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milage drop going from 2.76 -> 3.23's?
https://www.slantsix.org/forum/viewtopic.php?t=15934		 Page 1 of 2
Author:  CrAlt [ Sat Jan 28, 2006 3:57 pm ]
Post subject:  milage drop going from 2.76 -> 3.23's?
Hey all.

I need to put disc brakes on my 72 dart but i dont want to have 2 diff bolt pattterns and i dont know anyplace that sells small bp rotors....so im gona have to put in a 8.75 rear. BUT the highest geared pig i have is 3.23's. This is a daily driver so im looking for mileage not HP. Anyone notice a big drop in milage? should i just keep my eyes peeled for a 7.25 or 8.25 with 2.76s?
Author:  Eric W [ Sat Jan 28, 2006 5:16 pm ]
Post subject: 
I went from 2.76's to 3.23's in my '70 Fury (gone now) with a 400. It didn't really make much of a difference as is was never that great to start with. I would suspect milage wouldn't drop more than a few mpg if that. Don't forget to change the speedometer pinion gear.
Author:  Doctor Dodge [ Sat Jan 28, 2006 7:42 pm ]
Post subject: 
you will not see any change as long as you do "mixed driving" and keep speeds under 70 mph on the open road.
If you do a lot of around town driving, a switch to 3.23 may actually improve your mileage.
DD
Author:  65 dartman [ Sun Jan 29, 2006 5:53 am ]
Post subject:  Replacement Rotors
I bought a set of rotors at Advance Auto for the KH discs. No hub just the disc itself. You'll need to provide the hub.
Author:  dakight [ Sun Jan 29, 2006 7:07 am ]
Post subject: 
It turns out that the KH rotors are readily available from several places at very reasonable prices.
Author:  70valiant [ Sun Jan 29, 2006 10:23 am ]
Post subject: 
You said you are going to put disks on it but dont want 2 different bolt patterns so are going with an 8 3/4. All A-body 8 3/4 rears are small bolt pattern, unless someone else swapped in big bolt axles and brakes. if you are looking for a big bolt rear you are actually looking for an 8 1/4 rear.
Author:  Reed [ Sun Jan 29, 2006 11:28 am ]
Post subject: 
There was a guy who used to post over on slantsix.com who owned a bright yellow duster. I think his handle was oldmopars. He swapped his duster to late style disc brakes but kept the five on four bolt pattern by ordering a pair of rotor blanks and having them drilled in the four inch pattern and having studs pressed in. Sounds like this would be way cheaper and easier than a rear axle swap.
Author:  70valiant [ Sun Jan 29, 2006 12:44 pm ]
Post subject: 
That does sound more cost effective than $350 for new axles then having to find the right drums and other brake parts. Though swapping in an 8 3/4(or even an 8 1/4) does necessitate different U-bolts and plates as well plus shortening the driveshaft.
Author:  CrAlt [ Sun Jan 29, 2006 7:59 pm ]
Post subject: 
Quote:
You said you are going to put disks on it but dont want 2 different bolt patterns so are going with an 8 3/4. All A-body 8 3/4 rears are small bolt pattern, unless someone else swapped in big bolt axles and brakes. if you are looking for a big bolt rear you are actually looking for an 8 1/4 rear.
I already have a rear and axles that someone cut.I think it was a C-or Bbody rear. Now that I think about it, it has the big 11" brakes on it so i cant even use the rims i was planning on using..grrr

They made no bbp 7.25's? I would rather stick with the same size axle then pay to have yet another drivesaft cut.
Author:  CrAlt [ Sun Jan 29, 2006 8:02 pm ]
Post subject:  Re: Replacement Rotors
Quote:
I bought a set of rotors at Advance Auto for the KH discs. No hub just the disc itself. You'll need to provide the hub.
Will the hubs off my drums work? And will it line up with the spindles and singlepistion slidder cali's on the '75 dart setup I got?
Author:  Reed [ Sun Jan 29, 2006 9:46 pm ]
Post subject: 
Quote:
They made no bbp 7.25's? I would rather stick with the same size axle then pay to have yet another drivesaft cut.

Uhhhh, yes they did. 73-76 slant six a-bodies with disc brakes predominantly have 7 1/4s with the big bolt patter. It is the 8 1/4 big bolt pattern rear axle that is harder to find. BBP 7 1/4 typically can be had for $50 or less.
Author:  dakight [ Mon Jan 30, 2006 4:06 am ]
Post subject:  Re: Replacement Rotors
Quote:
Quote:
I bought a set of rotors at Advance Auto for the KH discs. No hub just the disc itself. You'll need to provide the hub.
Will the hubs off my drums work? And will it line up with the spindles and singlepistion slidder cali's on the '75 dart setup I got?
No, drum brake hubs will not work with diskbrakes; you have to replace the hub, spindle, and possibly upper control arm. If you already have parts from a 75 Dart then they are BBP hubs. If that is the case you are better off to go ahead and find a BBP rear axle.
Author:  70valiant [ Mon Jan 30, 2006 4:07 am ]
Post subject: 
the only real advantages of an 8 3/4 over smaller rears are the greater availability of sure grips and the ease of swapping gears for racing. For a stock slant or even a mildly built street slant your best bet is a 7 1/4.
Author:  CrAlt [ Tue Jan 31, 2006 3:41 pm ]
Post subject: 
Quote:
Quote:
They made no bbp 7.25's? I would rather stick with the same size axle then pay to have yet another drivesaft cut.

Uhhhh, yes they did. 73-76 slant six a-bodies with disc brakes predominantly have 7 1/4s with the big bolt patter. It is the 8 1/4 big bolt pattern rear axle that is harder to find. BBP 7 1/4 typically can be had for $50 or less.
Thats what I was asking...see the "?" :)

Its a stock slant that isnt raced or anything..just needs to run (which it does good now) and stop (which it doesnt do so good).

Thanks...a 73-76 rear is what i be needing.
Author:  imnoisydart [ Thu Feb 02, 2006 7:41 pm ]
Post subject: 
You might want to consider the Scarebird disc conversion.
You keep the drum brake spindles, and cut off one corner I believe and then use GM rotors and calipers. There is a guy in Seattle I think who makes this setup (do a search)
The advantage is that you have new cheap brake parts as opposed to
old SBP Kelsey Hayes stuff if you can even find it.
And yes, they did make BBP 7 1/4's - I have one lying around somewhere.
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