what gear ratios were available with disc rearends. I want to replace my 373 disc rear with freeway friendly gears, are the later so called australian rearends and better then the 10 bolt I have. Also are these rears a direct bolt in ...... I am specifically interested in 3:23 and numerically lower geared rearends and.

What tags will be on the rearends to mKe them easily identified, and also would a V-6 car have had disc rearends any info on what cars and years that had these desired gears would be appreciated.

at 65mph with a 5 speed my car turns about 2300rpm .... I'm looking to get the car into the 1500rpm range but what gears will it take to do this

 

I have a 700r4 and 2.73s and it turns almost 1500@ 55MPH. but, for seat of the pants the gearing sucks...

...if i were you, I'd stick w/ what you have, sounds like a great combo, and I don't know of anyone else that would complain about 2300RPM on the freeway...

your 9 bolt would be a direct swap, should have a small tag on the differential cover identifying servicing of the LSD, if equipped. I would shoot for 3.23s in this case, nothing under that. That's just MHO.

 

i think a 5 speed with 3.73's is a nice combo, but if you want abit more mileage out of it, then get 3.23's or 3.27's. still enough gear for some good acceleration but definately an improvement on 5th gear cruising.

assuming standard 25.7inch tall street tires, 3.23-3.27's would put you at 2000 rpms which is an improvement but not all that much difference.

any gears numerically lower than 3.27/3.23 would feel doggish in that T5. but a 2.73 would put you at 1700 ish rpms. i personally would stick with what u have as the 300rpm difference to a 3.23 rear doesnt justify the cost.

my 700r4 with 3.42's is at 2000rpms at 65mph. its a nice combo, and not bad on the highway at 60-70mph. i dont really drive to many areas at much faster than 65 anyway. the parkway to pittsburgh tho, most ppl average 75 on that road with 85 being a "fast lane" pace. i dont think i'd like having my car doing 2500 for along time like that, but its not too bad. i know a few guys doing alot more rpms than that at those speeds.

 

As Tobias points out there's a 2.73; there's also a 3.08, IIRC. As a point of reference, I have a 5 speed with 3.23's. I do around 2300 in the 70-75 mph range. For all-around driving, I like the 3.23's, but the 3.73's would probably be a lot more fun.

JamesC
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ok yes the car is a blast to drive with 3:73's but we are getting off my subject. I commute a 100 miles a day with the car so you can see I am not interested in how quik it accelerates but am in getting it's MPG up. I can always swap the 3:73 rear back into the car at anytime LOL, thats also why I am choosing not to do a gear swap in my rear end.

Did 2:73 rear ends come with disc brakes

 

yes some did.... my 2.77 geared 9 bolt rear end has big PBR brakes on it. 11.65 inch rotors. goood stuff

if you were closer u could buy it. lol but the posi and gears are not in the rear right now, but still work good

 

Orr89rocz

Was this 2.77 rearend stock in your IROC, and was it the so called aussie rearend. this sounds like what I am looking for. was this ratio and rear used in other years and models.

 

yes it was the bone stock rear end from my 89 Irocz 5.7L

Its the aussie rear end which is 7.75inch rear with 9 bolts in the diff cover. 10 bolts are 7.5 inch or 7.625inch. so the 9 bolt aussie is abit stronger. very popular in australia actually.. alot of cars have this type of rear over there.

these aussie rears were available in 87-89 fbodies. they either had the 2.77 gears or 3.27's for the auto 350 cars. most manual 305 cars had 10bolt 3.08s, but some manual 305 cars had the aussie rear with 3.45 ratio but its very rare and ppl charge alot of money for them. most of these rears had disk brakes. look for them off of Irocz or formula firebirds/ GTA trans ams. 87-88 had smaller 10.5inch rear rotors with iron calipers.. they are weaker disc brakes. startin in 89, they upgraded the brakes to 11.65inch rotors and aluminum calipers. this is what comes on LT1 4th gens as well and is what i have on my car's rear end.