4door!cutlass

Hello and thanks for your time, i have a 86 cutlass,455 ,400trans,mild cam but still has v-6rear.think its like 2.70 gears .I'm thinking about. taken it up to 3.55.my problem now is,what cars to look for. which rear ends will fit my g-body?.what is the best rout.

oldsmobiledave

Look for a GM 8.5" G body rear end from a 1984 HO or a 1985-87 442. These will have 3.73 gears with optional posi. Also the 84-87 Buick GN has the same rear end with 3.42 gears & posi optional.


Note you will also need the driveshaft from the same car or have a new one made from yours' as the 8.5" swap requires the shorter driveshaft.


Price wise I have seen these rear ends sell for anywhere from $600 for a 3.42 open to $1250 for a 3.73 posi.

joe_padavano

To expand on Dave's post, the only rear axles that bolt into your G-body are the 1978-1988 A/G-body axles (note that the 78-88 cars are all the same, but they were originally called A-body cars by GM until changed to G-body with the 1982 model year). Nothing else has the correct width or control arm mounting geometry. The 8.5" versions used under the 442s and GNs are coveted and usually sell for stupid money unless you get VERY lucky. It's almost cheaper to get an aftermarket axle designed to bolt in. You can get either a 9" or 12-bolt version brand new that bolts in from the usual aftermarket axle sources.

4door!cutlass

Very very awsome and helpful information. as a matter of fact,now i know exactly what to do.
thank u.

MXman112

You can buy an 8.5 for your G-body @ Gbodyparts.com ready to install if the have them in stock. No new items just rebuilt. Never purchased one from them since I have had luck finding them local. I have both 3.42 and 3.73 and have used both behind my 403. Just removed the 3.73 as it needs rebuilt and I want to tame the car down a bit to be more street friendly. With the 455 you will fry tires with either.

And yes you will need a different drive shaft.

4door!cutlass

Thanks.,so the 373 burns more gas or is it the rpms
Thank u

oldsmobiledave

Naturally the 3.73s will turn more rpm & use more fuel.


Once you decide on your final tire size & transmission (4 speed or 3 speed automatic) then decide on the 3.42s or the 3.73s based on how you plan to use the car.