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Old 04-10-2005, 07:04 PM
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390 posi help with understanding difference?

Hi everyone, my son's '56/3100 stepside pickup has a 350/350 with what I think is a 390 posi rear (10 bolt). We just had a 74 camaro clip welded in w/pwr steering and it is great! The guy showed me the pinion was very loose while he had it on the rack one day. I had pulled the axles and changed the rear wheel bearings/seals awhile back and everything looked good while I was in there (I'm no expert by any means). He said he noticed the back wheels were not rotating as they should when cornering and wondered if they had been welded together in the rearend. I've heard of using a minispool or the like to lock the axles together, but not welding. Wouldn't I have seen this when I had the axles out and the spider gears on the side come out also at the same time...at least they fall out on me and I have to re-assemble the things...fun. He said he would change the ring/pinion and the associated stuff (loose pinon bearing for example) if we would get the gear from Seco (we get a lot of stuff there). He also said the 390 or 391 was a little different from the usual gears and required a special setup, to tell the guys at Seco and they would know what I was talkaing about to get the correct stuff. Can someone "edumecate" me on this? We have done all the work on this truck up till now...finding an old 350 block and reworking and putting the tranny/motor in and everything associated such as a new "painless" wiring harness (very good at a lower price than the others) and putting bucket seats from a blazer and building a great console and disc brakes etc ... just need to know a little more about the rear end stuff before committing... and would I be better just finding another posi rearend???thanks...gary. (PS: I drive a 66 mustang/warmed over 302 so we do quite a bit of hot rodding around my house....you know the '56 chevy vs 66 stang and have a lot of fun at the drag strip. It's been a great thing to do with my son. I told him when he was 13 that I would help him do a "project" and he went and found the '56 when he was 14 and paid for it (no motor/tranny or much of anything else) and we started and he paid for everything with a part time job). Sorry for the length ...

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Old 04-10-2005, 08:26 PM
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As one of the Moderators here.........

Let me be the first to WELCOME YOU

If the rear end is a stock 3100 series rear end..........I would change it to a more user friendly type..............with a ratio of 3.50 or close. The stocker has a cover on the rear but really unbolts out the front like a 9 inch Ford.........once you have removed the clips......

I would get something with 5 lug wheels.......like your front end.......or better yet a 9 inch Ford.......

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Old 04-10-2005, 09:01 PM
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Hi Deuce, thanks for the welcome. I have been lurking and reading alot for several months around here. Great place. I have a friend at church with a really nice 74 Nova and he was asking about which spindles will fit to change to discs on the front. He saw what I had done with the 66 stang in changing to a dual mc and using the granada spindles which bolt right up and wala...front discs! I have hooked him up already with some guys on one of the other areas on here to set him straight...lol
I believe the rearend on the '56 is out of a camaro because it is already a 5 lug. I saw a post lower down about how to I.D. the camaro stuff and will do some looking tomorrow and post back. We definitely want to change the gearing as the rpm's are way up when he gets around 50-55. But, it will run like a scalded dog up to that... Just low mpg due to higher rpm's Gas $$$ is really starting to suck big time... Oh well, gotta pay to play I do pretty good in my 66 stang, about 18.3mpg if I can stay out of the secondaries...lol I do have a more friendly 3.0 rear though... Thanks again...gary.
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