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Rear end ID'ing
https://www.slantsix.org/forum/viewtopic.php?t=4590		 Page 2 of 2
Author:  Guest [ Mon Dec 09, 2002 5:20 am ]
Post subject: 
Lower rear gears will give you more snap off the line but leave your engine winding higher at freeway speeds, so how you approach the trade-off depends partly on what type driving you'll mostly be doing with this car. Long commutes---stay with the stock gears. Mostly city driving---maybe go lower. Super low gears will also have a negative effect on mileage if you do alot of freeway driving.

3.21 is a pretty good compromise for both...pretty tame. No changes to the trans necessary: that type gearing was a stock option. Are you going to add any performance enhancements to your engine (higher lift cam, 2 or 4-bbl carb, bigger valves, higher compression etc.)? Most people feel that 7-1/4" won't hold up well if stressed that way. Probably better to go with an 8-1/4" in that case.

Racers like Doc and Slantzilla can give you more specific information about the really low ratios..they've had more "hands on" experience with them than I have.

---Red
Author:  rustycowl [ Mon Dec 09, 2002 8:27 am ]
Post subject:  gearing
I've run 3.55 and 3.91's and kept good mileage. I think it depends on your combination. The rear axle ratio, cam torque curve characteristics, and tire rolling diameters, among others, influence the 'streetability of gear choices. For me and my combinations, 4.56 & 4.30 are not amenable to street use. 3.21, as mentioned before, is a good compromise for most applications.
Author:  Pierre [ Mon Dec 09, 2002 8:50 am ]
Post subject:  engine mods
Red,

The engine was rebuilt pretty much stock, the head/block was shaved a bit but not much, just to get rid of some shallow marks on each surface. Nothing near as steep as I see people doing here.. So I don't think compression has changed very much. Then after that I added headers/4barrel intake/holley 390cfm 4 barrel carb of which I am in the process of getting tuned now (another adventure within itself, hehe). That's why I'm starting to hunt around for a bigger rear now. There also might be a possibility of adding efi to the engine in the future. I'm not really sure how the 7 1/4 will hold up with that. Any thoughts?

As to the ratios.. yes sometimes I do long commutes (60+ miles one way!) and other times I use it to putt around town once a week, if that. Driving of that car is really sporadic, depends on wether I'm at school, etc etc. I just want to also have the possibility of spinning the tires when I feel like stomping it, which the stock gearing doesn't seem to afford me...
Author:  Patrick Devlin [ Mon Dec 09, 2002 11:09 am ]
Post subject: 
I think there is another good reason to pitch the 7.25" rear if you are going to be upgrading the drivetrain: the cheesy axle bearings on the 7.25" rear.

I really dislike the axle bearings in the 7.25" rear. They are very small caged ball bearings. I had one fail on me while doing highway driving this past summer. I lost an axle after coming off of a cloverleaf. I had been driving 90mph just a little earlier. Needless to say, I'm lucky the axle is all I lost!

Anyway, that's when I put an 8 3/4" rear with a 3.55 sure grip in my Dart. I really like the axle bearings of the 8 3/4" rear much better. They are good sized tapered roller bearings, which I understand are better for side loading. I admit, I probably cornered way too hard on almost every turn when I had the 7.25" rear in. That, no doubt, lead to premature bearing failure. But you gotta drive 'em like that, right? :twisted:
Author:  Chuck [ Mon Dec 09, 2002 2:47 pm ]
Post subject: 
Quote:
I think there is another good reason to pitch the 7.25" rear if you are going to be upgrading the drivetrain: the cheesy axle bearings on the 7.25" rear.

I really dislike the axle bearings in the 7.25" rear. They are very small caged ball bearings. I had one fail on me while doing highway driving this past summer. I lost an axle after coming off of a cloverleaf. I had been driving 90mph just a little earlier. Needless to say, I'm lucky the axle is all I lost!

Anyway, that's when I put an 8 3/4" rear with a 3.55 sure grip in my Dart. I really like the axle bearings of the 8 3/4" rear much better. They are good sized tapered roller bearings, which I understand are better for side loading. I admit, I probably cornered way too hard on almost every turn when I had the 7.25" rear in. That, no doubt, lead to premature bearing failure. But you gotta drive 'em like that, right? :twisted:
I would suspect that your rear axle bearing was making nasty noises long before it went. Gotta keep yout ears open for that "whump whump" sound from the rear! :wink:
Author:  Patrick Devlin [ Tue Dec 10, 2002 11:51 am ]
Post subject: 
Yep, you're right Chuck! You definitely shouldn't "check out that noise later" or after you get to work. Pull over and take a look. Learned that one the hard way. You can bet my attention to bearings is a lot better now.

Still, I couldn't believe how weak-looking the bearings on the 7.25 are. Look like bicycle or skateboard bearings to me.
Author:  Pierre [ Tue Dec 10, 2002 12:08 pm ]
Post subject:  rear axle off a 63 chrysler
Guys -

Calling attention back to my post about a rear end from a unknown 63 chrysler in this thread... anything? Also I just realized that the vin decoding page said valiant 200 not dart 200 as previously mentioned

According to this chart someone else gave me in another forum:
http://www.moparchat.com/forums/attachm ... tid=382855

The closest 8 3/4" rear is 3.6" wider then the A body version. This deff. makes me think the car I found is like an 'A' body, wether or not it is officaly classified as one
Author:  Tim Keith [ Tue Dec 10, 2002 3:07 pm ]
Post subject: 
The 8 3/4 was manufactured until 1974, only used in A-bodies thru '72.

http://members.tripod.com/~Mojo_Page/chry875.htm
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