building 8 3/4 489 section

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  1. Buschi340

    Buschi340 Well-Known Member

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    having an empty spare center section makes me think building an extra set to Change. Currently i have the same section with a 4.10 Ratio makes me run 12,7 with a 5 Speed but just using 3rd gear @ 5800 rpm in the trap. Wanne go quicker. So Ratio has to be shorter. 4.56 or even shorter? DrDiff shortest is 4.56, Mancini has a 4.86. from US gear ( who is that?) Need advise here and what brands to order to have a reliable diff for
    • ring & pinion ( how many splines best ), best Ratio? best brand?
    • sure grip ( i always been happy with clutch type ),
    • bearings and bolt sets,
    • yoke - Billet? Steel? ( 1350 / 7290 conversion? or just 7290? )
    • crush sleeve eleminator kit ( containing all shims ?)
    • girdles
    • U Joints
    • what else?
    never did this before and i am in the states next month and can take all with me... :) so i Need a complete Shopping list. And a racers advise on the Ratio to use... :)
     
  2. 65 Dartman

    65 Dartman FABO Gold Member FABO Gold Member

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    I can't help you with your questions but did have a question for you - what 5 speed are you using?
     
  3. Buschi340

    Buschi340 Well-Known Member

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    Hahaha, r154 toyota supra. Engine was 340, now 6.1 HEMI
     
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    • 65 Dartman

      65 Dartman FABO Gold Member FABO Gold Member

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      Thanks for the info!
       
    • j par

      j par Well-hung Member

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      If the rear end or the center section is just for drag racing I would highly consider a spool which would be lighter cheaper and probably stronger and more predictable than a Sure Grip. Food for thought...
       
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      • Buschi340

        Buschi340 Well-Known Member

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        You are right with racing but I drive approx 200mls to the races with the car. I don't trailer...
         
      • Coronet 500

        Coronet 500 Well-Known Member

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        Solid pinion spacer for sure. My thoughts are basically if you have "the must go faster bug" then over build it now. I would go with a forged or billet, bigger than 7290, yoke. A spool would be ok for the highway and think about 35 splines, I would back brace now and straighten with new ends if the finances are there. This way no matter what you do in front of the axle you'll never have to worry about that failure not getting you home, almost like insurance.
         
      • daveakre

        daveakre Well-Known Member

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        I think he's just talking about building another center section, not a whole new axle.

        For a car that's only going 12's, all those billet parts are probably way overkill. I would still consider running a spool on the street if your tires are tall. (28"+) The best way to pick gears is to use a calculator to help you figure out what your theoretical top speed in 4th (or 3rd on an auto, whatever 1:1 is) will be. Ringpinion.com has some helpful pages for that. Figure out what mph you will eventually want to trap in the 1/4 and gear the car so you'll be right around redline at the stripe.
         
      • j par

        j par Well-hung Member

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        20151014_104921.jpg I'm disputing the only 12 second comment. I was just under 12 and built the 489 case and it wasn't the axle or the spool it was the caps in the back holding the ring gear and spool. And this was a 4 speed car or 5-speed it doesn't matter, it unloads and reloads the rear end between every gear it is very hard on the rear end. You can see my threads wear I never even tried to 7 and a quarter the eighth and a quarter lasted quite some time and I sold it before it went out and I built a 489 case 8 and three quarters full new gears blah blah blah and it was toast in 30 passes or less. with a 4 Speed car I would build a Dana if I want insurance like I did. Another one of my expensive lessons I'd like others to avoid. Do it right the first time and be done. Especially if you have the bug to go faster. For me it was 1200 bucks for the eight and three quarter and 1200 bucks for the Dana.
         
        Last edited: Sep 3, 2016
      • JBurch

        JBurch Well-Known Member

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        If you haven't already; check this out.......www.doctordiff.com
         
      • j par

        j par Well-hung Member

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        Thats where all my aftermarket stuff comes from- 8 3/4 and dana...
         
      • justinp61

        justinp61 Well-Known Member

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        If I were building an 8 3/4 I'd start with a new nodular iron case.
         
      • sst3193

        sst3193 Well-Known Member

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        I put a Dana in my car when I built it to go racing. Big torque kinda had me thinking I could bolt thru the back, like the aluminum covers, that are available for Dana, 12Bolt and 8.8. Put big set screws on the caps and the housing may help hold everything together.
        What Y'all think?
         
      • A body

        A body SLO-KID

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        we went D-60 in both our cars when we went trans brake. My old Mirada had a truck D60, and my dads Duster (now mine) we got a S60 from Cass at Dr. Diff. When setting up gears the S60 is sooo nice with side adjusters rather than the shims. That said.... "IF" I was going after a 8.75 (not a good move with a stick imho....) I'd go the new modular piece too.
         
      • j par

        j par Well-hung Member

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        I'm not convinced and of course this is with no true World research butt a bolt coming off of an aluminum case is going to do much of anything for the kind of horses were talking here that did the damage to that 8 3/4 I showed the picture of. As we all know where there's a will there's a way and one of my favorite quotes from one of my favorite movies "time and pressure".
         
      • D-50394

        D-50394 Well-Known Member

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        Last night I broke my drivers side axle. It has a 9 in with after market 28 spline axles. I guess I need to upgrade to 31 or 35 spline.
         
      • justinp61

        justinp61 Well-Known Member

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        So how many horses do you think broke your 8 3/4?
         
      • justinp61

        justinp61 Well-Known Member

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        D go ahead and put 35 spline axles and spool in and be done. What pinion support do you have?
         
      • j par

        j par Well-hung Member

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        According to my time slip 375 to the wheels and I don't think - I know it broke. Brand new from dr. Diff ring and pinion spool and bearings. set up by the most reputable rear end shop here in Portland. And I added that to get to the quick about the next two questions were they old gears and did I set them up myself.
         
      • D-50394

        D-50394 Well-Known Member

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        I don't know what pinion support it has. It is what was in it when I got it. I probably need to go to a lower gear also. It has 4.56 now and only crosses the finish line around 6400 rpm. It made peak hp at 7300 on the dyno.
         
      • justinp61

        justinp61 Well-Known Member

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        Weight seems to kill 8 3/4 along with HP. I ran mine with 450HP and 3240 lbs for years and never had any issues, it went low-mid 7.20s with low 1.50 60'. The second pass it hooked with the 408 it broke the ring gear, couldn't stand 1.38 60'. There are guys running way faster and making them live, Thumper ran 9.70s with his and just went to a nodular housing so it can and is being done.

        If I was running a low mid 7 second fairly heavy car I wouldn't hesitate to run another one.
         
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        • Buschi340

          Buschi340 Well-Known Member

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          do you really think the centersection of a 8 3/4 is so weak? I am having this C/S in the car since 2001 ( bought the car )guess it is in since the car has been built in 1972. was from 72 to 2015 a 3,23 R&P and 4.10 just the last year. No wear, no damages. All what broke is the clutch ( worn out quicky ) and the rear U Joint this July. ( 7290 ).

          J Par, i don't think it is the power thru the Manual gear box that made the caps break. Maybe overtorqued, invisible cracks inside thru the years? Scary anyway...

          I don't wanna go the DANA way. Super expensive and I can't Change the ratios between the races for Long Autobahn Cruises... :)

          Do you think a swap to 4.56 is significant or should i step to the next shorter? Ring and pinion manufacturer are not the same in Quality. Who is the best in your eyes?

          will try the calculator from above.
           
        • justinp61

          justinp61 Well-Known Member

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          IMO 8 3/4's are good rears and there are thousands of fast cars running plenty of power running them. I've only heard of a few ever breaking on the street in the 40 years I've been messing with them, mainly because there isn't enough bite on a public road.

          I have a 8 3/4 center with a spool and 4.57 gear that came out of a friends Duster that ran 7.70's (1/8) if you're interested.
           
        • Buschi340

          Buschi340 Well-Known Member

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          i WOULD be interested if I would have a cheap way of Transportation. For now I just look for the internals ( and yoke ) that would fit my luggage on the flight back. but thanks anyway... my best was 8.27 on the 1/8 btw with the 4.1 gear ( 5800 rpm approx in the traps and shifting )
           
        • justinp61

          justinp61 Well-Known Member

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          Understood, these things are heavy. Your car is probably 3300-3400 pounds with you in it? Don't be surprised if you shuck some teeth of the r&p on a hard almost dead hook launch. Keep an eye on the pinion, if you start feeling any front to back movement in it pull it out and have it set up again.

          Jpar how heavy is your car with you in it?
           
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