Will an open 8-3/4" leave two black marks during a burnout?

[Chris 69]

I always thought the 8-3/4" rear on my '68 was open, and I never tried to do a burnout with the 383/auto in it. Now its a 440/4-speed, I did a burnout, and there were two stripes behind the car.

Will an open rear do this?

How can I verify whether the rear is open or a sure-grip?

I'll have to look at the build sheet tonight as I think it's the stock rear end in the car.

[lukedukem]

put the car in nuetral, jack up rear, then spin one tire. if they both spin in same direction then it is a sure grip

luke

[Chris 69]

put the car in nuetral, jack up rear, then spin one tire. if they both spin in same direction then it is a sure grip

luke

Thank you Luke. I'll try that when I get home tonight.

[c00nhunterjoe]

Judging from the marks, you have a wore out suregrip

[grdprx]

I've done it before.  I have an open 3.23, I've left a 200' single stripe power breaking, another time I left a pair of stripes similar to yours.  I've got pics at home on the computer.

I've got a 440/auto

[fy469rtse]

chris , ? whats the part number on side of case of centre , 68 you could have a tracklock
totally rebuildable and better than the sure grip
from photo definitely some thing in there

[Chris 69]

Thanks for the info guys. I'll post the numbers and the results of manually rotating the wheels when I get home from work this evening.

grdprx: Please post a picture when you have a chance.

Thank you, Chris

[grdprx]

Here's my pics.  My build sheet says open 3.23 as I recall and I'm pretty sure I've done the test spinning one wheel, the other goes the opposite direction...

[Chris 69]

Here's my pics.  My build sheet says open 3.23 as I recall and I'm pretty sure I've done the test spinning one wheel, the other goes the opposite direction...

Thank you for the photos. So an open rear can leave two stripes....

In the second photo, your stripes look much more uniform then the ones in my photo.

[Chris 69]

Here's the #'s and results of the tests.

With both rear wheels off the ground and car in neutral, when spinning one wheel any direction, the other does not move.

Numbers off the differential are as follows:

2070742. Under this number is "8015".

To the right of the numbers above is "11"

To the right and above the numbers above is "2".

The number on the small tag on the housing bolt is "3.23".

Per the build sheet:

1. "4" is listed under "Axle Code 40". So 404 = 3:23.
2. There is no code noted under "Sure Grip 408".

On the build sheet, under "Build Codes":

1. "Axle" = 237.
2. "Pinion" = 32.

I was unable to figure out what these numbers mean.

[lukedukem]

You tried to turn one tire and the other didn't move. Not sure if it's suppose to do that, but I could be wrong, dragging brake.??
Did you try to turn the other tire, the one that didn't turn in first try.
With an open diff the other tire should turn in opposite direction. Sure grip, it will turn same way.
But what you are describing might be a wore out sure grip.
Let's see what others say


Luke

[RallyeMike]

xxx742 case means it is the carrier with the clutch type sure grip (if it has one). This would be good.... if you have one.

There are no numbers on the outside of the case that will tell you if you have a sure grip. Since the tires do not rotate in the same direction, it's either shot or not a sure grip. The only way to be sure is to take out the pig and look at it.

[Homerr]

FYI the innards will look like this:

Open:



Sure-Grip:

[fy469rtse]

The bottom ones the one you want Chris ,
It could be this that's in it , if steel clutches worn will let it slip , locks up the clutches tighter under load, common sight when I have rebuilt them to find right side steels worn ,
742 is the second strongest rear end apart from 489 case, 489's only weak point is the crush sleeve, 742 solid
Hope you have luck and this is what you have ,
New bearings and new clutches and set up to FSM

[1974dodgecharger]

OPEN diff will only lay down both tires rubber if you have loose road traction, but to have sure grip its better don't want to look like a funny dude doing a burn out with one tire 

[bakerhillpins]

What's up with the gear wear on the clutch housing? Is that a sign of a beat up/thrashed unit?

[moparnation74]

What's up with the gear wear on the clutch housing? Is that a sign of a beat up/thrashed unit?

No kidding, what is up with that!

[Chris 69]

Thanks for the info.

Looks like I'll be pulling the differential apart, probably sometime in January. The goal will be to have limited-slip once it goes back together, either with a new unit, or rebuild existing (if it exists).

[John_Kunkel]

What's up with the gear wear on the clutch housing? Is that a sign of a beat up/thrashed unit?

Some axle ratios like the 2.76 use a huge 17-tooth pinion gear that is very close to the differential housing in normal operation but any flex or a loose pinion nut will allow the gear to make contact with the housing and leave the tooth pattern pictured. That example is extreme but it's not uncommon to see a light contact pattern with the 2.76 and 2.94 ratios.  

[Mytur Binsdirti]

An old Mustang can lay down a better one wheeler squealer. How embarrassing.



http://www.youtube.com/watch?v=eYQj9PlU_Zg

[grdprx]

An old Mustang can lay down a better one wheeler squealer. How embarrassing.



http://www.youtube.com/watch?v=eYQj9PlU_Zg

I had way more smoke than that poor mustang.   
Steve looked better doing it though!   

[bakerhillpins]

What's up with the gear wear on the clutch housing? Is that a sign of a beat up/thrashed unit?

Some axle ratios like the 2.76 use a huge 17-tooth pinion gear that is very close to the differential housing in normal operation but any flex or a loose pinion nut will allow the gear to make contact with the housing and leave the tooth pattern pictured. That example is extreme but it's not uncommon to see a light contact pattern with the 2.76 and 2.94 ratios.  

So is that a sign of overdue maintenance or neglect and therefore something that would make you want to move on to another unit? Or is it just an indication that it's going to need a major overhaul to be useable?

[1974dodgecharger]

Its still useable no issues with me laying rubber down with both tires creating smoke unlike before I could do one wheel burn outs and sometimes on occasion I would do 2 wheel burn outs with open diff because of loose dirt, but one side would be thicker than the other.

[RIDELIKEHELL]

Sure grip!