i am leaning tward the 8 3/4 because they are cheaper and the 742 case has the biggest pinion: http://www.moparts.org/Tech/Archive/axle/1.html
I like the looks of the 8 3/4 Mopar, nice and round without any bumpsalso theyare not on every rod Around, they are strong especially if it's got either a 2881488 or 9 part number carrier. That's all I know. I am putting one that has been cut to 44 inches at the outside of the drums under my 36 Ford pick em up truck. More info at www.geocities.com/motorcity/flats/1549/index3.html?200814
It kind of depends on how you plan to build the rear (stock or aftermarket parts) and how much you plan to abuse it. The 8 3/4 is stronger but depending on HP and traction might not be needed. I've reached axle twisting HP and traction. I highly recommend it!
the car is going to see both the street and the strip. running about 425-450 hp at the crank, 29.5-10.5 slicks and leaving on the trans brake at 2500-3500- depending on the dyno sheets. i was thinking the 742 case with a spool and 31 spline axles. some might say its over kill but i dont like braking parts.
Not overkill at all. I've broken a rear u-joint which busted the yoke, followed by the pinion support in the case... of my 9". When I took it apart the twist in my 28 spline axles was pronounced. I put it back together with 31 spline axles, a much stiffer traction loc, and a larger yoke and ujoint. I went with the 9" because I could get it cheap. The 8 3/4 is a great choice.
30Abone look for late 60's c-body car like a fury III, they have the 488 carrier same as the 489. You might be able to get one cheaper that way, 489's are found in the muscle cars and are probably fetching big bucks. I ran a 489 case w/4:10's,strange spool and moser 35 spline axles in my off topic car, never had a problem. later shawn oh yeah use those green axle bearings to get rid of that pain in the ass axle adjuster.
The 489 case isn't unique to muscle cars. I know guys who have found them under station wagons, trucks, vans...anything. I pulled one out of a C-body (boat). I don't remember if it's the 489 case or the 742 case, but for one of them, both pinion bearings are the size of the Daytona pinion bearing on big-built 9-inches. Also, ALL 8 3/4 rear ends have 30 spline axles, and they can be narrowed because they don't taper. -Brad
9" alot more of them out there, more different gear ratio's, and easier to get parts for. Go price some good gears for a 8 3/4", then a 9", BTW make sure your sitting down when looking at 8 3/4" gear prices!
Almost sounds like you should have beefed it up before you stuffed it in the first time... I know I'm going to get stupid with mine so it's got all the good stuff the first time around.
I wasn't tearing it up to bad till I put the 671 on the hemi and started running slicks at the track. Then it was a whole different story.
Actually the early '60s Mopar 8-3/4 rears DID have tapered axles. My '63 Polara Max Wedge clone had them so I swapped out the 3.91 posi guts into a later B-body case with the non-tapered axles. It's actually something you need to look for- the early rears with the tapered axles should be avoided.
I believe the 742 had the 1 3/4 pinion and the 488/489 had the 1 7/8 pinion. Brad54, thanks for the heads up. I didn't know if they were in non-muscle vehicles. I came across an 8 3/4 in a 71 dodge truck up at harry's u-pull-it but it was robbed of the hogs head already. later shawn
Depends on how much money you want to toss at it, and how you are going to use it. Stock, the 8-3/4 is tougher. All 8-3/4 carriers are nodular cast iron, unlike the fords. If you stick all the aftermarket parts in it, like a strange carrier and such, the ford might be better. I think in your case the stock mopar with a 742 or 489 case will be just fine. If you are going to narrow a housing just buy the aftermarket axles from Moser, you can get them with a dual bolt pattern at no cost, they are stronger and the unit will have some resale value later.
It's not necessarily the high nodularity case (N case) that makes Ford stronger, it's the 3rd pinion bearing preventing deflection of the pinion in high HP applications. One of the reasons many consider the 742 superior to the 489 is the larger rear bearing - helps prevent deflection, but still inferior design-wise to the third pinion bearing of the 9" (and even the 8"). Baffles me why anyone would run anything other than a 9" for racing applications due to aftermarket support, ratio availability, and strength. Sure, you can make a case for 8-3/4 or GM 12-bolt, but, honestly, why?
Tapered 8.75's last year was 1964. Mopar rear takes less H.P. to turn than a 9". To me there are two reasons for using a nine inch; both already stated, one is availability, but if you have one or know where to get one, that issue is moot. Second is cost of gears and parts (same argument people use for building a small block Chevy over a Mopar) But you've only got to buy it once; so I don't see the big issue. I'm a Mopar guy, I love 8.75's, and its about the only rear I'd use. I don't care how much HP you put in an A-bone, you will never need a DANA, that is overkill to the ridiculous.
Actually, in a stock FoMoCo dif, that third pinion support area is a weak link. The part of the casting that the bearing's race seats in is unsupported, or unsurrounded, about half way around. That metal is just hanging out there in space, ready to crack off and fall into the gears. And that happens a good bit. If you look at an aftermarket case, that area is really, really beefed up. Another issue with a lot of 9-inch limited slip carriers is that they break through the ring bolt holes. I've found a couple in junk yards that way. The Mopar PR machine has always sucked in promoting their goods to racers. They were happy to preach to the choir, but didn't much care to invite the rest of the masses to the party. That's always hurt them, and in my opinion, that's one of the reasons the 9-inch was embraced over the 8 3/4. TONS of availability, less power to turn than a 9-inch, BIG bearings, non-tapered axles (after the early ones), fairly decent selection of gears, lighter than a 9-inch, and a limited-slip unit that's nearly bomb-proof. From my unbiased opinion (I'm a Chevy guy), build a Mopar 8 3/4 until you make enough power to break it, then build a Dana 60 for less money than a fully-built 9-inch, and NEVER break that. The two Mopar rears cover the spread for the 9-inch... a stock or lightly built 8 3/4 will cover a stock and well-built 9-inch; a fully-built 9-inch with all the goodies will be stronger than the 8 3/4, but will cost a whole lot more, which would better be spent on the last rear you'll need to buy: Dana 60. I see no reason to build a 9-inch. -Brad
1 word: aftermarketsupport Never said 8-3/4 was a bad rear - they're not. Dubious to pit stock against stock when going racing - who's going to have a stock rear? Dollar for dollar, 9" is cheaper than 8-3/4. That third pinion support is plenty strong - yes, stock ones break/crack - as do stock housings of all flavors... At the end of the day, it's a bit like religion and politics...and oil choice!
What about in a FED? Say...with a 377 roller sbc, direct drive. I have some of both and don't know which to go with either.
The 8-3/4 will be more comfortable for the driver to put his legs over, and will look more traditional. A car that light doesn't need bedrock strength. Some light comp cars use an aluminum center section from Strange that runs 12 bolt chevy gears and fits in a 9" housing because the R&P takes less power to turn, and they don't have trouble. I ran an sbc/glide 8.50 FED for several years with a 55 chevy R&P in a M/T aluminum centersection with no breakage. Used a Mopar style dana posi, not even a spool. I didn't use a transbrake though, they add abuse to the equation. Next owner had me put a BBC in it and a transbrake, finally broke a tooth and split the centersection wide open, so I put a 9" in it for him.
The 42 case (1.75" pinion) pre-dates the 89 case (1.875" tapered pinion). They changed somewhere around 67 - 69. The 89 case uses a crush sleeve to set pinion pre-load and for this reason some prefer the 42 case. Stay away from other case numbers (like 41) as these have puny 1.3125" pinions and virtually no aftermarket gears available. Regarding the axle taper: you guys are talking about two different things. Someone mentioned that you can narrow the axles because they don't taper. That was referring to the inside end of the axles. The splined portion of the axle is a smaller diameter than the middle of the axle so, you can cut off however much you need and the axle is still thick enough to respline. Not so with most other makes. The pre-65 axles are tapered on the outside ends and the drum/hub is keyed.
I've got a 1957 Plymouth 8-3/4 rear end in my 1935 Dodge pickup. It's narrow, I'm not sure of the exact measurement, and out of a Fury. I don't know if its a 741 or 742 case, but I do know it has the tapered axles. Is it possible to install conventional axles from a 1965+ application if they were the right length? It seems as though all I would need would be the right measurements and I could have some custom axles made if width is a problem. I realize that I would probably end up having to switch to a 742 or 489 case if I have a 741 case, but this would make switching out my 3.55 gears easier. Any information would be appreciated if someone has used a pre 65 axle housing and non tapered axles.
1 st 8 3/4 gears are NOT expensive. often under $200. 2nd. and your gonna all kill me but it doesnt really matter how big the pinion bearing is because all three Mopar diff cases have exactly the same size shaft at the spline. You can have a ten foot diameter pinion bearing but if the shaft where the flange slides on is 1 3/8s then that is the weakest part. If you want to avoid the 741 case you may but i ran one since 2000 in my 426 max wedge 63 dodge. And recently put that diff 3.91 in my dragster) However use what is available. As much as I love mopars though I would probably encourage a model a owner to go with a Ford drivetrain. 8 3/4s are almost indestructable but the 9 inchers are too so?? Don just for the record. 741 case 1 3/8 pinion bearing 742 case 1 3/4 pinion bearing 489 case 1 7/8ths pinion.
The way to overcome crush sleeve problems in the 489 case is to use the crush spacer to set your preload - then remove it, measure the crushed length and make/have made a steel spacer to replace it. Won't collapse like the stock piece.
I don't know if its a 741 or 742 case, but I do know it has the tapered axles. Is it possible to install conventional axles from a 1965+ application if they were the right length? You can have a set made by Moser for instance and use the green bearing which is not a tapered bearing so requires no adjustment. Surpisingly Custommade axles are almost cheaper than used in some cases. I shortened a 8 3/4 for my dragster. I bought the axles used from the wreckers 35 bucks each I cut them myself and sent therm out for splining. $100 each or two hundred Dollars toal. I know have $270 in a rusty old set of axles with ifffy bearings and I need axle seal which i wouldnt wth the green bearing set up. Hardest thing you will have to deal with is the axle retianers you have a bit different but you will get retainers with the new axles and may have to modify your backing plates a bit. On the other hand I ask you why do you want to change? You wont ever break the tapereed axles. I know cause i have tried in my 63 Dodge Max Wedge and a few other cars in my mispent youth. Yeah they aree a pain to pull apart so when I do I replace everything. Hopefully that will last as long as I need thecar and I will never have to service it again. I dont think the 742 was around then. Yours should be a 741 or have an X on it. Don d
Hi! I used the 8 3/4 on my modell A, because i had one laying around, but the fun part is that i foud a set of conical B-body axles. This solved my problem, as i was going to use early Ford juice brakes. We just cut som off, then turned them down to fit the early Ford drums, and mounted dubble row ball bearings. Now it looks old, but handles more power from my suped up Flathead. Br Kjell ............................ Taildragger&fenderless
Strength wise itis a hard call. I used an 8 3/4 in my 74 charger whixh was 4150 lbs with driver race weight. It had a 5100 stall converter and ran 1.52 short times when bite was good. 9 years of abuse without a whimper. I would call that strong. Had a friend with a BB Chevy powered GTO judge. Our cars ran about the same in the 1/4 (mid 11s although we were always a bit quicker. He had a 9 inch instaled and while it worked well he did on two occasions blow it out. Our cars weigh within a couple of pounds of each other. I dont think I would ever be tempted to go from a 8 3/4 to a ford 9 inch. It would be to a Dana and that I have done on one high powered car we had. It would crack the bearing caps occasinally on the 8 3/4 althoug I am not convinced it wasnt because it was misaligned when narrowed. I built a Dana for my pal instead because they are cheap and almost bulletproof. We buy truck danas (3/4 ton) chop the ends off, buy Moser ends and a spool an aftermarket axles with greenbearings. With gears we can make one up for $1000-$1100 out of pocket. This urban tale that a Ford 9 is stronger because of that tiny little troublesome bearing stuck on the end of the pinion is absolute nonsense. The Dana has no such thing and is way stronger . The best Ford 9 inches are the custom case that uses the Chevy 12 bolt gears. 8 3/4 s were used in everthing for years even AA/FDs. Dont know where this deal that 9 inches are cheaper to run comes from. An 8 3/4 can be had almost anywhere for $100 or less. Cant buy a 9 inch for that around here. Then on the build you have that funny little extra MM bearing to buy. I priced Mopar gears last night to see. $199 or less for any gear. I didnt think that was too bad. Still if I was building a Ford I wold use a Ford Diff for the same reason Wilford Brimmley eats oatmeal." Cause its the right thing to do" Don
The Jalopy Journal
