Fifth Avenue 7.25 sure grip

Transmissions and Rear Ends

  1. desotoshane

    desotoshane Member

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    So did Chrysler ever make a sure grip for the 7.25 84-89? If not any after market out there?
     
  2. volare 77

    volare 77 Well-Known Member

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    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: Jan 24, 2019
  3. Oldiron440

    Oldiron440 Well-Known Member

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    Marginally weak, I'd say it's full on weak.
     
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  4. 7T8 Custom

    7T8 Custom Well-Known Member

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    I blew up 2 open ones with the stock 2 barrel 318 before swapping out for a sure grip 8 1/4.
     
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  5. volare 77

    volare 77 Well-Known Member

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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.
     
  6. 7T8 Custom

    7T8 Custom Well-Known Member

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    And that`s what I blew up both times.
     
  7. volare 77

    volare 77 Well-Known Member

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    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: Jan 24, 2019
  8. desotoshane

    desotoshane Member

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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
     
  9. Duke5A

    Duke5A Well-Known Member

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

    BudW Moderator Staff Member

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    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
     
  11. desotoshane

    desotoshane Member

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    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.
     
  12. BudW

    BudW Moderator Staff Member

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    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
     
  13. desotoshane

    desotoshane Member

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    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
     
  14. drpreposterous

    drpreposterous Well-Known Member

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    Thanks, Bud! BTW, saw a 3.54 gear set but no 3.2.
     
  15. Charrlie_S

    Charrlie_S Well-Known Member

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    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.
     
  16. Oldiron440

    Oldiron440 Well-Known Member

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    It must be a restoration project to spend that kind of money on a 7.25 axle.
     
  17. Charrlie_S

    Charrlie_S Well-Known Member

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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.