I'm looking to upgrade the rear-end in my '70 Cutlass S

Currently sporting an open 2.56:1, I want a limited-slip and I'm between 3.73 or 3.42 but leaning towards the 3.42's since the car is my daily commuter vehicle spring/summer/fall

I was also going to use the opportunity to do a rear disc brake conversion

I found this one
http://www.summitracing.com/parts/ms...baxa/overview/

Looks like it could be set up for either drums or discs? ...although I was hoping to spend less than 3k

Any other suggestions for a bolt-in rear-end that meets my specs?

 

I would look up 507olds (Brian ) or monzar(Jim ) I think they sell reconditioned rear ends for a lot less

 

X2 - actually it's monzaz (Jim Mitcshke) and 507OLDS (Brian Trick). Both are excellent to deal with. I bought my series 3 posi carrier from Jim. You don't need to buy the whole axle assembly, just the carrier/ring&pinion gears/bearings and shims. You can use your existing housing and axles to save on shipping costs. Have a local trusted shop do the guts swap or do it yourself if you're mechanically capable.

If this is a DD, you might want to think about 3.08 or 3.23 as your gear choice. 2.56 gears are a slug but offer very good fuel economy. IMO 3.08 is a better option for performance and fuel. 3.42's are going to decrease your fuel mileage a lot but will give much more performance (and with unstable gas prices I'd consider that especially for a DD). It depends what you're looking for in the overall finished product.

You can do a rear disc conversion, but in all honesty why bother? The rear brakes aren't the ones that do most of the braking anyway. Front discs and rear drums is a great combination. Save the money for something the car really needs.

EDIT: whatever you change your gears to will also require a new speedo gear adapter and possibly a new speedo gear sleeve.

 

Keep in mind that the Moser axle is all brand new parts (including the housing). The axles are HD billet parts. This is a hell-for-stout axle. Do you really need it?

As for ratio, the difference between 3.23 and 3.42 is barely measurable - it's a 6% difference in engine RPMs at any given speed.

 

I'm somewhat mechanically inclined, but I've never done diff internals before and would be hesitant to try... wouldn't the cost of shop labor sort of balance out shipping? Whereas I'm pretty sure I could drop & install an axle assembly myself
Either way, I will talk to the guys you & oldstata pointed me towards

Yes it's a daily driver, but my goals are reliability/driveability > performance > economy, kind of in that order, so fuel mileage isn't a HUGE concern. I knew when I bought the car it wouldn't be economical and I just accepted that from the get-go... so for a little worse mileage that's why I'm leaning towards the 3.42's or 3.73's (I initially was thinking 4.10/4.11 but am trying to be a little more practical lol)

I know it doesn't need them, but they would be a little better (plus I find it way easier to swap pads on a caliper then rebuild a drum) and figure if I was swapping rears it would be a good opportunity to hit this as well... although if I do end up with just the rear internals & keep my existing diff/axles then you're right I probably wouldn't bother

Hadn't thought of that!

 

Definitely not lol, just having trouble finding other options for what I was looking for

How 'bout the other way - from 3.42 to 3.73? About the same change? I know it's gonna be a big jump from the 2.56 either way

Edit: As always -- thanks to everyone for responding so far!

 

That's abouit a 9% increase in engine RPM. This is just simple math.

(New ratio - Old ratio)/Old ratio, or (3.73-3.42)/3.42

 

I think the shop labor would be way less than shipping. If you removed the rear brake hardware, dropped out the axle and took it to a gear shop to do the work, I bet it would cost a lot less. They obviously will have to pull the axles to do the swap, but will reinstall and add new gear oil/limited slip fluid. I would stick with 80/90 gear oil instead of synthetic. The syn may create too much slip in the posi clutches.

BTW, While you have the rear axle out it's an excellent time to redo the rear control arm bushings if they haven't been done.

 

What about a good used unit I bought a 12 bolt non posi olds 3:23 gear ratio for around 300.00 locally found it on ksl kinda like Craig's list

 

It all depends on what your shops charge for labor.
A complete rebuilt 12-bolt O-axle would be about $1400.00 plus freight.
A complete rebuilt 71-72 8.5" 10-bolt would be $1100.00 plus freight. However,if you are swapping from the O-axle to the 8.5" 10-bolt,you will also need to shorten the driveshaft,so you need to add that to the total cost of the project.
A 3:23 12-bolt O-axle non posi for $300.00 sounds good.Go through everything and replace all of the bearings & seals,and add a posi.If you do all the work yourself,you can get this one redone and ready for your car,for under $1,000.00

 

To ship a 10 bolt rear to Georgia from 507OLDS was around $200 IIRC picked it up at the shipping dock.

I used the RightStuff rear disc kit, if you decide to use theres, talk with Todd first! then you can get the CORRECT lines... a lot of the stuff they sell on Ebay may work for the chevelles, but fit on a Cutlass is another matter! (you need to do something with the front/rear distribution, there are posts discussing this)

It is bolted in and I hope to have it running soon!

 

Wow Dave, shipping in the lower 48 seems like a bargain compared to up here.

 

The USPS loses billions a year
The Canadian Post Office turns a profit

 

Not according to their annual report. Labor is one of their highest costs. They currently are looking at eliminating the postal delivery door to door to cut costs. Not a lot of peeps rely on the mail much anymore now that we do most of our communication and services on the puter.

 

Annual Report



In 2012, the Canada Post Group of Companies had a before-tax profit of $127 million and the Canada Post segment a before-tax profit of $98 million.

Rapidly declining mail volumes combined with the need to serve a growing number of new addresses are a major cause of Canada Post's serious financial challenges. Compared to 2008, Canada Post is now delivering 23.6 per cent less Transaction Mail per address. As a result, Canada Post expects a substantial financial loss in 2013.

 

Now we're talking....when have crown corporations actually made money or been efficient?

Hmm, this is getting borderline political so I think we should stop. Hopefully coldfire finds his differential and shipping price satisfactory.

 

Still shopping around

Finding time to research this stuff seems harder these days than the $$$ to purchase once I figure out what I need/want

 

Thank you for all the input. The shop is going to work with me on the price, so 373 posi here we come. I personally love the way she's geared now. She flies on the highway. Sadly, it's my son's car, and his money, so he has the final say. He never gets on the highway and uses it for school, work and the gym. I think he'll be happy with this choice, and maybe upgrading the tranny later will allow him higher speeds. The car has the 350 rocket w/3sp tranny for now...
I'll have him post some photos after the top gets replaced.
Thank you again.

 

Better start a tire replacement account! I don't know if he is the reserved type but when he hits the gas hard a few times it may turn on a light bulb above his head & will almost surely put a smile on his face.

Make sure he understands how car reacts w/ a limited slip diff when tires break loose. I know both my kids have had a couple of scares in the red car, especially on a wet road. Luckily the only contact made w/ anything was a ruined wheel & trim ring, can't remember if tire survived - granite curbs around here.

 

Make sure he understands how car reacts w/ a limited slip diff when tires break loose. I know both my kids have had a couple of scares in the red car, especially on a wet road. Luckily the only contact made w/ anything was a ruined wheel & trim ring, can't remember if tire survived - granite curbs around here.[/QUOTE]

That is what parking lots Snow and doughnuts are for. LOL. we use to take a little Dodge Omni and do reverse doughnuts in the parking lots when snowing. It was fun and believe it or not helps you learn how to pull the car out of weird situations that could only happen a few times in your life.

Front wheel drive is totally different in the snow forward but still gives an idea of recovery on cars out of control. OH make sure the parking lot is empty...lol. Now a days you will probably g to jail for this stuff.

Jim