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Old 04-28-2002, 07:50 AM
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Wink 9" Ford or 12 bolt Chevy

Hi, I just found this forum and it seems to be full of info. Thumbs up to the webmaster. I have an 87 Chevy S10 that I'm gettting ready to drop a 327 in and I'm not sure about the rearend. It seems to be a 12 bolt Chevy (its the stock rearend) but its not a posi. I'm gonna eventually tub this truck and install some big wide sticky Mickeys but I dont know which rearend to go with. Will the stock unit hold up if I install a posi and narrow it or should I just go all out and try to find a 9" ford rearend. I will be using a 350 turbo tranny for now but will eventually swap to a 2 speed powerglide. I'm thinking 9" ford but Im not sure how to identify them and dont know which ford vehicles came stock with these units. Any advice would be appriciated. Thanks, Charles

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Old 04-28-2002, 08:38 AM
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All you have to do is count the number of bolts on the diff. cover to know if it's a 10 or 12 bolt. I'm no expert on GM rears but I've seen some 12 bolts take some abuse. The nice thing about the Ford 9-inch is the center section (third member) is removable. The ring & pinion is set up with the member out of the rear. The nice feature with this is you can set up more than one third member with different gear ratios and all you have to do to go from a 3.50 ratio to a 4.11 ratio is slide the axles out and swap members. The pinion depth and bearing preloads are already set. The 9-inch also used a third bearing on the pinion shaft which gave it the ability to handle tremendous torque. I have seen many rods with sbc engines and ford 9-inch rears. The 8-inch is a smaller version of the 9-inch but not as strong. They are both easy to recognize because their is no cover on the back like in a newer 8.8 or a GM rear. I know on my Ford the 8-inch that was in it the third member was smooth but the 9-inch I bought for it looks like it has fins across the front of the third member. I don't know if they're all like that. They're not so easy to come by these days but if you can use a 9-inch it's a bullitproof rear.
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Old 04-28-2002, 06:41 PM
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hey,

I put a 327 in my s-10 blazer..... it still has the stock rear (for now) in 1988 they changed from the smaller 10 bolt rear to a slighlty bigger one... its a little stronger but aint that great... it will break if u put huge tires on it and all that.... u might have a limited slip unit.. check the codes in ur glvoe box... lets see if i can fidn this post on s-series wehre they had the codes for ratios... bah i m sick of looking.. i woudl recommend checkign that board out for various stuff... www.prestage.com/cars/RearEnds.asp

<a href="http://www.ridgenet.net/~biesiade/Fordrears.html]http://www.ridgenet.net/~biesiade/Fordrears.html[/URL]

p.s. - Nice choice with the 327 in the s-10

Jordan
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Old 04-29-2002, 05:54 AM
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Hey Jordan, thanks for the links. I just added them to my favorites for future reference.
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Old 04-29-2002, 11:47 AM
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The 12 bolt is a strong rearend, will have no trouble with a 327..
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Old 04-29-2002, 12:08 PM
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For you and any others interested, here's a great website regarding info. on Ford 9" rearends and what vehicles you can find them on.
<a href="http://dfwmotorsport.com/Fairlane/9inchrearends.htm" target="_blank">http://dfwmotorsport.com/Fairlane/9inchrearends.htm</a>
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Old 04-30-2002, 08:57 AM
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I'm currently building a 35 ford which had a 12 bolt chev rear. I was also going to narrow it 6" for use with the wider tires (17 inch MT sportsmans) but ran into a problem. The splines on the axles are tapered. You can pay the extra machine shop costs for dealing with this (which are substansial) or just go to a 9" ford, which does not have tapered axles and they are bigger/stronger anyway. I also elected to have the ford axles redrilled to the chev 4 & 3/4 inch bolt pattern to match the front clip which is also chev. I elected to go this route and feel like this is the best as well as the least costly solution.
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Old 05-04-2002, 04:25 PM
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I tell you what...I am so glad I found this forum. Everyone here is so helpful. Thanks to all that have responded to my post, I couldnt ask for more. You guys are great ! ! !
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Old 05-20-2002, 10:41 PM
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You can't just count the bolts on the back of a chevy rearend to see if its a 10 bolt. Both 8 and 10 bolts have 10 bolts holding the cover on. the blots holding the ring gear are the ones that count. However if you look at the back of an eight bolt you will notace that there are 2 narrow pieces of steel hainging down on the botom of the housing and the inside edge of them are cast round (they look like a whole was drilled in them and then one cornnor was broke off. The 10 bolt will look thesame, except the two hangey downeys will be larger, and square. does this make sense?
You can tell a 9" from an 8" by the third menber, If you can get a socket on the bottom two bolts then its a 9", if the drive shaft yoake is in the way so you have to use an open end to get to it then its an 8", at least thats what I was told when we went to get on for a friends dirt track car at the junk yard
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Old 05-21-2002, 05:27 AM
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The information in the post above this is wrong. GM 10 bolt rear ends have 10 bolts holding the cover on and 12 bolt rear ends have 12 bolts holding the cover on. I don't know where this person got his information from but this link will help him and everyone else ID rear ends.

<a href="http://www.prestage.com/cars/RearEnds.asp" target="_blank">http://www.prestage.com/cars/RearEnds.asp</a>
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Old 05-21-2002, 08:12 AM
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"You can tell a 9" from an 8" by the third menber, If you can get a socket on the bottom two bolts then its a 9", if the drive shaft yoake is in the way so you have to use an open end to get to it then its an 8", at least thats what I was told when we went to get on for a friends dirt track car at the junk yard"
-jeff of nc

Actually, its the absoulute opposite. If you cant fit a socket on it, then its a 9 inch. I have an 8 inch in my mustang and a 9 inch in my garage ready to put in it. THe 9 is substancially larger and has a big hump in the back to allow clearance for the ring gear. THe 8 is just a smooth globe.
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Old 05-22-2002, 08:31 PM
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mustang66manic: Thanks for the corection, Its been a long time since I worked ford rearend and come to think of it I do rember cursing them last to bolts laying in the mud.

centerline: I didn't mean to imply that 12 bolts have 10 bolts in the cover, but that 8 and 10 bolts both have 10 bolts holding the cover on. Some people refer to both 8 & 10 bolt ring gears as ten bolts but technicly if there are 8 blots in the ring gear then its an 8 bolt. regardless the one with the larger bosses at the botom of the cover are the stronger of the two, but not stronger than the 12 bolt.

[ May 22, 2002: Message edited by: jeff of nc ]</p>
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Old 05-23-2002, 07:11 PM
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they never put 12 bolt rear-ends in s-10's they have 7.5 inch rear-ends. They are the same rear-end that is in the camaro's with usually six-cylinders. I have a 350 in my s-10 pushin around 380-400 horse and i have the stock rear-end in it with 4.10 gears and it holds up fine. I am planning on putting in a 3.73 posi unit i picked up out of a astro van, same rear end also.
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Old 05-24-2002, 08:11 AM
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There are a lot of people guessing on this topic. Your s-10 has a stock 7.75" 10 bolt. They are not very strong. If you have a 4x4, there is a good chance that it is posi, but if not the junk yards are full of posi's for the stock unit. If you are going to build high power or get a good grip, then you may want to change rears. The 12 bolt 8.8" GM units are very plentiful and strong and can easily be narrowed. Replacing the axles cost $225 from Moser Engineering and they will do the job on a 2 day turnaround. All the major posi companies sell center units for them. These would be the poor man's equivalent to the Ford 9". The only downside is the C clips that hold the axles in. They are not recommended for circle track racing.

Or you can go to the Ford 9" which is very strong as well, easier to change gear sets and do not rely on C clips. They will be much more expensive unless you can find the rare one in a junk yard.
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Old 05-24-2002, 04:35 PM
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[quote]Originally posted by jeff of nc:
<strong>centerline: I didn't mean to imply that 12 bolts have 10 bolts in the cover, but that 8 and 10 bolts both have 10 bolts holding the cover on. Some people refer to both 8 & 10 bolt ring gears as ten bolts but technicly if there are 8 blots in the ring gear then its an 8 bolt. regardless the one with the larger bosses at the botom of the cover are the stronger of the two, but not stronger than the 12 bolt.

[ May 22, 2002: Message edited by: jeff of nc ]</strong><hr></blockquote>


I missunderstood your post. You're correct when talking about the differences in the 10 bolt internally.
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