Real deal or move along?

Transmission and Drivetrain Tech

  1. Mad Mechanic

    Mad Mechanic Member

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    Hello everyone,

    I too am one of the many looking for an upgrade from my stock 7-1/4".

    Here is my setup. 1964 Dodge Dart GT with the 225 Slant 6 and A904 trans. I'm keeping both the engine and the trans but I want something a bit tougher at the rear. I'm not looking to drag or launch the car, but I also don't trust the longevity of that axle because it's the original 1964 unit.

    So here is the deal. I found a guy on Craigslist that is very close to where I live that claims to have a Chrysler 8-1/4 supposedly from a 73 Duster. I have not seen it in person yet, but the few measurements he has supplied to me via e-mail seem to indicate that this axle has the same exact spring perch spacing and measurement from back plate to back plate.

    I've also read/been told that in 67 the A-body got wider so 67 and newer A-body axles are wider than early A body stuff and that spring perches have to be moved.

    The guy wants $250 for the axle, here is the link to the ad: mopar parts for a body
    Can someone confirm that is an 8-1/4? It sure looks like it to me, but it is just a picture.

    Beyond that, I have seen a lot of interest in the Ford 8.8 and I get one of those for about $60 (minus all the brake parts) from a local Pick n Pull yard. However, I would still have to have the axle tube(s) shortened.

    What I would like to know is if I shorten a Ford 8.8 to where both sides use the same length factory axle shafts (as I have seen this is the most common shortening method), will that be narrow enough to fit under my 64 A-body without needing some crazy backspaced wheel?

    I've tried looking for charts of axle widths, but even the chart on this site only goes as far back as 1966 for the A-body, so before I go spending the money I'd like to have a better idea of my options.

    Thank you all for your help.
     
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    • dirty white boy

      dirty white boy 47 yr old Juvenal delinquent

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      a stock 225 will never hurt a 7 1/4 rear end! 8.8 is a good up grade when needed but so is a dana 60! if ya just gotta have a 8 1/4 thay came under lotta jeep cherokees some with sure grip and assorted gear ratio's but only way to not need to torch n weld is from a A body! gonna have lug pattern issues and cutting drive shaft gonna be needed with most rear end up grades, good luck
       
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      • Mad Mechanic

        Mad Mechanic Member

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        You sir are awesome, I have not seen that chart anywhere online.

        Thank you for sharing. So if I'm understanding that correctly, the 8-1/4 from Craigslist is indeed bolt-on. Looks like I will have to get the driveshaft shortened, but I was going to have to have that modified no matter what axle I picked.
         
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        • 72bluNblu

          72bluNblu FABO Gold Member FABO Gold Member

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          And again! That stupid chart is so full of flat out wrong information it’s painful. Half of the measurements in that thing are wrong, including the A body widths. It’s not online anymore because it’s crap!
           
        • dirty white boy

          dirty white boy 47 yr old Juvenal delinquent

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          any idea on the correct measurements or where thay can be found? i thought this one was the one that had the mistakes, dont wanta be posting bad info! any thing else i get wrong??? Moparts on the Web - Main Index
           
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          • Cope

            Cope Fusing with fire

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            I see your in Ca.

            Drive yours till it's done and you can have my 7 1/4 For free when/if yours craps out.

            My new rear should be done by the end of this year.
             
          • Mad Mechanic

            Mad Mechanic Member

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            No thanks, I'd rather be moving towards a better axle.
             
          • 72bluNblu

            72bluNblu FABO Gold Member FABO Gold Member

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            That list on Moparts is correct. It’s stickied right at the top of this forum. This version has a couple of extra widths I added as well.

            An accurate 8 3/4" rear axle width list

            That jpeg is just awful. It has just enough good info to make you think it’s useful. But it only lists 1 width for B body axles, 62-70? There’s 4 different widths in that range. A-body 8 3/4’s are 52 5/8” flange to flange, which is different than the BBP 7.25/8.25’s which are only 51 1/2”. The SBP 7.25’s are different too.
             
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            • Mad Mechanic

              Mad Mechanic Member

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              I've seen that list posted here and over at big block molars, but the problem for me is that it starts (for a bodies) at 1966, and I'm trying to confirm information for 1964.

              Perhaps during the process of swapping my axle I could take measurements of my stock axle and contribute to the common knowledge.

              That still leaves me with the questions I asked in my original post.
               
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              • HemiSSDart

                HemiSSDart Dartus Interuptus

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                That is the correct 8-1/4 axle that is a bolt-in but you will have to shorten your driveshaft.
                 
              • cosgig

                cosgig MoBro Inc. FABO Gold Member

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                Also realize that the 8 1/4" axle will have the larger bolt pattern axles, and swapping to it will make a mismatch with your fronts. This is not a deal breaker, but may cause a problem if you have a flat, want to change to different rims, or other issues of the like!

                I would also confirm the ratio of the gears in the 8 1/4" before I bought it, as there are 2 different sized gearsets between cases, and the higher 2:40-ish case will not interchange with the lower 3:21-ish gears, limiting you to highway gears only!
                 
              • 68383GTS

                68383GTS Well-Known Member

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                Dirty white boy is wrong!! I blew apart a 7 1/4 with a slant 6 Dart burning off...
                 
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                • Mad Mechanic

                  Mad Mechanic Member

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                  Yes, thank you for the reminder on the bolt pattern. I forgot to mention this in the original post but the mismatch front to back will be dealt with at a later date. I'm already looking into a CPP A-body front disc conversion kit. But that will be purchased at a far later date.

                  I've read this in a couple places that their are two distinct gearset sizes and they are not interchangeable. If I buy the 8-1/4 from CL guy, ideally I'd like to end up with the gearset size in the 3:21:1 range. Reason being is that according to my 1964 Dodge service manual my car should have a 3.23:1 gearset in the 7-1/4 so a 3:21:1 would be virtually the same.


                  All of this brings me back around to some fundamental questions: Is $250 for the Craigslist 8-1/4 a "good deal"? I'm already figuring I'm going to have to put money into new bearings and new brake components.

                  Whereas if I go with the Ford 8.8 I can get a newer axle (potentially with factory disc brakes, although this would be overkill on my car) for less than $250 at a pick-n-pull yard. I would then still have to have the 8.8 shortened, which means either paying someone to do this professionally (read $$$) or do it myself and risk ruining the axle (read $$$ to start over).

                  The 8.8 has a lot of ratio options out there on the market plus limited slips.

                  Either axle means I have to have my driveshaft at least shortened and possibly modified with a ford compatible yoke.

                  Both axles will get me a 5x4.5 bolt pattern.

                  For longevity which axle would better serve me? My logic tells me the Ford 8.8 would be the better long term option and potentially more cost effective. However, the 8-1/4 does keep my car with a MOPAR axle. Even that argument doesn't hold much ground with me as I am doing a lot of modifications/upgrades to my car as I work to get it road worthy.

                  As always, thank you all for your constructive and objective input.
                   
                • 72bluNblu

                  72bluNblu FABO Gold Member FABO Gold Member

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                  So measure the axle? The jpeg says it’s the same as the later cars. But that jpeg is wrong about a ton of those measurements, so that’s not really a help. Bad information is worse than misinformation.

                  All of the swaps I’ve heard of use an A body 8 3/4 and I haven’t heard of any crazy backspaces being needed. Probably a little more than a 67+ A, but with stock spring locations the 67+ A’s typically use zero to low offset wheels. There are people that have done that swap on this board, I’m sure a search in the early A section would turn something up
                   
                • Mad Mechanic

                  Mad Mechanic Member

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                  I do plan to take good measurements of my axle to compare to any other axle I end up with.

                  As far as searching the early A-body section, I somehow managed to completely overlook that sub-forum, that's my mistake. Using the Search Tool and targeting only that sub-forum produced at least a couple threads from people doing the 7-1/4 to 8-1/4 swap and the unanimous consensus is that any A-body 8-1/4 will bolt into any other a-body providing that the drive shaft is shortened (as mentioned here) and new spring plates and u-bolts are used to accommodate the larger axle tubes.

                  That ultimately leaves me with one major question: is $250 for a 45-year old 8-1/4 axle worth it (granted there are a lot of unknowns in this like bearing play, gear slop, etc.).

                  Or is my money better spent on buying a newer Ford 8.8 and having it cut down.

                  I appreciate your constructive and objective feedback!
                   
                • KosmicKuda

                  KosmicKuda FABO Gold Member FABO Gold Member

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                  The link wouldn't open for me but here in the rust belt, if I found a CA-sourced 8-1/4 from an a-body I'd be all over it for 250 bucks. And don't assume it needs a complete rebuild but the brakes need to be Checked out.

                  I have a 225 64 Valiant with a 3-on-the-tree and the 3.23 7-1/4.

                  I don't know what your ultimate goal is for your car but personally I wouldn't be obsessed with 4 wheel discs. If you're road racing, maybe. If you're putting around with your slanty, no. Unless you're only doing it for status then that's up to you. (Chevy guys around here install gear drives just for the sound)

                  One thing to consider is the wheel change necessary for the BBP. More money but the wheel selection is MUCH better. If it was me I'd start sourcing parts to do the BBP 73-76 front disc brake conversion and drive the sucker.
                   
                • sireland67

                  sireland67 Well-Known Member

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                  I blew an 8 3/4 up with a slant in a 65 coronet.
                   
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                  • Mad Mechanic

                    Mad Mechanic Member

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                    Yeah, I'm not obsessed with 4-wheel disc. As you pointed out I'm not racing so rear drums will be plenty adequate and I'm not interested in doing any of this for the status. My motivations for this work is safety, reliability and serviceability, plus I enjoy tinkering. As for the fronts, I was going to buy the CPP kit (around $900) which includes later B and E body front hubs, a new upper control arm, discs and calipers and a new power booster with dual master cylinder. The CPP kit will make the front pattern the same 5x4.5 and as you said, the rim selection is worlds better.
                     
                  • cosgig

                    cosgig MoBro Inc. FABO Gold Member

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                    This is my opinion....

                    If the rear is an A body 8 1/4" with the 3 range gearset, yes, $250 is a good deal! You won't get it done any cheaper buying, shortening, and buying the extra short axle for an 8.8 Unit! Either will require a different length driveshaft, so that's a wash, so yes, if the criteria you are looking for is met with this particular unit, $250 (or less if you wheel and deal a bit) is a good price!
                     
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                    • dirty white boy

                      dirty white boy 47 yr old Juvenal delinquent

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                      you wont driving it like a stock /6 was designed to be driven,..not my falt!
                       
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                      • dirty white boy

                        dirty white boy 47 yr old Juvenal delinquent

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                        were you doing burn outs and such to,..or driving like a stock /6 was designed to be driven???
                         
                      • sireland67

                        sireland67 Well-Known Member

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                        It wheel-hopped on dry pavement and broke the spider gears, the only 8.75 I ever broke.
                         
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                        • Mad Mechanic

                          Mad Mechanic Member

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                          Dang, I've never heard of the 8.75 breaking, but essentially the gears got slammed when traction finally hit.
                           
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                          • bb66cuda

                            bb66cuda Well-Known Member

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                            The gears in that rear are 2.71 according to the owner.
                             
                          • Mad Mechanic

                            Mad Mechanic Member

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                            Guessing you contacted him? Admittedly that was one thing I either didn't ask or he didn't tell me during my initial inquiries.

                            If it's 2.71 gears, that's less desirable, to me anyway. That would mean it has the smaller carrier if I recall my recent reading. Someone please correct me if I'm wrong.

                            According to my '64 shop manual my car should have 3.23 gears in the 7-1/4, was really hoping that 8-1/4 would be the "common" 3.21 gears or at least 2.94 so it has the larger carrier.

                            Hmm...
                             
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