4" to 4.5" Bolt Pattern on a 7 1/4" Rear?

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shhnappa

shhnappa

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Hey Guys, I'm new to this forum, currently own an '06 Daytona, but got the itch for some good 'ol nostalgic Mopar. I just bought a '68 Cuda Fastback with 10" drums all around. I got my hands on a '74 Duster front-end, to do the disc conversion. So here's my question, After I install the front-end parts, I will have bbp in the front, is it possible to change just the rear axles & drums to the larger bolt pattern, or do I have to swap the entire rear to something else. I have always turned to forums for help, and have never been let down, thanks in advance for your help, Rob.
 
I would start looking for an 8 3/4 with bbp it will save alot of headache.That,s if your running a V8.
 
is it possible to change just the rear axles & drums to the larger bolt pattern, or do I have to swap the entire rear to something else.
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i thought they changed the slpine counts on the axles when they went to big bolt. not 100% sure though.
 
shhnappa said:
Hey Guys, I'm new to this forum, currently own an '06 Daytona, but got the itch for some good 'ol nostalgic Mopar. I just bought a '68 Cuda Fastback with 10" drums all around. I got my hands on a '74 Duster front-end, to do the disc conversion. So here's my question, After I install the front-end parts, I will have bbp in the front, is it possible to change just the rear axles & drums to the larger bolt pattern, or do I have to swap the entire rear to something else. I have always turned to forums for help, and have never been let down, thanks in advance for your help, Rob.
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look for a 8 1/4 out of the 73 and up A body V8 car for big bolt pattern
most 8 3/4 will still be small bolt pattern and very expensive, if you can find one
 
7 1/4 BBP rears are common and cheap enough. Adapters work also for normal street use. 8 3/4 rear with BBP will have aftermarket or redrilled axles, be nearly impossible to find and dificult to afford.
 
All 73+ A-bodies with \6 or 318 AND disk brakes came stock with a 7.25 with big bolt pattern. Should be easier to find one of those (I gave one away not to long ago) than an 8.25 and 8.75 will require new axles and re-drilled drums to get to big bolt pattern.
 
dgc333 said:
All 73+ A-bodies with \6 or 318 AND disk brakes came stock with a 7.25 with big bolt pattern. Should be easier to find one of those (I gave one away not to long ago) than an 8.25 and 8.75 will require new axles and re-drilled drums to get to big bolt pattern.
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Thanks, but want to clarify one thing. If I were to get a 73, 74, 75, 76 Dart/Duster (basically any A-Body) 7 1/4 rear axle shafts, I could just replace my existing SBP axles with no modifications at all, except replacing the drums? I mean, the spline number & diameter are identical?
 
shhnappa said:
Thanks, but want to clarify one thing. If I were to get a 73, 74, 75, 76 Dart/Duster (basically any A-Body) 7 1/4 rear axle shafts, I could just replace my existing SBP axles with no modifications at all, except replacing the drums? I mean, the spline number & diameter are identical?
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No. DGC said those years AND disk brakes are BBP rear. I have a 73 with drums all around and it is a SBP car. I used a 75 rear on the Demon and it has BBP. However, I do not know what brakes were on the donor car. Somewhere in the archives, I have read that all of the 75-76 models were BBP cars, but I can't confirm.

Since the 8 3/4 was an option on all cars, you may already have one. If the rear cover is smooth, bingo. My recommendation at that point is to buy a pair of A-body BBP axle shafts and drums to match the ones removed, save the bolt pattern, and live happily ever after.

If the rear cover of the axle has 10 screws and a 1½ inch axle tube is is a 7¼. If 10 screws and a 3 inch axle tube it is an 8¼ axles.

Another possibility is that you have or find a Sure Grip differential. With the wheels off the ground, twist a wheel counterclock wise. If the opposite wheel spins the same way, you have Sure Grip. If the opposite wheel spins in the opposite direction, you have an open rear end.
 
just gone done a few minutes ago....changing out 71 dart to lbp ...

bought new A body 5 on 4.5 axles, bought backing plates and drums from 74 duster with 8 1/4 rear.

in fact this is the second one I did this way....
 
I just read the thread and saw the pic in your last post. Are you sure which axle you have? a 340 should have 8.75. If so, then axle shaft swap is easy. I got my BBP axles from Moser Engineering fo my swap. http://www.moserengineering.com/ .
They have several perf levels , I got their street axles. They probably have a set ready to ship.
 
charger70 said:
I just read the thread and saw the pic in your last post. Are you sure which axle you have? a 340 should have 8.75. If so, then axle shaft swap is easy. I got my BBP axles from Moser Engineering fo my swap. http://www.moserengineering.com/ .
They have several perf levels , I got their street axles. They probably have a set ready to ship.
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It was an original 318 car, how can I tell for sure which rear I have, I was told it was a 7.25, but they could have been wrong, I will take a pic of it and post later, but if there is some other telltale way, please, let me know, thx.
 
I run LBP on my fronts due to the disc brake conversion and small bolt pattern on the rear. I have Wheel Vintiques custom steelies (15 x 8, SBP) with the 7.25 diff.

Works like a charm as long as the rims are the same diameter.
 
shhnappa said:
Thanks, but want to clarify one thing. If I were to get a 73, 74, 75, 76 Dart/Duster (basically any A-Body) 7 1/4 rear axle shafts, I could just replace my existing SBP axles with no modifications at all, except replacing the drums? I mean, the spline number & diameter are identical?
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Not sure. The housing changed and the bearing on the axles is different, you may be able to but if you find the axles they likely are going to be in the housing so why not take the whole thing.
 
Here are the pics, the drums are 10" and the pads are 1 3/4", so what rear do i have?
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looks very similar to the 7.25 that came out of my 64 dart.

also whats up with that crazy bent leaf spring in this pic????
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-tim
 
Optik said:
looks very similar to the 7.25 that came out of my 64 dart.

also whats up with that crazy bent leaf spring in this pic????
vbpgimage.php

-tim
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Helper spring that will be replaced by new springs. So are we all in agreement, is it a 7 1/4" rear?
 
Yes that is definately a 7 1/4" rear. No you can not take axles out of a BBP 7 1/4 and put them into your SBP 7 1/4. The axles have a different taper and different bearings.
you need to look for an A-body after 72 with disks and a V8(preferably with a towing package) to find an 8 1/4. That is your best option for getting BBP.
 
70Valiant said:
Yes that is definately a 7 1/4" rear. No you can not take axles out of a BBP 7 1/4 and put them into your SBP 7 1/4. The axles have a different taper and different bearings.
you need to look for an A-body after 72 with disks and a V8(preferably with a towing package) to find an 8 1/4. That is your best option for getting BBP.
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So if I find such a rear (8 1/4) as mentioned above, that will or will not be a direct swap of axle shafts? The bearings and all would swap out without any issues, or do I just say screw all this and get the adapters for the rear wheels and leave everything as is.
 
Do not use the old style cast aluminum adapters-good way to wipe out your rear quarter panels if they break! Not safe at all. I saw a 70 duster that had used them years ago, one side broke or came loose causing lose of tire-major body damage and a wild ride I'm sure! I think the new billet ones are alot safer, I hope! Just my 2 cents worth! Myron
 
Definatly do not use the adapters!!
I vote with the other guys to swap for an entire 8.25. Axles, housing, gearset, brakes and all. The whole Shebang.
There must be someone near you that has a 4dr Dart or Valiant you can use for a donor.
There are also Sure Grip units for 8.25.
Not sure if there is one available for 7.25
 
charger70 said:
Definatly do not use the adapters!!
I vote with the other guys to swap for an entire 8.25. Axles, housing, gearset, brakes and all. The whole Shebang.
There must be someone near you that has a 4dr Dart or Valiant you can use for a donor.
There are also Sure Grip units for 8.25.
Not sure if there is one available for 7.25
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I spoke with Rocky at Moser, he said he could sell me a set of factort axles for $215 (pr) with the BBP, same bearing & spline size, basically a plug & play swap, or I could send him my axles and he would drill them out for the BBP and include the studs for $65.00 for the pair. I think I'm going to go that route unless you guys feel I should just repalce the axles, your thoughts?
 
I found this thread while searching for answers to this exact same problem and wanted to let anyone know that I too contacted Moser and spoke with Aaron. He confirmed they will still do this "plug and re-drill" the axle Hub and Brake drum in order to get the 5/4.50 bolt pattern needed to get my 69 Dart back on the road again with updated wheels and front Willwood Disc Brakes! Thanks to shhnappa for starting this thread and to all those suggestions. If shhnappa has a an update on how all that worked out in 2008, I would really like to hear about it.
 
I am curious what it takes to "plug" the axle hub.
I found a DIY kit for re-drilling, because I don't have any machine shops near me that I know of.
Drill Guide

I might just send them into Moser or buy new axles with the bigger bolt pattern.
 
I've got a set of redrilled axles for an A body 8.75 if you haven't done yours yet.
 
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