8 3/4 Center Section H.P Ratings / Aluminum

[Lelo 500]

Just trying to understand, when the 8 3/4 breaks, what part usually lets go? From what I have read so far it has to do with the housing flexing or pinion angle. Is that correct? With a four link and panhard would that increase durability?

 

[Daves69]

FWIW, Even with a mid 12's Abody car we were chasing the weak links way back. Axle splines and ring/pinions were among them. As you add strength in one area another area takes the brunt and fatigue. Over time and use the weak will show up.

 

[1965wagon]

Here is my 8.75 that I built and is only 11 pounds heavier then the factory housing and I run a Moser center and motive gear
My car weighs 3900# and is a 4 speed and runs 11.50 no problems

 

[Shorthorse]

I know there are some inherent weaknesses of the 8 3/4 but as for the gears, my friend had his gears Cryogenic treated. They've been in his car for years and upon recent inspection still look brand new.
His car is a NHRA legal stocker, 426 wedge. I believe it runs in the 10:60's.

 

[Geri]

How Many of you guys are still running your 8 3/4 at the track, or Dana or Hate to say it 9" or After market set up's ?? I'm really wanting to keep my 8 3/4, its lite and easy to change center sections for track or street use, Mark Williams offer's Pro Gears for the 8 3/4 plus Shot penning and other service's not available to the mopar Guys before, I've also considered the Aluminum 8 3/4 Center section just like the Ford guy's have had for years !!

 

[Geri]

I'm running an 8 3/4 I actually bought from Mike Gaines. When I bought it I wasn't planning on making the power I am now but I think I've given it a fighting chance. Is a S60 in the future? maybe but for now the 8 3/4 is still in there.
disgustingly awesome~~~ color me envious
Narrowed 8"
Moser axles
4.10 gears
Detroit Locker
Back and Top Braced
Willwood disc's

View attachment 563493
View attachment 563494
View attachment 563495
View attachment 563496

 

[Geri]

How Many of you guys are still running your 8 3/4 at the track, or Dana or Hate to say it 9" or After market set up's ?? I'm really wanting to keep my 8 3/4, its lite and easy to change center sections for track or street use, Mark Williams offer's Pro Gears for the 8 3/4 plus Shot penning and other service's not available to the mopar Guys before, I've also considered the Aluminum 8 3/4 Center section just like the Ford guy's have had for years !!

many dragsters with 1500 plus HP still run the 8-3/4 but their weight is about half a door car.

 

[Geri]

When I decided I was going to be making some good power I went with a strange s60

differential tip- people think setting tighter backlash in ring/pinion( .004-.007) is correct, it is best if you are racing to set the backlash at .008 to .012. seen several carriers pushed out the back of the housing from close backlash- the cure?? was to add support bolts to the side gear caps. that is a band aid fix. what was found -during acceleration the pinion actually screws tighter against the ring gear and that is what breaks carrier caps. looser clearance= no broken caps

 

[Cranky]

FWIW, Even with a mid 12's Abody car we were chasing the weak links way back. Axle splines and ring/pinions were among them. As you add strength in one area another area takes the brunt and fatigue. Over time and use the weak will show up.
View attachment 563809

Seen a lot of ring gear bolts that looked like that!

 

[rumblefish360]

many dragsters with 1500 plus HP still run the 8-3/4 but their weight is about half a door car.

Ahhhh! There it is again, the key tip in so many issues besides the rear hams life.
Power to Weight!

differential tip- people think setting tighter backlash in ring/pinion( .004-.007) is correct, it is best if you are racing to set the backlash at .008 to .012. seen several carriers pushed out the back of the housing from close backlash- the cure?? was to add support bolts to the side gear caps. that is a band aid fix. what was found -during acceleration the pinion actually screws tighter against the ring gear and that is what breaks carrier caps. looser clearance= no broken caps

REALLY?!?! Cool tip. Thanks

 

[Geri]

Ahhhh! There it is again, the key tip in so many issues besides the rear hams life.
Power to Weight!

REALLY?!?! Cool tip. Thanks

the information about the differential ring/pinion backlash came from Chrysler,when they did differential testing they found the pinion would screw into the ring gear instead of being pushed away that led to the increased backlash. I am no where near smart enough to have figured that out. (Tom Hoover) doing the race tech seminars, they used their "white elephant" '68 dodge charger to do all their testing on engine /drive train components. their tests were always what they called A- B- A -
A- they would run the car as is
B- they would make one change only and run the car-
A- they would change it back to the original configuration and check results- if the B test improved, they would keep that and move on to the next issue of performance. their seminars were great in that era of direct connection.
I called Tom Hoover Jesus Chrysler..
BTW Toms personal car was a '68 Cuda notchback with a 340...

 

[Cranky]

I have setting instructions that mention what the backlash should be for circle/dirt track racing and it says the same thing....set the back lash on the loose side iirc .008 to .012? For drag racing, I've done the same but usually stayed pretty close to the loose side of what's listed for street settings....usually around .008-.009. Drag racing can produce a lot of heat in the gears and quickly even though the housing doesn't feel all that hot once the run is over with. The gear oil doesn't heat up real fast and so it has a tendency to cool the gears down quick too once the pass is over. The faster and heavier the car, the more quickly heat is generated. When I was racing I didn't have a temp gun and just felt of the housing once the car was back in the pits. It never felt as hot as my tow truck did. One time once back at home I got under back end of the truck for some reason and laid my hand on the rear cover of the 60 and that thing was much hotter than expected!! How much stress is created in a tow rig vs making a 10 second pass starting with a fairly cool rear end?

 

[Geri]

I have setting instructions that mention what the backlash should be for circle/dirt track racing and it says the same thing....set the back lash on the loose side iirc .008 to .012? For drag racing, I've done the same but usually stayed pretty close to the loose side of what's listed for street settings....usually around .008-.009. Drag racing can produce a lot of heat in the gears and quickly even though the housing doesn't feel all that hot once the run is over with. The gear oil doesn't heat up real fast and so it has a tendency to cool the gears down quick too once the pass is over. The faster and heavier the car, the more quickly heat is generated. When I was racing I didn't have a temp gun and just felt of the housing once the car was back in the pits. It never felt as hot as my tow truck did. One time once back at home I got under back end of the truck for some reason and laid my hand on the rear cover of the 60 and that thing was much hotter than expected!! How much stress is created in a tow rig vs making a 10 second pass starting with a fairly cool rear end?

I tended to stay at/ no more than .011 for backlash

 

[Cranky]

the information about the differential ring/pinion backlash came from Chrysler,when they did differential testing they found the pinion would screw into the ring gear instead of being pushed away that led to the increased backlash. I am no where near smart enough to have figured that out. (Tom Hoover) doing the race tech seminars, they used their "white elephant" '68 dodge charger to do all their testing on engine /drive train components. their tests were always what they called A- B- A -
A- they would run the car as is
B- they would make one change only and run the car-
A- they would change it back to the original configuration and check results- if the B test improved, they would keep that and move on to the next issue of performance. their seminars were great in that era of direct connection.
I called Tom Hoover Jesus Chrysler..
BTW Toms personal car was a '68 Cuda notchback with a 340...

Went to one of the DC seminars in Houston back in the 70's and it was very informative but was a bit sad that there were only a few guys that showed up for it. I knew Houston wasn't a Mopar town but didn't think it was that bad....

 

[Geri]

I have setting instructions that mention what the backlash should be for circle/dirt track racing and it says the same thing....set the back lash on the loose side iirc .008 to .012? For drag racing, I've done the same but usually stayed pretty close to the loose side of what's listed for street settings....usually around .008-.009. Drag racing can produce a lot of heat in the gears and quickly even though the housing doesn't feel all that hot once the run is over with. The gear oil doesn't heat up real fast and so it has a tendency to cool the gears down quick too once the pass is over. The faster and heavier the car, the more quickly heat is generated. When I was racing I didn't have a temp gun and just felt of the housing once the car was back in the pits. It never felt as hot as my tow truck did. One time once back at home I got under back end of the truck for some reason and laid my hand on the rear cover of the 60 and that thing was much hotter than expected!! How much stress is created in a tow rig vs making a 10 second pass starting with a fairly cool rear end?

I had a Dana 60 with 35 spline axles/ 5:13 gears in my 426 Hemi powered willys that I raced in the 70's. I would launch it off idle at 3500 rpm and it ran 9:60's at 145 all day. a racer friend said I should raise the rpm for launch -a 6000 rpm launch left the spider gears on the starting line- blew them right through the rear cover-the only rear end parts I ever broke. I went back to my 3500 RPM launch

 

[dvw]

As teeth bend the backlash tightens up. My Dana 60 started at .007". At the end of its life it was .000".
Doug

 

[Geri]

As teeth bend the backlash tightens up. My Dana 60 started at .007". At the end of its life it was .000".
Doug

I'd suspect the start point of .007 as to tight and the pinion did the work on the ring gear- I have never seen a bent ring gear tooth, .was that a "virgin" gear set that was supposed to harden as they wore in? just wondering. I had a "pro" differential builder put 4.56's in my '62 Dart SS clone, they lasted about two miles and were toast. some pro.

 

[dvw]

I'd suspect the start point of .007 as to tight and the pinion did the work on the ring gear- I have never seen a bent ring gear tooth, .was that a "virgin" gear set that was supposed to harden as they wore in? just wondering. I had a "pro" differential builder put 4.56's in my '62 Dart SS clone, they lasted about two miles and were toast. some pro.View attachment 564585

Street gear. 500 passes before they got noisy. That's when I inspected them. It runs 9.0's with mid 1.2x 60ft@3350lbs
Doug

 

[Geri]

Just trying to understand, when the 8 3/4 breaks, what part usually lets go? From what I have read so far it has to do with the housing flexing or pinion angle. Is that correct? With a four link and panhard would that increase durability?

another Missouri Mopar owner? cool.
I was thinking about this some more -it may depend on how much power you are going to put into it and the weight but the 8-3/4 is very strong, when I bought my Plymouth SS426 new in '63, it of course had the 8-3/4 ran 109 as delivered at mid 12's -never had an issue with the differential. even the keyed tapered axles gave no problems, I usually try what I have and make it prove it will or will not survive before I jump up to the next step, the Ford 9" to me is a joke, they started using them because the pinion gear is about an inch lower- which ,in a funny car allowed a lower car/roof, to them that means a lot.people seen them and decided they were the hot tip. but the $$ put into the Ford 9 to make it live just doesn't make sense (to me) the Dana 60 however is the final answer. (IMHO)

 

[383man]

I still have an 8-3/4 in my 63. But it's a street car that I only race once or twice a year. 99% of the time I am driving it on the street and I don't street race or run it real hard on the street. But my 8-3/4 is all stock with a Detroit Locker I installed. When I put the car on the road in 2006 I figured I will only be racing one or two times a year and I planned to go to the Dana sooner or later.
Well it looks like later as I still plan to update to the Dana or S60 when I can afford to buy the unit. I have raced it like this since 2006 and since 2011 with my 493 in the car running 10.70's best. The only thing that broke was a spider gear tooth and I still drove it home from the track that day. That's when I went to the Detroit Locker.

I can say that back when I raced my 340 Dart it was a 4-speed and ran a best of 11.90's and I broke rear end parts 4 or 5 times over a 4 year period. My 63 is heavier (3725 lbs) and faster but because its an auto car it has not broke anywhere near as much as my slower and lighter 4-speed Dart did. But I will say I launched the Dart hard as the gas pedal was on the floor as the clutch came out.

I guess my point is that even with a 10 second auto car if its a street car you don't run hard on the street and only race one or two times a year an 8-3/4 may hold up for a while. But I agree with everyone that if you have the money and can then go right with a Dana , S60 or Ford 9" rear. Good luck , Ron