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Old 12-24-2012, 05:57 AM
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Caprice Drive Shaft Length & 8.5" Rear End

Hi, i'm in the middle of building my 1980 caprice street sleeper. I have a MINT fresh 1980 4 door with genuine 65000 miles, but it's a 267CI. I'm dropping in a 1973 4 bolt 350 i'm building to go it with a built TH350 trans. My problem is this- I bought a 8.5" rear end out a 1978 caprice (low miles) it's got a eaton posi in very good condition with 2.41 gears (yuk i hear you say) but i want economy an the highway and some get up n go. My 350 build is for 340 hp @ 5500 and 397lbft @ 3500 so it's a torque monster for a 350! Anyhow back to my question i got this rear end and and fitted it to the 1980 but the original rear was 7.5" hence my drive shaft is too long (the 78 shaft was cut up for a friends pickup build, doh!) what length shaft should go between my th350 and my 8.5" rear??? The rear was out a caprice but is non C clip with B.O.P style rear cover, is this a olds type axle??? my 7.5" shaft measures around 58.70"?

Help my guys, by the way i cant measure my trans to axle as the motor is out..

this is the only pic i have of the rear at the moment as it's now under the chevy

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Old 12-24-2012, 06:57 AM
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I'd go back and get the driveshaft.. at the yard you got the rear.. if posable..
if not..
I'd hit the impala forums as the 77-78 impala is a caprice..
and ask there..
ME i'd wait till the engines in and measure...

shouldn't be all that hard to find a 77-82 b body shaft..
in a junk yard
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Old 12-24-2012, 08:03 AM
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That is a Traction Lock differential, not Eaton. There are new clutches available for it now. There is a guy who is reproducing them for $200 a set with shims. I'm glad that you mentioned the bolt in axles. I had thought that the '71 and '73 A body 8.5 was the only one that used those axles.
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Old 12-24-2012, 10:04 AM
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Don't worry about the drive shaft for now. Get everthing else set into place. That is what i would agree with also. If you're looking at making a real sleeper, put in lower gears in the 10 bolt and a good 700 or 200 4r tranny. That will give you a lower gear ratio for the sleeper and high gear for the road. I'd find that drive shaft and put it aside till your ready for it.
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Old 12-24-2012, 02:25 PM
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Quote:
Originally Posted by dwwl View Post
If you're looking at making a real sleeper, put in lower gears in the 10 bolt and a good 700 or 200 4r tranny. That will give you a lower gear ratio for the sleeper and high gear for the road. I'd find that drive shaft and put it aside till your ready for it.
It will sleep allright. A 2.41 with an overdrive...having a final ratio of 0.69 will give an effective final ratio of 1.66. Nothing is gonna pull a gear that tall.
A t 350 or 400 would be Ideal.
If you run an overdrive, you need a 3.55 or lower(3.73 or 4.11) to run it.
Many machine shops a can cut , shorten, phase and weld your shaft probably for 75 or 100 bucks. Get the one you have sliced down and forget it.
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Old 12-24-2012, 05:17 PM
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Like i said, lower rear gear, and overdrive. with overdrive, you have to use lower rear gears. I have 3.73 rear gears in my ten bolt and 200 4r tranny, so my final low gear ratio is 10.22 and final rear axel ratio of 2.50.
With my healthy 355, it moves quickly and floates down the road. lThe best of both worlds.
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Old 12-24-2012, 05:59 PM
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Sorry DWWL , my Bad. I read right through the lower gear part of your post.
I apologize.
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Old 12-26-2012, 04:37 AM
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Thanks guys, i'll get over to the impala forum to ask about the shaft. As i mentioned though i'm using a th350 with the 2.41 so i'm not worried about the 7004r or 200r4 as i already hav the 350. old school chevy drive train! If i had spare funds i'd go 3.08 in that rear end but cant warrant the extra yet, maybe once it's on the road i'll get another rear end, implala ss maybe bonus of rear discs then!
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Old 12-26-2012, 08:28 AM
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You have a 2 series differential in that rear end, so 2.56 is as far as you can go. You would need a 3 series differential for anything from 2.73 to 5.13.
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Old 12-26-2012, 08:58 AM
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Quote:
Originally Posted by big gear head View Post
That is a Traction Lock differential, not Eaton. There are new clutches available for it now. There is a guy who is reproducing them for $200 a set with shims. I'm glad that you mentioned the bolt in axles. I had thought that the '71 and '73 A body 8.5 was the only one that used those axles.
I thought that my posi unit was the old spring eaton type? Isn't a trac lok the older type still with less clutches in the clutch packs? Also what is my 10 bolt, a buick olds type and is that 1 8.5 or 8.2 inch?
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Old 12-26-2012, 01:50 PM
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The Eaton Posi uses 4 coil springs, the Trac Lock uses the S shaped spring. The Eaton Posi can have 14, 18 or 22 clutch discs depending on which clutch set is used. The GM Trac Lock uses 14 discs if I remember correctly. Ford Trac Lock uses 14, but only 6 have friction material on them.

You have the corporate 8.5 10 bolt. Some had c clip axles and some didn't, but that doesn't make it a BOP or Chevy, they are all corporate 8.5.
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Old 12-28-2012, 04:59 AM
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When swapping from 7.5" to 8.5" Rear, the Driveshaft will be 1.00" shorter. So if the 7.5" shaft was 58.70" - 1.00" = 57.70"
As BGH said you're gonna need a 3-Series Diff.
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Old 12-28-2012, 02:01 PM
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Thanks for mentioning that. I forgot that the 7.5 takes a longer drive shaft. Not sure the traction lock is better or not, but that is what i've got in my 8.5 10 bolt nova.
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Old 12-29-2012, 07:34 AM
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The stock 'Traction Lock' case isn't as strong as 'Aftermarket' Eaton etc... but, nothing wrong with them.
Good comparison Pics here >> Rear Photo Guide
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Old 12-29-2012, 10:35 AM
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Nilce looking 64. Had one of those in late 60's saden tan 4 speed ss 327 . Years later i wiched i had it back. Had alot of them nicer cars but that is the way it goes, lThat is why i kept my 1977 concours nova hatchback that i bought new.
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