Changing a standard rear to a Limited Slip

[BabylonBob]

I took the differential cover off the back of the axle housing and there is a speed sensor reluctor wheel next to the ring gear. The 2002 Pontiac Service Manual (Volume 1 of 3) indicates that the rear is a non-traction control rear. Also on the outside of the ham there is a speed wheel sensor mount in the top of ham portion of the banjo just above the reluctor wheel. However there is a TCS (traction control switch) in the floor of the console (what does it do).

The Pontiac manual say a standard differential case cannot interchanged with a limited slip differential case. Also that a traction control rear ha the reluctor rings permanently attached to to each drive axle.

Will I have possible problems with readings from the speed sensor because of the different size of the reluctor ring from a 3.08 (Series 2) to a Series 3 carrier?

I’m looking to convert this basic coup Firebird from a 3.08 standard rear to a 3.73 limited slip.

Any Ideas?

[bigbrian442]

Re: Changing a standard rear to a Limited Slip

You sure it's not a second gear start switch on your console? You need to do more research on the limited slip, just about everything you said is wrong.

[ssms5411]

Re: Changing a standard rear to a Limited Slip

You can also get GM Motive gears on ebay for pretty cheap , I think I paid $150-160 shipped for my 3.73's. LSD's will be alot higher new , but used you can pick up a LSD for $150 to $200. Like Brain said , you need to do your research before doing anything though so you know what to get. Unless you want a shop to charge you $1200 for gears and a LSD install , ewhen you could of just paid $300+ for parts and $300 for labor , about half of what they would of charged you.

[BabylonBob]

Re: Changing a standard rear to a Limited Slip

The switch is labled TCS. There is only one brake line to the rear, so there's no traction control on the rear. This is V6 not a V8 which would have two axle sensors (NW9).

What else do you need to know?

[BabylonBob]

Re: Changing a standard rear to a Limited Slip

I want a cluch type limited silp (auburn)- not a helical or a Zexel Torsen. The Zexel Torsen will not swap out with a standard differential.

The ring gear is a 7-5/8” diameter. I included the 3.08:1 gear ratio so you would know that this is a Series 2 Case (3.08:1 and down).

Maybe you are working with a 3.23:1 and higher gear ratio which would be a Series 3 case that would not present these situations.

Also another name for the reluctor ring is a Tone Wheel (it’s for the anti-lock braking system) and it is fitted to the outer diameter of the ring gear flange.

Do you know the spine count on your axles?

What LSD manufacturer did you use to swap out a standard differential case?

Are you working with Series 2 or 3 casing?

What is the diameter of your ring gear?

Did you install a new speed sensor reluctor wheel?
Did you make your ABS speed wheel sensor operable (the one on top of the banjo)?

[T-Mill]

Re: Changing a standard rear to a Limited Slip

Why do people ask questions and then get so pissed and defensive when they're given an honest answer?

[pace2006]

Re: Changing a standard rear to a Limited Slip

It obvious from the picture of the engine above (V-8) that you are not V-6 enthusiast which would explain why you said everything I noted was just about wrong. You most likely have Series 3 axle housings which would explain you’re unfamiliarly with the Series 2 axle housing.

Making assumptions... makes you look like a, well, you know how the saying goes.

First off... the 93-02 rear differential housing is a 7.5" or 7.625" (either interchanges), no matter what type of differential is within; limited slip (note posi) and open. This means that any 7.5"/7.625" differential can be swapped in, no matter of its type. Both clutch-type differentials like Auburn and Eaton, and helical types like Torsen will drop in no problem.

All late model (98+) 4th gen rear axles have 28 splines, whether V6 or V8. This is why the driveshaft and rear ends can be interchanged between trim models. ABS and traction control rears can be swapped, but are not a direct drop in ordeal. Search for the difference between a 3 channel rear and a 4 channel rear.

You mentioned your Firebird came with 3.08 open differential. This means that it has a Series 2 carrier (used on only 3.08s in V6s and numerically lower gearsets in V8s), and will need to be swapped out for a Series 3 carrier (used on gear sets that are 3.23 and numerically higher). You can use either Auburn, Eaton, or Torsen differentials for this.

You will also need a different size reluctor ring for the Series 3 carrier and different gears, otherwise your ABS will not work. Reluctor rings are not permanently attached to the differential. My replacement Torsen was used and didn't come with one at all.

I'd suggest you take a look through the threads and stickies in the Drivetrain section of this forum. Your FSM can only give you so much detail on the options available on your car, but doesn't give the specific options that your individual car has. The information on this forum will not only answer your questions, but show your options for upgrading. This topic has been discussed several times on this forum.

[ssms5411]

Re: Changing a standard rear to a Limited Slip

Well said Pace and T-Mill , if they know so much why even post , either your going to use a 2 series (which suck ) or go to a 3 series and just buy your LSD and yes I would install a new reluctor ring and new seals and bearings. Also a T/A cover with a stud kit is nice also , will help the rear last longer. Also Bigbrain knows alot about these cars whether its a V6 or V8 they have the same rear end setup, so it makes no difference. You'll see BigBrian on almost all posts on rearend setups, and other V6 threads in trannies, engines , exhuast ETC. so he knows his stuff, so does Pace and T-Mill.

[BabylonBob]

Re: Changing a standard rear to a Limited Slip

Thanks for the time you put in Pase. That’s a wealth of info and answered every question that I had, and then some (Search for the difference between a 3 channel rear and a 4 channel rear). I will find out the differences.
I will also look through the related threads and stickies to pick up additional pointers.

I’ve been using Auburn, they are very forgiving and not difficult to rebuild. The Torsen uses parallel axis helical gearing for its axial separating force with planetary gear separation force for the radial. They can really hold in there, but when they go, their gone.

I will scrap the Series 2 carrier (which suck) and pick up a Series 3 carrier from Cleveland Pick-A-Part. They have a couple of 3.42 LSD (Non-Tracking) rears in stock at $375 each (plus shipping). I'll swap out the gears before installing the rear. It will be a lot easer working on it while its out of the car.

And SSMS, I will take your advice and pick up a T/A cover with a stud kit.

Thanks for the info, you guys have been a great help.

[BabylonBob]

Re: Changing a standard rear to a Limited Slip

Well I checked out the differences between a 3 channel rear and 4 channel rear:

The 3 channel rear is what I have – Non-Tracking with a single replaceable press fit reluctor ring located on the differential flange next to the ring gear with a single ABS sensor located on top of the ham.

The 4 channel rear is a Tracking Control Rear with two reluctor rings; each one permanently attached to each axle with two ABS sensors, one at each end of each axle tube.

The Series 3 carrier that I ordered is a 3 channel Non-Tracking axle housing.

[ssms5411]

Re: Changing a standard rear to a Limited Slip

You shouldn't have any problems then if you got a 3 series. I would also look into Royal Purple gear oil , so far its been great and no need for additives since its in the oil itself.

[BabylonBob]

Re: Changing a standard rear to a Limited Slip

Will do SSMS.

Upon a little more investigation I found the following:
Like Pace said, there is no difference in the axle housings, just the carriers. The difference in the carriers is in the thickness of the flange where the ring gear mounts. The thickness difference is not about strength, but about design of the gear sets. The lower numerical gear sets have a smaller pinion gear (less teeth) and require a thicker carrier to take up the distance between the ring and pinion gears.

The stock axle housings series 2 and 3 should be able to hold up to 350-400 rear wheel horsepower with street tires. However if you are planning to run slicks or will have over 350-400 rear wheel horsepower, it looks like you should upgrade to an aftermarket housing.


I was also concerned about the difference in the size of the reluctor rings causing and improper signal to be sent to the PCM and screwing up the ABS. But I was told that the reluctor is going to transmit actual road speed to the computer and abs module, just like your old one did. That it does not matter what the gear ratio is; the output is still actual road speed. The only area of concern is programming the engine and transmission control computer with the correct rear gear ratio so vss signal speed matches the rear axle speed sensor. But that reprogramming can be done with a Hypertech programmer.

I also want to know how the traction control system works on a 3 channel rear. From what I can understand the traction control system uses one set of valves to actuate the rear brakes for the abs system. The traction control system looks at the wheel speed sensors front and rear and the vehicle speed sensor in the transmission to calculate wheel slippage for the traction control. If traction control is needed, the pcm will start cutting fuel to the engine by randomly turning off fuel injectors to limit engine power until traction is once again achieved.

[ssms5411]

Re: Changing a standard rear to a Limited Slip

Plus it pluses the front brakes so the driver can still maintain control of the vehicle somewhat, yes the lower gears and pinion on a 10 bolt are pretty thick , my 3.73's were huge, in thickness, compare them to a 12 bolts gears and pinion and their probably pretty close , if not the 10 bolt thicker. This is why 9" rear ends are popoular with chevy guys who are putting down some serious #'s. 10 bolts if built up can take 400 + Wrhp if not abused should last quite awhile esp. in a auto, guys in 5-6 speeds really abuse the hell out of their rears and trannies , then wonder why they break. Hptuners will calculate everything for ya when you input the #'s and even set up your shift points which is nice , I love hptuners does everything I want and expect to do with it, also allows you to expand your car in whatever dirrection you want to go N/A, FI or nitrous. When I added my UMI tunnel mount TQ arm it put all the stress to the rear and also makes the rear plant the tires like they should , I get no wheel spin. Even if I foot brake my auto to 2400 RPMS it just chirps and takes off chirping 2nd, and 3rd. This is with 3.73's , LCA's , Panhard rod, relocation brackets and 315 tires, even with the 275 rear tires it did the same. I'm going to add a 9" billet stall with a 2.0 STR and see what happens with that. I have a SLP line lock but on a dry road I won't flip the switch on it, just looking for trouble. I'm saving that for the track when I use my 275/40/17 M.T. drag radials.

[SixShooter'00Camaro]

Re: Changing a standard rear to a Limited Slip

You shouldn't have any problems then if you got a 3 series. I would also look into Royal Purple gear oil , so far its been great and no need for additives since its in the oil itself.

X2 I added RP to mine when I changed the fluid for the first time after my gears and posi were installed and it has been great.

[BabylonBob]

Re: Changing a standard rear to a Limited Slip

In the Auburn Gear – Limited slip differential installation manual – under its Maintenance section it recommends that the lube be changed every 7500 miles.

Did either of you ever change your differential lube?

I never gave it a second thought.