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post #1 of 14 (permalink) Old Oct 21st, 02, 11:26 AM Thread Starter
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Danny
 
Join Date: Oct 2001
Location: Los Angeles. CA
Posts: 38
my 67 rs has a small block that puts out just under 400 hp and has a 700r4 transmission. my rear axle just went out and i need to replace it. what size would be best for my car?
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post #2 of 14 (permalink) Old Oct 21st, 02, 11:38 AM
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Matt Jones
 
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Location: Renton, WA USA
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8.5" are cheap, easy to find, and are very durable. Less frictional loss than a 12-bolt, also.

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
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post #3 of 14 (permalink) Old Oct 21st, 02, 11:57 AM Thread Starter
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Danny
 
Join Date: Oct 2001
Location: Los Angeles. CA
Posts: 38
i wouldnt mind putting in the extra bucks if my money is well spent in another rear end. dependablilty and performance is what im really looking for. would the best choice for me still be the 8.5?
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post #4 of 14 (permalink) Old Oct 21st, 02, 01:52 PM
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Matt Jones
 
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I would, but that is just me.

My 2nd cousin does brackets with a 54 Chevy coupe and a 406ci motor...he's a very knowledgable guy when it comes to differentials (he worked on them for his career). All he will EVER run is a 8.5, no 12-bolts, no Ford 9". He just runs a spool, Moser axles, and US gear ring and pinion. If they'll hold up in his car, they'll hold up in most others.

Why spend much more when you could put that dough to something else (like me!)?

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
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post #5 of 14 (permalink) Old Oct 21st, 02, 04:51 PM
 
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Frictional loss!?!!

An 8.5" 10 bolt isnt really that easy to find either.....its right there with a 12 bolt.

I would like to see information on the frictional losses though.

[This message has been edited by chicane67 (edited 10-21-2002).]
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post #6 of 14 (permalink) Old Oct 21st, 02, 05:07 PM
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Matt Jones
 
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Around here, the 8.5" is easy to find. I don't know about other places...In this area, a 12-bolt will go for several hundred dollars, while a 8.5 will sell for $75-150 at a swap meet.

By frictional losses, I mean it will absorb less power. Now, for a street vehicle, the difference is probably not noticable. I know for a quick vehicle (10 sec. or so), there is a difference.

I say this because the aformentioned family member of mine, who runs very high 9's, picked up a couple hundredths. Not too much, but enough to make a difference. Something to think about...

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
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post #7 of 14 (permalink) Old Oct 21st, 02, 06:03 PM
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Freddie
 
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Location: Central City, Ky.
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The 8.5 should be plenty good for you. The 12 bolt is a little stronger, but the 8.5 can be built almost as strong. If you are going to build a 12 bolt or a 8.5, the cost would be the same, other than the cost of the core.

------------------
'69 RS/SS396 pro street
427/4spd/9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead
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post #8 of 14 (permalink) Old Oct 21st, 02, 06:25 PM
 
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Most of all the 67-69 platforms came with an 8.2' 10 bolt. 8.5 are not all that plentiful for the narrower F-body. There are very few 8.5's that will fit without modifications.

If I were to compare a Ford 8/9" to a GM 10 or 12 bolt, I would agree. The reason for this, is that the pinion is so much farther off ring gear center line....and that has basic mechanical theroy and application to back it up.

This is the only real change that would add/subtract a measureable amount of 'frictional' loss and its not really a frictional loss its mechanical, (being of a compound/hypoid type gear).

As for a 10 or 12 bolt, the ring and pinion's are on the same centers and are only a 1/4" different in diameter, not to mention that the surface contact aera on the two are almost the same. As for weight, the 10 bolt is a little lighter but only by a few pounds. So its not that much of a factor...
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post #9 of 14 (permalink) Old Oct 22nd, 02, 09:18 AM
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Matt Jones
 
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Location: Renton, WA USA
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The weight is a factor, but really only if you run the times I mentioned earlier.

Some people gun-drill their axles for this very reason. The weight savings is small, but every ounce reduced in rotating mass is important when you run quick ETs.

Like I said before, in a street vehicle, it doesn't make a difference. I'm just trying
to cover all bases...

As far as ease to find one, yes it will be difficult to find a 8.5 or 8.875 that will fit w/o any modifications. You have to expect to do SOME modifications if you want to go cheap...either shorten the axle tubes, or weld on new spring pearches. Either of which is not a big deal.

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/

[This message has been edited by Silver69Camaro (edited 10-22-2002).]
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post #10 of 14 (permalink) Old Oct 22nd, 02, 10:27 AM
 
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I wish someone would make a bolt in 8.5" for the 1st Gen cars, like they have done with 12 bolt for other years, like the 3rd and 4th Gen cars......it would sell like mad....
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post #11 of 14 (permalink) Old Oct 22nd, 02, 11:34 AM
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Matt Jones
 
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Sounds like you've got an idea...



------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
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post #12 of 14 (permalink) Old Oct 22nd, 02, 12:49 PM
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Freddie
 
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Location: Central City, Ky.
Posts: 5,883
Are you talking about making a new 8.5 for the first gen? I'm assuming that you know about the Nova, Apalo, Omega and Ventura 8.5 rear ends being a bolt in.

------------------
'69 RS/SS396 pro street
427/4spd/9"
Byars Performance
High Performance Drive Train Parts And Service
www.lubedealer.com/biggearhead
big gear head is online now  
post #13 of 14 (permalink) Old Oct 22nd, 02, 01:50 PM
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Matt Jones
 
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Location: Renton, WA USA
Posts: 2,765
Yes, but those are becoming difficult to find.

Every year I'll see a 8.5 w/ disc brakes at the swap meets from a Trans Am (or whatever)...I should pick one of those up one of these days. The guy usually sells them for $150 or so.

------------------
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my webpage at: http://www.geocities.com/compuboy007/
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post #14 of 14 (permalink) Old Oct 22nd, 02, 02:19 PM
 
Join Date: Oct 2002
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Yes, but it would be nice to have a center, tubed to different widths and leave the perches loose.....

Thicker tubes and a mulitude of brake flange would be nice too.....
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