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| Birthday Present Ideas (3.55 for 7.25) https://slantsix.org/forum/viewtopic.php?t=25412 |
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| Author: | project72dart [ Wed Oct 17, 2007 7:38 am ] |
| Post subject: | Birthday Present Ideas (3.55 for 7.25) |
So...I asked the boy what he wanted for his upcoming birthday. Despite being away at college (freshman) without the dart (parking expensive, afraid someone will "mess with it"), he said something for the dart. Specifically, some go faster gears. We've worked on just about every part of the dart except for the rear end. We changed the springs but that's the only thing we've touched back there. First question is confirming we have 7.25 rear end. How? Next, what's the recommended way to get lower gears (3.55) into the rearend? We'd like to be able to go back to the highway gears without too much trouble. Getting dirty is preferable to throwing $ at it. We don't know enough about it to even ask intelligent questions so any advice would be helpful. I'm sure it will be like when we did the front end. It took a week of studying the FSM ("what the heck is a torsion bar") and four days to do but now would take about 4 hours. Thanks, Larry |
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| Author: | SlantSixDan [ Wed Oct 17, 2007 8:48 am ] |
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The 7¼" rear axle has a 9-bolt cover. There are no easy gear swaps in this rear axle; each and every swap is a long, exacting process you will not want to do more than once. If you are intent on swapping ratios easily and keeping the 7¼" rear axle, then the quickest and easiest way is to have two rear axle assemblies. Swapping the entire assembly is a great deal faster and easier than changing the gears. What are the specs on this car? Is it an automatic, or a stick shift? |
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| Author: | ROADRUNNER7169 [ Wed Oct 17, 2007 10:05 am ] |
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if you want an easy change rear you want to go with an 8 3/4, but to do this you will need 2 jack pots it is a little easier than changing the whole rear but not by much. also gear oil will get expensive if you are changing it all the time |
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| Author: | project72dart [ Wed Oct 17, 2007 10:15 am ] |
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It's an automatic. 99% sure it has 7.25 axle but will check this evening. Looked on car-part.com and closest "Axle Assy Rear, non-removable carrier, 9" brakes" for 72 Dart was 400 miles away. Doesn't sound like they're very common? Sounds like swapping out the entire axle assembly is the way to go. Is there another size (8.25, 8.75) that's more common? Thanks |
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| Author: | 65 dartman [ Wed Oct 17, 2007 10:36 am ] |
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I've got 3 early A Bodies with the 7.25 rear end ( most likely 2.93s in a Dart - was a slant/904; and 2 with most likely 3.23s in them - Valiant slant/3 speed and Barracuda 273 2 barrel 4 speed). All will be available hopefully by spring as I will be converting all to 8.75s, which I have on hand. They will be free for coming to pick them up. |
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| Author: | SlantSixDan [ Wed Oct 17, 2007 11:22 am ] |
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Automatic trans + 3.55 rear gears = annoying car to drive. Yes, you'll be able to smoke the tires from a standing start, but car speeds much above 45 mph will be loud and "thirsty" (bad mileage). Are you sure that's what you want? What tire size are you running? What rear gear ratio have you got now? If you've got 2.76s and reasonably ordinary 14" or 15" tires, a change to 3.23s would provide a significant increase in around-town "snap" without making the car too noisy or busy/thirsty on the highway... All A-body rear axles are now scarce in good condition. 8¼" (10-bolt cover) rear axles from F- and M-body cars are more common than the A-body 7¼" and 8¾"units, but some modifications are required to install such a rear axle in an A-body (driveshaft shortened, spring perches moved inward). |
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| Author: | project72dart [ Wed Oct 17, 2007 1:15 pm ] |
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SSD, 65 Dartman, ROADRUNNER7169, thanks for the help. Now I have a little direction which is sometimes half the battle. Doesn't look like he's getting the gears for his birthday unless we give him the dreaded "gift certificate". I think I'll look for 7.25 with 3.23 close to home. Thanks for the offer, 65 Dartman, but I would think it would cost a fortune to ship a rearend. ...and at the same time, look for an 8.25 and read-up here about what it takes to switch. One more question, if it's not too much trouble. What vehicles and years should I search for on car-part.com to find an 8.25 rearend. Thanks |
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| Author: | SlantSixDan [ Wed Oct 17, 2007 1:24 pm ] |
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First pick would be to look for a '76 Dodge Dart. A '73-'76 A-body 8¼" rear axle will require only that the driveshaft be shortened. Second preference would be a '79 Aspen or an '85 Diplomat. To install one of these, the driveshaft would need to be shortened and the rear axle's spring perches moved inward (cut off/replace/reweld). Be advised that all of these 8¼" rear axles have the large wheel bolt pattern (4½"). Your '72 would've come standard with the small bolt pattern (4"). So that's something to keep in mind if you still have the 4" pattern up front. |
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| Author: | project72dart [ Wed Oct 17, 2007 3:26 pm ] |
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The search for 85 Diplomat shows lots of rearends available close. Question: car-part.com asks for "round cover" or "square cover". Any difference? Also, should I look for the desired gears installed or can I reasonably replace them (cost, availability, low skilled labor) unlike the 7.25 gears? This may be the way to go as long as we're careful about the pinion angle and driveshaft length according to what I've read here. Any other "gotchas" we should know about from those that have done this swap. So far, we've got: drive shaft length, move perches, 4.5 bolt pattern. Thanks |
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| Author: | SlantSixDan [ Wed Oct 17, 2007 4:35 pm ] |
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The only difficulty is that when you get into the Diplomat units, you will almost certainly not find 3.23s. Lots of 2.93/2.94 units and lots of 2.45 and 2.26 units, but almost no 3.23s. The F-body (Aspen/Volare) cars and the A-body (Dart/Valiant/Duster) cars got 3.23s with manual transmission. Round cover = 8.25" Square cover = 7.25" A 3.23 gearset for either of the rear axles won't be difficult to obtain, but installing them and setting them up is an involved, precision procedure requiring special tools. |
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