I'm always on the look out for items i will be using when I finally tear into my 69 Firebird. As the swap and show season is about to get going here in the Northeast I was wondering about rear ends.
I have a bone stock 69 350 with th350 but will be looking to upgrade the rear end from the original one wheel spinner to posi and making some gear changes. Probably 3:08 - 3:23 neighborhood. Hoping after engine rebuild for 325ish hp.
Now and then I run into this or that, or see something on CL and I have no idea what to look for... are these changes to the existing axile/rear or entire new set up necessary?
I also would prefer to make as few modifications as possible.
There are quite a few rear end options. Sorta depends on your budget, and how original you wanna keep your car.
If you wanna keep the BOP 8.2, you can just buy a new posi carrier & gears. If you wanna use 3.23 or numerically lower gears, you'll have to buy used gears. Auburn makes posi units for the 3.23 & numeircally lower gears.
3.36 is the numerically lowest ratio that is still sold new. There are several brands of posi units for the 3.36 & up gears.
Another option is to switch over to an 8.5 rear end. An 8.5 out of an X-body is said to be a bolt-in replacement for the BOP 8.2 in a 1st gen. I think it requires a slightly shorter driveshaft. Others here may be able to verify that. You can use the 8.5 out of a 2nd gen Bird or Camaro, but the leaf spring perches must be moved in some.
Then of course there are the 12-bolt & 9" Ford rear end options. Unless you have future plans for a big power engine, the BOP 8.2 will be OK. But, If I were going to spend several hundred dollars on a rear end, I'd upgrade to an 8.5. They have several advantages over the 8.2. Unless you luck across a real good deal, from somebody who don't know what stuff is worth, a complete 8.5, with posi & the gear ratio you want will cost $1000 or probably more. Lots of guys have spent closer to $2g for a properly set up 8.5.
I suppose the cheapest way would be to find a good 2nd gen 8.5 with a good posi & the gears you want already set up in it, then move the spring perches in, or have a friend do it correctly for you. An X-body 8.5 posi with your ratio would be MUCH harder to locate. But, there were lots of TA's that came with a posi & 3.08 or 3.23 gears. But, many of these are over 40 years old. So, finding one in good shape, for a reasonable price, isn't near as easy as it use to be.
Yes you have to shorten the driveshaft to go with the 8.5, I got a 1970 and had it rebuilt with an Eaton posi.
It may appear that you don't have to shorten the driveshaft but YOU DO, if you don't at the least you'll bend it on the first major bump you hit. the carrier for the 8.5 is 1" longer where the driveshaft connects. But if you are going to push the car at all and you have an old 8.2 you will break it. If you are going to just cruise around there isn't much point in all the work and expence.
Good to know. How do you find those gears just cruising around? Highway?
As for the HP my guess would be that my tired old 350 would be real happy to make 250hp. The factory number in 69' was 265hp and we know they lied. Now it has 300k miles on it. Granted some things been replaced but... she still wears the 2bbl, #11 heads which are ok but no upgrade, log exhaust manifolds and single exhaust. And even with all that i'm always impressed that she moves out pretty good!
When I was running my TH400 tranny, at 60 mph, I was turning 3000rpm. In town, I could break the tires loose at will. I now run a 700r4. I like the 3:55’s.
Re HP: you’ve got a lot of potential there. My only advice is to get your plan together ahead of time...radiator to rear end. You’ll save a lot of money with a good plan, instead of doing, and re-doing modifications as you go.
I'm a hobbyist. Not a professional. Don't be hatin'!