Rear ends

[snowmangaggift]

Just a few questions, my monte has its original rear end which I hear is junk and Im wanting to change it. Problem is I dont have much knowledge about them.. Maybe you guys can help.
Im wanting my car to be a fast street car. Maybe some trips to the track but for the most part a quick cruiser.
So what kind of rear end ratio should I be looking for? 4.11? 3.73? 2.73?
I see quite a few "ford 9" posi" for sale. I hear they fit in our cars? what other ones are able to bolt into our cars?
Thanks, just trying to expand my knowledge.

 

[Brother Al]

Stock GM "Direct Bolt-In Axles" for these cars are limited to the:
'78-'85 10 Bolt axle w/ 7.5" ring gear.
'86-'88 10 Bolt axle w/ 7.625 ring gear.
'78?-'88 10 Bolt Oldsmobile "Hurst/Olds" or "442" w/ 8.5" ring gear.

Aftermarket axles come in GM 12 Bolt and Ford 9" variants and they are NOT CHEAP.

ANY other axles will need professionally performed modifications to fit into the G-Body.

IF you plan to drag race your car drown the strip routinely and have the money to burn, then look into an aftermarket axle.
IF NOT, find a low mileage 7.625 axle, preferable out of a Monte SS, Turbo Regal, or Grand National... Monte SS cars have 3:73 gears, but be aware, not all are Positraction, so buyer beware.

3:42 and 3:73 gears are pretty decent fun gears... 3:42's will give you decent throttle and mileage, the 3:73's are a little more aggressive and work out well with a 200R4 Transmission, but anything more than that would really not be decent for cruising.

 

[dogsht]

All the turbo regales came with the 8.5 rear.

Most likely & economical find would be an 81 to 88 7.5/7.625 which would be fine behind a moderate 350. Since you only have a three speed transmission and it is also a driver your ideal gears would be a 3.08 or 3.23. A 3.42 will also work especially with a taller rear tire say 27" or taller and if it's a car that does not see a lot of highway/interstate also if fuel economy isn't a priority.

 

[snowmangaggift]

Thanks for the replies, I just scored a posi 3.73 gear off a buddy. He had it in his 81 cutlass. 250 bucks I think its a decent deal.

 

[MrHernandez]

Actually Dogshit, If I'm not mistaken I think only 84 & up turbo regals had the 8.5

 

[Brother Al]

You are welcome snowmangaggift. Glad to help. 8)

Yes, the '84-'87 Turbo Regals did indeed receive the Olds 8.5". The earlier '78-'83 Turbo Regals and '80/'81 Turbo Monte came with the 7.5"

 

[snowmangaggift]

So I installed the new rear end, and with my 3 speed th400 it runs at brutally high rpms lol I dont mind it but there's no way I could go any faster than 100km/hr. Good learning experience for sure!

 

[thepcsurgeon]

So here is some info. I'm running a ford 9inch rear with a th400 and now 3.50 gear set and spool. The 2004r when built right will handle 400 hp and the 3.73 rear gear. That's a *ss kicking combo. Mean on the street and great on the highway. If you stick with the th350, you will need to drop the gear ratio as dogshit mentioned. My 3.50 gear is doing 60mph at 2800 rpm. I could go into the low 3.0's but for now, im good. If your making any decent HP, you better get better axles, the stock 26 spline won't last long and get twisted up if you launch hard. Hth

My old monte had a strong 2004r with a 350 SB making 400 hp and I snapped the main shaft in the transmission while shifting into second. Also found my 26 splines wit a slight twist.