Rebuilding my 8 3/4

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MuuMuu101

MuuMuu101

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I've got an A body 8 3/4 in my garage. It was a pull out from a junkyard from a 1970 Dart and has an open 489 case with 2.76 gears in it. I'd like to do a complete overhaul to it and rebuild it before I throw it in my 1968 Dart. This includes taking it all apart, powder coating the case, installing new bearings, carrier, and bbp axles from Dr. Diff as well as installing new lines and a disc brake kit (Dr. Diff again). I know it's going to cost an arm and a leg, but I was wondering how much can get done at my garage at home. Is this a difficult task? Unfortunately, I don't have a press at home for the bearings. Are there any other tools needed?

I do have the 1969 service manual, but sometimes I have trouble following that and tend to do better when taken instruction by people.

I'm also unsure if I should get 3.55 gears or 3.91 gears. I do drive the car on the freeway on occasion, but I would like to install an overdrive transmission of some sort to it in the future (may be a couple years before I get to that).
 
I just had mine done and yes an arm and leg. I had the housing and backing plates stripped and powder coated all new bearings and brake parts new lines and vent. I found a 323 sg for 250 (a steal) it had a 323 open 489. I ordered new espo springs and had all the hardware and perches redone to oem. I think the total is going to be around 1500 but I am on a time frame. I am sure you could do it cheaper. Way cheaper.
 
Rebuilding a 489 case 3rd member isn't for the faint of heart. The only reason I say that is it uses a crush sleeve to set the pinion bearing preload with which requires a delicate touch to crush to the right amount to get the right bearing preload. You also need a yoke holding tool of some sort to hold it still while torqueing the nut to 240 ft. lbs. In addition to a press and bearing plate to install new bearings you'll need an inch lb torque wrench to set the pinion bearing preload with and a torque wrench that goes to 250 ft. lbs to torque the pinion nut with. You'll also need a spanner wrench to adjust the side bearing adjusters, a dial indicator to set the backlash. Race drivers to install the races with. One other issue is how to properly hold that 85 lb odd shaped chunk of iron still while your trying to torque the pinion nut to 240 ft. lbs. I built an attachment that fits my engine stand. Before that I clamped them down in my big vise and that sure ain't easy to get them to stay put do to their odd shape and believe me the last thing you want to happen is it fall out on the floor, or worse yet your foot. If that's the only way you have to do it make sure and have a buddy there to help so you don't get hurt or break something.

That's all I can think of right now but I'm probably forgetting something.

You might want to look on YouTube and see if you can find a video of someone doing it to give you an idea what your up against
 
fishy68 said:
Rebuilding a 489 case 3rd member isn't for the faint of heart. The only reason I say that is it uses a crush sleeve to set the pinion bearing preload with which requires a delicate touch to crush to the right amount to get the right bearing preload. You also need a yoke holding tool of some sort to hold it still while torqueing the nut to 240 ft. lbs. In addition to a press and bearing plate to install new bearings you'll need an inch lb torque wrench to set the pinion bearing preload with and a torque wrench that goes to 250 ft. lbs to torque the pinion nut with. You'll also need a spanner wrench to adjust the side bearing adjusters, a dial indicator to set the backlash. Race drivers to install the races with. One other issue is how to properly hold that 85 lb odd shaped chunk of iron still while your trying to torque the pinion nut to 240 ft. lbs. I built an attachment that fits my engine stand. Before that I clamped them down in my big vise and that sure ain't easy to get them to stay put do to their odd shape and believe me the last thing you want to happen is it fall out on the floor, or worse yet your foot. If that's the only way you have to do it make sure and have a buddy there to help so you don't get hurt or break something.

That's all I can think of right now but I'm probably forgetting something.

You might want to look on YouTube and see if you can find a video of someone doing it to give you an idea what your up against
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Well, I'd purchase the entire carrier assembly from Dr. Diff so I'd assume it would already be together, but that all does seem like too much to take on in my garage. I saw a video of a friend of mine trying to set the preload on the crush sleeve and it was not fun. I wish I had the infrastructure to work on stuff. It seems like I may have to send my 8 3/4 out... Bummer.
 
MuuMuu101 said:
Well, I'd purchase the entire carrier assembly from Dr. Diff so I'd assume it would already be together, but that all does seem like too much to take on in my garage. I saw a video of a friend of mine trying to set the preload on the crush sleeve and it was not fun. I wish I had the infrastructure to work on stuff. It seems like I may have to send my 8 3/4 out... Bummer.
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Yes if you purchase one from Dr. Diff it will be assembled. I didn't catch where you said you were going to purchase a 3rd member from him. You mentioned rebuilding what you have and buying parts from him.

Unless your wanting this to be a mostly race car I'd suggest 3.55 gears also. 3.91's are not very highway friendly gears. Their more of a track gear, unless you have a OD trans. or are running 30" tall tires (which won't fit under a stock wheel well) I'd shy away from them.
 
Double M said:
MuuMuu101,

Give me a call if you still have my number, if not PM me.

Russ.
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Hey Russ! How are you doing? I hope you're in good health. I still have your number. I'll give you a call when I'm ready. I'm still trying to figure things out and find the money. :D
 
fishy68 said:
Yes if you purchase one from Dr. Diff it will be assembled. I didn't catch where you said you were going to purchase a 3rd member from him. You mentioned rebuilding what you have and buying parts from him.

Unless your wanting this to be a mostly race car I'd suggest 3.55 gears also. 3.91's are not very highway friendly gears. Their more of a track gear, unless you have a OD trans. or are running 30" tall tires (which won't fit under a stock wheel well) I'd shy away from them.
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That's what I was initially thinking at first. But then I was worried about having too high of a gear when I install the overdrive. For now, I'm sticking with a 25.6" tall tire.

Edit: Just fiddled around with my engine speed calculator and I think I should be fine with 3.55 gears with or without the overdrive. I forgot to bump the rpm a bit due to rolling resistance and aerodynamic drag.
 
Give me a call before you spend any money on having the gears done. As far as powder coating goes, the only person I know that does that is a red headed pool shark and she lives in Tennessee. Her name is Leanna. LOL

Russ.
 
Double M said:
Give me a call before you spend any money on having the gears done. As far as powder coating goes, the only person I know that does that is a red headed pool shark and she lives in Tennessee. Her name is Leanna. LOL

Russ.
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Of course... Give me a week or two to finish up school and I'll give you a call. I believe I already have the connection for powder coating so we don't have to ship my 8 3/4 to Leanna. :D
 
MuuMuu101 said:
That's what I was initially thinking at first. But then I was worried about having too high of a gear when I install the overdrive. For now, I'm sticking with a 25.6" tall tire.

Edit: Just fiddled around with my engine speed calculator and I think I should be fine with 3.55 gears with or without the overdrive. I forgot to bump the rpm a bit due to rolling resistance and aerodynamic drag.
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Those are real short tires so you should be fine either way. If your running an automatic don't forget to add some for converter slippage too. If it's a stock converter I figure 3-4% for slippage. If it's a good size performance converter figure 6-7% if it's a good converter.
 
fishy68 said:
Those are real short tires so you should be fine either way. If your running an automatic don't forget to add some for converter slippage too. If it's a stock converter I figure 3-4% for slippage. If it's a good size performance converter figure 6-7% if it's a good converter.
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They're short because they're going to be wide. I'm looking into a 275/35/18 tire. I will be running my 904 for now with the stock converter. At 60 mph my calculator is guesstimating the engine will be spinning at about ~2800 rpm. I'd assume it be closer to 3200 once everything is factored in. 70 bumps it to ~3260 rpm on the calculator.

http://www.csgnetwork.com/rpmcalc.html
 
MuuMuu101 said:
At 60 mph my calculator is guesstimating the engine will be spinning at about ~2800 rpm. I'd assume it be closer to 3200 once everything is factored in. 70 bumps it to ~3260 rpm on the calculator.

http://www.csgnetwork.com/rpmcalc.html
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It'll definitely be a lot more than 2800 at 60. I have 3.55's in my car with a pretty loose converter and 28" tall tires and it runs 2800 at 60.
 
fishy68 said:
It'll definitely be a lot more than 2800 at 60. I have 3.55's in my car with a pretty loose converter and 28" tall tires and it runs 2800 at 60.
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So my assumption of a 300-400 rpm increase over the theoretical engine speed seems correct.
 
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