kramer70cutlass

Hey Guys,

So I recently picked up a 455 to swap into my 70 cutlass Supreme, I have been doing a bunch of research and finally decided to just get some input. The car now currently has a 350/TH350 and 10 bolt non posi rear end. I was planning on going 455/TH400 and 12 bolt posi with 3.23 gears in it. But after looking at somethings Would the current 10 bolt be strong enough for the 455? and maybe just drop a posi unit in it? I was planning on doing a disc brake conversion on it as well. But the motor is going to be rebuilt and it is going to be left pretty much stock except for a cam, I don't plan on taking the car to the track just more or less a friday night cruiser and some possible drives up north. I am sure i am asking something that has been asked before, But I guess if I was more or less wondering if I can just "beef" up the rear end that is already in there or get some different economical setups to put in there instead I am all about it. As it seems to be a little difficult to find an old 12 bolt posi at a reasonable price.

Thanks for all the help and advice!

don71

Your current rear end will be just fine for now. The one wheel peel will be fun for awhile and not kill the budget.

I suggest get your engine swap taken care of. Then move on to the little challenges and choices the rear details. This is the path I chose a few years back.

The most economical and easy choice is remove and install the desired rear of your choice, as one unit. VS taking apart and changing components.

From what I gather in your post, budget at least 1500 bucks and up when considering discs and newly rebuilt rear. I chose to stick with drums. You don't have to upgrade things like control arms, unless you are considering a sway bar also.

Contact this member and let him know your plans/budget. Have fun, that's what its about.
https://classicoldsmobile.com/forums...rs/monzaz.html

Macadoo

X2. I also thought a disc brake upgrade was important but ended up just rebuilding my drums. If the drums are good (have them mic'd) then the cost is really minimal. And they work just fine. Put the $$$ into that 455!

sammy

X2^^..man I wish I knew how to highlight....concentrate on the 455...heck I am running around with a 2.56 non posi with a 455 out front...great one-
wheel peels, and the gas mileage is pretty good when cruising...

Macadoo

Running 2.56s myself (for now). Curious, what kind of cruising mileage do you get, Sammy? I was getting around 14 but didn't realize the choke wasn't opening all the way.

And to highlight, just left click and drag over the text you want to enhance, then do whatever it is you want to do from the menu above. Example "B" for bold text.

Octania

sometimes to get all the editing features you want you have to "go advanced" while creating or editing a post.

As for the diff... just because you have a 455 doesn't mean you neeeeeeeed a 12 bolt.

Even if you had an engine with infinite torque, the torque actually run thru the final drive would be limited by the value that breaks traction... with an open differential, that is one tire's worth. One relatively unloaded tire [due to the torque tending to plant one tire and lift the other].

drop top olds

With a stockish 455 your factory rear end will be fine(strength-wise). Eventually a 3.23 gear set will be on your upgrade list. In my opinion rear drums will be fine for your intended use. I think a complete rear rebuilt will be $1200 or so unless you find a deal.

Macadoo

When I click the "quote" button, I'm automatically taken to advanced. Maybe this isn't true for everyone. I sometimes forget not everyone is sitting at an actual computer. For myself? A phone is just too dang small! Lol.

I've been looking high and low (on this forum), is there such a thing as a direct bolt in rear end swap for a '70 or '71 supreme? I, myself, would like to swap in 3:43s. Or do I have to have someone dig into the pumpkin?

I don't mean to highjack your thread, kramer, but I thought maybe you could use the info as well.

mrolds69

I would agree with the above opinions on your swap. Worry about the diff later. As for Mac,...sure find a 3:42 posi 442 rear end. The whole deal, they are out there. It's probably cheaper than changing your carrier, buying gears, having it set up, etc. You can re-use your new brake stuff, you can probably sell your rear off. But you can't put bigger gears on your carrier now, and a new posi carrier is expensive.

sammy

I am getting around 17 mpg on the highway...but it is rare that I get it,as I am usually going a wee bit faster than what is allowed

Macadoo

Does it have to be a '71 442 rear end or will other years work as well? Thanks mrolds, I appreciate it.

But just a wee bit, yeah? Lol.

don71

Macadoo, it doesn't have to be the same year. For example my car has a 69 'vista cruiser rear installed. No mods required.

sammy

Yup, just pick away....like^^, my 71 442 has a rear end out f a 72 Cutlass S



Ted

Macadoo

Kramer, you still around, buddy?

Greg Rogers

Don, you got a Vista rear in your Cutlass? Aren't the brakes wider on the Vista? I'm curious about this swap myself. Does the drum to drum measurement end up the same? Thanks, Greg

don71

Yes Greg, the brakes are bigger. Drums and shoes are wider than standard.

I've never cared to measure, or didn't see the need two.

Though this could be important to some, it wasn't for me.

kramer70cutlass

Hey Macadoo,

Yep I am still here!.. Thanks for all the information on this thread!... This is really my first Muscle Car Build so I am trying to just make sure I do things the proper way (eventually) to make sure the car is functional yet fun.

But yeah the biggest thing was just to make sure the stock rear end i have was going to be enough for the 455 with some mild work, which was really just a cam and long tube headers.

But I figure I will get the engine and transmission upgraded first and go from there, I have found a few disc brake conversion kits for around that 350 mark, which I did not think was too bad, I guess for me I just perfer the functionality of a disc brake setup over a drum.

Macadoo

Oh I think you'll find that 455 to be fun, alright. ;-)
Do you have any pics of said '70 Supreme?

kramer70cutlass

Hey Mac,

I did attach a couple of photos of the car. it will need some body work at some point, but for now i am working on the drive train first.

Macadoo

Sweet ride. I love the color combo. Doesn't look like it needs a lot of bodywork from here but hard to tell from pics.
How's the current 350? And the 455? You said a cam but are you going with an aluminum intake, headers, and dual exhaust?

kramer70cutlass

Macadoo-

The 350 that is in it now, runs alright for what it is, it appears to have had some work done, but the previous owner was not sure what was done too it. But it works for cruise nights and has a decent amount of power too it for what it is. But the water pump pulley maybe wrong on it as teh pulley's don't exactly line up but it still runs pretty well.

the 455 I bought is from a 70 delta 88, but came with big valve e heads and the proper manifold to run a 4bbl, The cutlass i have now already has the 4bbl option on it, and I will just be using that on the 455 when I get to that point, which i will have it rebuilt to accomodate the 455. As far as exhaust i was thinking of a long tube header of some sort probably of teh hooker or hedman variety, I really want to run into an xpipe and then back to a set of flowmaster 40 series mufflers. The car now has true dual with long tubes running back through glass packs, sounds tough at idle but on the road it is rather obnoxious.

Macadoo

Sounds like you have your plan worked out. And a good one to boot. I know some folks have a heck of a time getting long tubes to fit in there. It gets pretty tight.
Keep us updated on the progress.

Bob Kelso

What rear end is in it ? 12 bolt o-axle or 10 bolt BOP 71-72 style ? It should be the o-axle but people change these out at some time . I can build you a 3:23 posi 10 bolt 71-72 BOP if you have the rear end . I am located on the Illinois - Wisconsin border just south of Lake Geneva . BOB

kramer70cutlass

Hey Bob,

Let me look again and see what is it, are there any special tags i should look for that would help identify that? I usually just count the bolts on the diff cover, and if I remember there was 10..

And how much woudl something like that cost? I actually live in Sun Prarie so your probably not that far from me.

Bob Kelso

Pictures would help the most . They made several 10 bolt rears that would bolt in to your car . BOB