what hp can a 742 case 8 3/4 handle

-
Duster Drag Car

Duster Drag Car

Well-Known Member
Joined
Dec 29, 2011
Messages
332
Reaction score
47
Location
connecticut
what kind of horsepower can a 742case 8 3/4 rear handle in a 2800 lb duster dont know whats been done do it running 29.5x 11.5 x15 slicks now thinking of going to 28.5 do to my 5.17 gear ratio the leafs have been moved in 2 inches and have 2in spacer blocks for height going to launch at 3500 think she will hold up with 600- 650 hp. yes i know a dana would be stronger but this is what i got for now. Appreciate you knowledge long time gearhead but new to bracket racing. its a foot brake car for now!
 
I run a 742 case with a mini spool with 4.10 gears on my 67 Dart.
Runs 10.70's
Weigh's 3000 lbs with no driver.
Over 300 pass's on the case.
I have also run 741 case's

P7040803.jpg
 
It will. The 489 case is actually stronger than a 742 when you use a crush sleeve eliminator.
 
StrokerScamp said:
It will. The 489 case is actually stronger than a 742 when you use a crush sleeve eliminator.
Click to expand...

X2 on that! Both my 489s have the solid instead of the crush sleeve.
That being said, you can order an all aluminum 742 case but not on the other two.
 
I have been using the 742 case for the last 19 years. I think your light weight and foot braking are key to making it last at those power levels. My car is ~3200, 4.10 gear, spool, 35 spline axles, 5k converter, foot braking, runs high 10's.
 
womanator said:
I run a 742 case with a mini spool with 4.10 gears on my 67 Dart.
Runs 10.70's
Weigh's 3000 lbs with no driver.
Over 300 pass's on the case.
I have also run 741 case's

P7040803.jpg
Click to expand...
I agree- Womanator and I have a friend who has a 70 440 blown Cuda that runs low 11's high 10's- all steel body- he's used all cases with no problems. NOT saying that you CAN'T break them though!
 
Greg's car is a very nice blown car.
he needs to post some pic's
 
72BBSwinger said:
The 742 case is stronger, has beefier bearing caps. 489 has beefier pinion.
Click to expand...

No it's not.

http://www.hotrodders.com/forum/how-identify-mopar-differential-191378.html

http://www.moparfins.com/Repairs/8-3-4_Rebuilding/Information_on_Mopar_Rears.htm

http://www.mymopar.com/Mopar8_75RearEndGuide.htm

I can keep posting links all night on it. Not that it really matters because they all three are very close in strength. It's a retard arguement, but the 489 case wins because of the pinion diameter. End of story.
 
742 case broke 2 pinion gears first one poped a couple teeth 2nd time destroyed everything swapped to a dana 1.4 60 foot just under 3000lb really depends on how hard you launch both of mine broke at the line
 
I had a 489 case with 4.30 gears, the car ran 10.20s in a 3400 lb car and got about 40 runs before it broke. I was running the pro gear set (Pro Street). Pro gears from what I was told by a manufacturer will only handle 550 hp. They don't make drag racing gears (Pro Comp) for a 489 case and only make 4.89 gears for the 742. I went to a Dana.
 
I have the aluminum carrier 742 in my car. I am running the Strange pro race gear, 4.86 ratio but yeah, it is the only one available. 30 spline moser axles and a spool. Mine is only 44" flange to flange. I haven't had a problem yet.
 
Add one of these
http://www.markwilliams.com/detail.aspx?ID=609
Brace the housing and beat it with impunity at your weight and h.p.
A 9" or a Dana would be a better option for various reasons , but the 8 3/4's are plenty sturdy if you do these two things.
The difference between 489 and 742 is not as huge as some might think.
With the crush sleeve eliminator , it is apples to a little smaller apples.
 
I'll add.......bracing your housing will require straightening because of the heat incurred with welding the brace on.
You can minimize it , but it will move some.
Now is when you want to shorten it as well. ;-)
 
I was not having any problems with the caps it's just the lack of Pro Comp gears available. I was running a 4.30 and would like to have gone to a 4.56. Will any manufacturer make the Pro Comp gears?
 
489 case, 4:87 Richmond gears, spool,crush sleeve eliminator, set up perfect, with back brace.29.5 X11.5 Hoosiers 12 PSI,S/S springs.3300 # car, 451 BB 461 H.P.to rear wheels. Power Glide with brake.3 passes and broke on the line on the 4th.
The last 489 case I ran behind a SB with 5:38 gears, back brace etc.made 10 passes and the same thing happened.
I ran a 742 case in a back half Duster with 4:87's and 15 X 32 Hoosiers, leaving off a Grinner transbrake 727, they were fine for 3 years (300 passes), before the ring gear teeth starting chipping. They were not Pro Gears. Three of us got better life out of street gears believe it or not over the Pro Gears.
I am running a 742 case now, in the 451/power 'glide combo, have 30 passes thus far.

http://www.facebook.com/racerforchr...4454290644596&set=t.1421974018&type=1&theater

http://www.facebook.com/media/set/?set=a.3005419780814.2121260.1421974018&type=3&l=786c6a6244
 
Switched to 9" Ford, with nodular case, don't trust it.Everytime I let go of the button, I grit my teeth.Never broke, wanted a narrower rear, so decided to switch.
Up to 400 H.P. Rear wheel is pushing it. Maybe foot braking is better I agree.
 
My buddy here has a 74 duster with an aluminum headed 451 and a brake.. Leaves on the brake with the 4.30 gear 742 case for over 2 years now with not one issue. All metal duster except for the hood. Car runs 10:40's....
 
It may hold for a bit,just be prepared to upgrade in the future.I ran a narrowed 8 3/4 .489 case with 4.30 spool,Strange axels.I had twisted splines,replaced axel then started to bend the housing(no brace.Doh!)After the first twisted axel I ordered my Dana60,CM driveshaft with 1350 u-joints.Now going transbrake,so we,ll see how she does.Good luck,just don,t be surprised if breakage occurs.
 
You must log in or register to reply here.
-

Back
Top