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7-1/4 vs. 8-3/4 rear ends.....
https://slantsix.org/forum/viewtopic.php?t=63758		 Page 1 of 1
Author:  GregCon [ Tue Jun 25, 2019 8:02 pm ]
Post subject:  7-1/4 vs. 8-3/4 rear ends.....
I pulled the 7-1/4 out of the Valiant tonight...after 52 years of service it's headed for the differential rack outside.

Though I'm a fan of the 7-1/4, I'm changing to an 8-3/4 for a few reasons.

I have a big pile of 8-3/4's I need to make use of before I die
I wanted the big bolt pattern
I have a bunch of third members with different gear ratios already


But....the 7-1/4 has some distinct advantages...it weighs less and rolls easier. For the average A body with a Slant Six..it's plenty of rear end.

So, when I get the 8-3/4 all together I'll weigh it for comparison. I'm expecting it to be about 60lbs. heavier. That's serious poundage. Here's the complete 7-1/4 - brakes, drums, parking brake cables, etc.

Attachments:
7.25 weight.JPG
7.25 weight.JPG [ 180.2 KiB | Viewed 8295 times ]
Author:  Dart270 [ Wed Jun 26, 2019 3:13 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
60 lbs is about right. If there were strong limited slips and gears available for the 7.25, then I would have one in a car.

Lou
Author:  Charrlie_S [ Wed Jun 26, 2019 3:38 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Quote:
60 lbs is about right. If there were strong limited slips and gears available for the 7.25, then I would have one in a car.

Lou
Likewise. I have been a fan of the 7 1/4, but the parts just aren't available any longer. I had one with 5.13 gears that I am rebuilding with 3.91's. Everything in it is brand new except for the spider gear cross shafts (just not available). Took me about a year to find all the parts and cost somewhere around $400. And I haven't seen the SG clutches for sale in many years. I had one set on hand.
Author:  GregCon [ Wed Jun 26, 2019 5:14 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
So the later vehicles that used the 7-1/4 don't provide a source of parts? Like, didn't some Dakotas use the 7-1/4? It seems like trucks would have used Sure Grips, etc.

Then, there's the added weight that comes with the bigger tires/wheels you migrate to with the bigger bolt pattern.

The only saving grace is that if you have to add 60lbs. to the car, the rear end is one of the better places to add it....at least it's not over the front axle. But, it is unsprung weight which ain't good....
Author:  Greg Ondayko [ Wed Jun 26, 2019 5:31 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
The dakotas. And f-j-m bodies with sure grip that I have seen were 8.25's..

I think sure grip 7.25's were phased out early 70s or so

Greg
Author:  Rob Simmons [ Wed Jun 26, 2019 6:36 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Very timely post. We just upgraded our small bolt pattern 7 1/4 for a large bolt pattern... 7 1/4... for endurance road racing... :mrgreen: :mrgreen:
Author:  sixinthehead [ Wed Jun 26, 2019 7:44 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
YEH BOIIII :twisted:
Author:  GregCon [ Wed Jun 26, 2019 10:27 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Something you never hear anyone talk about....pushability.

I can't push my truck in the garage 2 inches. I could push the Valiant pretty easily. The Chrysler, somewhere in between. That's gotta tell you something about how much power a car wastes just moving itself. I'm sure when the 8-3/4 in installed, my Valiant will take a hit on pushability.
Author:  SpaceFrank [ Wed Jun 26, 2019 9:14 pm ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Planning to put an 8-3/4" in the Lemons Dart some time this year, but we already have an 8-1/4" (from a Jeep) so it shouldn't be as much of a weight hit. We switched to that from the 7-1/4" partially because it was an easy/cheap way to get better gears. Speaking of which, Greg... got any 3.55 pumpkins you don't need? :D

One supposed benefit to the 8-3/4" in road racing is the lack of C-clips, although I doubt that's a major concern for a street or strip car. Granted, we also haven't broken a C-clip on our 8-1/4" in 5 years (~15 Lemons races).
Author:  Dart270 [ Thu Jun 27, 2019 2:31 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
8.75" is about the same wt as an 8.25". Maybe 10 lbs heavier?

Lou
Author:  GregCon [ Thu Jun 27, 2019 6:55 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Sorry Frank, none of that ratio!

I do have (1) 14" 5.5" rim if you ever need it....
Author:  THOR [ Fri Jun 28, 2019 11:17 am ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Hey Greg,

If you have a bunch of those floating around, could you see if you have a spare brake adjuster and associated hardware floating around? My 8.75 in the 58 is completely missing the adjuster on the driver side. It's the later non-tapered axle type. Not sure if there's a difference.

Thanks!

~THOR~
Author:  GregCon [ Fri Jun 28, 2019 3:12 pm ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
If it's the later style, that stuff is all still available. I just ordered a bunch from Rock Auto this week for my project. If you have the original 12" '58 brakes I probably do have some of that.
Author:  SpaceFrank [ Fri Jun 28, 2019 4:22 pm ]
Post subject:  Re: 7-1/4 vs. 8-3/4 rear ends.....
Quote:
Sorry Frank, none of that ratio!

I do have (1) 14" 5.5" rim if you ever need it....
I might take you up on that next time I'm on the north side of town.
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