Fifth Avenue 7.25 sure grip

volare 77

Well-Known Member
Joined
Jun 12, 2014
Messages
1,415
Reaction score
203
Location
maryland
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.
 
Last edited:

volare 77

Well-Known Member
Joined
Jun 12, 2014
Messages
1,415
Reaction score
203
Location
maryland
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.
 

volare 77

Well-Known Member
Joined
Jun 12, 2014
Messages
1,415
Reaction score
203
Location
maryland
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.
 
Last edited:

desotoshane

Member
Joined
Jan 24, 2019
Messages
5
Reaction score
0
Location
Leavenworth,KS
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
 

Duke5A

Well-Known Member
Joined
Apr 6, 2018
Messages
1,640
Reaction score
858
Location
Michigan
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

All F/J/M axles will interchange. Just look in the yards for police package cars or wagons.
 

BudW

Moderator
Staff member
Joined
Mar 4, 2012
Messages
5,121
Reaction score
1,485
Location
Oklahoma City
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
 

desotoshane

Member
Joined
Jan 24, 2019
Messages
5
Reaction score
0
Location
Leavenworth,KS
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.
 

BudW

Moderator
Staff member
Joined
Mar 4, 2012
Messages
5,121
Reaction score
1,485
Location
Oklahoma City
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
 

desotoshane

Member
Joined
Jan 24, 2019
Messages
5
Reaction score
0
Location
Leavenworth,KS
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
 

Charrlie_S

Well-Known Member
Joined
Jul 27, 2016
Messages
90
Reaction score
11
Location
silver springs, Florida
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.
 

Oldiron440

Well-Known Member
Joined
Apr 25, 2017
Messages
3,048
Reaction score
739
Location
Iowa
It must be a restoration project to spend that kind of money on a 7.25 axle.
 

Charrlie_S

Well-Known Member
Joined
Jul 27, 2016
Messages
90
Reaction score
11
Location
silver springs, Florida
It must be a restoration project to spend that kind of money on a 7.25 axle.
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.
 
Back
Top