Question about various rear ends

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Stepper

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Hoping someone doesn't mind taking a quick minute to help educate me on something.

In doing research, it's become apparent to me that the 8 3/4 rear end with sure grip is the most desirable.....and some people even swear by the 8 1/4.

What I'm not clear on is the difference between the large bolt pattern and small bolt pattern. Why is the large bolt pattern preferred? Is the LBP only available on certain setups?

The other item that eludes me is the 3rd member variations. I keep reading about various numbers, but am not sure what the difference is and what is best suited for certain uses.

I currently have the dreaded 7 1/4 rear end and want to switch it out with something, but am trying to educate myself on what the various options are and what will work with various engine power/torque specs.

Also if there's some other tidbit of data that goes along with this topic that ties things together and I'm missing it, please let me know

Thanks guys.

Merry Christmas!

Mike
 
Stepper said:
Hoping someone doesn't mind taking a quick minute to help educate me on something.

In doing research, it's become apparent to me that the 8 3/4 rear end with sure grip is the most desirable.....and some people even swear by the 8 1/4.

What I'm not clear on is the difference between the large bolt pattern and small bolt pattern. Why is the large bolt pattern preferred? Is the LBP only available on certain setups?

A body cars until 1973 were small bolt pattern. Large bolt pattern gives you more choices for wheels and brakes.

The other item that eludes me is the 3rd member variations. I keep reading about various numbers, but am not sure what the difference is and what is best suited for certain uses.

Like gear ratios? 4:56 : 1 would be a gear for 1/4 track racing for example, and 2:76 : 1 would be for driving highway speeds at a lower RPM




I currently have the dreaded 7 1/4 rear end and want to switch it out with something, but am trying to educate myself on what the various options are and what will work with various engine power/torque specs.

You could get a SBP 8 3/4 and solve that. A bit pricey, perhaps. Or you could get a 8 1/4 (likely a BBP) and have a good reasonably priced axle. If you go BBP in the rear, you may want to upgrade the front to BBP so you don't need two spares...

Also if there's some other tidbit of data that goes along with this topic that ties things together and I'm missing it, please let me know

Thanks guys.

Merry Christmas!

Mike
Click to expand...


good luck, and read this forum...do a search for what you are looking for,, I'm sure it has been covered!
 
The Large bolt pattern and small BP are, how your axles are drilled for the studs, where your wheels bolt to the axle. The pattern is 4 1/2 " -5 Lug (Large), or 4 "- 5 Lug (small). When buying wheels, you have a much larger selection with the 4 1/2 ".

The 8 3/4" rear has either the 4" or 4 1/2" axles.

It also has one, of 3 different pumpkins, or third members.

The 741, the 742, or the 489.

All three are good, but parts are scarce for the 741 and the other two are better for drag racing.

These identifying numbers are found on the out side of each pumpkin, and they are the last three numbers.

There are also two different sure grips, the cone and clutch. There are pros and cons about these.

Then there are the different yoke sizes and I think there are 3 different rear brake sizes, 1 3/4", 2 1/4", 2 1/2" . I don't know much about these , either.

Hopefully I got this right and it helps get you started.
 
Stepper, I'll take the time for ya buddy. Crate covered it for ya pretty good. Ill share my knowledge as that's what this site is about. By the way, WELCOME.
Early model 8.75's up till about 72 would have been small bolt pattern. In 73 they could have been either due to the fact that was the year they made the change. To determine which one you are looking at, place your tape over one stud and pull it diagonally to the oposing stud. It will either measure 4" or 4.5" to the center of the next one.
On the case issue. Some will debate the issue of which is stronger. The 489 case does have the largest dia. pinion shaft at 1.75". When ordering any parts you will need to specify which one your working with. The guts are different. I'm partial to the 489 case and wont argue with others about which is better. Keep this in mind. The bolts on the ring gear are left handed and most generally will have been locktited. You should do the same when you reassemble the unit. Depending on what kinda power you'll be putting to it will depend on needs. Ma Mopar felt that an 8.75 was adequate for use behind an automatic Hemi 68 SS Dart. 4 speeds got the Dana 60. Perches will all be located in the same spot for all of em. Let us know if ya need anymore help.
Small Block
 
Small Block. Great info but I was under the impression that a 489 case was
1 7/8" (1.875) and a 742 had a 1 3/4" (1.750). The 741 has 1 3/8" (1.375).
By the way the Ford 9" has a 1.303" if I'm not mistaken. Orv
 
Thanks guys. That's exactly what I was looking for.
I wasn't sure what the 3rd member numbers were all about...i.e 489 etc...
That helps a lot.

Merry Christmas and Happy New Year to you all.

Mike
 
:wav:Thanks for the information, demon seed. Ever Mopar Guy should read these articles, good comparisons with Ford and Chevy. Appreciate it very much! :read2:
 
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