Should I buy the 8.25" rear I found at the local parts yard? Are there any obvious/common problems to look for, keeping in mind I've never looked inside one of these before? They want $250 for it. No telling how long it's been sitting. It's on a '74 4-door Valiant; the rear wheels are still on and the rear end is not in the dirt.

Here's the background on why I'm looking at it. I'm planning drum-to-disc swap on the front of my '74 Swinger. I was initially thinking to keep the 4" bolt pattern (TheRamMan has a disc swap kit with SBP rotors), but if this 8.25" rear works out I could swap to LBP.

If the rear end is in decent condition in a gear ratio that you can use I would buy it. Beware that many V8 cars received 2.45 gears and that's too high for most any car with a 225.

If you buy it get the shock mounts as they accommodate the larger U-bolts of the 3" tube housing. Your 7 1/4 has 2.5" tubes.

_________________
Joshua

$250 isn't bad for a plug and play 8.25"....

Likewise these came in the following ratios over the years and are undesirable (and would need a new centersection along with the gears),
these ratios are 2.24/2.26, 2.45, 2.56...... 2.76-4.56 gears use the same center section....

One sure way to know what you are getting would be to see if you are allowed to pull the rear cover off, bring a good rag and roll the ring gear around wiping the grime and varnish off and look for the stamp on the gear....the ratio is stamped there...and if OEM mopar it will have a mopar part number, that's a little more sure fire than trying to count pinion and ring gear teeth.... this also will allow you to see if it's a sure grip.....

Here's to hoping you get a nice 2.94 or 3.21....

Snag the driveline also...that would be a bonus.

I brought home the new rear. The guy at the yard told me it was a 2.9-something after he looked at the tag. However, now that I've cleaned the tag off, I can see it actually says 2.71. The housing has number 2852905 stamped on it. I need to clean it up some more before I can open it up to count teeth (there's a pretty thick layer of road grime all over). It has 11" drums, which I didn't expect. What do you all think?

The tag isn't always the truth so I'll wait to pass judgement until you pull the cover. Unless you're towing regularly the 11" brakes are needlessly heavy.

_________________
Joshua

The 11" brakes seem like they are going to be very hard to find parts for; so far the only thing I've seen online is a complete buildup including backing plates for $440--wow. Nothing at RockAuto or any of the usual parts shops. According to the 1974 shop manual, these 11" drums were only on taxis. Does anyone know of a different car (later year, etc.) with interchangeable parts?

Maybe I should part out this rear, clean up the brakes and sell them on eBay! :-)

parts of late 70`s and 80`s van and pickups will fit even 9.25 rearend. just check bolt pattern. I think mid late 80`s went from 4.5 to 5in bolt pattern.

The parts manual isn't 100%.... I've pulled 11"x2" drums off of 1973-1974 rear axles...they were both out of stock 340/360 cars (owner's going to Dana-60's because of the build they were putting in....)

There are a few variations on the late 11" brakes too, so you really have to watch it... if you look at the parts manual there will be a line item for different makes... my 1973 part catalog lists the 11"x2" rear drums as being for mid-sized Plymouth/ Dodge (and in the 1978 catalog these are listed as HD for F bodies and M bodies as well)... you should also notice, that the Chrysler land battleships (Imperial, New Yorker, etc...) are equipped per the catalog with 11"x 2 1/2" brakes.... so you will need to confirm what version you have...Vans and Trucks will have 11" on the larger side of the scale, small parts like the springs, cables, etc...will still be interchangeable).

What DI said.

I installed an a body 8.25 rear axle in my brother's 74 Duster and it came with 11 inch drum brakes. I rebuilt them using parts form a 74 C body.

The wheel bolt pattern changed from 4.5 to 5 in 1985.

OK, so the 11"x2.5" drums should be doable. According to what I see at Rock Auto, it looks like some of the mid-70s trucks had the same brakes. In other good news, the drive shaft from the donor car looks like it will fit on my car with the 8.25" rear end, since it's 1.5" shorter than the driveshaft I currently have with the 7.25" differential installed. Now back to the question of the differential ratio...

Looking inside (see pic below), I count 17 teeth on the pinion and 46 on the ring gear, making a ratio of 2.71, just like the tag says. Am I going to have a car that stops on a dime but can't get moving?

Drop it in.....see how it goes. You can change ratios later if the 2.71 is too high.

...........or go find the rear you want with the ratio and brakes you want and sell the one you have.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Yes, but why would you want that? A-bodies didn't have 11" drum brakes, front or rear. Not from the factory—not even on the top-super-max 1976 A38 cop-spec cars. They'll bolt right in place of the 10" items that belong there, which is one reason why they show up from time to time in wrecking yards under A-bodies, but that's an enormous amount of rear brake for an A-body, way more than the factory ever put in. More is not necessarily better; keep in mind these cars, with discs up front, tended to lock up the rears at the drop of a hat even with stock 10" rear drums. Various techniques are used to reduce the braking force of the factory 10" brakes to tame the easy-lockup tendency...so why do you want to go the other direction and create a situation where sneezing or farting in the general direction of the brake pedal will make the car want to lock up the rears and spin on you? And those 11" drums aren't just big, they're also really heavy. Needless weight, and unsprung weight at that. Is there some particular reason you're fixated on the idea of having 11" rear drums?



What engine and transmission do you have, and what's the elevation above sea level where you live? 2.7 was the standard-equipment rear axle ratio with automatic transmission and 225 or 318 engine. They drive okeh that way at sea level, especially if all you do is cruise on the highway and don't care much about acceleration. Nicer to drive with 2.9, and a lot nicer to drive with 3.2 plus tire size selected to give a final-drive ratio of a hair over 3.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Not fixated at all...but they were installed on the rear end I picked up, and I originally assumed changing to 10" would require cutting and welding. Now that I've looked closer, it seems swapping in a 10" backing plate might be as simple as removing the axle and those four nuts holding on the backing plate (though I'm not sure how simple it is to remove the axle). I'd actually prefer the stock 10" drums. In general I want to keep factory equipment unless there's a compelling reason to upgrade something.



Stock 225 /6 and 904. As to elevation, my office building flooded during Hurricane Irene. My house is a little uphill from there, but not enough to make your ears pop. So basically sea level... As to driving intent, most of my driving is in town, in moderate traffic. I don't want to burn rubber, but I don't want a total pig, either. I guess I can always swap gears in the differential later if I'm not satisfied with the acceleration from the 2.71.

Great! Then skip the 11" brakes and avoid a seriously dangerous setup.



Yup, it's just that simple. The 10" backing plates and all other hardware bolt right on. While you are at it, there is a particular rear wheel cylinder you'll want to install to stave off the aforementioned rear lockup no matter what front brakes you wind up with.



Not difficult, no puller or special tools required.



2.7s will be tolerable and OK. If you eventually swap to 3.2s you'll like 'em a lot better.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

The 8.25 and 9.25" rear is pretty easy because they use axle clips...

Do one side at a time, once you got it on jack stands or on a place you can work.... pull the cover plate, drain the nasty old fluid... roll the tires/hubs until you can access the center section push the axle in board and look for the C-clip...remove then slowly pull the axle shaft out of the tube... (on some ratio diffs you may need to find a 1/4-5/16" bolt that holds the assembly together in the center section then work on the aforementioned c -clip and axle pulling)...

Reinstall reverse of above...

Note...take care in pulling the axle ends out of the tube...you don't want the splines to marr the seals at the end of the tubes...

After that it's a matter of a couple of nuts to remove to change backing plates....

If your current rear axle ratio with the 225 and 904 is 2.76...the 2.71 won't feel any different.... but agree with Dan 2.94 is a good all around cruising ratio...3.21 will be peppier...