body, 64-72 63.4 47.3</tt> <tt>D-body, 64-72 63.4 47.3</tt> <tt>E-body, 70-74 60.7 46.0</tt> <tt> </tt> The 8-3/4 was also available in the 58-74 D100/W100 trucks (and variants), the 64-70 A-100 trucks and vans, the 67-70 A-108 trucks and vans, the 71-74 B100/B200 vans and non-listed 57-64 full and mid-size car models. Notes: 1) The axle centerline to yoke/universal centerline is 12.35" for the 8-3/4" axle. 2) Any 8-3/4" center section may be interchanged for another as an entire assembly. 3) All 8-3/4" axle shafts, 65-74, are retained by a bolt-on flange. Axles can be interchanged within housings of the same width. The passenger side axle has a threaded adjuster to set axle shaft end play. 4) There was a slight dimensional change in axle shaft length when the Sure Grip design changed. If interchanging axles with the slight difference, the threaded end play adjustment can be used to accomodate it. 5) The 57-64 8-3/4 axle driveshafts were tapered and used a keyway and locknut to retain the brake assemblies and end play was set with shims. The 65 and later units use flanged axle shafts and a threaded adjuster to set axle end play. 6) See Appendix A for information about the A-body 8-3/4" axle and bolt circle changes. Center Section Types The 8-3/4" axle was available in three basic types. The types are differentiated by the pinion stem diameter....1-3/8", 1-3/4", 1-7/8". The choice of axle pinion assembly was determined based on the application. Differential bearing setting (ie. backlash) is set with threaded adjusters on all carriers. All 8-3/4" carrier assemblies can be identified externally by the casting numbers. 1-3/8" small stem pinion (aka. '741') Carrier casting numbers: 1820657 (1957-1964), 2070741 (1964-1972). This assembly was typically used in low weight/low horsepower applications through low weight/medium horsepower and high weight/low horsepower applications. Pinion depth and bearing preload is set with shims. 1-3/4" large stem pinion (aka. '742') Carrier casting numbers: 1634985 (1957-1964), 2070742 (~1961-1969). This assembly was replaced by a phase-in of the 1-7/8" pinion starting in the 1969 model year. 1970 RW (Plymouth and Dodge mid-size) were the last models to use the 1-3/4" which appeared in a 2881489 case. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth and bearing preload is set with shims. 1-7/8" tapered stem pinion (aka. '489') Carrier casting numbers: 2881488, 2881489 (1969-1974). This assembly was introduced in 1969 and was phased- in to relace the 1-3/4" unit through 1970. Note: the 1-3/4" pinion also appeared in some '489' carriers during this period. By 1973, the '489' was the only unit available in passenger car applications. This assembly was typically used in high weight/medium horsepower applications through high weight/high horsepower applications. Pinion depth is set with shims, preload is set with a crush sleeve.The '741' commonly has a large X cast on the left side, the '742' may have a large 2 cast on the left side, and the '489' has a large 9 cast on the left side. Through 1965, the factory ratio was stamped on the identification boss, followed by an 'S' if Sure Grip equipped. After 1965, a tag was affixed under one of the carrier mounting nuts to identify the ratio. If Sure Grip equipped, an additional Sure Grip lube tag was sometimes affixed; later years sometimes had the filler plug painted orange. Gear ratios available on the 8-3/4" axle through the years include: 2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57. On OEM gear sets, the ratio is usually stamped on the ring gear edge. Ratio may be determined by the number of teeth on the ring gear divided by the number of teeth on the pinion gear or by counting the ratio of the number of turns of the pinion relative to one turn of the axle shaft. The 8-3/4" center section is removed from the front of the housing. To remove the center section, remove the wheels, brake drums, and drive shaft (note: pre- 65 units have a pressed-on brake hub.. requires a puller for removal). Remove the axle shafts, 5 bolts on the backing plate flange on post- 64 units, use puller for pressed-in pre-65 units. Remove the 10 nuts on the housing studs around the carrier perimeter. Remove the carrier...may require prying, fluid will drain when carrier gasket seal is broken. Sure Grip Sure Grip is the Chrysler name for a limited slip differential. It was optional on the 8-3/4" axles, 1958-1974. Two styles were used. 1958-1969 used the Dana Power-Lok (# 2881487). This unit utilized clutches for the differential locking action. The Power-Lok can be rebuilt using kit # 2070845 ( Mopar Performance [MP] # P4529484 ). In this assembly, axle driveshaft end thrust is taken by the thrust block assembly (replacement # 2881313). This Sure Grip appeared in the '741' and '742' assemblies. The axle bearings are: 25590 (Timken cone), and 25520 (Timken cup), (Chrysler numbers 1790523 and 696403). The Dana Power-Lok can be recognized by its bolt-together assembly, bolts around the side opposite the ring gear, and multiple openings exposing the cross shafts. 1969-1974 used the Borg Warner Spin Resistant (# 2881343). This unit utilized a spring-preloaded cone friction arrangement for the locking action. Axle end thrust is taken by the cross shaft. This Sure Grip appeared in '489' assemblies and 70 and later '741'/'742' assemblies. The differential axle bearings are: LM 104912 (Timken cone), and LM 104949 (Timken cup), (Chrysler numbers 2852729 and 2852728). The Borg Warner Spin Resistant unit can be recognized by its lack of bolts on the side opposite the ring gear (like the Dana), and two openings exposing the preload springs. Borg Warner sold this design to Auburn Gear who currently offers the replacement Sure Grip assemblies. Non-Sure Grip differentials can be identified by the large openings in the differential exposing the differential (aka. spider) gears. There are no springs or clutches. Interchange Notes: The two Sure Grip types can be interchanged between the carriers if the matching differential axle bearings are retained. The outside diameter of the cups are the same between the '741'/'742' and the '489'; the inner cone differs. The Sure Grip differential can be used as a direct replacement for the non-Sure Grip within the carrier/bearing limits previously noted. Universal Joint Yokes The 8-3/4" axle was offered with two size cross & roller style universal joint. These are referred to as the '7260' (2-1/8" yoke ID) and the '7290' (2-5/8" yoke ID). Most Imperials and some C-bodies used a different universal joint. The '1330' type joint was used on Imperials and others with a constant velocity joint. The '1330' uses outside snap rings instead of the inside snap rings used by the '7269' and '7290'. The cap diameter for the '7260' is 1.078". The cap diameter for the '7290' is 1.126". The '1330' style joint cap diameter is 1.063". There are four different yokes that have been used with the 8-3/4" axle for the '7260' and '7290' style universal joints. The '741'/'742' assemblies used a coarse spline (10 splines) drive pinion. Most of the aftermarket gears also use this coarse spline yoke mount. There is a small yoke for the '7260' and a larger one for the '7290'. The '489' assembly used a fine spline (29 splines) yoke. Note: during the phase-in period of 69-71 for the '489' unit, there were several permutations of pinion size and yoke availability. 69-70 '489' units may be equipped with a coarse (10) spline pinion, particularly for the '7290'. There are two yokes for the '7260' and '7290' universal joints with fine (29) splines. Two additional yokes were used for the '1330' style universal joint in constant velocity applications, one for 10 splines and one for 29 splines. Interchange Notes: 7260, 7290, 1330 yokes may be interchanged if the spline count is the same. Note: the 9-1/4" axle (73-up) uses the same fine spline yokes as the 8-3/4" fine spline units (29 splines). Strength Considerations Pinions The 1-3/8" '741' pinion is the weakest. It is still a capable unit in most moderate power, moderate traction street applications. For high torque applications with high traction tires, the 1-3/4" or 1-7/8" should be considered. The 1-7/8" '489' is supposedly the strongest. Although the stem tapers down along it's length, it appears inherently stronger from a pinion stem perspective and the inherent strength of the fine splines (OEM gears). The 1-3/4" '742' has a larger rear pinion bearing yielding greater strength in this area. The 1-3/4" shares yoke mount diameter and mounting nut with the 1-3/8". For perspective, the 7-1/4" has a 1-3/8" pinion, the 8-1/4 has a 1-5/8" pinion, the 9-1/4" (70s) has a 1-7/8" pinion. Sure Grips The Dana Power-Lok is inherently stronger and provides better, equal torque transmission to both axles. It's locking capability is also proportionate to the applied torque. The Borg Warner unit is weaker, but is a more versatile unit for practical street applications in inclement traction periods. The Dana unit is the better of the stock sure grips for racing applications and has clutch rebuild kits available. An updated cone-type sure grip unit is available from Auburn Gear with 30% increased torque carrying capacity over the old version. Lockers and spools are also available from various sources. Service Parts Information Most replacement parts for the 8-3/4" axle are still available. Some items not available are new Dana Power-Lok assemblies, most OEM gears, most carrier housings and complete differentials and housings. A revised version of the cone-type Sure Grips are available from Auburn Gear. The Power-Lok clutch kits are available from MP and other sources. Gear sets (typically performance oriented ratios) are available from MP and the aftermarket for the ' 489' and '742'. Bearings and seals are readily available. Some sources Mopar Performance dealers, Chrysler dealers. Moser Engineering, 1616 Franklin St, Portland IN, 47371 (219-726-6689). Reider Racing, 12351 Universal Dr., Taylor MI, 48180 (313-946-8672). Aftermarket for general replacements, ie. seals, bearings, etc. Selected Parts Reference Numbers listed for reference, some may be superceded or discontinued, some variances among models/years may occur. Reference factory or replacement parts catalogs for exact replacement details. <tt>Universal Joint Items</tt> <tt>Item Chrysler Precision Dana TRW</tt> <tt>(Detroit ref.) (OEM or MP) (Moog) (Spicer) (FederalMogul)</tt> <tt>--------------------------</tt> <tt> 7260 joint 4364400 315G 5-1306X 20030, 20030P</tt> <tt> 7290 joint 4057025 316 5-1309X 20059, 20059P</tt> <tt> Combination * --- 347 --- 20226</tt> <tt> 1330 joint 2533202 354 5-213X 20064, 20064P</tt> <tt> 7260 strap kit P4120468 318-10 2-70-38X 20704</tt> <tt> 7290 strap kit P4120469 492-10 2-70-28X 20705</tt> * This is a combination of the 7260 and 7290 universal joints to allow mating of the two styles. Yokes 3432485 -> 29 spline 7260 (2-1/8" ID), also P4529481 3432487 -> 29 spline 7290 (2-5/8" ID), also P4529483 3004872 -> 10 spline 7260 (2-1/8" ID), also P4529480 P4529482 -> 10 spline 7290 (2-5/8" ID), replaces 2808384, 3004873 2931813 -> 10 spline 1330, for constant velocity, ie. Imperial. 3432489 -> 29 spline 1330, for constant velocity, ie. Imperial. 1556556 -> pinion washer, concave, 3/16" thick, 13/16" hole diameter. 2070117 -> pinion washer, concave, 3/16" thick, 15/16" hole diameter. 1795175 -> pinion washer, flat, 3/32"thick, 13/16" hole diameter. 1795173 -> pinion nut, 3/4"-16 thread, 1-1/4" hex. 6027323 -> pinion nut, 3/4"-16 thread, 1-1/8" hex. 6028041 -> pinion nut, 7/8"-14 thread, 1-1/4" hex. Sure Grip Items Mopar Sure Grip axle additive - 4318060 Dana Power-Lock thrust block set - 2881313 Repair Kit, Dana Power-Lok - P4529484 (replaces 2070845) Note: there is no repair kit for the Borg Warner/Auburn unit, but the internal cones have been remachined by others to successfully restore performance. Shim Package 1-3/4" pinion -> P4452027 1-7/8" pinion -> P4452026 Ring Gear Bolts P4529486 -> 71 and later (also 4131255, pkg. of 10) P5249163 -> 70 and earlier Note: the 71 and later bolts may be installed in the earlier units by drilling a shoulder relief in the attachment holes. <tt>Gaskets, Seals</tt> <tt>Position Chrysler National C/R Fel-Pro</tt> <tt>--------------- -------- -------- -------- --------</tt> <tt>Axle inner seal 4796698 8695S 15460 ---</tt> <tt>Axle outer seal 2404216 8704S 19000 ---</tt> <tt>Axle flange, foam 2070933 see flange kit see flange kit 55032</tt> <tt>Axle flange, shim 2881314 see flange kit see flange kit ---</tt> <tt>Carrier gasket 1673367 --- --- RDS 65833</tt> <tt>Pinion seal, 1-7/8 2931862 5126 18708 ---</tt> <tt>Pinion seal, 1-3/4 2931862 7216 18912 ---</tt> <tt>Pinion seal, 1-3/8 2931862 8515N 18708 ---</tt> <tt>Yoke repair sleeve --- 99187 99187 ---</tt> <tt>Bearings</tt> <tt>Position Cup/Cone, Timken, BCA Notes:</tt> <tt>------------- --------------------- ------------------</tt> <tt>Differential, side LM 104949/LM 104912 70-74, Borg Warner</tt> <tt>Differential, side 25590/25520 57-69, Dana</tt> <tt>Pinion, front M88048/M88010 1-7/8"</tt> <tt>Pinion, front HM89443/HM89410 1-3/4"</tt> <tt>Pinion, front M88048/M88010 1-3/8"</tt> <tt>Pinion, rear M804049/M804010 1-7/8"</tt> <tt>Pinion, rear M803149/M803110 1-3/4"</tt> <tt>Pinion, rear HM89446/HM89410 1-3/8"</tt> <tt>Axle, outer BCA A-7 65-74</tt> <tt>Axle, outer C/R BR7 65-74</tt> Axle bearing service kit: Chrysler # 3683966, one axle. BCA differential kit: 1-7/8", # RA-301, 1-3/4", # RA-300. BCA axle mounting flange repair kit: Left # A-7-LK, Right # A-7-RK. C/R axle mounting flange repair kit: Left # A7-LK, Right # A7-RK. Vent bolt - Chrysler # 4032798 Spring mounting pads (perches) - Chrysler # P4120074 '489' collapsible spacer (pinion bearing preload) - Chrysler # 2931687 Mopar gear lubricant - 4318058 Mopar wheel bearing lubricant - 4318064 Note: the 8-3/4" axle shaft outer bearings require packing with grease as they are not lubricated by the gear oil. ----------------------- Appendix A: 8-3/4 A-body axle upgrade to 4.5" bolt circle The 65-72 A-bodies were available with the 8-3/4" axle. This was standard on all 340 equipped cars. It was also included in heavy duty packages such as 318 with manual transmission and towing options. It was often included in post 65 273 high performance manual applications. The bolt circle (BC) on these vehicles was 4". All other Chrysler vehicles (except some Imperials and trucks) of this era were equipped with a 4.5" BC. It is commonly desired by A-body owners to change to the 4.5" BC when upgrading to later style disk brakes or to expand wheel choice. A-body 8-3/4" axle shaft swap: There are several methods to accomplish this. Custom axles such as Strange, Summers, Moser, etc. can be specified with the larger lug pattern for the A-body housing. Longer axles from a larger vehicle may be cut and resplined to fit the shorter A-body axle. Donors for this operation are C-bodies, D-bodies, trucks and vans with the 8-3/4" axle and 4.5" BC. Moser Engineering can perform the cut and respline operation. When selecting a donor axle shaft, look for one that does not taper along its length. Note: A-body 8-3/4" axles were equipped with 10x1-3/4" drum brakes. Replace these with 10x2-1/2" or 11-2-1/2" brakes and associated hardware from the donor vehicle or similar. Appendix B: How to Put One in a Javelin (Or Other AMC) AMCs use a 43 1/2 perch to perch spacing for all models from 1964-78, and possibly even further. Narrow body cars (68-70 Javelin & AMX, Gremlin, Hornet, etc.) use a 57 track width, and wide body cars (71-74 Javelin, Rebel, Matador, etc.) use a 60 track width. Comparing these numbers to the table above, it would appear that all of our axle needs can be fulfilled with either A-body or B-body axles, depending on which AMC vehicle we own. The 1969 A-body axle that I installed in my 1969 Javelin measured 57 1/4 from drum face to drum face, although the listed track width is 55.6. The spring perches dont need to be moved in order to install the axle. Most leaf springs will allow 1/4 of side movement to permit the installation easily. You can purchase new Mopar Performance spring perches from Jeg's for $11.69 a pair if you feel the need to relocate them. You can use the stock AMC shocks, but you need the shock/spring mounting plates from the donor Mopar. Use the passenger side plate on your drivers side and vice versa (Chrysler mounts the shock on the outside of the leaf spring, AMC mounts it on the inside). Another mounting option is to use Lakewood's "Traction...Action" bars, which are a combination shock/spring mount and traction bar. Buy some u-bolts for a 69 Cuda and bolt the axle in. The driveshaft and u-joint require no modification typically. Moroso makes a fine u-joint girdle set to replace the stock straps for about $22.Brake lines will have to be modified to fit each application. On the rear end I used the distribution block was located on the drivers side. I relocated it to the passenger side and made new lines. References - Chrysler factory service manuals, various, 1964-1974 - Chrysler parts catalogs, various, 1957-1974 - Hollander Interchange Manuals, 40th edition - Mopar Performance catalogs - Mopar Performance Chassis Manual - Mopar Performance Oval Track Manual - Mopar Action magazine, selected articles - High Performance Mopar magazine, selected articles - Chrysler Car Enthusiast, Engines, Etc magazine, selected articles - BCA/National catalog # 510-1, 1995 - CR Seals & Bearings catalog # 457205, 1991 - American Bearing catalog # 710, 1980 - Fel-Pro Master Gasket Catalog, # 900-96, 1/1996 - Precision Universal Joint catalog # MC-86, 1/1986 - TRW Universal Joints catalog # X-4003, 1995 - Mopar Mailing List (MML) postings ======================================
I was watching Nascar as usual and saw a professionally built race car get a little love kiss on the back bumper. The car lost traction and spun 180. Well no one expected that little air dam on the trunk lid to catch air thus lifting it to fly high like a jetliner up into the blue yonder!
The 3 cases are different in the size of the pinion shaft. The 741 has a pinion diameter of 1-5/8". The 742 is 1-3/4" and the 489 is 1-7/8" and is the strongest. Garlits used it until the HP got to be too big for any standard auto rearend. It is lighter the the Ford 9" and much lighter than the Dana 60.
I have broken them on the street. Twice. Both were 489 cases, broke teeth off the crown in both of them. I would rate them just behind the 12 bolt chevy. I have broken R&P's in those too. 8 3/4s are adequate down to mid tens in reasonably light cars with AUTOMATICS. Stick, I would start to get worried as soon as its in the elevens. Oh, and if you want to know which rearends are the strongest, you dont look in dragsters or altereds, you look in lower class MP and Gas class cars. EDIT: By the way, I REALLY like 8 3/4s, I'm just not delusional.
8-3/4's do work. any style works for street use. for street/strip i like #742 case with the clutch type sure-grip (30 spline). for race only a spool and 35 spline axles. the only problem with using a spool is that you need to use an aftermarket one piece axle bearing that doesnt like a lot of street use.
Keep in mind, Big Daddy, and many other top fuel cars, used the 8.75 Mopar rears well into the rear engined dragster era. We ran them in pro stock with a hemi Duster with an 8.75 on leaf springs running low, low 9's. I was just talking to the DTS guys at Indy's all Mopar show today, and with a spool, they can handle over 1,000 HP, no problem.
Confirmed.....You can have a bullit proof center,the best gears,posi/and or spool. BUT- the housing is the weak link. How do I know? Mine twisted like a pretzel... Back brace is a MUST!
The 8-3/4 is a very strong axle when the ring & pinion are set properly. But with an improperly set ring & pinion, well any axle can fail then... Read the manual and learn how to properly set it up and you won't have trouble with it. The axle endplay adjuster is very simple and rugged. The OEM tapered roller bearings are better than the 'green' bearings in my opinion. The Dana-designed powr-lok differential is far stronger than any traction-lok used in the ford axle. The powr-lok was last used in 1968. 1969 was the introduction of the 489 case as well as the inferior BW spin-resistant differential.
I had some guys tell me I was "wasting'' an 8 3/4 behind a slant six/3-speed in my Dart.. sure fellas... I'll take out the rear end I got for free and already had that bolted right in the car and sell it, then go find something else.
Great info here. I am curious abour setting up the pinion snubber on a non mopar platform. I am butting a 8 3/4 in my 50 stude gasser build. I have a set of traction masters but was thinking of running a snubber on it for heavy launckes. I am running a 4 speed with a 56 Olds in it.
I cant stand seeing 9" in Mopars when 8-3/4's are stronger, plentiful and brand correct and there is still a good aftermarket for them. Especially in old MoPar trucks I took a 8-3/4 out or my buddy's A12 clone Roadrunner (since he was replacing it with a 60) perfect width from a B & E body car to 50's and earlier truck. I was just reading a article in HotRod magazine from a few years back doing a side by side comparison of the 9 & the 8-3/4 and the 8-3/4 won every category And I do believe it was the 741 case too.....I need to find that magazine and post it up here....If I can find it...
The 8-3/4" is what God runs in his car. That said, I haven't broken it but my current car weighs 4400lbs. and has a big engine, 4.10 gears, and sticky tires that hook really well. It's got me a little concerned about the 8-3/4"...but I'll wait until it breaks before I worry much more.
It's torque that breaks axles and diffs not horsepower. The 8.75 is good up to around 450 ft/lbs with an automatic and OK with a stick if you don't do standing start burnouts with wide sticky rear tires. It can go alot higher if you use your head.
The "book" says to pre-load the snubber for drag racing. For the street I'd set it up with a 1/2 - 1" gap at ride height.
Man this thread is old - not sure if anybody gives a turkey but I run a 8 3/4 in my 3650 lb bracket car 15 years now, first with SS springs and snubber, now with CalTracs. Stock housing, spool, 30spline axles...never had a problem. Car has an automatic and 60fts 1.45...
It's probably most accurate to say that it is torque in its instantaneous form that breaks axles and diffs. In other words, shock loading. At least that's the case in drag racing applications which are often not as tough as real world applications such as towing a 15,000lbs trailer through the Rockies.
The 489 is stronger but the 741 isn't junk. The strength difference between a 741 and 489 is the pinion. Both the 741 and early 489 pinions are the same o.d behind the yoke but the 741 pinion has a smaller o.d. where it rides on the bearings. only the newer fine spline 489 gearset is stronger. The real difference is the 741 pinion does not have the taper that the 489 pinion does. potato,.... patato
Anybody interested in a empty489 case? I was told the rear end was from a 69 charger Posted using the Full Custom H.A.M.B. App!
The 1969 Suregrip 8 3/4 with 489 case is my no 1. Had a race stroked 440 magnum like 600hp and dident brake it...
We ran one n a C/A 56 vette , clutchflte with a lineloc , launched at 6000 and never had any issues with the 8 3/4"or axles . The "yellowsubmarine " AA/FA used one also.
They seem to be strong, but I haven't seen one in a yard for 15 years. One Junkie told me someone sent a truck over to pick up all he had in the late 90's.
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