Transbrake with 8 3/4 (489 case)
#523940
11/12/09 05:33 AM
11/12/09 05:33 AM
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Purpleheart
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I'm new to this forum and have a question regarding a 8 3/4 rearend with the 489 case . Will the rearend survive repeated launches on a transbrake at 4000 rpm on slicks with my car running 11-11.5 and hopefully pulling 1.5 60ft ? My car is actually a 71 AMX 401 powered with a manual reverse 904 race tranny and a 8 inch ATI 4000 convertor . It's got a 4.10 with a cone clutch type posi and it weighs 3600 lbs with me in it .I've had it to the track once and it went 11.97 @ 113 with a 1.7 60ft http://www.youtube.com/watch?v=UWSjgTL--uUPaul
71 AMX best time 11.97 @ 113 mph 1.71 60ft
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Re: Transbrake with 8 3/4 (489 case)
[Re: SunburstKid]
#523942
11/12/09 05:56 AM
11/12/09 05:56 AM
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Purpleheart
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It was a lot closer at the finish line but he did beat me . The Jeep is also 401 powered and it's run 11.66 @ 112 with a 1.57 60ft . I had to launch easy on the gas because I lit up a set of 325/50/15 M/T drag radials all the way through 1st gear on 3 passes prior to that one .
Paul
71 AMX best time 11.97 @ 113 mph 1.71 60ft
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Re: Transbrake with 8 3/4 (489 case)
[Re: Purpleheart]
#523945
11/12/09 01:53 PM
11/12/09 01:53 PM
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Joined: Dec 2003
Posts: 5,314 Carstairs, Alberta, Canada
dave571
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Quote:
.... a 8 3/4 rearend with the 489 case . Will the rearend survive repeated launches on a transbrake at 4000 rpm on slicks with my car running 11-11.5 and hopefully pulling 1.5 60ft ?
Not likely. Some have managed to hold it together, but most come a part at the level you are at.
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Re: Transbrake with 8 3/4 (489 case)
[Re: dave571]
#523946
11/13/09 03:01 AM
11/13/09 03:01 AM
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Purpleheart
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I really appreciate your comments guys . After reading them I'm kinda worried about breaking the 8 3/4 . I've already got a problem with it and I haven't installed the transbrake and slicks yet . I'm at the point that I'm seriously considering changing over to a 9 inch . I want to launch my car as hard as I can and find out what it's capable of running . When ordering my convertor , I talked to the tech guy from ATI and gave him all the specs for my car , he said it should run 11.3 . With traction and tuning I'll get there if they don't kick me off the track for not having a cage . I've only got frame connectors and the Arizona body has never had any rust so it's rock solid .
Paul
71 AMX best time 11.97 @ 113 mph 1.71 60ft
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Re: Transbrake with 8 3/4 (489 case)
[Re: Purpleheart]
#523947
11/13/09 03:31 AM
11/13/09 03:31 AM
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Posts: 9,826 las vegas
70AARcuda
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got 71 dart with 360 with 904 transbrake...
car probably weights around 3100 with driver.
using a 4.56 with 10x 29 slicks...have 3 yrs on 8 3/4.
car has ran a best of 11.03 @ 121...but usually 11.20 in heat...with 60 fts in 1.53....
Tony
70 AARCuda Vitamin C 71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield) 71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas) 71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)
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Re: Transbrake with 8 3/4 (489 case)
[Re: 70AARcuda]
#523948
11/13/09 04:43 AM
11/13/09 04:43 AM
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Purpleheart
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If my car weighed 3100 lbs I think I'd be ok with the 8 3/4 . My car is a full weight street car that weighs 3600 lbs with me in it . It seems that the lighter cars aren't having much problems .
Paul
71 AMX best time 11.97 @ 113 mph 1.71 60ft
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Re: Transbrake with 8 3/4 (489 case)
[Re: DoctorDiff]
#523953
11/15/09 09:04 PM
11/15/09 09:04 PM
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Joined: Jun 2006
Posts: 85 Wellington, Ohio (20 minutes f...
MrMoparRacing
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With your combo, I would say that you are good to go with the 8 3/4 like Wild Bill said suggesting to have the housing braced and to remove the posi for a spool. My 1970 Dart with a small block Koffel's Place motor, 904 transmission with a Griner transbrake, 8 3/4 braced rear end with the smaller 742 housing, stock caps, 4.88 gears, spool, 33x16x15 slicks. I have made a best pass of a 9.78 @ 140mph! My 60' times are consistently 1.28 - 1.29 leaving @ 3,000 rpm's! With me in the car and 100 lbs. of ballast, I went over the digital scales at 2,795 lbs.!
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Re: Transbrake with 8 3/4 (489 case)
[Re: DoctorDiff]
#523955
11/16/09 01:03 AM
11/16/09 01:03 AM
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Joined: Dec 2003
Posts: 5,314 Carstairs, Alberta, Canada
dave571
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Quote:
A comparable drag style 9" weighs the SAME as a NEW Dana 60 assembly.
The 9" is less efficient and costs more, however.
I agree. 9" is not light at all.
D60 has a rep as being a heavy pig, and they are heavier than an 8 3/4, but they are not that bad.
I added a second battery, AND a dana, and the car was only 100 pounds heavier
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Re: Transbrake with 8 3/4 (489 case)
[Re: dave571]
#523956
11/16/09 04:46 PM
11/16/09 04:46 PM
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Purpleheart
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Some people have done really good with the 8 3/4 and I did too until my car got faster . I'm looking at it as a long term investment . If I repair the 8 3/4 and put some good axles in it , the cost would be almost half of a aftermarket 9" with a stronger axle housing and center section with good axles . I expect it to be a little heavier but not as much as a Dana 60 .
Paul
71 AMX best time 11.97 @ 113 mph 1.71 60ft
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