Considering a 9" swap, need to know everything involved

[olds307 and 403]

I get housings fairly local for $495 plus tax with a $30 exchange on my 7.5". His housing looks good and excepts stock brakes. I still have to decide on gears, my blown 7.5" has 3.42's. I am thing 3.55 or 3.70 this time. I also am thinking 31 spline axles and a posi. Which posi is best street/strip posi for the 9"? Does my drive shaft need shortening? Is there a conversion U joint? My 7.5" blew the spider gears 3 days before the test and tune. The spiders exploded, destroying my girdle cover. The pinion had chips at the back, some ovaling of the housing where the pin goes in. I put it back together after a good cleaning, pretty sure a bearing is gone. Sounds like going over railroads tracks 🙁. I just don't see the point of rebuilding this turd again.

 

[Dragonist]

There is a thread on this conversion in a el camino, by the dude(his name escapes me) with the caddy 500 el camino. Also what might easier and possibly cheaper a A-body 12 bolt, you will just need to get the umi control arms for the conversion!

 

[1980PontiacWagon]

If you can get the housing for a good price, i would do it...the a-body 12 bolt swap is a good alternative, but you need to find one first...I have 3.50 gears in my 9 inch, i run an auburn posi, a lot of people like the eaton unit too...i love my 9 inch because besides changing the fluid, I don't have to think about it..nothing is ever going to happen to it...as for your drive shaft, it depends on the rest of your set up...motor and trans....any drive shaft shop can set you up with a conversion u-joint.

 

[olds307 and 403]

Olds 403, in place off the Olds 307 and a TH2004r, which was stock. I am leaning towards 3.50 or 3.55 for gearing. Anyone buy a rebuilt 3rd member off Ebay?

 

[1980PontiacWagon]

One, your trans probably hates you lol...but if you plan to keep it, get a shorter rear gear, such as 3.73. because with the OD of the trans you want 4th gear to still be usable...right now I have a TH400, 350 gears and 26 inch tall tires, at 60MPH i'm spinning 3000 RPM...As for buying a used/rebuilt 3rd member off ebay..make sure it was rebuilt with quality stuff, and ask if they can give you a picture of the gear mesh with the grease on it..and of course dubble check everything when you get it.

 

[olds307 and 403]

The trans isn't the original. I mildly built the original but a cheap high stall converter imploding took out the trans. I will go with an EA stage 1 2004r when this one dies. Still need to figure what needs to be done to a TH350/2004r drive shaft. 3.70 gears or 3.89 would be max.

 

[1980PontiacWagon]

ok...3.70 gears would probably be good...good power at the track, but with the OD you could cruise at a reasonable RPM..

as for your drive shaft issue...I think it will fit...but might need to be shortened an inch or so

 

[Dragonist]

I get housings fairly local for $495 plus tax with a $30 exchange on my 7.5". His housing looks good and excepts stock brakes. I still have to decide on gears, my blown 7.5" has 3.42's. I am thing 3.55 or 3.70 this time. I also am thinking 31 spline axles and a posi. Which posi is best street/strip posi for the 9"? Does my drive shaft need shortening? Is there a conversion U joint? My 7.5" blew the spider gears 3 days before the test and tune. The spiders exploded, destroying my girdle cover. The pinion had chips at the back, some ovaling of the housing where the pin goes in. I put it back together after a good cleaning, pretty sure a bearing is gone. Sounds like going over railroads tracks 🙁. I just don't see the point of rebuilding this turd again.

Here is the link for Mike P's 9in conversion

http://gbodyforum.com/viewtopic.php?f=14&t=25389

 

[GuysMonteSS]

Probably no need for the extra expense of a 31 spline,I've been using a 28 spline behind my 550+ HP big block for 7 or 8 years now with no issues,and I occasionaly beat on it pretty good.The Ford Limited Slip sems to work pretty good,I put all new clutches in mine when I put it in,and that was 5 or 6 years ago.You can still feel the inside tire "chatter" when its cold and making a sharp right hand turn.The trick is to soak the clutches in a mix of gear oil and Ford Limited Slip Additive for a day or two before assembly.And use a bottle of the Ford additive when filling it with gear oil.Mine came with mid to late 80's LTD brakes,they are huge compared to the stock ones,sure made a big difference in stopping power.
Guy

 

[Mike P]

I agree on the Ford Posi (Traction-Loc) being a good unit. You will want to shy away from the earlier 2 pinion units however, as they are a bit weaker and have fewer (but bigger) clutches. Whatever unit you decide on you will need to make sure the side gears match the spline count of the axels (28 or 31).