77 cadillac going from 223 to 308 gears?

going from 223 to 308 gears is that a big change in performance? my caddy has a 472 with a th400. im doing a similar
project to a caprice making it 308 to. but my Cadillac im wondering about cause im changing out its rearend cause
of no aftermarket stuff was made for caddy rearends from that area.

Don't do it. The rear end in your 77 is an ultra strong 8.75 12 bolt, and will give you decent mileage without overdrive. With 3.08s, you will really need to swap in an OD trans. That big Caddy 425 is designed to make lots of torque at low RPMs. Come on over to the Cadillac Forums for lots more info:

http://www.cadillacforums.com/forums/rwd-19xx-1984-deville-fleetwood-1985/

BTW, your 77 has a 425, unless you swapped in a 472.

i have a 472 in it now, the 308 rearend i have i thought would wake it up a bit.

What year 472? Any mods? Cam? Which heads? Rockers? Intake? This will help me suggest a rear gear.

You can actually get gears for the Cad rear. Up to 3.42s (came in 81 V6 cars). Posi, too. Rare, but they're out there. I have the same rear in my 81.

its a stock 1971 472ci out of a sedan deville dropped in a 77 fleetwood and i have "demo headers" put on it just for looks. there 4 in a row pattern, thats mainly it. the engine alone is strong but im not an expert on gear ratios. putting in a posi 308 gear set i would imagine the car will throw more power to the road and take off faster with that?

jjs88 wrote:

its a stock 1971 472ci out of a sedan deville dropped in a 77 fleetwood and i have "demo headers" put on it just for looks. there 4 in a row pattern, thats mainly it. the engine alone is strong but im not an expert on gear ratios. putting in a posi 308 gear set i would imagine the car will throw more power to the road and take off faster with that?

Power to the road won't change,. but it will accelerate better,.

jjs88 wrote:

its a stock 1971 472ci out of a sedan deville dropped in a 77 fleetwood and i have "demo headers" put on it just for looks. there 4 in a row pattern, thats mainly it. the engine alone is strong but im not an expert on gear ratios. putting in a posi 308 gear set i would imagine the car will throw more power to the road and take off faster with that?

another thing to think about as mentioned is engine speed. with those gears and no overdrive you are going to be running pretty high RPM at highway speeds. (high for a 472 anyway)

What will make a big difference in performance without lowering your rear gears is a switch pitch transmission. With a variable pitch torque convertor you get the best of both worlds.. The V/P TH400 was only made in 1965,66 and 67 but many th400 transmissions up to about 75 can be converted to switch pitch, also called variable pitch.. Do some research..

drmenard wrote:

What will make a big difference in performance without lowering your rear gears is a switch pitch transmission.  With a variable pitch torque convertor you get the best of both worlds.. The V/P TH400 was only made in 1965,66 and 67 but  many th400 transmissions up to about 75 can be converted to switch pitch, also called variable pitch.. Do some research..

How would he run the speedometer,.?

The tail of the transmission is the same. So what ever tail he has on the transmission now he could use on a switch pitch. All the cases on the early transmissions were the same and can be used. If not drilled for a switch pitch it can be drilled easy, its only one hole. But somewhere in the 70's they took out metal of the cases and can't be used.. around 76-77 I'm guessing.. These transmission came in Olds, Buicks and Cadillacs... Not Pontiac's that's 65 to 67... The used them in 64 but not in the TH400. In 64 they were in the ST300.. Not sure about other years in the ST300... At 105 years you should remember these..

the out put shaft of a switch pitch has no provisions for a speedo gear
btdt,. i used to build short shaft switch pitch trans for my 442,

This is true that Olds did not drive the speedometer off the transmission, it was off the front wheel. But Buick and Cadillac did have a speedometer drive on the tail shaft.. All those parts can be swapped around.. When your building a strong th400 it is best to use the earlier year parts. The aluminum pistons in forward and direct drums. Use sprags and not roller clutches . There are many different mods that can be done to make them preform well.