8 3/4" rear end failures
#10577
05/04/04 05:35 PM
05/04/04 05:35 PM
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Let hear the opinons and theories on why 8 3/4 rears fail in drag applications. I'm thinking housing twist and flex is the biggest killer, then main cap failures.
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Re: 8 3/4" rear end failures
#10578
05/04/04 07:17 PM
05/04/04 07:17 PM
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Joined: Jan 2003
Posts: 25,200 Upper Midwest
MoparforLife
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I have seen so few fail that it is hard to tell, and the ones I have seen go took out teeth on the ring and pinion.
Clean it, if it's Dirty. Oil it, if it Squeaks.
But: Don't fix it, if it Works!
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Re: 8 3/4" rear end failures
#10579
05/04/04 08:05 PM
05/04/04 08:05 PM
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Like Don1 says, setup correctly they take a beating. How fast ya gonna go? I know they are good down into 10 second zone. And in the past chevy racers took the 12 bolt out-put the 8 3/4 in. Not sure how long they last in say a 4500 pound racecar with 500 cubes, 700 hp and 538 gears, slicks, 4500 stall and a trans brake launches???
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Re: 8 3/4" rear end failures
#10580
05/04/04 08:15 PM
05/04/04 08:15 PM
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Crush sleeves are the biggest culprit. When the end play gets loose the teeth of the ring and pinion dont mesh up properly and its just a matter of time. Solid spacer and good caps make them last a good long time.
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Re: 8 3/4" rear end failures
[Re: mcat4321]
#10582
05/05/04 04:30 PM
05/05/04 04:30 PM
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Joined: Jan 2003
Posts: 803 Texas
Beeracuda
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Texas
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If you have a backbrace and pro gears (only available in a 4.86 for the 742) you can make them live. We got 365 transbrake passes on our last set of gears. We have since added the MW caps, but we never had a failure with the stock caps. Our best 60' is 1.2576.
Last edited by Beeracuda; 05/05/04 04:31 PM.
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Re: 8 3/4" rear end failures
[Re: torkrules]
#10584
05/05/04 07:15 PM
05/05/04 07:15 PM
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I already have a spool and Moser axles. I've been thinking of adding the back brace and the billet caps. If i was building this rear all at once, I'd just go with a Dana for sure.
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Re: 8 3/4" rear end failures
#10585
05/05/04 08:30 PM
05/05/04 08:30 PM
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Greg, I've not had personal experience w/an 8 3/4 failure. However most everyone I've talked too said the loss was due to cap failure.
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Re: 8 3/4" rear end failures
#10586
05/05/04 09:12 PM
05/05/04 09:12 PM
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Joined: Jan 2003
Posts: 1,235 TN
65racer
2009 IHRA World Champion
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Personally, I have broken a wheel barrow full of r&p's, never once did I have a cap failure, I had a backbraced housing in the car, used a spool, and good axles, maintenance on it was replace the r&p, every 200 runs, and that for me was getting on the edge, after I built my newest engine 3 years ago, I went thru 3 r&p's in one season, but this was in a heavy car 3400lbs, but off the foot brake, I finally got tired of working on the rearend, and trans, all the time, went the dana route, and have been very pleased, 2 seasons, and 285 runs, and it still looks like new, I am not condeming the 8 3/4, they are very good rears, I ran them for a bunch of years, just got to the point, it was not feasible to use it anymore.
Dave
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Re: 8 3/4" rear end failures
#10587
05/05/04 10:12 PM
05/05/04 10:12 PM
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Joined: Sep 2003
Posts: 6,847 Missouri
StrokerPost
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Greg, Some good points have been brought up, like Foggy's example of just plain asking to much of it. I've never experienced cap failure, always teeth, but I did some things this last time around that so far seem to be working. personally, I think the #1 reason for failure in a car that is not OVER powered for an 8 3/4 is incorrect set up, by that I mean, as someone pointed out, with one exception, there are no "good" gears available for them, so we get steel gears and set them up to the manufacturer's specs...WHICH WONT WORK for very long. Those specs are for a stock, daily driver, not a race car. Every set I've ruined were set up stock, and had tooth failure because under load you can see that the wear pattern ran right off the edge of the teeth, eventually breaking them off. Heres what I did, First: had a new set of gears shot peened for added strength (forgiveness), Second, deberred the interior of the case where the bearings & caps go to get correct tork, Third, corrected the bore alignment...it was way off, Fourth, Installed main stud in place of bolts and shot peened the caps, Fifth, set up the gears favoring the toe about 5 thou more than they called for. Now its got a good pattern on it even with the stroker motor and has about 150 runs with all its teeth where they belong. You can check the numbers in my sig. Has all this been the key? Dont know, but its finally living.
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Re: 8 3/4" rear end failures
#10589
05/05/04 10:47 PM
05/05/04 10:47 PM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
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What Gary said, makes good mechanical sense to me. It would also explain Strokerposts symptoms of his rear pinion gear pattern running off the side of the ring gear before breaking some gear teeth. It seems most are breaking the gears and not the caps. This post is important to me because I still run the 8.25 but have a 8.75 489 on standby, next up. mike
Last edited by Sport440; 05/05/04 10:49 PM.
73 Sport 440, 509 cam w/Eddys 3.91 and 28.1"/27.3 tire. Et. 60 ft. 1.435, 1/8th. 6.61 @ 101.80 mph. 1/4. 10.472 / 127.78 mph. 2950# race/with me,and pump gas.
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Re: 8 3/4" rear end failures
[Re: Sport440]
#10590
05/05/04 11:12 PM
05/05/04 11:12 PM
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Joined: Jan 2003
Posts: 5,762 Hot Rod Ridge
FastmOp
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I still have the 8&3/4 under the valiant, with who know's how many passas, this year I'm going to start beating on it hard with the trans break. I have beefed up the caps, and installed some moly bolts in them, and still have the crush sleave, the housing has a backbrace and the ladder bar mounts are tied in to the shockmounts and backbrace, the housing is the problem for me, I have bent the housing more then anything else. I have the 489 case with a spool and moser axels, and 4.30 street gears.
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Re: 8 3/4" rear end failures
[Re: FastmOp]
#10591
05/06/04 09:55 PM
05/06/04 09:55 PM
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i've been running a 8 3/4 rear in my 70 dart 440 ,600 hp this year and no trouble yet. i changed from 4.89, to richmond 4.30 r&p. i put the rear together myself. car runs 11.0- 11.30 at 122 mph. foot brake only car and is lite weight but still around 3000- 3300 lbs. i don't abuse the rear and leave the line at 2500 and shift at 6400 rpm. the car has 10 1/2 in mt,s and they break loose alittle easing the strain on the rear somewhat. bashing off the line at 5500 on a trans- break, with 13 in or so tires hooked to the max, i don't think it would hold up. i don't race every weekend either. i have a complete dana 60 ready to put in, if i want, but i don't need it now. in fact it is for sale on ,diff- on this forum. heli301@comcast.net..........RON.
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Re: 8 3/4" rear end failures
#10592
05/07/04 08:23 AM
05/07/04 08:23 AM
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now we are getting somewhere! Great info guys.
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Re: 8 3/4" rear end failures
#10593
05/07/04 08:42 AM
05/07/04 08:42 AM
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Joined: Nov 2003
Posts: 2,273 Greenville, South Carolina
BBLM23
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top fuel
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Greenville, South Carolina
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Mark Williams cap on driver's side. 489 housing. Solid pinion spacer. 4.56 ring and pinion, less than 200 miles, around 100 passes. Like new except for one tooth missing from ring gear... I had to put one of my 4.10's back in. I was surprised. 400HP maybe, auto, no-transbrake, 3300-3400 pounds.
Walter 1969 Dart Swinger w/ARC Pump Gas 493 B1/BS 10.18 at 130mph Racing Pro in street trim. 1981 Aries ARC 548 B1 8.88 at 147mph (footbraking) 1996 Ram 2500 V10 16.52 at 80mph 1981 Reliant 400
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Re: 8 3/4" rear end failures
[Re: IronWolf]
#10595
05/07/04 01:21 PM
05/07/04 01:21 PM
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What's the opinion on the MW caps? One, both ?
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Re: 8 3/4" rear end failures
[Re: BBLM23]
#10596
05/07/04 01:23 PM
05/07/04 01:23 PM
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Joined: Jan 2003
Posts: 16,123 Grand Haven, MI
patrick
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I Live Here
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Grand Haven, MI
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Quote:
Mark Williams cap on driver's side. 489 housing. Solid pinion spacer. 4.56 ring and pinion, less than 200 miles, around 100 passes. Like new except for one tooth missing from ring gear...
I had to put one of my 4.10's back in. I was surprised. 400HP maybe, auto, no-transbrake, 3300-3400 pounds.
don't forget, the lower the numerical ratio (bigger numbers) the more and smaller the teeth are. take a ring gear of the same diameter, same material, I GUARANTEE a 2.76 ring gear is stronger than a 3.23 is stronger than a 3.91 is stronger than a 4.10.
so as far and R&P strength, run 2.94's and 23" tall tires for the same overall gear ratio as 4.10's and 32" slicks you won't break teeth as easy (of course, you won't have the sidewall flex for as much bite, either)
that's another nice advantage of the TKO tranny-- the deep first gear allows a low higher (lower numerically) gears to get a deep overall 1st gear ratio, which makes for a stronger ring & pinion.
1976 Spinnaker White Plymouth Duster, /6 A833OD 1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!*** 2011 Toxic Orange Dodge Charger R/T 2017 Grand Cherokee Overland 2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
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