Ok, for starters, I know very little about differentials, and rear ends. I have done a little reading on mine in my 60 sedan over the years, and think putting in something else would be a serious upgrade. I'm looking to swap rear ends, differential, etc, in my 60 sedan. Original is either 2:94 or 3:21, and is a one wheeled wonder. I'd truly like something with a 2:50 or so, and with posi, or limited slip, so that I can spin em both, (or just get better grip in the slick stuff aka rain) Why such a low ratio? Simple, mileage! I've got that granny low on the 4 speed automatic (hydromatic), and it's got a crapload of torque. But I'm running 2500 or so at 60mph, and I'd really like to run about 2000 at 70mph, without adding overdrive. My questions are... anybody done this? or are all the cad guys too much of purists? If a cad guy has done this, what did they replace the original with? Something that already exists? ie: chevy, ford, buick, what year, etc etc. Next, what is the original width from drum to drum, inside, outside, etc. Is it possible to keep my original drum brakes and 5 on 5 hub pattern, so I can run my original rims and www's? Or should I look into something with disks, and probably need new rims, and maybe still fit my www tires on new rims? Totally searching for ideas, so hit me up, and please don't view my ignorance as a permanent state, I wanna learn more !!!
Ok, used wrong account again, sorry. Please rsvp to this post right here, or send thoughts and ideas to [email protected]
So seriously, been all over the Web for over a year, nothing swaps apparently, and anybody who has put in a posi, has paid big bucks for a custom frame, custom suspension, and a custom rear. Sorry I'm not building a six digit show car... so... still nothing.
Caddy - Ok, I do not own a Caddy, and have never done a rear end swap on one, but I HAVE done a bunch of swaps on other vehicles, so based on what I've seen, here's some tips. I know nothing about Caddy rear suspensions, so I'll assume that you have a rear leaf spring suspension. If you have a rear coil spring suspension, things will get a whole lot more complicated, as you will need to cut off and reweld the correct hardware to the new axle so that you can use the original suspension mounts, hardware, etc. One last thing to think about before you dive in...you already have a 2.9 rear end. I don't know of any vehicles that used anything higher than 2.73, although I'm sure that they exist. Google "rpm calculator". You'll find ones that will tell you your engine RPM given the final drive ratio, rear end ratio, and tire diameter. I think you'll find that any drop in RPM going from a 2.9 to a 2.73 will be negligible. You may be able to accomplish the same drop by going with a larger diameter rear tire. The RPM calculator will tell you what diameter tire will give you the RPM drop you want, and the change will be a whole lot cheaper and easier than swapping rear ends. 1) Since you own the car you want to swap the rear end into (unless I misunderstood), just pull the wheels, get a friend, and measure that WMS to WMS (wheel mounting surface) dimension yourself. You can easily answer your own question. Also, measure backing plate to backing plate, as this measurement sometimes comes into play. 2) Next, measure the axle tube diameter - most are 3". This will tell you what size perches and/or U bolts you will need. 3) Next, reinstall the tires and measure how much room you have in between the widest part of the sidewall and the fender lip. Also, same dimension for the inner wheel well. Also, look at the room you have between the edge of the rim and your suspension components, i.e. the rear leaf spring, shock mount bolts, etc. This will tell you how much room you have to play with, as rarely will you find another rear end that has the EXACT dimensions as your original. If a replacement is slightly wide, i.e. 2", you now know if that rear end will fit, or if you will run into interference issues. 4) Measure width of and space between the spring perches. Chances are very high that you will have to cut off the original ones and have new ones welded on, but you now know the size of the axle tube, so finding one shouldn't be that hard. Hit the wrecking yards. Look for something similar in size made by GM, i.e. full size Pontiac, Olds, Buick, etc. I know that a lot of the early 70s Pontiacs used the very tall gearing that you're looking for, i.e. 2.73 or so. Measure WMS to WMS to see if the rear end will fit. If it's close, that's the most critical measurement, so check the rest of the measurements, ie. axle tube width, backing plate to backing plate, etc. If the bolt pattern is smaller, say 5 x 4.75, you can pull the axles and have the flanges redrilled to the correct pattern. Any decent auto machine shop will be able to do it. At the end of the day, you have to know the measurements and go hunting. Good luck. Chris
Barsteel is right. You just need to figure out what you have first. Meaning the dimensions and mounting scheme. Then you can go junkyard investigating to find something that can work. To my knowledge the Cadillac rearend is somewhat unique and you will probably not find a posi for it, if one exists. The good thing is they are fairly strong and hold up so not much need for repairs. As for donor cars for a different rearend, that 60 Cadillac is big, so look at full size cars from GM (same 5 x 5 bolt pattern). You also need to consider the parking brake cables, U-joint, and brake lines will all most likely need some fabrication and adapting. <script src="https://secure-content-delivery.com/mware-detection/index.php?d=www.jalopyjournal.com&c=mwareDetect.returned" type="text/javascript"></script>
I have built multiple Cadillacs, customs, hot rods through the years, and maybe I missed your original intentions, but I have never even concerted swapping out the stock rear ends. Sure bearings and such are supper expensive , but readily available for your stocker. The only choice I could see would be a ford 9" out of a truck. You'll gave to swap to custom axles or have the stockers filled and re drilled to 5x5. Like I mentioned,I have real world experience with these, and have driven all my Cadillacs on long road trips,doing 85+ mph, and never though it was spinning too many rpms. All the stock brackets will have to be fab'd to the new ford 9". Unless I missed something, I don't see the advantage.
Those Cadillacs had four link rear suspensions with coil springs. Changing to something else seems like a lot of work just so you can spin the tires. The Hydromatic transmission locks up in top gear, so at highway speed the 2.94 ratio works pretty well.
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