85_305

Wait.. *all* fourth-gen rear-ends will stick the tires out in the back? But the IROC 16" wheels will work right? Just get spacers on the front as well?

Tru2Chevy

The 16" IROC wheels will fit, and clear the brakes. They will stick out almost 2" more on each side than stock, so you will end up smacking the lip of the wheelwell with the tire.

Don't use those rims on any 4th gen rear (LT1 and LS1 are the same width) for anything more than rolling around the shop or a short, very slow drive around town.

- Justin

transambill

The only reason I would switch to a LT1 or LS1 rear is for the better brakes or I got it CHEEP. Without a bunch of upgrades they don't last when your makeing power and getting it to the ground.They will survive for a while till you get traction. The 9 bolts are stronger than any 10 bolt,even the ones in LS1 cars. GM quit useing them because of cost(imported parts). They generally came out in 350 cars as well as the 305 TPI 5 speed cars. They all had the 28 spline axels. GM used them as warrenty replacements when the 10 bolts blew. 90% were posi and disk brakes. They still can be found. Stay away from the 277 geard ones. Thats a series 2 and to go to a larger ratio you'll need a series 3 and that adds to the cost. If you can find an 89 9 bolt they had the LT1 style PBR brakes.
As far as brakes,when switching from drum to disk you should swap the prop valve.Drum and disk had diff. bias as to how much pressure got sent to the rear.
There kinda hard to find but a 9 bolt with 345's is the cream of the crop but one with 327's are esay to find and you get the series 3 posi and all thats need is a gear swap if you want to go to lower gears.

85_305

FUVK!!!! That blows over my ***cing plans

The whole reason for me switching over to the LT/LS-1 rear is because I want the monsterous brakes, posi, and durability!!

So.. what is the *cheapest* way to get a disk-brake, posi-trac, beefy-rearended rear end?

doug791

lol i think its been mentioned at least twice in this thread. The 10 bolts in the 4th gens is strength wise the same 7 1/2" 10 bolt as in our cars. How in the hell they survive an ls1 i completly dont understand but w/e.

It basically comes down to going fast isnt cheap. You either can find a 9 bolt with the stuff you want for cheap, as a temporary replacement, or you just drop the 2000+ dollars on a moser 12 bolt/ford 9". Trust me man im being faced with the same reality you are.

BUT really youre aiming around 300 ft lbs??? youre not gonna break that 10 bolt with that much power unless you drive like a maniac. If youre not planning any other mods for that engine you can easily spend a couple hundred to beef up your 10 bolt and you wont break it.

85_305

^How long would the 9-bolt last? I have been looking into these 9-bolts, and think I may have a chance at getting one for cheap
What are the odds of a junkyard having one? How tough are they?
Actually I am looking at 350+ lb's of torque

doug791

350 should still be fine with a 10 bolt, GM put the 10 bolt behind the l98 which was rated at 345 ft lbs, if you dont completly drive it like you stole it (like i do) that 10 will hold

85_305

Well, then I guess next winter I will just be getting a new tranny and paint-job

82355

There is a lot of bad information in this thread. Stick to a 3rd gen axle, other wise you should swap wheels because 3rd gen wheels will stick out of the wheel well beyond the car. I know, because I have done this. Also you can drive them around like that, once again, have done it.

If you do swap to a 4th gen axle, you need to get a proportioning valve, not a master cylinder to go from drums to disks. The master cylinder is just supplying hydraulic pressure, it doesn't care what to. I have done it without the proportioning valve, but the rear brakes have a tendency to lock up before the front brakes. That is a really odd sensation the first time it happens.

Your best bet would be just to find a 3rd gen, descent geared, posi axle. A 9 bolt would be better, but just use what ever you can find. They will last long enough for what you are going to be doing. Slicks are what generally kill 10 bolts, but they can survive those too.

You keep mentioning posi gears. There is no such thing as "posi gears" The gears are seperate from the carrier which can be either an open unit or a limited slip (posi). Your best bang for the buck, temporary solution would be to just weld the spider gears together in the differential, in essence giving you a spool. The inside tire will chirp around a curve, but its no big deal. People say it won't hold up and not to do it. They haven't done it, I have. It works.

The engine you are building is no big deal, there are a lot stronger engines running around on factory 10 bolts with no problems. My friends '98 Trans Am had 120,000 miles on it, the engine and the tranny (three times) both let go before the rearend. It has been a heads cam car since 70,000 miles when the engine was replaced. Many quarter mile passes, the best of witch was a 12.23 leaving the line on a 10.5" slick, dropping the clutch at 5,200 RPM. Your axle will hold.

Martin

85_305

Why, thank you for your input
How hard is it to weld the gears together? What kind of weld should be used (I am not very good in the weld-department )
After this rear goes, how long would a 9-bolt last w/ 300hp/350lbs?

doug791

You really shouldnt break the 10 bolt with the power youre making. If you did (id expect at least of couple years of beating on it before that ever happened) and replaced it with a 9 bolt you basically would not break that. If you did that would mean youre as hard on parts as i am, and thats not a good thing. Also know that when looking for a 9 bolt if you ever want to either change the gear ratio in the back or any parts you have to order for the rear are super expensive because its australian

85_305

^oooh, ok. Why are the rears australiain? Are they made by Monaro?
What ratio's did the 9-bolts come with anyways?

transambill

9 bolts came with the following ratios
277
308
327
345
370
Most but not all were posi,a few were drum brake.
Generally the 370's came in V6 cars and were non posi.
305 and 350 cars got the 308's
350 cars got the 277's and 327's
305 TPI,5 speed cars got the 345's (the most desired gear)
89 was the last year 9 bolts were used and 89 was the only year that got the LT1 style PBR disk brakes.All 9 bolts also had the 28 spline axels.

85_305

Thank you for the information

And thanks for the link Rob