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Old 06-03-2012, 11:26 PM
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weld rear gear

i have a 91 caprice classic 5.0 305 700r4 it has the limited slip rear end. Im not building a drag car by far just a show car that can grip and rip. I want a posi but i can not afford a posi gear so i want to weld my gears.

What i want to know is going from limited slip to posi will it eat my gas milage up and does the gear have shim packs or the inside thread caps.
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Old 06-04-2012, 06:31 AM
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A limited slip rear is a posi. Obviously you know little about rear ends. A welded spider rear is asking for trouble on the street.. Been there and cost me many thousands of dollars..

Broken axles and poor handling are the least you will encounter. It gets worse..
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Old 06-04-2012, 06:51 AM
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Quote:
Originally Posted by mafiacustomz
i have a 91 caprice classic 5.0 305 700r4 it has the limited slip rear end. Im not building a drag car by far just a show car that can grip and rip. I want a posi but i can not afford a posi gear so i want to weld my gears.

What i want to know is going from limited slip to posi will it eat my gas milage up and does the gear have shim packs or the inside thread caps.
Don't weld the rear end. More info here.

Info on checking what the gear ratio is, here.
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Old 06-04-2012, 08:02 AM
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Simply put, you know how on a High School track inside lane on the track starts back behind the the next lane? Then lane number 2 starts behind lane number 3 and so on? Why do they do that? It's because the inside lane is shorter than the outside lane. Draw two circles, one inside the other. Now take a ruler and measure those circles, the inside one is going to be much shorter than the outside one.

When you go around a corner the wheels on the inside of the corner are following a shorter path than the outside.

Your front and rear end of the car are designed to handle this in two different ways.

The front has what is called the "akerman angle" designed into the front steering geometry which makes the inside wheel turn more than the outside because it is going in a smaller circle than the outside wheel.


The rear has a differential that allows the inside tire to spin slower thru the spider gears. If it is a posi or not, this still happens. If you weld up the gears this can't happen and you have a real MESS where the tires want to turn at the same time, think about this, how can this work? It DOESN't not on a street car at least. You have alternate skidding of tires when you go around a corner!

Forget about it, save your money for a posi.

Brian
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Old 06-04-2012, 09:08 AM
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My first car had the spider gears welded. As the posters above stated when you turn a corner one or both rear wheels have to slide. The rear end broke loose causing me to hit a tree because of it. I was doing less than 30 mph on wet pavement. Don't do it is my humble advice.

John L
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Old 06-04-2012, 11:05 AM
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well i was wrong i dont have a LSD i have a open differential so i will be asking a new question. Should i weld the rear gears in a open differential.
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Old 06-04-2012, 11:06 AM
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NO, for the exact same reasons.

Brian
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Old 06-04-2012, 11:09 AM
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Hey Mafia. The same answers apply. o matter what type of rear end you have The differential needs to do it's job.

John L
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Old 06-04-2012, 11:14 AM
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ok thanks dont weld the rear unless your going to drag.
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Old 06-04-2012, 02:53 PM
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EVEN dragracing its not a good idea. Think about driving through the pits and all the crud that can get on your tires; or turning at the end to go on the return road. One side has to slip somewhat somewhere or youre going to be unhappy. Best advice, get a posi axle and put under your car. Avoid Lockers and the horrible 'Gov-Lock' used under some GM cars
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Old 06-04-2012, 03:18 PM
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The only time I have seen a welded differential is on low budget (can't afford a real locker, which is the right way to do it) 4x4 rock crawlers.
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Old 06-04-2012, 03:22 PM
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well ya a lock is best for 4x4 but here in this small town in ky they weld rear gear all the time for racing and 4x4. I will keep a eye out for a posi just looking for some more grip but not to kill my gas mpg.
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Old 06-04-2012, 03:24 PM
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how is a posi going to kill MPG?
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Old 06-04-2012, 04:55 PM
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the size of the gears if i dont get the right size it wont run right killing my gas mpg. I think my gears now are 3.72 its a 7.5 10 bolt I think not sure of theat.
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Old 06-04-2012, 05:19 PM
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Quote:
Originally Posted by mafiacustomz
I think my gears now are 3.72 its a 7.5 10 bolt I think not sure of theat.
I gave you a link that tells you how to figure out what ratio you have.

Here's another one you can ignore that tells you how to ID the rear end.

There were 8.5" rear ends, and I read somewhere they also used a 7.625" on one application w/2.73:1 gears. You don't have 3.73 gears unless someone installed them.

8.5" ring gear 10 bolt rear end RPO codes from the glove box (probably where the RPO sticker is located- it could be under the trunk lid):

GM8 - 2.56
GU2 - 2.73
GU3 - 2.93
GU4 - 3.08
GU5 - 3.23
GU6 - 3.42

G80= Positraction

Standard ratios:

1991 - L03 Caprice(5.0) 2.56Gears

1991 - L03 Caprice Wagon(5.0) 2.73Gears

1991 - L05 Caprice 9c1(5.7) 3.42Gears

If you have a working OD in your transmission, you can run a lot of rear gear w/o a hit on the mileage.

Last edited by cobalt327; 06-04-2012 at 05:41 PM.
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