Transmissions and DrivetrainNeed help with your trans? Problems with your axle?
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How Do I know If I Have a 10-bolt?
Count the bolts on the differential cover.
What Ring Gear Do I Have?
The ten-bolt 7.5 (7 1/2) and 7.625 (7 5/8), the latter introduced in 85, are virtually the same. With the exception of size, all else is the same. For example, all ring gears fit all years of carrier whether they're 7.5 or 7.625.
What Gear Ratio Do I Have?
Jerk the diff cover. The numbers are stamped on the ring and pinion. The RPO’s are usually found in the center console:
41 : 15 = 2.73 (RPO GU2)
41 : 14 = 2.93 (RPO GU3)
40 : 13 = 3.08 (RPO GU4)
42 : 13 = 3.23 (RPO GU5) / Approx. RPM’s at 70 mph--2133
41 : 12 = 3.42 (RPO GU6) / Approx. RPM’s at 70 mph--2255
41 : 11 = 3.73 (RPO GT4) / Approx. RPM’s at 70 mph--2463
Or from Randy’s Ring and Pinion:
Jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posi’s and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.
Axle tube codes can be found in the following link (though rust usually makes them indecipherable, and they, like the RPO codes, indicate how the car was equipped new, and not necessarily what’s currently in place): http://sethirdgen.org/reardata.htm
*Apparently, G80 was an extra-cost option which could be special ordered on any rear regardless of ratio.
**The most reliable way to determine if your car is equipped with a limited slip is to look. That said, this from big gear head: With the tires off the ground and the transmission in neutral, you should be able to turn one wheel and the other will follow in the same direction. This is limited slip or "posi". If the wheels turn in opposite directions, it’s a standard/open differential—OR a worn out limited slip.
Can I Swap in a Limited Slip (aka Posi)?
Yes. Purchase the carrier of your choice and use the appropriate axles for that carrier. For example, the 93-97 Auburn carriers and the 98-02 Zexel-Torsen carriers will swap in as long as the axles used are 28-spline. (A carrier that accepts the stronger 28-spline axles would be more desirable than one that accepts 26-spline).
What Carrier Do I Have?
There are two: Series II is 3.08 down, series III, 3.23 up. Steeper gears, say 3.73’s, can be swapped into a series II with gears designed for such a swap, or by purchasing a series III carrier. (This would be an appropriate time to upgrade to limited slip and 28-spline axles.)
What Is the Width of My 10-Bolt?
Approx. 57" from backing plate to backing plate and 62" from axle flange to axle flange.
How Many Splines Do My Axles Have?
82 to 89 cars have 26-spline axles, though a few 28's may have found their way into late 89 cars; 90 up have 28 splines. After market axles, such as Moser and Superior, can be had from Summit and Jegs. According to big gear head, beware of Alloy USA axles. Apparently the C-clip button isn't cut correctly, which causes problems with C-clip and cross-shaft installation.
How Long Are My Axles?
All thirdgen axles are 30 5/16" long. (Always replace the axle bearings and seals when installing new axles.)
Are Drum/Disc Axles Interchangeable?
Yes, but the drum axle flange will have to be turned down to fit the rotor.* The flange diameter on the drum shaft is 6.0"; the disc shaft is 5.850" and the ID of the brake rotor is 5.900". (Oddly, there is no distinction made between drum and disc when ordering after market axles.)
*The exception to the above seems to be the drum to PBR swap. Apparently LT1 rotors (93-97) have a 6.25" ID which will fit over the drum flange. Raybestos part number 56407.
What Gear Oil Should I Use?
Standard 80-90 weight and a friction modifer (GM P/N 1052358) if the limited slip is an Auburn.* A Gov-Lock or open/standard differential doesn’t require the additive. The rear holds approximately two quarts of gear oil.
*Though some TGO members use a full synthetic, such as Mobil 1 75-90, along with the above friction modifier, both Auburn and Eaton do not recommend synthetics for usage with their limited slips.
Where Is the Fill Plug?
On the pass side of the center casting, close to the axle tube. Fill until fluid dribbles from the hole.
What is the White Plastic Piece on the Center Casting?
Axle vent (press fit) GM 1236317. 82-88 driver's side, 89+ pass side. It should have a cap that allows venting but obstructs foreign material from entering.
Is There a Round Magnet on the Inside of my Diff Cover?
Some models were so equipped, some weren't.
How Is the Rear Fabricated?
With mild steel tubes and a cast-iron center.
What Rear Disc Brakes Do I Have?
82-86* cars are equipped with iron, single-piston Delco-Moraine calipers and 10.5" rotors. In those years, the pass side caliper with its flex line is mounted in front of the axle, the drivers’ side with its hardline to the rear (I've heard that some early model cars, perhaps 82-83, have hardlines to both sides). The parking brake on these years adjusts the brakes, so use it frequently. If yours doesn't function correctly, take note of the "recall": http://members.shaw.ca/crussel/recalls/86c28/86c28.html
See the link to follow for the fix kit: http://www.flynbye.com/catalog/i208.html
90-92* cars are equipped with alum, single-piston PBR calipers and 11.6" rotors (the so-called 1LE or performance package; however, all rear disc brake cars, 89-92*, have them). Both calipers are mounted to the rear and both have flex lines. All four-wheel disc cars, regardless of year, are RPO J65.
*87, 88, and 89 cars with rear discs are equipped with 9-bolts (87 and 88 with the Delco-Moraine calipers and 89 with PBR's).
Why Does My Rear Have Spacers?
The spacer was apparently used on 16" wheels when GM switched from aluminum to iron drums, which created a .187 size difference. The spacer, however, seems to be hit or miss and essentially unnecessary. Even some disc brake cars received them.
Could My Car Have Been Equipped With Aluminum Drums?
Yes (RPO J42), but most were cast iron (RPO J41).
If I Swap From a Drum to a Disc Rear End Do I Have to Change the Combination Valve?* If I Swap From Standard Discs to PBR's Do I Have to Change the Combination Valve?
Yes, for the best brake performance. Use a standard disc brake valve for 82-88 swaps**. Use the appropriate 1LE valve for 89+ swaps into an earlier model year. Either of the 1LE valves can be purchased from Ed Miller at http://www.flynbye.com/catalog/c1_p1.html
*The combination valve is often called the proportioning valve; however, the proportioning valve is only one section of a block which also contains a metering valve and a brake light warning switch.
**Apparently the 82-83 (I've seen reports of some as late as 85) cars have SAE fittings unlike the metric fittings on later cars. Moreover, the alum valves look nothing like the earlier cast iron ones and the line connections are different as well. Note post #1 and #2 of the following link for a comparison of the early and late valves: http://www.thirdgen.org/techboard/br...rop-valve.html (disc/disc prop valve question......) Note: There has been verification that in later years some of the old-style combination valves are metric.
In the 3rd gen Camaro and Firebird welding the axle tubes doesn't help much. Amlost all of the torque is transfered into the torque arm, so there is very little twisting in the tubes.
There isn't a lot that can be done for the 10 bolt. It's just a small rear end and you can't get past that. There are a few things that can help a little. A few upgrades like an Eaton posi, 28 spline axles and a T/A Performance aluminum cover will help some, but not much. As always, correct set up of the ring and pinion gears is VERY improtant.
I didn't want to post something like this up, But, I'm looking at getting a 10 bolt rear with 4.11 gears, and a 8" Pinion gear from a 60's Chevelle... Is there any light of hope that these will work on my 91 Bird? Thanks in advance.
ps, Gear Head, How much $ are the Mosers running? I'm guessing a few grand?
The ring gear will be 8.2 inches. The pinion gear will be much smaller than that. The Chevelle rear end will not fit your car without a lot of fabrication work. There is no mount for the torque arm on the Chevelle rear end.
The Moser is over $2000. I don't have my price sheet with me right now, but I can look it up later. There are several options for the Moser rear ends that affect the price.
The ring gear will be 8.2 inches. The pinion gear will be much smaller than that. The Chevelle rear end will not fit your car without a lot of fabrication work. There is no mount for the torque arm on the Chevelle rear end.
The Moser is over $2000. I don't have my price sheet with me right now, but I can look it up later. There are several options for the Moser rear ends that affect the price.
Can I use a pinion yoke from a 10 bolt on my borg warner 9 bolt?
the 2nd gen 10 bolts...are they the same width as the third gen rears? Besides the need for different brackets to be welded on, is the swap easy? What did you do for the torque arm mount?
Major questions here, I didnt see anything about the 3.27 (RPO code GW6) thats what I have in my 87 Iroc. Just called the dealership & they said it was the 7.75" but I cant find anything for that rear end. I am planning on moving up to 3.73 gears since My car is slatted to go in to pinks all out this summer.
Major questions here, I didnt see anything about the 3.27 (RPO code GW6) thats what I have in my 87 Iroc. Just called the dealership & they said it was the 7.75" but I cant find anything for that rear end. I am planning on moving up to 3.73 gears since My car is slatted to go in to pinks all out this summer.
3.27 would be a 9-bolt.
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
the recall on cars with rear discs equipped with delco moraine calipers. does the dealership only have to fix the recall if the car is equipped with a manual transmission?
the recall on cars with rear discs equipped with delco moraine calipers. does the dealership only have to fix the recall if the car is equipped with a manual transmission?
Yes.
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
I have a 10 bolt with 2.73 gears and i'm wanting to switch to 3.73s or 3.90s. do i have to order a gear with a 2 series carrier? There are many different kinds of 10 bolts and i have no idea which one is equipped on mine. after i blew a 3.42 kirsch auto put this one in with limited slip and stock 2.73s. what can i do to figure out the right gear to buy?
I have a 10 bolt with 2.73 gears and i'm wanting to switch to 3.73s or 3.90s. do i have to order a gear with a 2 series carrier?
There are two: Series II is 3.08 down, series III, 3.23 up. You have a series II. Steeper gears, say 3.73’s, can be swapped into a series II with gears designed for such a swap, or by purchasing a series III carrier. (This would be an appropriate time to upgrade to limited slip and 28-spline axles.)
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
There are two: Series II is 3.08 down, series III, 3.23 up. You have a series II. Steeper gears, say 3.73’s, can be swapped into a series II with gears designed for such a swap, or by purchasing a series III carrier. (This would be an appropriate time to upgrade to limited slip and 28-spline axles.)
JamesC
Ok thanks alot, I do have limited slip, but how do i know which 10 bolt i have? did they only make certain years with 2.73s? i either have 7.5" or 8.5" correct?
Ok thanks alot, I do have limited slip, but how do i know which 10 bolt i have? did they only make certain years with 2.73s? i either have 7.5" or 8.5" correct?
You might reread the FAQ: The ten-bolt 7.5 (7 1/2) and 7.625 (7 5/8), introduced around 86, are virtually the same. With the exception of size, all else is the same. For example, all ring gears fit all years of carrier whether they're 7.5 or 7.625.
A thirdgen was never equipped with an 8.5.
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
You might reread the FAQ: The ten-bolt 7.5 (7 1/2) and 7.625 (7 5/8), introduced around 86, are virtually the same. With the exception of size, all else is the same. For example, all ring gears fit all years of carrier whether they're 7.5 or 7.625.
A thirdgen was never equipped with an 8.5.
JamesC
Right, but my cars been replaced with a 10 bolt and all i know is that it has 2.73 gears. do 8.5" 10 bolts not fit my car?
Right, but my cars been replaced with a 10 bolt and all i know is that it has 2.73 gears. do 8.5" 10 bolts not fit my car?
If your car is a 92, the OE rear is a ten-bolt with a ring gear of 7.625. Just an FYI: There is only one 10-bolt; early cars have a ring gear of 7.5, later cars a 7.625. The 10-bolt will have a variety of gears, from 2.73 to 3.73 and be equipped with either drums or discs. IIRC, the 8.5 or whatever won't fit without major modification.
JamesC
__________________ "There are more things in heaven and earth, Horatio, / Than are dreamt of in your philosophy." Hamlet
"Convictions are more dangerous enemies of truth than lies." Nietzsche
__________________ New Custom Rally Red paint , Custom Black racing stripes ,Open-air 14 by 3in. Spectre Element & Spectre X - Stream filter top /Goodmark Steel Cowl Hood /3in. American Thunder Flowmaster Cat Back / Magnaflow Cat / Corvette servo upgrade/ Extra manually switched Front Fan with 180 Thermostat / Derale Engine oil -Trans. combo Cooler ,28 spline Eaton Posi, 28 spline axles & gear ratio changes to 3.42 with L.P.W. Ultimate 10 Bolt cover.
Last edited by ronusmcmma; 12-08-2011 at 02:35 PM.
Reason: add image
im not going to race my car.. i just go out cruising. im looking for 300 to 350 to the wheels. i want to rebuild my drive train b4 i put in my 350 just wondering if i could save some money on my rear getting these two items
You can use a 28 spline Detroit locker and 28 spline axles in your rear end. Why did you choose the locker over the Eaton Posi if this is just going to be a cruiser?
500 bucks is alot... this locker is like 375.... i hear good things about detroit locker. thanks alot im going to buy this now im tired of having a peg leg
I didn't check the link before. That's not a Detroit Locker, it's a Detroit Truetrac. Big difference. Be sure that you get bearings and shims for it so that you can set the backlash and bearing preload.
What would I have to do to my 92 rs Equiped with a 454 and t-56. Like you said before it should be a 10 bolt. But it's a non posi. I want to make it posi, what is the cheapest proffesional way of doing this?
There is the hard to find replacement that i had at one time. They are priced right, but in the late 80s early 90s, GM did offer and sell several dana 44 rearends that were the 8.5 ring and pinion. They will take what most dish out for a street car. I sold mine since i got a 12 bolt Moser, but the parts are there for them, but they are just not easy to find.
This is what the cover looks like if you ever see one in the junk yard.
If I Swap From a Drum to a Disc Read End Do I Have to Change the Proportioning Valve?
Yes, for the best brake performance. Use a standard disc brake valve for 82-88 swaps*. Use the appropriate 1LE valve for 89+ swaps into an earlier model year. Either of the 1LE valves can be purchased from Ed Miller at http://www.flynbye.com/catalog/c1_p1.html
*Apparently the 82-83 (and maybe 84) cars have SAE fittings unlike the metric fittings on later cars. Moreover, the 84-92 valves look nothing like the earlier ones and the line connections are different as well. How this would affect a swap I’m unsure.
JamesC
James,
I've swapped a PBR rear from a '91 Z into my '87 Sport Coupe. I tried to swap the proportioning valve today, but as you have mentioned above, the proportioning valve fittings are different. Looks like in '87 they used extra fine threads, and in '91 they used standard threads. I went to Napa today to try and get an adapter, the best he could come up with is this: NAPA adapter
Do you think this will work, or am I going to have to trade the '91 proportioning valve for a valve from a 88 or older car with rear disks?
James,
I've swapped a PBR rear from a '91 Z into my '87 Sport Coupe. I tried to swap the proportioning valve today, but as you have mentioned above, the proportioning valve fittings are different. Looks like in '87 they used extra fine threads, and in '91 they used standard threads.
You need the first design proportioning valve. Ed Miller stocks them. Try the following link:
Should almost be mandatory to read stuff like this before you register 
.
New Custom Rally Red paint , Custom Black racing stripes ,Open-air 14 by 3in. Spectre Element & Spectre X - Stream filter top /Goodmark Steel Cowl Hood /3in. American Thunder Flowmaster Cat Back / Magnaflow Cat / Corvette servo upgrade/ Extra manually switched Front Fan with 180 Thermostat / Derale Engine oil -Trans. combo Cooler ,28 spline Eaton Posi, 28 spline axles & gear ratio changes to 3.42 with L.P.W. Ultimate 10 Bolt cover. 
