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#1
06-13-2019, 11:28 AM
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8.5 posi carrier, rebuild or replace?
Hey guys. I've recently noticed that my 8.5" posi carrier is getting a bit tired. This is a factory posi out of a late 70's camaro that I dropped in a '71 Buick GS 8.5 axle. When I pulled this from the junkyard I disassembled and the original clutches looked good. I left them in there. I ditched the "S" spring and put in an eaton style spring set. It isnt holding up real well with my slicks at the dragstrip.
I'm wondering what the best option is at this stage? Rebuild the current unit or pony up for an Eaton. If rebuilding is an option, can you please share which clutches (and other parts) you prefer? Thanks.
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************************************* 1968 Lemans. 37,000 original miles. GTO clone. 462ci/KRE 290 heads. UltraDyne 280/288 Solid/850 Qjet by Cliff/Performer RPM/TSP 9.5" in TH400/8.5" 3.42 gears/3950# Race weight/12.58@106 at Bandimere speedway high altitude |
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#2
06-13-2019, 11:36 AM
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I was in the same spot a few years ago..I swapped in an Eaton posi and 30 spline axles.
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 466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
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#3
06-13-2019, 11:37 AM
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I don't think clutch plates are available anymore for the factory units with the square tabs. You can try shimming it or go Eaton.
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
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#4
06-13-2019, 11:46 AM
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Quote:
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74 Formula Below motor destroyed last fall 469, 6X-4's, 72 Intake, Ramair Manifolds. 3 inch exhaust with x-pipe Custom Roller Cam, 1.52 Roller Rockers Quadrajet done by Cliff 3:42 gears 12.061 @ 110.74 12.092 @ 112.43 12.128 @ 111.71 New motor 461 stroker Edelbrock 87 cc dport heads Performer RPM Same Ram Air manifolds, and quadrajet Results will be posted after the track 
Last edited by form74; 06-13-2019 at 12:06 PM. |
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#5
06-13-2019, 11:48 AM
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How much of a weak point are the axles?
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************************************* 1968 Lemans. 37,000 original miles. GTO clone. 462ci/KRE 290 heads. UltraDyne 280/288 Solid/850 Qjet by Cliff/Performer RPM/TSP 9.5" in TH400/8.5" 3.42 gears/3950# Race weight/12.58@106 at Bandimere speedway high altitude |
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#6
06-13-2019, 12:02 PM
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There is a guy making the clutch plates. I forgot his contact on some of the Camaro and Buick also boards I think.
My stock 28 spline with an Eaton posi have a lot of 12 second then 11 second and a few 10 second passes. That said when I freshened the 10 bolt in the 81 I went with a 30 spline carrier and Dutchman axles. Dutchman was the only pnes that would make the brake pilot longer for discs and hubcentric wheels. I also have a 30 spline set up for the 78 when I swap more street friendly gears.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#7
06-13-2019, 12:11 PM
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At the 550 hp level with slicks and a 462 cid the axles are as much of a weak point as are the tack welded axle tubes to the center section!
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#8
06-13-2019, 12:30 PM
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Quote:
I did the same thing but went with the Eaton Trutrac and 30 splines yukon axles
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74 Formula Below motor destroyed last fall 469, 6X-4's, 72 Intake, Ramair Manifolds. 3 inch exhaust with x-pipe Custom Roller Cam, 1.52 Roller Rockers Quadrajet done by Cliff 3:42 gears 12.061 @ 110.74 12.092 @ 112.43 12.128 @ 111.71 New motor 461 stroker Edelbrock 87 cc dport heads Performer RPM Same Ram Air manifolds, and quadrajet Results will be posted after the track
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#9
06-13-2019, 01:11 PM
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Quote:
IMO the OEM axles are plenty strong for a street car. If you running slicks, going to the track or running a manual trans dumping the clutch you have a much greater chance of killing an axle. |
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#10
06-13-2019, 01:22 PM
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Tom of Tom's Differentials(RIP) told me years ago the factory posi will usually break before the factory axles do. Actually told me at my HP at that time I did not need to buy his axles.
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#11
06-13-2019, 01:24 PM
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Looks like an Eaton 30 spline posi and some axles are in my future... Any harm in reusing the stock GM gears and just smacking it back together with the same backlash without touching the pinion gear?
__________________
************************************* 1968 Lemans. 37,000 original miles. GTO clone. 462ci/KRE 290 heads. UltraDyne 280/288 Solid/850 Qjet by Cliff/Performer RPM/TSP 9.5" in TH400/8.5" 3.42 gears/3950# Race weight/12.58@106 at Bandimere speedway high altitude |
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#12
06-13-2019, 03:03 PM
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Quote:
__________________
466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2 373 gears 3200 Continental Convertor best et 10.679/127.5/1.533 60ft 308 gears best et 10.76/125.64/1.5471 |
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#13
06-13-2019, 03:11 PM
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Yes the 30 spline carrier takes a different bearing.
__________________
Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#14
06-13-2019, 06:58 PM
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I am surprised to see so many people using 30 spline axles at 500 + hp / tque.
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#15
06-14-2019, 04:03 PM
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I did this exact same upgrade for the exact same reason just last week. Went with the Eaton True Trac, already had Moser axles.
My clutches were just torched, and the cost of the True Trac wasn't that much more than the clutches.. Enough to make the upgrade worth it to me anyway. I re-used the 3.42s that I had in there.
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77 Trans Am, 469 w/ported E-Heads via Kauffman, matched HSD intake, Butler Performance forged rotating assembly, Comp custom hyd roller, Q-jet, Art Carr 200 4R, 3.42s, 3 inch exhaust w/Doug's cutouts, D.U.I. Ignition. 7.40 in the 8th, 11.61@116.07 in the quarter...still tuning. |
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#16
06-14-2019, 05:48 PM
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This was the site were I found the person selling the clutches. Its an older post so the contact info may be no good.
https://classicoldsmobile.com/forums...upplier-44882/ |
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#17
06-16-2019, 06:33 AM
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The spider and side gears in the factory posi’s are a little “brittle”.
I grenaded two of them in less than a dozen runs with slicks and perfect traction. Went to the Eaton and it’s been fine now for almost 20 years.......Cliff
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#18
06-16-2019, 06:47 AM
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Forgot to add that the Eaton unit are redesigned for a larger contact patch between the side and spider gears plus they aren’t hardened as much as the stock 8.5 stuff.
I was also told it really helps to shim the factory spiders for a tight fit to help them survive better for drag racing. I replaced mine instead of searching for parts to rebuild it, plus the second explosion took out a btand new US Gear R/P which wasn’t cheap.......Cliff
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#19
06-16-2019, 10:57 AM
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__________________
 3 Generations of "Beach Boys Racing" ! Everybody knows somthin. Nobody knows everything ! 1st time on a dragstrip, 1964. Flagstart ! "Thanks for the entertainment." "Real Indians Don't Wear Bowties" |
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#20
06-16-2019, 10:13 PM
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Another vote for the Eaton Truetrac over a the clutch posi.
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"The Mustang's front end is problematic... get yourself a Firebird." - Red Forman |
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