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  #1  
Old 06-28-2011, 08:42 PM
Lukes86 Lukes86 is offline
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Default Rear End Information

I need some steeper gears to get my car moving faster. First off, where can I look to find some codes so I know exactly what I have. The vehicle in question is a 1986 Chev Caprice Coupe. Do I need to go as far as prying the cover off? Hopefully all stamps are external, thanks

Luke
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Old 06-28-2011, 09:46 PM
Big Dave Big Dave is offline
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Luke on the front of the axle tube about the middle of the passenger side there should be a bunch of stamped letters and numbers. This is the coded information you seek that signifies which of three assembly plants built your rear end and it tells you when and what parts went into it back when it was new.

In 1986 the overdrive transmission had been out as an option for only two years so most vehicles where equipped with a 2.41 or a 2.56:1 ratio two series Corporate ten bolt differential. If you are lucky enough to have a 2.73 gear or higher numerically (a 3.07 was considered a towing gear) you have the only other differential they offered and any factory gear ratio from a 2.73 to a 4.56 will bolt into it.

Big Dave
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  #3  
Old 06-28-2011, 10:46 PM
Lukes86 Lukes86 is offline
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Alright, I'll post the numbers and letters when I get to the car this weekend. If it happens to be a carrier that we can put up to a 4.56 gear in there, I'd like to change out the whole carrier to incorporate a posi. I was reading up about the Auburn, Dana, and even the Detroit Locker seems interesting. But I think the Auburn carrier is just a limited slip, meaning power will only go to one wheel.. isen't that the same thing as my current one wheel peel I have in there now?
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Old 06-28-2011, 11:08 PM
HockeyFan HockeyFan is offline
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Not exactly. If one wheel is on dry concrete with hot rubber and the other is cold tire on warm butter you may see a one wheel peel. If both tires are the same size and on close to the same surface one may spin a little bit farther than the other. That's assuming you can break both of them loose. I'll need photographic evidence to prove it.
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Old 06-28-2011, 11:40 PM
Big Dave Big Dave is offline
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You have an open differential now. Which means which ever wheel looses traction will slip and spin at twice the RPM of the tire still in contact with the ground.

There are three levels of traction above an open rear end. The first is the limited slip differential like the Auburn Sure Grip or the Eaton PosiTraction. Both use spring powered friction clutch discs or cones to attempt to drive the planted wheel to reduce the differential in the wheel speed.

The second level of performance is an un-locking differential such as an Eaton Detroit Locker which spends 95% of it's time locked up delivering equal amounts of torque to both wheels and unlocks only when you corner as the wheels are pushed in and pulled out by forces applied to the rear tires by the car's motion. An alternative is an Air Locker which is always open until you flip a switch on the dash and an on-board air compressor pumps 300 psi into an internal piston thus locking up your rear end just like a solid spool.

Finally they sell a spool or solid piece of steel that connects the two axles to the ring gear and will not allow one wheel to spin faster than the other no mater what the car is doing. You can not drive a spool on the street as it will break an axle sooner than latter.

As you progress from an open rear to a spool the car's handling changes noticeably. The car will not only behave differently than before when you change a rear end out for something different but the noise and wear it causes on tires and axles changes as well. The factory chose an Eaton PosiTraction rear end to upgrade when replacing an open rear end. The advantage of the Posi is it is fully adjustable from street to full race when you are putting it together, and it is rebuildable as the clutches wear. The same can not be said about the Auburn rear end.

The Detroit locker is noisy, popping and grabbing as the lugs engage and disengage during cornering with the ease of operation dependent upon how hard you corner. Eaton als sells a gear drive (using worm gears which are unique in that they can drive a device but can not be driven by a device: which is the exact opposite behavior exhibited by the planetary gear set in your transmission). This is a quite and efficient differential but torque limited to 600 or under horsepower.

A Dana 60 is a bigger version of the 10 bolt (equivalent to a Dana 30) and the 12 bolt rear end (equivalent to the Dana 44) that GM bought from Spicer to use in all of their cars between 1965 and 1971. Dana and Spicer are two different names that refer to the same company (think of it like a Pontiac and an Olds. Both are different names for the same GM car that they also sell as an Impala or Buick or Cadillac with there being very little substantive differences). The Dana 60 (the largest numbered Dana you can legally use in a car under NHRA rules) is the biggest strongest car differential made (because it is actually a one ton truck rear end). It is lighter than a Ford nine inch when using drum brakes, and stronger in stock condition (as found in a salvage yard). Whats more it requires less horsepower to drive the rear end than the Ford nine inch uses up as lost frictional heat as well.

Big Dave
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Old 06-29-2011, 02:55 PM
Lukes86 Lukes86 is offline
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So it sounds like you're suggesting the Detroit Locker? Will it go into the housing? and will it spline into the 26 spline axles I probably have in there? Or should I just change the gears on that stock carrier and weld the diff..
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  #7  
Old 06-29-2011, 04:22 PM
Big Dave Big Dave is offline
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An '86 Caprice has an 8.5 inch ten bolt rear end with 28 spline axles, not 26 spline axles as found in the 7.5 inch ring gear 10 bolt used under the third and fourth generation Camaro.

Eaton does make a Detroit Locker for your 8.5 inch 10 bolt rear end (it is designed for the bigger 30 spline axles that will slide right into your 10 bolt housing as the factory used a 30 spline axle in all rears after 1994).

http://www.4wheelparts.com/Drivetrai...pn=EAT187C148A

I personally think it is going to be over kill, especially on a stree driven car, but if you have $730 bucks to spend on it they will make one for you (you will have to buy thirty spline axles). If you are racing you need to get rid of the C-clips first so be sure to buy 30 spline axles for Ford Torino bearings.

I personally would recommend an Eaton Posi-Traction unit which uses clutch discs; as that is a much more freindly, streetable rear end (unless you are building a car to live on a trailer and the only driving you do is on Sunday; a quarter mile at a time).

Big Dave
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  #8  
Old 06-29-2011, 09:05 PM
Lukes86 Lukes86 is offline
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Dave, I really think that my car has a 7.5", when I bought a diff cover gasket for it, I told them it was a 7.5" and it fit. Are the gaskets for 7.5 and 8.5 the same? I really want to get those numbers from the axle, so we know what it is. this weekend I'll post them. I'd be really surprised if it was an 8.5 with 28 spline.
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  #9  
Old 06-29-2011, 09:52 PM
Big Dave Big Dave is offline
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No the 7.5 inch is a much smaller Vega rear end that had only a 26 spline axle because mid eighties Camaros were evicorated by a lack of compression, EGR and conversion to OBI ignition control. Since they where not exactly power houses GM decided to save costs so they put the baby rear end under the Camaro mounting it in rubber. I don't belive a 7.5 inch ten bolt would be wide enough to mount under a B-body car if you tried.

Here is a picture of the 8.5 inch ten bolt Corporate rear end.



Note the two square (or triangular since the come out of a round shape) tabs that makes it look as though a straight bar was attached to the rear end and the inspection cover is hiding part of it.



The 7.5 has the same square tabs but they are drilled out so there is a half round hole cut in each ear and looks like this:



Here is a picture of an Eaton Posi in an 8.5 inch rear end with the inspection covered removed so you can see the two ears on the bottom of the case.



Big Dave
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  #10  
Old 06-29-2011, 10:58 PM
Lukes86 Lukes86 is offline
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Dave, don't want to disagree, but I could put money that some 80's Caprice's came with 7.5" Ring gears. I do believe only the police (9C1) and fire department vehicles and possibly special orders came with the 8.5" ring gear. As you can see in my picture that I happened to have on my computer, the two half holed notches in the ears you mentioned.
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  #11  
Old 06-30-2011, 09:05 AM
Big Dave Big Dave is offline
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Yup you have a 7.5 inch rear gear ten bolt. I can see the identifying casting lugs that where machined in the back. Sorry I though a weak rear end and a heavy car was bad combination.

All of my eighties Caprice-Impala cars have 8.5 inch ten bolts. I even acquired another one accidentally (I actually paid for a twelve bolt from a salvage yard, but turns out that it was out of an Olds Vista Cruiser which turned out to be another 8.5 inch 10 bolt, and the yard wouldn't give me my money back when I went to pick it up).

An 8.5 inch corporate rear end is very common (as far as that goes a twelve bolt out of a 1965-71 Impala is available and fairly cheap). I wouldn't spend a dime on a 7.5 inch Vega rear end (that rear end was designed to go under a 2,600 pound sub compact economy car powered by a four cylinder engine).

Big Dave
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  #12  
Old 06-30-2011, 03:17 PM
Lukes86 Lukes86 is offline
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Now I found one here in the local ads, Here is the ad.

http://toronto.kijiji.ca/c-cars-vehi...AdIdZ282196385

Will everything bolt up to this, springs, arms, etc? He said its an 8.5" but its non-posi. I could at least then buy a posi unit. Or should I just look around at the wreckers around here for a 8.5" out of a 90's caprice that will have disk brakes with 30 splines.. the only thing is with that one, will everything bolt up? Has anyone ever done this swap before?
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Old 06-30-2011, 03:59 PM
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As the OP is learning, the 7.5 rear is very common in the 80s Caprice. Dave deals with cop cars, and those got the 8.5 since it was much stronger. Even 91-96 Caprice got the 7.5, with 8.5s being found in cars with the 350 or the 94-96 LT1. Full size RWD Cadillacs actually got 7.5s from 82-89!


The later 30 spline 8.5 will bolt right in. However, it will have the larger 5x5 bolt pattern, while your car has 5x4.75. You can either redrill the axles and the drums for the smaller pattern, or swap your front rotors for the ones with the larger bolt pattern. ALSO, grab the driveshaft from the donor car, since it is a different length from cars with the larger 8.5. To confirm the gear ratio and posi (or not), just look at the SPID sticker on the trunk lid. No need to scrub axle tubes for codes. Look for the "G" codes on the sticker. G80 is posi
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Old 06-30-2011, 05:10 PM
Big Dave Big Dave is offline
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Quote:
Originally Posted by Lukes86 View Post
Now I found one here in the local ads, Here is the ad.

http://toronto.kijiji.ca/c-cars-vehi...AdIdZ282196385

Will everything bolt up to this, springs, arms, etc? He said its an 8.5" but its non-posi. I could at least then buy a posi unit. Or should I just look around at the wreckers around here for a 8.5" out of a 90's caprice that will have disk brakes with 30 splines.. the only thing is with that one, will everything bolt up? Has anyone ever done this swap before?
The disc brake equipped 30 spline 8.5 inch ten bolt rear with a posi out of the SS Impala will bolt directly into your car without any modification. If you buy a replacement 8.5 inch rear end (housing) then it will also bolt in place of your 7.5 inch rear end (there will be a difference in drive shaft length but the spined front yoke should be able to accomodate it).

With a bone yard 10 bolt you can strip it down clean it and then weld the axle tubes fully to the differential housing ...



it is plug welded now.



A clean straight housing can then be assembled with all new bearings and seals. Your carrier will dictate if you need to buy new axles. The 28 spline axles can be reused if you buy a 28 spline posi or you can scrap that idea and buy a 30 spline differential (posi, gear drive, or locker). Before you buy the axles for your new rear end decide if you are going to eliminate the C-clips (required on all NHRA tracks if you run under 11:00 seconds). If you are going for big press on wheel bearings (as installed on a Ford Torino)



then you will need a special axle to accept the Ford bearings.



Big Dave
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  #15  
Old 06-30-2011, 07:31 PM
Lukes86 Lukes86 is offline
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So Dave, are you saying then that a replacement rear end from the impala ss with an 8.5 Will require the driveshaft from that car? I don't really have the time to weld up a whole rear end, although it would be a nice learning experience.. I guess I'll keep my eyes opened for a "G80 on the trunk lid"

Ps, whos the OP, me? and whats an OP anyways lol
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Old 06-30-2011, 08:34 PM
Big Dave Big Dave is offline
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Because the 8.5 inch rear end uses the same "large" pinion as the 8.875 inch 12 bolt rear end it will stick out more than your smaller 7.5 inch pinion would. I am thinking that the difference in length should still be able to be picked up by the front yoke's splines. You need about an inch of travel to keep the yoke from bottoming out inside the transmission with a hard bump.

Other wise you will need to get the drive shaft cut down and high speed balanced to fit with the 8.5 inch ring gear rear end swap. Or as Jason states just grab the drive shaft when you pull the rear end.

Big Dave
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Old 06-30-2011, 08:52 PM
jayoldschool jayoldschool is offline
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You are OP: original poster.

Grab the drive shaft, especially if it is from an SS. They are balanced to a higher speed than the lower limit cars (108mph LT1 civilian, 155mph SS, 9C1 depended on tires).
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Old 06-30-2011, 10:05 PM
Lukes86 Lukes86 is offline
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Alright, thanks guys, looks like I'm set for now. And I guess the SS models I'll be seeking will also have disk brakes too? Cool, better stopping. but, as you guys said it will have the larger 5x5 bolt pattern so I'll have to either get some adapters or drill some holes.
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Old 06-30-2011, 10:21 PM
jayoldschool jayoldschool is offline
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All 91-96 have the 5x5 standard. Last year for 5x4.75 on full size Chevy was 90. Yes, the SS rear gets you rear discs. The 9C1 (police) rear gets discs, too (94-96s only). The 9C1 rear is slightly narrower (only a few mm) than the SS rear. One more note for your shopping: the SS rear gets standard posi. G80 was optional on 9C1.
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Old 06-30-2011, 11:14 PM
Lukes86 Lukes86 is offline
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So if I found a 9c1 with the g80, that would be the best pick, do you know what gear ratio those came with stock?
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  #21  
Old 07-01-2011, 09:37 AM
Big Dave Big Dave is offline
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3.07

Big Dave
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Old 07-01-2011, 11:19 AM
jayoldschool jayoldschool is offline
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Actually, 3.08s. Only if it was an LT1 9C1. L99 (4.3 V8) 9C1s got 3.23s. There was no 3.07 in the 91-96 B/D cars. 2.56, 2.73, 2.93, 3.08, 3.23, 3.42, 3.73 were the various factory installs.
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Old 07-01-2011, 02:19 PM
Lukes86 Lukes86 is offline
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I guess theres only one real way to estimate, spin the wheel once and see how many times the driveshaft spins. Either way though, once I get the unit, theres a lot more to work with, with the 8.5" rear end
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Old 10-03-2011, 03:27 PM
Lukes86 Lukes86 is offline
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Guys I was at the local wreckers today getting some parts for my daily driver, and I spotted an 89 Caprice! Rare to see those things in the scrap yards here. Anyways, I looked at the trunk code and it says its a G92. I looked at the rear diff and it looks like an 8.5" rear. I did some research and it looks like this might have a 3.08 gear in there. I know it states this rear end as a "performance rear end" but it doesn't say if it has posi. I know the G80 has it. So does the G92 have it aswell? I think I'm going to go pull the rear end out of this car later this week. I assume it would have drum brakes too.. Let me know, I think I may have a good donor for my rear end swap!

Luke
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  #25  
Old 10-03-2011, 06:12 PM
Lukes86 Lukes86 is offline
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Also, will I need to grab the driveshaft from this car? because it is an 8.5" rear whereas mine is a 7.5"
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