IROCUDREW

iTrader: (6)

I'm at a cross road. My car currently has the stock posi rear with 2.73 gears. I own brand new richmond 3.73 gears and a master install/rebuild kit. Also I have a fourth gen rear but the housing is cracked so I have access to ls1 rear disc brakes. I am willing to install pretty much anything on my car however I am not going to set up my own gears and a local shop charges $300 to set them up.
My plan was to transfer the ls1 rear brakes on to the rear I have and then have the shop set up the gears for me. I figured now is a good time since its out of my car.

I found a rear on craigslist for $300 from a 99 camaro with 4.10 gears already installed. I can't decide to either rebuild the rear I have since I already have the parts or to just buy the 4th gen rear and call it a day.

PS I already have a disc/disc proportion valve.

I figured if I buy the 4th gen rear with 4.10 gears, I can sell my gears and the install kit and the extra set of ls1 4th gen rear brake assembly and get some of my money back. However at the end of the day it's still a used rear and may have unforseen problems. If I stick with rebuilding my rear I will have a fully rebuilt rear with new bearings and seals.

What's your opinion?

khulsebus

iTrader: (2)

Choice is yours, however know the differences between the two rearends. Mainly the different widths will push your wheels out a little. If it were me, I'd throw the 3.73:1's in the 10 bolt that came in the car, or consider changing to a different rear all together. There is little strength to be gained between a 4th gen rear and a 3rd gen rear. I have a 4th gen rear in mine, and I can't stand it. I've already got my eye on a 12 bolt.

jrhaus76

Is your car a 9 bolt BW or a 10 bolt?

Here is the problem, if you have a 9 bolt with 2.73s, you have a 2 series carrier and it won't hold anything except the 2.73s. You need a 3 series carrier. I just went down this road with my car. $485 later I had a rebuilt 3 series carrier from Australia. I am pretty deep into my gear swap. Maybe $1000.

I am not sure what you could swap around if in fact you have the 9 bolt 2.73 bastard like I did.

IROCUDREW

iTrader: (6)

I always thought that the wider 4th gen rear was more desirable because it would allow the user to run different wheels without spacers. What about the 4th gen rear bugs you? I would love to run a 9" but that's out of my budget right now.

The rear I have now is a 10 bolt with drum brakes. I already bought 3.73 gears for the 2 series carrier I have. Sounds like I lucked out having a 10 bolt compared to a 9 bolt.

It makes sense to swap ls1 rear brakes onto the rear I have and put in the 3.73's. I was thinking maybe it would be easier to just get the 4th gen rear however I am sure I'll run into an issue with that. I guess I'll stick with mine.

jrhaus76

I'd rather have the 9 bolt Borg Warner and deal with the issue. Plus, it's only on the 9 bolts that came with 2.73s.

IROCUDREW

iTrader: (6)

The 9 bolt seemed to be more of a pain, what makes the 9 bolt more desirable opposed to the 10 bolt?

jrhaus76

Strength.

92droptopws6

iTrader: (10)

The 9- bolt is a little more durable, downfall is replacement parts when needed...

The biggest problem with 4.10s they tend to break teeth off of the gears. I went through 2 sets in a year and a half in my bolt on Z28.
3.73S have more teeth allowing it to withstand more abuse. The difference between the two gears will be roughly 1 tenth in the 1/4 mile.
If you can get the 4.10 rear for 200.00 or less it will be worth it especially if it comes with the brakes and ZEXEL-TORSEN LSD..

John in RI

iTrader: (167)

If you can get a good LS rear with the brakes for $200 - Your stealing it.

The 98+ rear end has a much better POSI in it than your 89 10 bolt does. The $300 price for "setting it up" doesn't account for the fact that it's still an Auburn POSI unit & probably past it's prime already. For that reason alone I would recommend the complete LS1 rear end since it's more or less a 'bolt-in'.

* LS rear into a thirdgen = parking brake mods required.

I had a 3.70 9-bolt in my 84 with T56 and decided to swap to a LS1 rear just for the brake upgrade. The LS1 rear-end I used was built a few years earlier for my 95Z with a 4.10 gear & it already and I had put 20K ( not so easy ) miles on it. 3.70 to 4.10 doesn't seem like much, but I'm very happy with the results !!

BW 9-bolts were 2.77.


Going from a 2.73 to a 4.10,........ You will be SHOCKED at the difference in your car once you get that baby installed !!!

jrhaus76

Correct. 2.77. My bad. Lol

khulsebus

iTrader: (2)

What bugs me is that the edge of the tire is even with the quarter panel, like I only have an inch of travel before the quarter touches the tire. There is no way I could put a fat chick in the car, and you never really know what you're going to bring home from the bar. While it is true that you can run 4th gen or corvette wheels without spacers, that's not what I'm going for. Even it being a LS rear, I'm already looking at breaking parts. I'd rather switch now than break it at the track and then figure out how to get it back home an hour drive away.

jmd

iTrader: (4)

Maybe. 98 had an auburn or slp optional torsen. 99-up had torsen with optional HD auburn.

Ultimately, the answer is 3.90 gears.

InfernalVortex

iTrader: (4)

Using a fourth gen rear and 3rd gen tires is hillbilly. Get wheels that fit or put the fourth gen stuff onto a 3rd gen rear.

I have a 4th gen Torsen carrier in storage for the day my 9-bolt breaks.

AutoRoc

iTrader: (1)

Complete rear for $300?? Jump on it!! Plan on breaking parts often, its the 10 bolt way of life.. There used to be a kid on cz28.com that we called crazy mike... had a bolt on lt1 car, not a ton of power but he broke 8 or 9 rear axles in a short time... powershifts and wheelhop break stuff fast.

Install 4th gen rear.. live with the oddball wheelspacing while you rebuild the original rear properly, as money allows. Keep the spare gearset, you will probably need it. Both gears are a nice nice improvement..

khulsebus

iTrader: (2)

InfernalVortex, I didn't do it, it came that way. I'm planning on putting a 3rd gen width back under it, just trying to figure out between a 12 bold, 9 inch, or a Dana 60. Won't be until May that I can do anything about it anyways.

IROCUDREW

iTrader: (6)

I'm going to stick with my rear and rebuild it since I'm going to stick with my stock wheels because I purchased new tires for it not to long ago. My rear is already out of the car so I figured it's not a big deal to drop it off at the shop. I can't wait to get this vert back on the road with 3.73's. Going from 2.73's to 3.73's should change the fun factor just a "little" lol

AutoRoc

iTrader: (1)

It will be much easier to drive and easier on your clutch.. Unfortunately... you dropped your calculated top speed from 300mph down to 200....Im not sure how you will get by....

2.73's. General motors worst attempt at better gas mileage...

Ron U.S.M.C.

It may be a big mistake using the stock posi unit to build this with. When you start actually pounding on the stock one with your 3.73 gear ratio it may not be long before you need a new one. Chevy did not do us any favors when they installed the Auburn and most definitely not with the Gov-lock. I would slow down just a bit and at least consider a $450.00 Eaton Posi. Its a strong ,reliable, quality posi unit that I believe you will be much happier with. You will have to buy the 26 spline version because you're not replacing the axles and you have already bought the 2 series gears.
Its your car but I would want something better. = http://www.eaton.com/Eaton/ProductsS...als/PCT_339923


You have the Auburn so at least have the shop look closely at the cone and determine if there is any life left in it.
The Gov-lock does just that. Locks the unit hard and is called the "bomb" because that's what it does. "Explode".

IROCUDREW

iTrader: (6)

I'll definitely have to look closely at it. I don't know if I feel like dumping $450 into this rear if it won't last in the long run. I have a zexel-torsen unit in my garage but that's 28 spline and 3 series. I guess that doesn't help. It makes sense to bite the bullet and get the Eaton because if the auburn breaks I will have to spend the $450 and another $300 to get them set up.

I think the 10 bolt would last because I'm not going to be doing clutch drops, I'm not going to run slicks. If I have the urge to go fast I'll just roll onto the throttle. As you can tell I'm debating out loud. To many choices.

Ron U.S.M.C.

You will know if it’s usable when they go to install it. You say you have a 28 spline zexel-torsen unit 3 series. You could exchange the gears you bought for regular 3.73 3 series and find a set of either used 28 spline axles or just buy a new set for around $ 250.00.and you will have something that will be leaps and bounds nicer than your original build plans. Sorry but it’s just one more thing to think about. It would be a good choice it the Auburn turns out to be on its last leg.

If you put a support cover on it your rear will resemble one of the stronger differentials you can build for a 10 Bolt at a fraction of what I paid for mine.
= https://www.thirdgen.org/forums/tran...de-photos.html

I’m not trying to push you into this just pointing out an alternative.