Mopar Action On-line – Tech Questions
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 toupgrade from 4″ to the 4.5″ bolt pattern for the rear. So I’m replacing myaxleshafts.
(1) I’m assuming that axleshaft lengths vary between models and perhapseven particular cars. Is there a way to identify my axleshaft lengthwithout actually removing the axleshaft?
(2) Do you have any general advice for performing this axleshaftreplacement? I have quite a bit of general mechanic experience, but this ismy 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, reliabilityand safety are my primary concerns. Thanks very much!
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 slantsix 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 theretainers 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 shaftsshortened and resplined. Nobody does this since most people wanna dump theblow-up-prone 7.25″ axle anyway so there’s little experience base. But ifyou’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 aboutthis.
The most common swap is to use a 65-72 A-body 8.75″ axle, then use shortenedand resplined C-body axle shafts and matching brakes. Another plan, alsogood, it to use a complete rear axle from a 73-76 A-body, 8.25″ RG. Thisbolts in and already has the 4.5″ BC. Either of these swaps can handle a V-8swap should that day come.
Remember, you need the matching brake setups and drums, complete.