Rear End & Gear I.D.

[BlindSquirrel]

Hello, Guys and Gals,

I need some help identifying my rear end, and an extra set of gears that came with the car. As you can see from the photos, the rear end is not a Mopar 8 3/4. The rear currently resides in a '67 Barracuda.

As for the gears, the numbering that I can make out stamped into the ring gear is (pentastar) 2852938-3.21 2852 PP MM5 291 HT04 HELIXFORM.

Any help identifying the rear end and gear ratio would be appreciated.

BlindSquirrel

 

[RustyRatRod]

Looks like an 8.25.

 

[SirDan]

You can ballpark gear ratios by marking the wheels and pinion and seeing how many turns it takes the pinion to turn the wheels one time. My bet is on 8 1/4. how many bolts does the cover have?

 

[crackedback]

The numbers show a 3.21 gear ratio and that posi/sure grip looks like an 8.25 unit.

The rear in that car is an 8.25

 

[BlindSquirrel]

Thank you to all that replied. I have an 8.75 rear end with a 741 center section. If i were to install that rear end, I would want to replace the 741 with a 742 or 489. Would the rear end swap be a simple bolt on replacement, or is there more involved?

Thanks again for any help.

 

[crackedback]

Why replace the 741?

Stop reading that hogwash about it's lack of strength, it will save you money...

Unless you are launching a decent HP/TQ that literally dead hooks, you won't likely hurt a 741 rear.

I've run 440-6 4 speed cars with 741 cased 8.75's.

 

[BlindSquirrel]

Crackedback,

I appreciate the help and advice. Is the swap from 8.25 rear to 8.75 rear just a drop out and bolt back in, or do I need to have parts fabricated for the swap?

I don't plan on running the car hard, so a 741 would probably suit my purposes just fine.

Thanks again,

BlindSquirrel

 

[crackedback]

Driveshatft might need to be a bit shorter for a 8.75, that's the only thing this chart is good for...

An 8.25 can last a long time as long as you keep the fluid level up and check it occasionally. There are guys running low 11's with 8.25 rears.

Luckily, almost everything will go right across when going from 8.25 to 8.75 rears. The DS is the only significant thing you need to check

 

[BlindSquirrel]

Crackedback,

Would the pinion gear that I have now with a set of 3.91's mate up with the 3.21's, or do I need to change pinions to change gears?

Thanks,

BlindSquirrel

 

[crackedback]

Have to use the matched gearsets.

So no you can't use a different ratio pinion, 3.21, with a 3.91 ring gear.

Reason being that as the ratio numbers get larger, the pinion diameter gets smaller. The ring gear is thicker to move the tooth over to engage with the smaller pinion.

If you get a chance look at a 3.23 gearset in an 8.75 vs say a 4.10 or 4.56. You'll notice the ring gear thickness.