REAR END MODS

Overview

When it comes time to build a rear end in a Thirdgen F-Body, you have a few options.  Actually, two main options...either you can rebuild the one you have to handle more power, or you can replace it with a different type of axle assembly.  Those who decide to replace it usually go with either a GM 12-bolt, or a Ford 9".  Both can handle gobs of horsepower without breaking a sweat.  But, they are also a lot more expensive.  And, they often require some pretty extensive rear brake work - especially if your car has rear drums (like mine does).

I decided not to replace mine, but to rebuild it.  I did this for a few reasons - it was cheaper, it was more fun, and i don't think i necessarily needed to go with a super strong rear end.  I'm not putting down any serious numbers, I don't have a manual tranny, and I don't run slicks.  The GM 10-bolt used in Thirdgens isn't the best rear end in the world, but it can be built to be relatively strong.  Here is what I decided to go with, which should be enough for the modest amount of power that my car has:

bullet Complete Cleanup/Restoration - I removed the whole rear axle as one assembly out of the car.  I then took it apart piece by piece (literally).  I replaced just about every single part I took off with a new piece - most of which I had to get from the local dealer.  Once I had it down to the housing itself, I started to clean it up with a sandblaster and wire brushes.  Not fun, but it came out pretty good I think.  Once it was cleaned up, I brought it to a local shop and had them perform all of the internal work.  Once I got it back, I put a few coats of POR-15 on it (see below).
bullet Differential, Gears, Etc. - All internals (and some externals) except for the axles were replaced with new pieces.  Most were upgrades from factory, but some were stock replacements.
bullet Welded Axle Tubes - at the time of the rebuild, I had them do perimeter welds around the axle tubes where they enter the center housing.
bullet Girdle - I added an aluminum rear end girdle to strengthen the whole assembly.
bullet Hardware - all new hardware was used.

 

Here are some shots of the rear end when I pulled it out of the car.  As you can see, it's definitely had better days.

 


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Here are some shots of the newly rebuilt/restored rear end as I was installing it in the car.  Looks a lot better than it did before - especially with the contrast between the black and the red.

 


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Rebuild

Performed by White's Reliable Speed Shop, Cicero, NY

$280

 

 

These are shots of the finished installation of all of the internal components of the rear end.

 


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This is a picture of one of the axle tube perimeter welds.

 



 

 


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Differential

Zexel Torsen T-2 Differential

www.slponline.com

SLP Part #: 64501T

$100 from SLP

There were a couple different options available when I had to pick which differential to get.  It came down to two, the SLP Heavy Duty Zexel Torsen one, and the SLP Zexel Torsen take-off.  When SLP decided to raise the price of the heavy duty one, they made up my mind for me.

The take-off differentials, in case you didn't know, are just what they say...they were literally taken off another car.  Which, makes them technically "used".  That is good because the price is a lot lower than a new one.  But, you may be thinking, "why would I want a used differential?"  Well, SLP made every Camaro SS and Firebird Firehawk, WS-6, etc. from regular Z28s, Trans-Ams, and Formulas.  When they make them into their higher-performance counterparts, they replace the differentials with the heavy duty one I was talking about before.  When they take out the old ones, they sell them for a hundred bucks and make us budget-minded enthusiasts pretty happy.  When they do the swap, the cars usually have less than 10 miles on them.  So, they are used...but just barely.  And, I figured if they were good enough for a brand new Z28 or T/A, then they would be good enough for my car.

SLP Zexel Torsen Take-Off Differential
(click to enlarge)

 

Gears

Motive Gear  3.73 Gears

www.slponline.com

SLP Part #: 64046

$200 from SLP

I went back and forth about ten times before I decided on what gear ratio to use in the rear axle of my car.  It was between 3.42s and 3.73s. 

Here is what I was worried about...

In the 1/4 mile, I only use the first three gears.  If I needed fourth gear, it would be a problem, because the 700R-4 transmission doesn't shift into fourth at wide open throttle (WOT).  There are ways to modify it to do so, but mine doesn't have those modifications.  So, basically, I only have 3 gears to use in the 1/4 mile.  Using some calculations (using tire size, engine rpm, gear ratios, driveline efficiency, etc.), I figured my top speed in third gear with stock tires with 3.42s and 3.73s.  The 3.73s only gave me a top speed of about 108 mph, while the 3.42s would be about 10 or so mph higher (if I remember correctly).  I was worried that if my car ever got faster than 108ish mph in the 1/4, I would run out of steam and just coast past the finish line, instead of accelerating past it.

I finally decided on the 3.73s. They should give me a better acceleration off the line, but a lower top end.  But, if the situation comes up where I run out of steam in the 1/4 mile, then I will deal with it then.  I will either get larger tires, or just figure out a way to increase my redline.

The gears I chose are from SLP.  I chose them because they are a good, high quality gear, and they are known for being quieter than other gear sets (especially Richmond).

SLP Ring & Pinion
(click to enlarge)

Differential Cover

TA Performance Rear End Girdle

www.taperformance.com

TA Performance Products Part #: TA1809

$159.95 from TA Performance

I decided to go with this cover for one reason...it is the strongest cover that you can buy.  The 10-bolt is known for being far from ideal when it comes to performance.  The design is simply too weak for very high horsepower applications.  But, this cover (actually, it is considered a girdle) improves the strength of the rear end by preloading the main bearing caps, and simply by being much structurally stronger than mot other covers available.

The cover also has drain and fill ports in it to allow ease of draining the fluid and filling the differential with fluid.  The flange on it is extremely thick (over 1/2").  The cover also allows an additional 1/2 quart of differential fluid capacity.

 

 

Main Bearing Studs

ARP Main Bearing Stud Kit

www.arp-bolts.com

TA Performance Products Part #: TA1815

$25.95 from TA Performance

 

 

Bearings, Seals, etc.

SLP Differential Installation Kit

www.slponline.com

SLP Part #: 64047

$120 from SLP

This installation kit includes almost all of the components needed to rebuild the rear end.  The only things that you will be missing are the outer axle bearings.  This kit is basically what you would need to replace the differential, and ring and pinion.

It includes the two main axle bearings, as well as the two pinion bearings.  It also includes a shim kit, a crush sleeve, and a pinion seal.  I chose to upgrade to a solid pinion spacer instead of the crush sleeve, which you can also see on this page.  And, there is information about the axle bearings (wheel bearings) and axle seals.

SLP Heavy Duty Installation Kit
(click to enlarge)

Ratech Solid Pinion Spacer www.ratechmfg.com
Ratech Part #: 4111 $20 from Summit Racing Equipent

 

GM O.E. Rear Axle bearings and Seals
GM Part #: 12471606 (bearing)
GM Part #: 554631 (seal)
$41.36 each from dealer (bearing)
$10.93 each from dealer (seal)

 

 

Pinion Yoke

GM O.E. Replacement

GM Part #: 12479030

$85.46 from dealer

 


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Differential Cover

SLP AAM Aluminum Differential Cover

www.slponline.com

SLP Part #: 65004

$100 from SLP

(I DECIDED NOT TO USE THIS COVER, AND WENT WITH THE TA PERFORMANCE GIRDLE ABOVE.)

The 7-1/2" 10-bolt in Thirdgens is known for being the weak link in the drive train, so I want to do everything that I can to help make it stronger.  One thing that adds a LOT of strength is a cast aluminum differential cover.  It adds a lot of strength by being a structural member of the axle housing, nit just a cover like the old steel one was.

This cover also helps keep the differential fluid cooler.  It has cooling fins on the outside, and a cooling "channel" built into it.  You can see these things in the pictures below:

 

SLP Differential Cover
Front View
(click to enlarge)

 

SLP Differential Cover
Back View
(click to enlarge)

 

The differential fluid goes into the square looking hole in the cover and goes out through the two circle holes near the edges.  The fluid is forced up into the square hole by the spinning of the ring gear.  This forces the fluid through the cover's cooling fins and cools it down.