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Re: how much hp can a 8.75 differential take?
[Re: 7D9LRE]
#1170518
02/04/12 12:06 PM
02/04/12 12:06 PM
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Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
Here's a 489 case that came apart in a demolition derby car last summer.
I have one that looks worse. 30+ year old unit the exploded when I applied a mild 440 and 6 psi of boost to it. it might have 3 teeth left on the ring gear. That car only 60 footed at 1.65, but it was an oollllld unit that had some buzz to it before hand.
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Re: how much hp can a 8.75 differential take?
[Re: rattler]
#1170521
02/04/12 06:04 PM
02/04/12 06:04 PM
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Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
I put a narrowed 8 3/4 under the truck and wondered how long it would last. I think i will be fine untill i get a stickyer tire. The Mickey T's that i have on there now have O traction, or maybe it's the stroker up front. 
cool truck but dude that tank is LOW. And those big M/T are for cruising they are worthless at the track as you already know.
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Re: how much hp can a 8.75 differential take?
[Re: 70Cuda383]
#1170523
02/04/12 08:40 PM
02/04/12 08:40 PM
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Joined: Feb 2009
Posts: 773
Crofton, Ky.
rattler
super stock
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super stock
Joined: Feb 2009
Posts: 773
Crofton, Ky.
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I will probably change tires on my truck this summer, and will probably add a set of cal-tracs at the same time. That should help it to hook a little better. As far as the fuel tank, it is never lower than the bottom of the 8 3/4 center section, so that is not too bad.
1957 Dodge truck, Snakeskin Green with a little stroker motor. 1964 Plymouth Savoy wagon ( my new project)
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Re: how much hp can a 8.75 differential take?
[Re: 62maxwgn]
#1170525
02/04/12 09:20 PM
02/04/12 09:20 PM
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Joined: Feb 2003
Posts: 1,532
crisfield, maryland 21817
82ramIndy493
pro stock
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pro stock
Joined: Feb 2003
Posts: 1,532
crisfield, maryland 21817
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Quote:
Quote:
Go get a Furd 9"...all the racers use them 
Never will there ever be a Ford or GM part in my Mopar. I run over 500 hp to the wheels in a short bed truck with a 4.56 gears with a 493 and 1.47 to 1.50 60foots with Caltracs and my 8 3/4 has never given an issue. My next choice will be a Dana.
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Re: how much hp can a 8.75 differential take?
[Re: 82ramIndy493]
#1170526
02/05/12 01:05 AM
02/05/12 01:05 AM
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Joined: Aug 2011
Posts: 44
Maine, USA
4spdswinger340
member
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member
Joined: Aug 2011
Posts: 44
Maine, USA
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There is another member on here from maine who can tell you 1st hand that they break pretty easy w a 4 speed and a stroker motor. He has broken a couple 3rd members. Broke the pinion rite off. 742 cases.
Life can be like fighting a dinosaur. Very hard
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Re: how much hp can a 8.75 differential take?
[Re: 4spdswinger340]
#1170527
02/05/12 01:58 AM
02/05/12 01:58 AM
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Joined: Jan 2007
Posts: 125
Stockbridge, GA
7D9LRE
member
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member
Joined: Jan 2007
Posts: 125
Stockbridge, GA
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Yes. spiders were welded, 3.91 out of a 74 4x4 truck. At least I got 4 derbies and 2 wins out of this rearend before it exploded. no sign of sloop or anything getting loose before giving up the ghost. Stock '72 440 out of a New Yorker. It would lay rubber threw 1st and 2nd gear on dry pavement.
Last edited by 7D9LRE; 02/05/12 02:04 AM.
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Re: how much hp can a 8.75 differential take?
[Re: 4spdswinger340]
#1170529
02/05/12 02:39 AM
02/05/12 02:39 AM
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Joined: Feb 2003
Posts: 1,532
crisfield, maryland 21817
82ramIndy493
pro stock
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pro stock
Joined: Feb 2003
Posts: 1,532
crisfield, maryland 21817
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Quote:
There is another member on here from maine who can tell you 1st hand that they break pretty easy w a 4 speed and a stroker motor. He has broken a couple 3rd members. Broke the pinion rite off. 742 cases.
Whole different story when popping a clutch on a 4 speed than just launching with an automatic. The other thing is a 742 pinion is smaller in diamenter than the 489 which I run. I am not saying they can't break only that mine has held up fine for 16 years and I would choose it over a Ford Or GM rear anytime. Like I said my next choice is a Dana which the other member should have had to start with with a 4 speed.
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Re: how much hp can a 8.75 differential take?
[Re: 7D9LRE]
#1170533
02/05/12 11:58 AM
02/05/12 11:58 AM
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Joined: Jan 2003
Posts: 75,066
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,066
U.S.S.A.
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Quote:
Here's a 489 case that came apart in a demolition derby car last summer.
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Re: how much hp can a 8.75 differential take?
[Re: 82ramIndy493]
#1170534
02/05/12 12:09 PM
02/05/12 12:09 PM
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Joined: Jan 2003
Posts: 75,066
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,066
U.S.S.A.
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Quote:
Quote:
There is another member on here from maine who can tell you 1st hand that they break pretty easy w a 4 speed and a stroker motor. He has broken a couple 3rd members. Broke the pinion rite off. 742 cases.
Whole different story when popping a clutch on a 4 speed than just launching with an automatic. The other thing is a 742 pinion is smaller in diamenter than the 489 which I run. I am not saying they can't break only that mine has held up fine for 16 years and I would choose it over a Ford Or GM rear anytime. Like I said my next choice is a Dana which the other member should have had to start with with a 4 speed.
this is not a knock at you ....
You have a little misconception in your thoughts about what is stronger . The smallest part of a 742 pinion is the area where the outer pinion bearing is , coincidently the 499 and the 741 are also the same size in that same area , the 489 and the 741 use the same outer bearing . If the 742 broke I'd wager that is where it broke so your theory on the 489 being stronger because the pinion is .125 large under the pinion head doesn't hold up.
In my opinion the 742 is the strongest of the 3 , it's inner pinion bearing has rollers that are about twice the length of the 498 , more like that of the dana 60 and it doesn't have a crush sleeve like a 489, yes you can replace it with a solid spacer. When Chrysler made the aluminum center section they chose the 489 pinion even though the 489 has more gear sets available.
The gear teeth are still the weak point .
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