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Tech Question
todd sexton, Saint Paul, MN, 1975 Dodge Dart 225
My 1975 slant-6 Dart has a 7.25 rear axle (which is not uncommon, apparently). I'm switching to disc brakes up front, which means the 4.5" bolt pattern for the front wheels, which in turn means that I need to upgrade from 4" to the 4.5" bolt pattern for the rear. So I'm replacing my axleshafts.
My questions:
(1) I'm assuming that axleshaft lengths vary between models and perhaps
even particular cars. Is there a way to identify my axleshaft length
without actually removing the axleshaft?
(2) Do you have any general advice for performing this axleshaft
replacement? I have quite a bit of general mechanic experience, but this is
my first vintage Mopar adventure.
(3) Would there be any advantages to replacing the entire differential
(and therefore a different length driveshaft) instead?
I'm not planning on racing a slant-6 sedan, so serviceability, reliability and safety are my primary concerns. Thanks very much!
Todd-
Amazingly, the factory DID have 73-up A-body (Dart/Duster/Valiant, etc) 4.5" bolt circle 7.25" axle shafts which were installed on cars with the slant six and the disc brake option. You might luck out and find a set. If you get 'em, just swapping axle shafts its very easy on the 7.25", just unbolt the retainers and slide 'em out. But it may be easier to find an F-body (Aspen / Volare, which were all 4.5" BC) with a 7.25" axle and have those shafts shortened and resplined. Nobody does this since most people wanna dump the blow-up-prone 7.25" axle anyway so there's little experience base. But if you're staying with the stock slant six, that might be the cheapest way out. If I were you I'd call someplace like Moser Engineering and ask them about this.
The most common swap is to use a 65-72 A-body 8.75" axle, then use shortened and resplined C-body axle shafts and matching brakes. Another plan, also good, it to use a complete rear axle from a 73-76 A-body, 8.25" RG. This bolts in and already has the 4.5" BC. Either of these swaps can handle a V-8 swap should that day come.
Remember, you need the matching brake setups and drums, complete.
Rick
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