8 3/4 (489 casting) gear problems

rit, I agree with you on this one. the thing is should he run a deeper ring gear to pinion tooth depth ? was the 8 3/4 squared in a jig to begin with? I mean, its been shortened, braced spooled and tooth pattern ran in several positions.this 8 3/4 imo should not be breaking. what kind of bearings you using and are you using aftermarket carrier caps?  

without getting into details how to set the ring and pinion, assumming you already know no parts will interchange between the 657 741 742 and 489 case including the pinions,bearings, and cases but the suregrip will fit any case #. assumming your using and remember the left side is the critical side. hi strength alloy steel axle caps or differential caps if preferred make sure they are machined to the exact tolerances of the older caps. your running a shortened rear, braced and setting rear gears to within tolerances you need a new mechanic who can set it up correctly. that or spend the 2 grand for the ford or more for the dana.probably wasnt even checked in a jig for squareness to begin with lol,I run a tad less hp 50, maybe 75 at most and run an 8 3/4 rear with alloy caps, unbraced standard length A body rear,a strange spool with moser axles and been 9,83 in a 32 3300 A body with no trouble whatsoever.end of story.  

richmond pro gear  

ya on hit the pinion is getting crushed the crush sleeve gets crushed Put a Dana60 with good parts in it and have p1ece of mind. With Abrake and that horsepower im surprised you are getting that life. on every leve you pinion depth gets changed.A 1.34 shin cage be better if you dont wanna swap.  

yes ,I agree 110% on the dana but like I said mines held up well. turned a 9.83 with different gearing and a 3800 launch but I play it safe now and launch at 2500 rpm and a 4.30 gear with just a strange spool .moser axles ,billet caps turned down from the old originals and a standard length A body, nonbraced 8 3/4 ,hahaha, I draw a level line down axles to see if any twisting is occuring by checking after a few runs if the line isnt straight.I just run 3 inch inboard B body spring with a top solid adjustable bar type pinion snubber.minimal wheel lift,simple, but this things been 9.83 with minor mods,4.88 gear,4000 rpm launch.I was then sent to the stands for the rest of the day,hahaha maybe im lucky or maybe im good ,dunno,,, hot,of course crush sleeves get crushed  

I also drew a straight line from axle to axle and see no twist yet.  

your answer lies in the rear suspension grasshopper..  

I have a friend with a road runner who installed a brake and is going through the same problems, it looks like the rear end is being shocked by the trans. brake and riping up the ring gear.
With the kind of horsepower and probably very large tire you are likely running a dana or a Ford 9" is the way to go.  

I cant find a 8 3/4 pro gear anywhere

I also have a 65 ply that makes 645 RWHP with a 8 3/4 have not broke yet but have not used the trans brake yet car weighs 3150 with driver  

Sixty passes on street gears might be the max.  Pro gears are softer and don't fracture, but they due wear fast.  Steel caps will help.  They keep flexing down.  Use normal settings with min backlash.  This gives the most gear contact.  Mopar put Dana's behind Hemi's and HP 440's for a reason.  A Ford 9" is not much stronger than the 8-3/4.  I've seen them blow at the track too.  If you make a change, go Dana.  They are harder to work on but worth it.  If you go with a Dana, buy or make a case spreader.  It makes changing gears go faster and it's the only way you can get the proper pre-load on the carrier bearings.
Don  

I just pulled my chunk out and found 13 teeth chipped.  I will be going to a Dana but wanted to try a gear set that Randys Ring and Pinion sells.  They said it is made out of 8620 steel.(Need to research) Yukon is the make.  The gears are pricey but if they can withstand the shock I will let you know

http://www.ringpinion.com/PartsList.aspx?SearchMode=Diff&TypeID=2&DiffID=8&CatID=10

Check it out.  I will be calling them on Tuesday to ask them about that material.  

Check out this data on 8620 steel

Chemistry Data : [top]

 
Carbon  0.18 - 0.23  
Chromium  0.4 - 0.6  
Manganese  0.7 - 0.9  
Molybdenum  0.15 - 0.25  
Nickel  0.4 - 0.7  
Phosphorus  0.035 max  
Silicon  0.15 - 0.35  
Sulphur  0.04 max  



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Principal Design Features    AISI 8620 is a hardenable chromium, molybdenum, nickel low alloy steel often used for carburizing to develop a case-hardened part. This case-hardening will result in good wear characteristics.  

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Applications    In the carburized condition this alloy is used for gears, ring gears, shafts and crankshafts.  

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Machinability    Machining is done prior to carburizing to within as close a tolerance as possible. Finish machining, after heat treatment and/or carburizing, should be at a minimum so as not to impair the hardened case of the part. Machining may be done by conventional means prior to heat treatment - after carburizing machining is usually limited to grinding.  

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Forming    Forming characteristics of 8620 alloy are good in the annealed condition.  

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Welding    The alloy may be welded by conventional methods, usually gas or arc welding. Preheating at 400 F is beneficial and subsequent heating after welding is recommended - consult the approved weld procedure for the method used.  

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Heat Treatment    This alloy may be hardened by heating to 1500 F followed by a water quench. Carburize at 1650 to 1700 F in an appropriate carburizing medium and oil quench to harden. Improved carburized case and core properties can be obtained by furnace cooling from carburizing at 1650 - 1700 F and then reheating to 1575 F.  

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Forging    The alloy may be forged at 2200 F down to 1800 F prior to the hardening heat treatment or carburizing.  

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Hot Working    Hot working may be accomplished prior to hardening or carburizing. Consult the alloy supplier for information as to temperatures.  

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Cold Working    The alloy may be cold worked in the annealed condition by conventional methods. Cold working, as with machining, should be done to as close a tolerance as possible before heat treatment or carburizing.  

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Annealing    AISI 8620 may be given a full anneal at 1550 F and slow cooling at not more than 50 F per hour down to 850 F. From there it may be air cooled.  

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Aging    Not applicable to this alloy.  

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Tempering    Tempering of carburized parts is done at 250 to 300 F and this will result in the alloy having a core strength of approximately 135 ksi minimum with Rockwell C case hardness of 90. Tempering of heat treated and water quenched parts (not carburized) is done at 400 F to 1300 F with greater hardness the lower the tempering temperature.  

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Hardening    Hardening is done by oil quench from 1675 F. See "Heat Treatment". Carburizing is accomplished at the same 1650 to 1700 F range in a carburizing "pack" or environment, followed by oil quench for thin sections or a furnace cool for heavier (over 3/4") sections. Following carburizing of heavy sections a reheat at 1575 F will enhance both case and core properties of the alloy.  

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Other Comments    This alloy is typically used for carburized parts where a hardened case is desired for wear resistance.  

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Physical Data : [top]

 
Density (lb / cu. in.)  0.283  
Specific Gravity  7.8  
Specific Heat (Btu/lb/Deg F - [32-212 Deg F])  0.1  
Melting Point (Deg F)  2600  
Thermal Conductivity  26  
Mean Coeff Thermal Expansion  6.6  
Modulus of Elasticity Tension  31