8-3/4.....strength

[Cudafever]

At what point do you put down the 8-3/4 and plan for a Dana 60?????

I know that chry put the limit at 440 six pack and all 426 Hemis............

Example, I have been racing my cuda at the track for to many year to count

my trusty 8-3/4 has been faithfully from, embarrassing 19 sec 1/4 miles(2.76 gears and a stock 318) to my present low 14's (4.56 warmed over 340)...........................

Now, looking down the road of a 360/stroker.......that, in the end may make 450-550 Hp (enough Hp to get me into the 12's with 3800 pound to push.

I know i will have to get better axles...........but does my long turn plans require a 60???????

NOTE: 742 or 489 housing.

[63Fury]

You will be good to go with that HP and Torque levels & auto trans. If your were going to run on a trans-brake, or manual trans with slicks then maybe you would want to switch.

I ussually suggest that anyone running 600 HP or more in a car more that 3400 lbs should run a dana.

I'm doing a 8 3/4 to dana 60 for a friend rate now. I do not know the HP of this car but it is a 74 cuda build 440 with a blower, 3800 stall and full manual 727. He didn't brake the 8 3/4 but never ran it with slicks only street radials. He origanally just wanted to upgrade gears from 3.55 to 4.11 but I suggested the dana 60 with 4.10's so he said that would be best because he wants to run it at Milan this year with sticky tires. The funny thing is when I inspected the 8 3/4 it was a 741 case. I have seen this guy hammer on this car and I would have never thought the small pinion 741 would have held.

[Cudafever]

741 wow, thats incuraging...........

Yeah Drive train usually is NOT the weak link, Until you add sticky, aka Slicks to the mix.

I'm running slicks, but with a 2.21 "60" foot time, I'm not exactly putting much twist, where it count the most.

Hoping the stoker will help that problem a bunch

[KSTripleMstr]

Most dont know it, Im sure some do know it on here, but there are 3 different grades of 8 3/4 rear diffs. I think I read it in my Mopar Performance Chassis book I have at home.........on the pumkin, underneath on the pass. side on the webbing there is a stamping number cast into the casting and like the last 3 digits ID the pinion gear diameter. If interested Ill dig my book out and post up the numbers and pinion sizes that correspond to them. When I do my Dakota Im most likely gonna stuff a newer style 9 1/4 under it and just tap and plug the RWAL speed sensor hole.

[passing you]

I run a 741 3.73 auburn style sure grip, street strip/strip no problems.
Plan on using the same chunk behind my 410 stroker.

You would probably break a stock axle, bearing cap, or even eat a pinion bearing before you'd break a ring/pinion.jmo

[rumblefish360]

Originally Posted by Cudafever

At what point do you put down the 8-3/4 and plan for a Dana 60?????

It's a combo of cars weight and torque output and how much bite your getting.

For a ref point, my buddy runs a 500 inch Indy headed engine in a all steel 69 Dart the runs a 1.6 60ft. the 1/4 @ 9.6 before the stock OE parts failed. It was the pumpkins cap that broke. The only upgraded part in the rear was the ring and pinion with the large U joint.

Tuff enuff? I think they are.

[Dennis Jokela]

Untill not to many years ago a lot of alcohol dragsters were running 83/4 rear ends.

Dennis Jokela

[ehostler]

Originally Posted by KSTripleMstr

Most dont know it, Im sure some do know it on here, but there are 3 different grades of 8 3/4 rear diffs. I think I read it in my Mopar Performance Chassis book I have at home.........on the pumkin, underneath on the pass. side on the webbing there is a stamping number cast into the casting and like the last 3 digits ID the pinion gear diameter. If interested Ill dig my book out and post up the numbers and pinion sizes that correspond to them. When I do my Dakota Im most likely gonna stuff a newer style 9 1/4 under it and just tap and plug the RWAL speed sensor hole.

Maybe you should look around this board, before assuming that we don't know about the three different pumpkins. This thread is a continuation of another thread. In that thread, we discussed the 741, 742 and the 489. Hence the reason people are surprised that a 741 held up to the mentioned abuse.

Those numbers are actually cast in the housing, not stamped as you stated. Those numbers are NOT the pinion gear diameter. If that were the case, the 489 would be the weakest of the 3. The 741 has the smallest pinion shaft and bearing surface. The 742 has a larger shaft and bearing surface. The 489 is larger at the bearing and then it tapers down.

As I have posted several times in the past, there is a great wealth of information at Auto Hobby Digest.

[KSTripleMstr]

Originally Posted by ehostler

Maybe you should look around this board, before assuming that we don't know about the three different pumpkins. This thread is a continuation of another thread. In that thread, we discussed the 741, 742 and the 489. Hence the reason people are surprised that a 741 held up to the mentioned abuse.

Those numbers are actually cast in the housing, not stamped as you stated. Those numbers are NOT the pinion gear diameter. If that were the case, the 489 would be the weakest of the 3. The 741 has the smallest pinion shaft and bearing surface. The 742 has a larger shaft and bearing surface. The 489 is larger at the bearing and then it tapers down.

As I have posted several times in the past, there is a great wealth of information.......

Assume??? No and I wasnt trying to insult anyone intellegence either, just been down this raod before with a buddy.
Reread the first line again of what I posted........"Most dont know it, Im sure some do know it on here".....and again "....side on the webbing there is a stamping number cast intothe casting" A number on a part is known as a stamping number whether it be casted, imprinted or indifferent. And no, those number are not the pinion size, it is actually the part stamping number that ID's the 3rd member, 741's were built with XX size/style pinion, 742's with XX style/size, and then the 489's was built with XX style and size.

Again following a typical open forum discussion I was just trying to share my knowledge of the matter at hand, seeings how I spent an entire weekend hunting for a Large pinion 8 3/4 for a Duster a buddy and I were building about 9 years ago or so, finally found the "one" under a Monoco or a New Yorker (cant remember which). In all actuality the 741 would have more than handle what he was planning to throw at it, but he wanted the best.....LOL.

Again sorry if I stepped on anyone toes or offended anyone, that was not my intention, Ive stated my story of the 8 3/4 hunt weekend to several other MoPar buddies of mine, who were actually alive in the good ole days of the Muscle Cars, and had built several street and strip terroizing machines and they were oblivious to the fact there was a difference.

[Cudafever]

Originally Posted by ehostler

Maybe you should look around this board, before assuming that we don't know about the three different pumpkins. This thread is a continuation of another thread. In that thread, we discussed the 741, 742 and the 489. Hence the reason people are surprised that a 741 held up to the mentioned abuse.

Those numbers are actually cast in the housing, not stamped as you stated. Those numbers are NOT the pinion gear diameter. If that were the case, the 489 would be the weakest of the 3. The 741 has the smallest pinion shaft and bearing surface. The 742 has a larger shaft and bearing surface. The 489 is larger at the bearing and then it tapers down.

As I have posted several times in the past, there is a great wealth of information at Auto Hobby Digest.

WOW!!!! That's a grate link! THANKS

[dave5711]

Weight and power is the deciding factor.

Alot of this debate depends on whether you are an optimist or a pessimist.

Yes, there are guys running very fast cars with 8 3/4.

On the flipside, late 60's there was a TSB from chrysler recomending dana 60 replacement on 383 4 spd road runners that were breaking 8 3/4's. These were 330 hp cars.

I think the 600 hp in a car over 3400 pounds is probably a decent guideline for an auto car with no trans brake. even sooner with a stick or a t brake.

Smart to plan ahead. I just put a dana in my car. ran the 8 3/4 for several years. If I had built the dana originally, I would have saved a lot of cash.

I have a friend who is building a 67 dart. It is a lighter vehicle, that will get a 600hp or more 440. He is going dana. It may be premature, BUT the car only has a 7 1/4 right now, so why spend the cash on an 8 3/4 from scratch, when it will cost very little more to do a dana.

[BelvedereII]

As another for-instance, my 67 Belvedere weighs around 3800lbs with me in it, automatic tranny with 9.5" Dynamic converter, 8.5" slicks. I ran a 741 cased 3.91 set with a 360 under the hood (weight about 150lbs less) and got a best of 8.8sec in the 1/8th.

With the 440, best last year was an 8.14 in the 1/8th and best 60' was 1.81sec iirc. I went with a 742 case and 4.30 gears last year, and through all of this I've been using yokes with 7260 u-joints. I'd had a 3" tube driveshaft made using 1330 joints with a conversion unit at the back and figured that was the weak point. Today the shop installed a 7290 conversion joint and I'll swap out the yoke tomorrow, so things should be as good as needed although to date it's all been trouble-free. For drag racing, my setup is on the mild side for sure. Best I've seen in conversion charts, that 8.14 might be a very high 12 sec in the 1/4.

What does anyone know about the relative strength of u-joints with and without grease fittings/passages? Both conversion joints have been solid, and the shop guys didn't know how much weaker a joint becomes if it's got grease passages drilled through the cross.

BII

[ehostler]

My apologies for jumping on the defensive.

[bulldog426]

i saw a guy once with a 73 charger full body car with a rollcage with a 502 probaly a 4000lb plus car running mid to low 10s with an 83/4 and they are really tuff rearends, i've ran them in derbycars and taken several HARD hits to the same rearend and not break an axle, in my opinion it's as tuff as 9inch, if not tuffer

[KSTripleMstr]

Originally Posted by ehostler

My apologies for jumping on the defensive.

No harm, no foul.

[Ray Bell]

Originally posted by BelvedereII
.....What does anyone know about the relative strength of u-joints with and without grease fittings/passages? Both conversion joints have been solid, and the shop guys didn't know how much weaker a joint becomes if it's got grease passages drilled through the cross.

Not what I know, but an educated guess...

If the grease nipple is in the cup, then I don't think drillings through the centre of the cross would make much difference at all.

However, if the grease nipple is in the cross itself, then the mounting hole for it becomes a stress raiser and must take away strength from the cross. How much, of course, is anybody's guess.

[BelvedereII]

The ones I've seen have the nipple in the inside radius of the cross. You're right, it's hard to say how much of a difference it makes anyhow.

BII

[Tarrbabe]

Most Mopars run them but you need to ask what you expect from the rear. 8 3/4's came behind Automatic Hemi's unless they were ordered with the Dana.
For 500 hp and some maintaince the 8 3/4 will do it for drag only use. For street, it will do very well. If you use the car for track use every week, you would be better served with the Dana 60 even though it weights more. It will hold up much longer than the smaller rear.

Sorry. Just thinking out loud.

[63Fury]

Here is another link that shows the physical differeance between Dana's, all 3 8 3/4, Ferd 9" and Cheby 12 bolt car and truck. When you look at the pinions side by side you can see the differance. I agree with the last statment the author of this artical makes "the 741 is highly underrated"

http://www.moparts.org/Tech/Archive/axle/1.html

[Cudafever]

Originally Posted by 63Fury

Here is another link that shows the physical differeance between Dana's, all 3 8 3/4, Ferd 9" and Cheby 12 bolt car and truck. When you look at the pinions side by side you can see the differance. I agree with the last statment the author of this artical makes "the 741 is highly underrated"

http://www.moparts.org/Tech/Archive/axle/1.html

Thanks, to all of Yeah for you opinions.
This make me fill better about my 742 housing............Kind wish i would have kept my 741 housing now