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Transbrake with 8 3/4 (489 case)

Posted By: Purpleheart

Transbrake with 8 3/4 (489 case) - 11/12/09 09:33 AM

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--uU

Paul
Posted By: SunburstKid

Re: Transbrake with 8 3/4 (489 case) - 11/12/09 09:42 AM

Holy %^$! you got beat by a Jeep!

Thats one fast Jeep!!
Posted By: Purpleheart

Re: Transbrake with 8 3/4 (489 case) - 11/12/09 09:56 AM

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
Posted By: jef408

Re: Transbrake with 8 3/4 (489 case) - 11/12/09 11:20 AM

LAUNCHING THAT HARD WITH A 8 3/4 REAR AND A CLUTCH TYPE POSI,YOUR DEFINATELY GOING TO BE IN TROUBLE SOONER OR LATER,INVEST IN A spool and a dana,save yourself alot of head aches.
Posted By: WILD BILL

Re: Transbrake with 8 3/4 (489 case) - 11/12/09 01:49 PM

Lighter cars seem to be able to get away with an 8 3/4 making a lot of power. If you have to stay with one be sure it's built the best it can to handle it.

A brace is a must, a spool would help. The stock caps can be the weak link. MW caps are a good way to go but have to be "fit" to the case.

Then there are the after market carriers. Alum cases are strong but very pricey and getting hard to find. The Nodular Iron case from mancini is another option.

I'm using a T brake W/ an 8 3/4 and have gone consistant 11.0's W/ 1.51-1.54 60' times. I did destroy a stock case once but I think it was a u joint failure that cuased the chain reaction.

I now have the nodular case and have had no issues yet but my car is considerably lighter.

IMHO, if you can't (or don't want to) get the weight of the car down by at least 800 to 1000#'s I think you'ld be much better served by installing the D 60.
Posted By: dave571

Re: Transbrake with 8 3/4 (489 case) - 11/12/09 05:53 PM

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.
Posted By: Purpleheart

Re: Transbrake with 8 3/4 (489 case) - 11/13/09 07:01 AM

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
Posted By: 70AARcuda

Re: Transbrake with 8 3/4 (489 case) - 11/13/09 07:31 AM

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....
Posted By: Purpleheart

Re: Transbrake with 8 3/4 (489 case) - 11/13/09 08:43 AM

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
Posted By: WILD BILL

Re: Transbrake with 8 3/4 (489 case) - 11/13/09 01:50 PM

From what I've heard getting a 9" to live requires many high dollar componants. Yes they are available but after all that you would probably be around the same money as a Dana yet not near as durable.

Check into the costs related to swapping over to either axle.
Posted By: mistress

Re: Transbrake with 8 3/4 (489 case) - 11/14/09 01:39 AM

Been down that road before with the 8 3/4 and tore it up badly with a t/brake. 3300lb with driver 67 dart 5000 stall and launch at 3400. had a spool in it with 4.56 gears and 30 spline, twisted the housing and axles. now dana 60 with 35 spline and it hold 60 fts of 1.32 no problem, it just adds about 75 lbs more weight.

Mike
Posted By: Purpleheart

Re: Transbrake with 8 3/4 (489 case) - 11/14/09 07:05 AM

The 8 3/4 rearend was in my old car for 8 years running 12.4 @ 109 mph with 1.7 60ft on street tires without a transbrake . It served me well the whole time so when I scrapped that car I kept the rearend for my new 71 AMX that'll be about 1 second faster when I launch on the brake with slicks and actually hook . I've already hurt it with M/T drag radials . I really like the 8 3/4 but I feel it's time for something stronger with an endless supply of aftermarket parts at reasonable prices . The Dana 60 is pretty much bullet proof but I don't want the extra weight so I'm leaning toward a 9 inch . Your comments have helped me make my decision , Thanks guys !

Paul
Posted By: DoctorDiff

Re: Transbrake with 8 3/4 (489 case) - 11/14/09 05:22 PM

A comparable drag style 9" weighs the SAME as a NEW Dana 60 assembly.

The 9" is less efficient and costs more, however.
Posted By: MrMoparRacing

Re: Transbrake with 8 3/4 (489 case) - 11/16/09 01:04 AM

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.!

Attached picture 5607294-FirstRoundsmall.jpg
Posted By: CrAzYMoPaRGuY

Re: Transbrake with 8 3/4 (489 case) - 11/16/09 03:19 AM

Quote:

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--uU

Paul



Your numbers are almost identical to my brother's 1967 Coronet only your weight is about 400 pounds LIGHTER.
He was running an 8 3/4 with a 440, 600+hp and a727 with a brake. He used the trans brake all the time. NO backbrace, NO aftermarket caps!
He had 1.60 60 foot times, I think he went a best of 1.58, and to be honest I thought he was gonna gernade the diff. But he did it year after year.

To be SAFE I would probably go to a Dana 60, as it would allow more improvements in time down the road.
Posted By: dave571

Re: Transbrake with 8 3/4 (489 case) - 11/16/09 05:03 AM

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
Posted By: Purpleheart

Re: Transbrake with 8 3/4 (489 case) - 11/16/09 08:46 PM

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
Posted By: ETASPEN

Re: Transbrake with 8 3/4 (489 case) - 11/16/09 09:37 PM

Dana 60 in it, and forget it...4.30 pro gear, while you're at it for t-brake insurance (drag car only?).
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