8 1/4 to 8 3/4 1973 Charger

[Charger73mopar]

I have 8 1/4 .323 limited slip rear end. I've been wanting to convert it to a 8 3/4 posi 4.11.

I've spoke to some other people about doing it. I was told I would have to take out the whole rear-end axle and all. Then put the new one in with the 8 3/4. Thought i'd run it past you all to see if there would be a short-cut or if it's just what needs to be done.

I own a '73 charger, tuned to a key with a 727 torqueflite. I want to get off the line faster and I don't enjoy the one wheel squeal.

For the short time. I've heard about people welding their spider gears for full posi. Is it reliable? Worth it?

Seeing as I'm only 16, my budget is low and I don't want to break the bank.

Thanks,

Jake

 

[Moparmatt72]

Yes you would need to remove tye 8 1/4 to install the 8 3/4 two different type housings. The 8 3/4 is a pretty stronge housing but everything crosses over as far as brake set up. You might not even have to change the length of the driveshaft don't think there a difference.

 

[71charger_fan]

Don't weld your spider gears. It's just a bad idea and an exceptionally bad idea for a street car. Assuming you really have a limited slip in there, it sounds as if it's worn out. If your running a 318 or even a stock 400, the 8.25 is plenty strong enough. Just invest in a new limited slip unit for that and go with a steeper gear. However, unless you never drive on the highway, I'd shy away from 4.11s. I'm swapping my 3.23s for 3.55s looking for a little more pull out of the hole, but mine has become pretty much just a street car over the years and want to be able to cruise it on the highway at a reasonable speed.

 

[WP29440SE]

whats a posi , isn't a 411 a chevy gear , I thought mopars used a 410 it must be aftermarket

 

[rebootej]

Welding your gears give you a spool. In my opinion not it not worth it, but dangerous. I locks your rear wheels together, you will lose handling and turning is a b*tch, tires will chirp and hop in sharp turns and will wear a lot faster. Had one in my 74 Satellite and hated it replaced it with open gears for now. I would save for new gears in yours or for the 8 3/4 got mine out of a local junk yard and i think you will be happier.

 

[RustyRatRod]

The short cut would be to slap a 4.10 in the 8 1/4. They will take lots of abuse. I have a friend who has a Demon he used to run an 8 1/4 in. It used to leave the line with the wheels in the air to low 11 second passes. He upgraded the 416 with aluminum heads and what not and put an 8 3/4 in it then. He didn't break the 8 1/4, he simply upgraded. Hasn't run in it's current configuration, but he thinks it's gonna go 10.50s. The 8 1/4 is way stronger than people give it credit for.

 

[YY1]

I think the OP is confused on terminiology.

Limited slip is a generic term for whar GM calls Posi-traction and Chrysler calls Sure Grip.

Buying different gears for the 8.25 could get expensive, after paying someone to install and set them up.
I'm assuming the OP doesn't know how.

Obtaining an 8.75 in the correct, or reasonably correct length could be a cost saving move as well as an upgrade, provided that a good quality unit can be obtained. It would only require a bolt on installation, and no special tools, which is not true for the gear change in the 8.25.

Keep in mind that the 73 has "Iso-comp" rubber insulators on the leaf spring-axle perch.

Finding an "Iso" 8.75 is somewhat more difficult than finding one that isn't.

Changing over from Iso to non-Iso, IIRC, requires modifying the shock mounts- using washers to reduce the locating hole size, after removing the rubber isolators.
I haven't actually done it, but I'm doing reasearch in preparation for putting my E body 8.75 under my 73 Satellite.

- - - Updated - - -

...and 4.1x is definately a steep setup on the street. You'll be at 4000 RPM at highway speed!

 

[mach123]

So then would a 3.91 in a 742 with sure grip be a good way to go, thx