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Discussion Starter · #1 ·
Hey guys i'm new here and need some help. I have a 1988 Broughm 4 dr that i'm turning into a sleeper street/strip car. I need new rear end gears (either 3.73's or 4.11's) and would like to know a reputable source to buy from. I'm not tubbing the car, axle legnths will stay the same just want to increase my gearing for best possible launch and figured what better place than a B-Body specific site to ask.
Any help will be greatly appreciated.

Grady
 

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find a ss rear end or 1 from a 9c1 94-96 may need to get a aftermarket driveshaft do to vibration with those gears.does it have a 700r4 or a 350 tranny back then?theres other factors to throw into the mix, torque converter stall speed,cam shaft ,tire size motor mods.size of wallet
 

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Discussion Starter · #3 ·
The car will have a TH400 behind it. I already plan on getting a new driveshaft to fit legnths properly so that is not an issue :eek:k3:...what ratio do the 9c1's have?
 

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all different, in fact the one i got had 256 :( but i didnt care cause i was after the disc brake look for my drill slot rotors,if not sure remove the cover and count the number of teeth on the ring gear and divide by teeth on pinion gear (or the other way around) also u can tell if its a posi or not,mostly likely its shot, you'll need a new set up anyway when that time comes,but thats another post
 

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9c1 should be 2.93 or 3.08 for a 94-96, you aren't after the gears though. Your 88 most likely has a 7.5 inch housing, which won't hold up to power, that's why you want the 8.5 inch from the LT1 car. Plus gears are much easier to find for it.
 

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I would do a 700R4 and 4.10s in an 8.5" housing The 700R4 will give you an awesome first gear, lockup so you can run more stall comfortably on the street and an OD to soak up the 4.10s.
 

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8th Gen Antagonist
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The 700R4 does have a lower first gear ratio than the TH350 or 400.
 

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Discussion Starter · #8 ·
It had a 700r4 in it but with the power the motor is pushing and the life expectancy of the 700r4, at least in my experience, is not a good match. I am parital to the TH400 and thats what i'll be sticking with despite the disadvantage in first. I have a 1996 buick roadmaster with an lt1 that got crushed by a tree a couple years back but i never got rid of it. I may steal the rear 8.5 in housing and put different gears in that. Best place to buy a good 4.10 or maybe even 3.73 to make it more street friendly?
 

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Look at my signature, that 4L60E is like 9 years old.

The 700R4/4L60E are not weak trannies, they are just easy for sloppy shops to build badly and that is the real source of their bad reputation.

IMO 3.73s with no OD no lockup is not street friendly.
 

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Discussion Starter · #10 ·
I have a 96 roadmaster with lt1 and 4l60e that has over 150,000 on it so i know they are not weak trannies. I am also aware 3.73s are not street friendly but i would consider them more friendly than 4.10s. The 700r4 the caprice had in it before is going in a different project so i trust the tranny i just plan to have the th400 in this project. Don't get me wrong i do appreciate your opinions but i am going to keep the SBC, TH400, and am now looking for a different rear end. If you guys could help me with that portion only that's what i would really appreciate.

Hope i didn't offend anybody,
Grady
 

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The 8.5" from any of the LT1 cars or even any of the b-body sedan 8.5s after '89 would be fine. I am just not sure what cars got the 8.5" '89-93. I specify '89 because I am pretty sure that was the year they went to 30-spline which is near 12-bolt strength. I still have stock axle shafts in my car and this axle was in a nitrous car before mine that was even quicker. 1.5 60ft times at 41-4200lbs means it will take a beating.

I know the 94-96 wagon housings are wider with wider mounting points, I would assume this goes for the 91-93 cars at least as well so look at sedans specifically.

The 94-96 cop cars got rear discs but the proportioning valve was still drum so they don't work as well as they should have in normal driving but if you were interested in rear discs this would be the easy way to go.

Should also state the later axles are 5on5 bolt pattern where your car might be 5on4.75 so wheels are a consideration or you could just redrill or replace the axles if that is a concern. Always consider that with a used rearend even if posi assume the posi is dead, be happy if it works and be prepared for the possibility of a bad outer axle bearing having eaten into the surface of the shaft causing you to need to replace.

I know I blurted out a bunch of stuff there, if it is unclear ask.
 
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