Fifth Avenue 7.25 sure grip

I looked in my 77 parts book. I didn`t see one listed but I do believe there was a sure grip in certain years. I doubt the aftermarket supported such a marginally weak rear.
 
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7 1/4 open rears usually lose the spiders first. Going around a turn while doing a burn out usually ends it in a hurry.
 
The 74 parts book shows a 7 1/4 sure grip in a A body. 2881342 is the part number. I don`t know if they will interchange. I don`t have a 84 to 89 parts book to verify.
 
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Thanks for the help I was just wanting more traction not a hot rod . I have other cars for that my fifth avenues are my drivers and the weather in Kansas is unpredictable. But maybe considering a 8 1/4 does anyone have a chart on rear end measurements for the FA's, diplomats, GF's etc that will bolt in? I know the drive shaft will have to be shorter but what about the perches? I found charts showing older rear ends but not the late 70's and 80's
 
desotoshane said:
Thanks for the help I was just wanting more traction not a hot rod . I have other cars for that my fifth avenues are my drivers and the weather in Kansas is unpredictable. But maybe considering a 8 1/4 does anyone have a chart on rear end measurements for the FA's, diplomats, GF's etc that will bolt in? I know the drive shaft will have to be shorter but what about the perches? I found charts showing older rear ends but not the late 70's and 80's
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All F/J/M axles will interchange. Just look in the yards for police package cars or wagons.
 
Yes, Chrysler did make available a limited slip for 7¼”, for many years as an option and as a dealer installed upgrade. Parts are out there but I hadn’t seen one for sale in some time.

All FMJ differentials will fully interchange – with one exception.
The early F & M bodies with 7¼” had 2½” diameter tubes the entire distance and their ISO-clamps had different spacing because of the tube diameter. In the late ‘70’s, the 7¼” tube diameter got increased to 3” so ISO-clamps interchange – but the tube tapered down to 2½” just before it went into the center housing.
7.25 Diff Identification.png

To me, looking for this taper is a quick way to tell if you have an FMJ 7¼” (which the tube taper only exists for FMJ 7¼” – and no other Chrysler product has it).

Any 7¼” limited slip carrier, made from ’60 to mid ‘90’s will work, Chrysler or aftermarket.


Other differentials that will bolt in place with minimal amount of work, is the ’65-70 B-body 8¾” differential. All other differentials will fit – but lots of modifications will be needed.

Of the ’65-70 B-body differentials, there is three different widths:
’65-67 are 59.50” drum to drum (or wheel mounting surface to wheel mounting surface)
’68-69 are 60.13” drum to drum
’70 is 59.70”” drum to drum.
The perches for above are 44.00” perch center to perch center
All 3 groups have different width axle shafts and housings – but if you know which one you have and its complete – you have nothing to worry about.

FMJ’s are 58.50” drum to drum
Perches are 44.46” perch center to perch center (or 0.23” wider per side – which most can get the leaf spring to move over for, without issues).


Personally, I won’t build or repair a differential without installing limited slip into it, for any friend, family (or self). I encourage you to install one, as well (if possible).
BudW
 
Thanks for the info Budw. I have been doing research on my own and have found the same information. But I still have not found a used oem or aftermarket sure grip as of yet I'll keep looking and thanks again.
 
Finding a decent set of 7¼” gears is also hard to do. 2.2 and 2.4 gears – I just can not recommend to “reuse”. 2.7 is the absolute bare minimum gear ratio I would (ever) go – and that is for highway usage only. For city usage 2.9 is the minimum I would go, with a 3.2 even a better choice.

The problem with what I just said – is almost all 7¼” came with 2.2 or 2.4’s, except for the pre ’75 cars and in Dakota’s. For the parts behind the inspection cover (and yoke) – all gear sets and carrier/cases will interchange. The 60’s A-bodies and Dakota’s both came 3.2 and 3.5 gear sets and Limited slips – but I don’t recall anyone keeping parts for those differentials. The 8¼” (and 8¾”) were the ones people kept parts for, for even in the 60’s – the 7¼” was like playing with a hand grenade.

For money coming out of my pocket, I won’t put any money into a 7¼”, except for minor repairs. Money would be better spent on a larger differntial.

I didn’t mention earlier, but FMJ 8¼’s only came in:
Special order cars
Most (but not all) police / taxi cars
Most (but not all) station wagons
Most (but not all) FMJ’s with towing package option
Also, in about 1/4th to 1/3rd of cars with 4-speed manual cars (not sure what rhyme or reason was that some got it and others didn’t get the 8¼).

Also, the ’68-70 B-body 8¼” differential will fit (only came on /6 and 318 2-bbl cars) – but those have slightly different gear set (less popular finding parts for, than even the 7¼” is) – but as a whole, it will fit fine.



There is a differential that will fit our cars (but never came in an FMJ) – which is still being produced/manufactured, today. It has very strong aftermarket support and is a very strong (almost unbreakable) unit – and that is the ‘66-70 B-body 9¾” (AKA Dana-60). I only know of three downsides to the D-60, and that is: initial cost, weight (its very heavy) and there are hardly any gear sets under 3.2 (gear sets range from 3.2 to in the 7’s) – but that is not a problem for most folk.

If you get a D-60, you will never have to buy another differential (but is a bit of overkill in strength and in price). https://www.strangeengineering.net/strange-s60-dana-60-rear-ends/ (about $2,000 US)
http://www.moserengineering.com/Moser-60-Built-to-Order-Rear-End-Package.item (a bit more than above)
A plus, is if you are getting a new one made, you can specify the perches to be welded at 44.46" instead of 44.0" as the B-body is.
BudW
 
Thanks again for all the info and I have a lot to think about. But the car is just a driver and I only want better traction so I'm considering all option though. Thanks again
 
I ran 7 1/4 rears for many years. Both on the street and track. That said, I don't recommend them. It is next to impossible to get parts for them. The sure grip clutches are pretty much non existant. Even if you find a SG carrier, the clutches are probably shot. I have a large bolt pattern "A" body 7 1/4 rear that I am rebuilding, and it took me several years to find the SG clutches, spiders, and axle end gears. Never did find the cross shafts. I have about $500 in parts in this rear. It was a 5.13, that I just changed to 3.91's. All wear items are new.
 
It must be a restoration project to spend that kind of money on a 7.25 axle.
 
Oldiron440 said:
It must be a restoration project to spend that kind of money on a 7.25 axle.
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Not really. I had the rear in one of my race cars, with the 5.13 gears. There is not much demand for a 7/14 rear with 5.13's. I had a new 3.91 gear set, and clutch parts in stock. So decided to rebuild it "as good as new". I was able to find everything else except for the spider gear cross shafts, but mine were OK.
When it is finished I will put it up for sale for about what I have in it. Someone may want it for a restoration. If not, I will most likely put it in my 64 Valiant more door, when I replace the 3 speed with a A833OD 4 speed.
PS: I have had 7 1/4 rears running in the 13,s on slicks, and never broke one, just wore out SG clutches.
 
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