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Just how bad are 7.25 rears?
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Author:  Daddiojoe [ Thu May 31, 2007 8:41 am ]
Post subject:  Just how bad are 7.25 rears?
Hey folks, I'm building a hotrod 1950 Plymouth P-19. It has an 111 inch wheelbase and is close to the same weight, length, and width as an A-body. A lot higher, though.

I also have a '74 Valiant that I'm going to take the /6 from. I'm planning on just a mild build with maybe an RV cam, Super Six, Dutra Duals. Electronic ignition already there.

Transmission is a 904.

I'm not sure yet what the 7.25 ratio is. I would want at least a 3:23. Do 7.25s come in 3:55 rears?

So----would keeping the 7.25 be a waste of time? What would you all recommend?


Thanks,

Joe
Author:  SlantSixDan [ Thu May 31, 2007 8:45 am ]
Post subject: 
Sounds to me like a 7¼" rear axle would be a perfectly fine choice for that vehicle.

7¼" rear axles were available over the years in a large range of ratios. 2.29, 2.45, 2.76 (very common), 2.93, 3.23, 3.55, 3.91.
Author:  Charrlie_S [ Thu May 31, 2007 12:07 pm ]
Post subject: 
The 7 1/4 rear should be fine. However, if you want a limited slip rear, an 8 inch Ford might be a better choice. 7 1/4 sure grip units are not very common, and not available new. The 8 inch Ford from an Early Mustang, Falcon, Comet, Granada, etc. is the same width and spring perch dimension as the "A" body 7 1/4. It is somewhat stronger, has the 4 1/2 bolt pattern. Gears and limited slip units are available new, if unable to find used. These rears are in salvage yards for about $100, drum to drum. It also has a drop out center section.
Author:  Jeffc [ Thu May 31, 2007 2:16 pm ]
Post subject:  Re: Just how bad are 7.25 rears?
Quote:
Hey folks, I'm building a hotrod 1950 Plymouth P-19. It has an 111 inch wheelbase and is close to the same weight, length, and width as an A-body. A lot higher, though.

I also have a '74 Valiant that I'm going to take the /6 from. I'm planning on just a mild build with maybe an RV cam, Super Six, Dutra Duals. Electronic ignition already there.

Transmission is a 904.

I'm not sure yet what the 7.25 ratio is. I would want at least a 3:23. Do 7.25s come in 3:55 rears?

So----would keeping the 7.25 be a waste of time? What would you all recommend?


Thanks,

Joe
7.25 is fine, but pretty weak if it has too much wear, one hard
jump on one that is worn and it's gone......

Check your spider gears in the carrier, if sloppy replace them,
there kind of the weak point.

Randy's Ring and Pinion, as well as others, still have pretty
good selection of gear sets from 3.23, 3.55 down and the
prices are not too bad (around $300 for spiders and R&P
together, not installed, open set).

The later 7.25 axles also have a adjustable carrier lash (somewere
after 69?)
and I do not like it as well as the shimed type carrier early axles.

If it were me and I had a choice, go with a heavier axle and carrier.
Author:  dakight [ Thu May 31, 2007 2:50 pm ]
Post subject: 
Ratios are available up to 4.11. Randy's Ring and Pinion is one source and Jaws Gear is another. Jaws ( Moser ) is a little lower cost, Randy's has a wider selection of manufacturers to choose from.
Author:  sandy in BC [ Thu May 31, 2007 3:36 pm ]
Post subject: 
Being a DeSoto guy (51 Sportsman hardtop with LA v8 , B car front suspension , Lincoln 9" rear w/disc) I wonder why you dont just keep the Plymouth rear. They are usually a removable carrier and have pretty good brakes. The 7.25 is not a drop in fit.

The good part about the 7.25 is that it will solve some E brake problems.
Author:  DionR [ Thu May 31, 2007 3:59 pm ]
Post subject: 
Probably going to be too narrow.

I put an 8 3/4 out of an A100 Van in my '48 Plymouth, and it fit great. I know the sheet metal is pretty different, but I think they are very similar under the skin, '50 Plymouth vs. the '48 Plymouth.

I will look, but I think the A-Body rearend is much narrower than the A100. Number I remember for the van rear is 61", flange to flange.

[Edit] Moparts shows 57 1/8" for the A-Body and 61 3/4" for the A100, drum to drum.

You could make it work with deep wheels, but then you’re stuck buying, or modding, a set just to get it to roll.

My setup fit 235/60-15 on a set of stock 15x7 wheels, and I don't remember there being much room next to the spring. Offset should be around 4". A six inch rim would need something like a 1 1/2" offset to fit an A-Body rear under there.

I could be wrong though.

Hey, you wouldn't be looking for a disk brake kit for that car, would you? :lol:
Author:  DionR [ Thu May 31, 2007 4:20 pm ]
Post subject: 
Quote:
Being a DeSoto guy (51 Sportsman hardtop with LA v8 , B car front suspension , Lincoln 9" rear w/disc) I wonder why you dont just keep the Plymouth rear. They are usually a removable carrier and have pretty good brakes.
Biggest problem I see is you need a drum puller to do anything to the rearend.

Probably not the right name, what I mean is that the drum is a pressed on piece and requires some kind of a tool to get at anything, including dropping the center section. Kind of a hassle, unless things never go wrong.
Author:  sandy in BC [ Thu May 31, 2007 4:21 pm ]
Post subject: 
My linclon rear is 63 "wide and with 15x7 cop car rims its a lil tight on the outside of the fenders with 235 /78 / 15 wide whites. Clearance on the stock springs is close.

Your Plymouth would be identical to my DeSoto.

Image
Author:  Daddiojoe [ Fri Jun 01, 2007 7:29 am ]
Post subject: 
Thanks for all the replies.

Nice looking ride you've got there, Sandy. My concern with the rear end is mainly about the brakes, e-brakes all of that stuff.

From the numbers I've looked at (unfortunately don't have them here at the moment) the A-body rear is about 1" too wide, not too narrow. Somewhere around 56-55" for my Plymouth.

Yes I am interested in disc brakes for the front.

I have a 74 Valiant w/ disc brakes up front that could go for barter/sale, etc.

Joe
Author:  volaredon [ Fri Jun 01, 2007 10:54 am ]
Post subject: 
Find an 8-1/4 from a Dakota or Cherokee. I dont remember which one but one of them is 54" inside of backing plate to inside of backing plate.
I remember measuring them both up when I was looking for an alternative rear for my Volare before I found one that came from another F body. Seems it was the Cherokee IIRC. Also Dakotas '91 up went to a 6 lug flange so find one from 87-90.
Author:  Tim Keith [ Fri Jun 01, 2007 3:56 pm ]
Post subject: 
Sandy, that hardtop DeSoto is a good looking car.

There are several sources of disk brakes for you to consider, most use parts you can get from NAPA or Autozone.

Having to pull the axles is a hassle, JC Whitney used to have a good price on the drum puller. I don't see much work with maintaining the brakes. I have a '47 DeSoto, I think I will leave it stock.
Author:  featherduster76 [ Wed Jul 25, 2007 8:30 pm ]
Post subject: 
A 7.25 would be ok for the use of your ride, a decent rear for a non performance application and they can be had cheap or better yet free!
I run a 7.25 sure-grip rear in my street/strip car but however 7.25 suregrips are difficult to find. Ive made several passes with mine and it's tough as nails! Ive ran slicks on this thing and it hasnt even offered to break and it's lighter than the 8.25 and 8.75 rears. I guess if I ever break this rear I'll go to an 8.25 which is more than enough to handle all but the most of extreme of slants. Cheaper to get a suregrip for an 8.25 than the 8.75 as well. I find the 8.75's are way to expensive to fool with.
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