Posi rearend for my 65 coronet 440

[Wyo65Coronet]

Really want to have posi in my 65 coronet 440.
Its 4Dr with 383/4bbl, original driveline.
This is my first car doin resto on.
Gonna do mild engine mods to boost power a little when I rebuild motor.

Suggestions for easiest/cheapest way to do this?

Thanks in advance.

 

[Basoline]

Think 3.55:1 would be a good compromise for street and highway. The fastest way to do this is to replace the third member.

 

[Wyo65Coronet]

Ok but you'll have to explain.
First car I've worked on to this extent.
Speak slowly and use small words... LOL

 

[MarPar]

what's a posi??? lol

 

[Basoline]

Hm, ok euhm...let's give it try. English is not my mother language so...Here we go:

The rear-axle has the housing, that's where the wheels are attached to. The rear of the housing is round and looks like a (hemi)sphere. In front, where the driveshaft is, that is called the third member. There are 3 types: 741, 742, 489. Check out the number casted on the driversside of the third member (find the three last digits). You will find people refer to this as "casing type".

You said it has the original driveline intact so the number on the side probably ends with 741. Also, the gears inside the third member will be 3.23:1. That tells you something about the gear ratio of the ring- and pignonwheel of the differential. The smaller the first number, the larger the ratio. Low numbers give you high topspeed, low numbers give you a lot of torque.

The fastest way (and probably the cheapest) is to purchase a complete new third member that says 489 (the strongest type) on the side and has a 3:55.1 gear ratio with a Sure Grip. I've had 4.10:1 in mine with 383 4bbl and that's way to much...

This is a populair seller: http://www.ringpinion.com/

Hope this helps.

 

[Cranky]

The 489 being the strongest vs the 741 being the weakest is a myth. Something some magazine started 30 years ago just because of the size of the tapered pinion shaft at the gear head. They saw how large it was and said, wow, look at that! I've never seen the head of the pinion broken off...has anyone? Nope. The size of the pinion where the yoke fits is pretty much the same on all of them (the 742 included) and if they are going to break, that's where it would occur. The only thing the 89 might have over the others is reduced pinion deflection but I've shaved the teeth off just as many of 89 rears as any of the others.