just wondering where it lands in the strenth category compaired to other rear ends?? as well as ups and downs??
There are 3 versions of the MOPAR 8 3/4 rear end (Casting numbers 742, 489, and 741). The first two are supposed to be as strong as a Ford 9 inch or stronger (handles up to 500 HP). The 741 isn't nearly as strong. Do a search, there's more info available on upsides and downsides of each version.
I had the weakest of the 3. My 741 model 8 3/4 withstood a 4100 69Plymouth Fury with a small block bored/stroked to 415", a low 1rst gearset planetary in the trans, and big sticky Mickey Thompson ET Street wrinklewalls for several years. I believe they are the same or even fractionally stronger stock for stock with a 9 inch ford. Upgrades to both make them both stronger still. the 741,742, and 489 centerchunks can be swapped into each other's housing if you use the correct bearings for the center that you're using. They came stock with good 30 spline axles, dont have c clips, so if you break a shaft, it wont chuck the wheel into the quarterpanel, and you can have one or two centersections ready to go with other ratios, if you wish to hot swap at the races. The reason people love the Ford 9 is the HUGE support for them in gear selection, and other components. But the Mopar 8 3/4 is not "rare" its just not everywhere like the 9 is. I've got my 69 Fury's 8 3/4 in my 61 Ford Falcon Gasser (along with the 415 and the 727 trans). Looks like a 9, strong like a 9, but not a 9. I dont require a billion gear ratios since i'm not a racer swapping them during a track event. Proud to run an 8 3/4
Handles up to 500 HP? Well it handles quite a bit more than that. Many early fuelies and altereds used these rear ends. In fact in older race cars you find them more often than not. They will take huge power and load. I use them for everything i build. Big Daddy once told me back in the late sixties he used them right out of the auto wreckers after a quick check over. He said he tried to buy ones out of old Mopar Taxis. Seemed he felt the extra miles a Taxi put on helped toughen the gears etc. They use 3:23s in those cars BTW. Downs ? There are none. First choice should always be a mopar 8 3/4. if you can't find one and are desparete you could sub a 9 inch Ford but it will need some beefing. Don The 741 gets a lower rating because it has a 1.375 rear pinon bearing (742 = 1 3/4 , 489 = 1 7/8) however maybe before we finalize that we should measure the bearings on a Ford nine inch and a Dana. It night surpise yu to find they are similar . Since all Mopar 8 3/4 use the same diameter pinion U joint flange hole (either coarse or fine spline.) The weakest link if there is one is the same spot for all three. Failure is pretty rare. I ran a 741 case in my MAX WEDGE 426 car with 3.91s for almost ten years and I abuse that car . 3800 stall Lupo converter and 30.5 inch tall rear tires with a 9 1/2 inch tread. I replaced it about a year or so ago with a 3.55 gearset for cruisin which just happened to have a 489 case and i took the 741 with its 3.91s and put it in my rail. They are a real good diff and while a 489 or742 would be desireable unless you have a firebreathing monster under the hood any of the three will stand anything you can give it.
You'll have to have a pretty manly motor and a whole lot of traction to break anything in an 8.75". Everybody says 741 cases are weak, but my old man's Charger has had a 741 case 3.23 Sure-Grip in it for 20+ years of tough 440 abuse and it's never failed.
'Back in the day', circa mid-to-late '60's, 8 3/4 Mopar rearends - particularly the 'big pinion' 489 types - were commonly used in dragsters, altereds and funny cars, so that should answer the 'strength' question. Also, they're a bit lighter than a 9-inch Ford and due to the pinion being somewhat higher in relation to the ring gear than on a Ford 9-inch, they take less power to spin too. Mart3406 ================================
i've been looking for a 9 in,but you have changed my mine, i'll be looking for a 8 3/4 mopar now. can anyone tell me what donor cars, trucks that they come in ???? thanks, this site helps me more everyday.........
They are stronger than a 9 inch IMO.As said before the 489 case is suppose to be the beast of the 3 cases because of the 1 7/8 pinion shaft ,but its tappered and uses a crush sleeve like a 9 inch Ford.The 742 case uses a 1 3/4 shaft and spacers instead of a crush sleeve .The caps and other parts look the same (i have both cases).Move up to sum 35 spline axles and a spool like mine has its pretty much bullet proof .Both cases with fit in the same housing ,even though they use different gears between them .I know guys that are running low 9's in the 1/4 with 8 3/4 rears in a 3500 lb car ,launching at 5000 on a Tbrake with no problems ...
Practically everything late 60's or early 70's Mopar might have one.The problem will be finding one the right width.New Yorkers ,Darts ,Cuda,Chargers ,1/2 pickups ,Challengers ,etc.Looks simular to a 9 inch Ford with the drop out center section and no cover on the back.Look on the drivers side of center section to see which one it is .The last 3 #'s of that # will be either 741 ,742 or 489 ...
Very stout rear axle.Only thing odd is some had an adjustable axle bearing to deal with end play. It's interesting that on 440 and Hemi stick cars ,Mopar always used the Dana 60 rear axle.They must have thought the 8-3/4 was strong enough for drag strip shock loads.
There are three different factory widths with the "A" body being the narrowest and apparently the rarest. I have several "C" body 8 3/4s if you want to take a long drive.....
The Dana was stock on MANUAL transmission Hemi and 440+6 cars. Automatics had the 8-3/4" rear end. A 440 4-bbl 4-speed could be had with either, IIRC. The adjustable bearing was standard an ALL 8-3/4" axles, and was ONLY on the right side. More and more common these days is the replacement "green" non-adjustable bearing to replace the adjustable pre-load bearing. Personally, I am not a fan of the "green" bearing - so-called because of the color. It takes no time at all to perform the adjustment. Here is a pretty good list of the cars that had the 8-3/4" rear. I know it is not all-inclusive, feel free to add on...I am NOT including the 8-3/4" with the pressed drums (1965 and earlier) 1) 1961 - 1971 Dodge/Fargo 1/2-ton pickups 2) 1966 - 1972 B-body 3) 1966 - 1972 C-body 4) 1967 - 1972 A-body Scarce, yes. Rare, no.
One of the local racers in the late 70's had a '69 1/2 A12 Super Bee (for non Mopar guys, 440 6 pack with a lift off hood) The car was an automatic car so it came with the 8 3/4 rear. At Lebanon Valley Dragway, running a very nasty motor and 12" slicks, he launched the car and ended up twisting both axle tubes and pulling the driveshaft out of the back of the transmission. Car sat high in the back now because the pinion snubber was loaded against the floor of the car. No other damage to the rear end other than the housing. Cliff Ramsdell
That's why for race use you weld a back brace on the housing. I used to run the small pinion case with 3.91 gears and a sure grip in my Duster with a well built 360 and never broke it, broke some u joints but the rear was fine. the Mopar 8 3/4 axle is one of the best designs ever to come out of detroit. It was light, strong and had much less drag than other axles. Bonus of being able to change gears in under an hour and no c-clips as well. Looks good too!
i have several 8.75 mopar rears with detroit lockers in them,742 cases and I bought them from Harry Hyde of Nascar fame,they were run in the superbirds at daytona,they are for sale.
Some good info here already, the 9 inch ford consumes a lot of horse power due to the pinion location. The 8 3/4 is lighter ,just doesn't have the gazillion different ratios. One word of caution, on the 8 3/4 you must lube or pack some grease on the wheel bearings when installing the bearings. best of luck.
great info guys, keep it coming if you got it, helps alot, good to know i have the best damn resourses around!! haha
Just as an example, most fuelers ran them right up into the rear engine days, into the ninties. They will take over 700 horse power, no problem. Consider now how old the stockers are, but that Moser has a modified 9" Ford housing that will take the Mopar 8.75 third member. The Mopar takes considerably less H.P to turn than the Ford. I've always used them, they've been about bullet proof.
seems as tho' I remember an after market axle manufacturer (Strange?) whose ad proclaimed there axles 40% stronger than GM; 30% stronger than Ford; and 10% stronger than Mopar.... not too necessary on a Mopar,huh? Also many of the Mopar track widths work great in 30s-40s cars that need narrower rearends. 83/4 have been one of the better kept secrets and they're cheaper than 9" Fords.
The only down side to an a-body 8 3/4, is they use the smaller 5 on 4 inch bolt patter instead of the 5 on 4 1/2 that every other mopar used. they also had the real narrow 1 3/4 inch brakes that are kind of hard to find parts for. I had Moser make me some new axles with the 5 on 4 1/2, and extra spacing so i could use the common 2 1/2 inch brakes. Tim
Some late '72 A-body axles have the larger 4-1/2" bolt pattern. These are about the most difficult of the bunch to score, so expect to pay accordingly.
My Dad ran one in his '34 coupe with a blown BBC and 4 speed and later a hard shifting clutch-turbo 400. He narrowed the rear in the late 70's/early 80's having the local machine shop cut the axles, drill one end out, nitrate press fit it together, and weld it without resplining the axles! He abused the hell out of it with very sticky and wide Hoosies sprint car dirt tires. He has a box of trashed muchie 4 speeds as proof of the weak link, and several drive shafts, but the 8 3/4 never failed him. Of course these days, one would order good axles that are race ready and proven.
THIS IS ALL BS, I TELL YOU!!!!!!!!! They are hard enough already to find, now everyone will want one, so: DON'T LISTEN TO THESE GUYS. BY A 9". Gene
We set up a friends '71 Dart race car with a 416 small block,hemi 4 speed,and an 8 3/4 .The third member had a spool , 4.30 gears , and the housing was trussed . We took the car racing and after 4 hits the car had bent the housing both up and back . When we took it apart the spring pads were curled up on the back and saw the drive shaft had probably hit the floor. When we first put the car together we put a 6 point roll bar in to stiffen the car up and then we squared and weighed it to check for preload and there was none. Being a stick car probably was the culprit but it also combined the 650 hp small block the 9 inch slicks . Maybe the stock ,though reinforced, housings axle tubes are weak funnily the center section and axles were fine. That is our little story and maybe it was just bad luck who knows but if you what to use the rear end in a street car great , but a race car we changed to a dana 60 an now there are no problems. Rob
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