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#525094 - 01/24/08 02:37 AM convert open 7.5 to posi?
Bad Co Offline
Member

Registered: 06/16/07
Posts: 868
Loc: Earth
My 85's got an open 7.5 rear (stock, so 3.73 gears I think). What's the easiest/cheapest way to change to a posi (3.73 or 4.11)? Is it easier to swap the whole rear for a posi one or is it better to just change the carrier? I see lots of posts about using GN or Ford 9" rears but I'm not racing so I think a 7.5 should hold up ok.

I've never done this before, will I need any special tools?

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#525095 - 01/24/08 02:46 AM Re: convert open 7.5 to posi? [Re: Bad Co]
Onebadbowtie86 Offline
Member

Registered: 11/20/07
Posts: 4352
Loc: Traverse City Michigan
you could get a powertrax lock right, intalls in the carrier of your open differential so you dont have to take the diff out of the rear end, theyre only 370 bucks to
_________________________

'86 Monte carlo ss-Frame off resto-mod.
DONE!

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#525096 - 01/24/08 02:52 AM Re: convert open 7.5 to posi? [Re: Onebadbowtie86]
carloss Offline
Member

Registered: 04/22/07
Posts: 991
Loc: Burnaby, BC
my sc has posi with a bent housing. how hard is it to install it in my open SS?

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#525097 - 01/24/08 03:00 AM Re: convert open 7.5 to posi? [Re: carloss]
Onebadbowtie86 Offline
Member

Registered: 11/20/07
Posts: 4352
Loc: Traverse City Michigan
bent housing? like an axle tube or something? anyways you will have to pull the cover, remove the little bolt thats holding the center pin in the differential, slide out the center pin, then you will have to take the tires off and possibly the brake drums and push in the axle shafts, then the c clips will fall out and you can pull out the axle shafts, then remove the 4 bolts that are holding the diff in place and pop it out, reverse for the install, its not to hard but since your taking it out and putting a differnt one in you may have to set it up, shim it correctly, and why its out you might want to have new bearings pressed on. i recommended the powertrax because it would just be easier, if i had an open dif thats what i would do, but i have a reaalll good stock posi!
_________________________

'86 Monte carlo ss-Frame off resto-mod.
DONE!

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#525099 - 01/24/08 03:14 AM Re: convert open 7.5 to posi? [Re: Onebadbowtie86]
Bad Co Offline
Member

Registered: 06/16/07
Posts: 868
Loc: Earth
Powertrax looks good but I'm not sure how it will be on the street? It says it unlocks around corners so I guess it would work.

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#525100 - 01/24/08 03:16 AM Re: convert open 7.5 to posi? [Re: Bad Co]
Onebadbowtie86 Offline
Member

Registered: 11/20/07
Posts: 4352
Loc: Traverse City Michigan
theres a couple other ones out there to to put inside of your open diff, get out the summit magazine
_________________________

'86 Monte carlo ss-Frame off resto-mod.
DONE!

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#525171 - 01/24/08 10:13 AM Re: convert open 7.5 to posi? [Re: Bad Co]
84LS1T56SS Offline
Member

Registered: 12/26/05
Posts: 2701
Loc: Central, Arkansas
 Originally Posted By: Bad Co
Powertrax looks good but I'm not sure how it will be on the street? It says it unlocks around corners so I guess it would work.


It's probably going to make a lot of noise on the street.
_________________________

85 MCSS, 02 5.3/4L60E stock daily driver, (given to daughter-in-law)
84 MCSS, Another stock 5.3/60E.

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#525184 - 01/24/08 10:58 AM Re: convert open 7.5 to posi? [Re: 84LS1T56SS]
Sixtoes1313 Offline
Member

Registered: 01/23/06
Posts: 2222
Loc: Abingdon, Maryland
I contacted powertrax about my car and they said they didnt have anything that would fit our rears at the moment.
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LsX: DO IT~ 11.32 @120mph

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#525230 - 01/24/08 01:44 PM Re: convert open 7.5 to posi? [Re: Sixtoes1313]
boom boom Offline
Member

Registered: 08/16/05
Posts: 273
Loc: Corpus Christi, TX
What? Man I thought they made one for practically every gm application. That sucks! So who makes one that will fit our ride then?

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#525234 - 01/24/08 01:56 PM Re: convert open 7.5 to posi? [Re: Sixtoes1313]
Onebadbowtie86 Offline
Member

Registered: 11/20/07
Posts: 4352
Loc: Traverse City Michigan
 Originally Posted By: Sixtoes1313
I contacted powertrax about my car and they said they didnt have anything that would fit our rears at the moment.



Yes they do, open up a summit magazine, powertrax lockright, they have a 7.5 and a 7.625 for 26 spline axleshafts, also a 28 spline for 7.625
_________________________

'86 Monte carlo ss-Frame off resto-mod.
DONE!

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#525278 - 01/24/08 04:27 PM Re: convert open 7.5 to posi? [Re: Onebadbowtie86]
Bad Co Offline
Member

Registered: 06/16/07
Posts: 868
Loc: Earth
Ok, thanks for the info. I didn't realize there was two types of powertrax. I think the powertrax no-slip traction is what I want (smoother on the street) rather than the powertrax lock-right.

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#525524 - 01/25/08 11:24 AM Re: convert open 7.5 to posi? [Re: Onebadbowtie86]
Roadie Offline
10+ Year
Member

Registered: 04/08/01
Posts: 1535
Loc: Wilmington,N.C
Go to the Richmond Gear web site and watch the video of the powertrax being demonstrated. It's impressive. You just get the clicking noise in the corners. I've also heard that if you floor the gas while in a corner, you can strip the ratchet mechanism.
_________________________
Roadie
1986MCSS

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#525531 - 01/25/08 12:02 PM Re: convert open 7.5 to posi? [Re: Roadie]
TPI Monte SS Offline
Moderator
10+ Year

Member

Registered: 06/24/01
Posts: 5484
Loc: North Jersey
The Powertrax does work great on the street, but you gotta be careful around corners, especially in wet weather. If you punch it while in a corner, it can cause the unit to lock up, and put you in a spin (been there, done that!). Drive it nice, and you won't have any trouble in rain. They are also noisy (even the No-Slip version, which I have) but after 20K miles or so it's quieted down a lot. The noise is mainly just a loud click or pop as it locks/unlocks for tight parking or cornering.
_________________________
SSeeya,
Steve Ragusa - North Jersey
'88 SS - BudgetTourer - ZZ4-cammed 355 TPI, serpentine belt conversion, World Class 5-speed, 17" wheels, 12" front discs, Eibachs/Bilsteins, 1LE lower A-arms, tall lower balljoints, 34mm front swaybar, 3/4" straight rear bar, Celebrity headlights, and more. Sold on 2/28/11.

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#525664 - 01/25/08 09:11 PM Re: convert open 7.5 to posi? [Re: TPI Monte SS]
jigsaw Offline
Member

Registered: 09/02/07
Posts: 3174
Loc: Laredo TX
just out of curiosity? which is better for the strip, open or posi?

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#525693 - 01/25/08 10:14 PM Re: convert open 7.5 to posi? [Re: jigsaw]
ga86aero Offline
Member

Registered: 12/25/07
Posts: 406
Loc: Northeastern Ga
Why not change out a torsen unit out of an S10 or Camaro 7.62 rearend? You can pick one up off flebay for around 100 bucks, and they work great. No cornering noise and it is a pretty staight forward swap out. Although, if you really have a 7.5, you will have to upgrade to the larger splined axles from a 87 or 88 rearend.
_________________________
85 SS Coupe, black, 350 w/ Serp, 700R4, lowered with Global West upper A's, 12 disc on front, 10.5 disc on rear.

86 Aerocoupe,runs great, and original, but needs complete restoration.

It is a proven fact that light is faster than sound. That is why some people appear intelligent until they open their mouth to speak.

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#525706 - 01/25/08 10:31 PM Re: convert open 7.5 to posi? [Re: jigsaw]
SSPARKY Offline
10+ Year
Member

Registered: 12/28/01
Posts: 2943
Loc: Delavan Illinois
 Originally Posted By: jigsaw
just out of curiosity? which is better for the strip, open or posi?


Posi for sure. I have hear of people using an airbag on the inside of the coilspring on the right to keep the the axle from twisting counterclockwise and keeping the tire firmly planted on the pavement.

Disclaimer: Above is hearsay never "seen" it done but sounds good in theory...:) I have airbags on my car I'm not sure how much it helps for traction but it keeps it level when I launch.
_________________________
7.88 @ 86.35mph
Take the Long Way Home


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#525707 - 01/25/08 10:33 PM Re: convert open 7.5 to posi? [Re: ga86aero]
SSPARKY Offline
10+ Year
Member

Registered: 12/28/01
Posts: 2943
Loc: Delavan Illinois
 Originally Posted By: ga86aero
Why not change out a torsen unit out of an S10 or Camaro 7.62 rearend? You can pick one up off flebay for around 100 bucks, and they work great. No cornering noise and it is a pretty staight forward swap out. Although, if you really have a 7.5, you will have to upgrade to the larger splined axles from a 87 or 88 rearend.


Don't get a "gov-lock" posi a.k.a. grenade-lock by mistake!
_________________________
7.88 @ 86.35mph
Take the Long Way Home


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#525709 - 01/25/08 10:40 PM Re: convert open 7.5 to posi? [Re: SSPARKY]
ga86aero Offline
Member

Registered: 12/25/07
Posts: 406
Loc: Northeastern Ga
 Originally Posted By: SSPARKY
Don't get a "gov-lock" posi a.k.a. grenade-lock by mistake!


Well, you could always do a " redneck posi" by welding the spiders up solid. Guaranteed, no popping in the corners.
_________________________
85 SS Coupe, black, 350 w/ Serp, 700R4, lowered with Global West upper A's, 12 disc on front, 10.5 disc on rear.

86 Aerocoupe,runs great, and original, but needs complete restoration.

It is a proven fact that light is faster than sound. That is why some people appear intelligent until they open their mouth to speak.

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#525720 - 01/25/08 10:59 PM Re: convert open 7.5 to posi? [Re: ga86aero]
Onebadbowtie86 Offline
Member

Registered: 11/20/07
Posts: 4352
Loc: Traverse City Michigan
my buddy blew an axle shaft in his 85 s10 winter beater this last spring, i was with him, it has the gov lock, 4 10 gears and a 2.8 carb., spinning one tire fast then BAM! the thing deffinetly works tho
_________________________

'86 Monte carlo ss-Frame off resto-mod.
DONE!

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#526927 - 01/29/08 04:27 PM Re: convert open 7.5 to posi? [Re: Onebadbowtie86]
Bad Co Offline
Member

Registered: 06/16/07
Posts: 868
Loc: Earth
I'm leaning towards the posi...even though I can't install it myself I think it'll be better for the street. Anybody have an opinion on the Detroit Truetrac? Like a posi but no clutches to wear out.

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#526936 - 01/29/08 04:48 PM Re: convert open 7.5 to posi? [Re: Bad Co]
Onebadbowtie86 Offline
Member

Registered: 11/20/07
Posts: 4352
Loc: Traverse City Michigan
its all your choice, the tru trac looks nice, and you have a point of the limited slips wearing out, the one in my 96 plow truck is completely gone, but on the other hand the one in my monte is the original with 175k on it and it works like new, never had it go to one tire, but it hasnt had a hard life and didnt spin its tires to much with the 305(it wouldnt do it to great anyways)
_________________________

'86 Monte carlo ss-Frame off resto-mod.
DONE!

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#527655 - 01/31/08 01:39 PM Re: convert open 7.5 to posi? [Re: Onebadbowtie86]
Turbo G-Body Offline
Junior Member

Registered: 01/17/08
Posts: 16
Loc: Upstate NY
Here is my suggestion, leave the rear open and put the $$ into good control arms. I have had many G-bodies and several 3rd gen F-Bodies and can tell you first hand that if your making a decent amount of power (over 375hp) you will break a 7.5" posi. I have had the carrier split in half, broke numerous axles, broke pinions, twisted housings, then I found that if you leave the open carrier in and go with solid lower arms and adjustable uppers you can adjust the rear suspension so the car plants both tires and acts like a posi. This has been my expirence and I'm sure many others on here have sufferd the broken rear end syndrom. Believe it or not a open 7.5 is stronger than a posi 7.5. Best bet is to just get rid of the 7.5 and find a 8.5 or 9".

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#528470 - 02/02/08 10:10 PM Re: convert open 7.5 to posi? [Re: Turbo G-Body]
valvefloat ss Offline
Member

Registered: 07/07/07
Posts: 120
Loc: St.Joseph, MI
I installed an Auburn unit. It was around 320 bucks. I works great for me. I studied my existing diff before removing it. I also used my Comp Cam gauge out of my cam degree kit and measured the free movement between the ring and pinion. I set the gauge on the ring tooth and slightly rotated the wheel to measure the amount of slop between the ring and pinion. I then pulled the stock unit out, put on the new bearings, followed the instructions from the shim kit, and bolted everything back together. You may need to measure the slop more than one. I took the perspective I would do what it take to do it right. I did not have the money to pay for the work or by a new set of gears along with another unit. I woul not say its easy but its awesome when you hookup, realize everything is working right, and you did it! I've been driving my unit for 4 years now.
_________________________
1985 SS, 358 010, art carr 700r4, Comp Xtreme 4x4 cam, 50SeriesFlows,Afterburner headers, ported SR Torquers, 750 3310 Holley, Auburn Posi, 3.73, 3in exhaust, dual electic fans.

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#528635 - 02/03/08 11:44 AM Re: convert open 7.5 to posi? [Re: Turbo G-Body]
First Project Offline
Member

Registered: 05/06/06
Posts: 889
Loc: Pittsburgh, PA
 Originally Posted By: Turbo G-Body
Believe it or not a open 7.5 is stronger than a posi 7.5.


I don't think the 7.5 open is stronger than the posi, it just stays alive longer cause it won't hook for $#!+!!!!!
_________________________
-Sean- Project "SStealth"

86ttop: That will buff right out.
tri5ss: Maybe with a 36 grit sanding disc!

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#529081 - 02/04/08 12:09 PM Re: convert open 7.5 to posi? [Re: First Project]
Turbo G-Body Offline
Junior Member

Registered: 01/17/08
Posts: 16
Loc: Upstate NY
 Originally Posted By: First Project
I don't think the 7.5 open is stronger than the posi, it just stays alive longer cause it won't hook for $#!+!!!!!


A open rear with the suspension adjusted right will plant both tires, will act like a posi, and will live longer than a posi rear.
Not tring to start a arguement, but when you guys are talking about spending $300 & $400 on a posi for a 7.5", now that is just plain crazy. Buy the suspension stuff, that stuff will work when you find a 8.5" to put in the car.

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