Rearend help!!!

[Mopardreams]

Hey guys new here first post actually. I have a number matching 1970 roadrunner but don't know what all the numbers on the rearend means or how to tell if it's a sure grip I know it's a 8 3/4 but that's it. Please help.

 

[747mopar]

The 489 means you've got a good one (large pinion), to see if it's a sure grip jack the tires up and spin one wheel.. if both turn the same direction it's a sure grip.

 

[65-440]

Is the gear ratio tag still attached to one of the center section nuts ?

 

[Daves69]

Some info here............
http://www.bigblockdart.com/techpages/875axle.shtml

 

[Mopardreams]

The 489 means you've got a good one (large pinion), to see if it's a sure grip jack the tires up and spin one wheel.. if both turn the same direction it's a sure grip.

Got ya just wasn't sure if the were any numbers to indicate it.

 

[Mopardreams]

Is the gear ratio tag still attached to one of the center section nuts ?

Unfortunately no my dad bought the car new but he died when I was young and I couldn't find the info on the window sticker or broadcast sheet.

 

[Mopardreams]

Some info here............
http://www.bigblockdart.com/techpages/875axle.shtml

Thanks for the info good stuff

 

[Mopardreams]

Went to garage jacked it up and both tires do spin but I don't see where he was charged extra for a suregrip rear on the window sticker

 

[Daves69]

The 489 means you've got a good one (large pinion),..............

Yes, more than likely, but.......... there can be exceptions.
Look what came out of my 489 case.................

 

[PP1RT]

Fender tag or build sheet will tell. Also could be a small tag on the rearend under one of the nuts holding the center section to the rear end. It has a few numbers which is your ratio. Like 3.23...

 

[Mopardreams]

Here is broadcast numbers on axel

 

[PP1RT]

Both wheels spin the same direction?

 

[Mopardreams]

Both wheels spin the same direction?

Yes same direction

 

[HT413]

You need to see D91 somewhere I believe indicating sure grip.

 

[HT413]

Btw, black velvet 70 roadrunner... your dad has good taste... 383 auto, also practical.

 

[Mopardreams]

Btw, black velvet 70 roadrunner... your dad has good taste... 383 auto, also practical.

Not sure I follow black velvet??

 

[BeeKool]

A simple way to get ratio.
Put car on hoist or handstands in neutral.
Mark 12 O'clock on tire.. and 12' O'clock on driveshaft.
Slowly rotate the driveshaft, paying attention to both the tire and the driveshaft. How many rotations of the driveshaft does it take to make the tire rotate once completely.
3.25 apprx turns of the shaft means 3.23 ratio
2.75 apprx turns = 2.76 ratio ect.........

I'm guessing it's got highway friendly gears

 

[BeeKool]

A simple way to get ratio.
Put car on hoist or jackstands in neutral.

Damn spellcheck

 

[PP1RT]

3.23 gear. ^^^like he said find a D91^^^
Check fender tag too

 

[PP1RT]

Black interior.