I have a 68 Bird and I'm about to swap out my 2.56 open BOP for a 3.42 8.5 inch posi from a 71 Nova. I have a couple of questions regarding this swap.
How do the BOP axles come out. I know they don't have C clips. Are they held in by the same bolts that hold the brake assembly on? I just looked and didn't see any extra bolts behind the brake assembly.
I know I am going to need to shorten my drive shaft. Has anyone done this and if so do you have a length measurement for the new driveshaft? I am going to measure, I just want to make sure I am close before I have it cut. I have been told that the 8.5 rear is 1 inch longer than the BOP. It would make sense that I need to cut 1 inch off but I really want to make sure before I have this done.
One more... is there a break in procedure for new gears? Or do i just hop in and nail it and enjoy two black marks instead of one?
if you put a chevy rear in you will have the c clips and the axles wont interchange.why dont you do the swap the correct way?new posi units are available through eaton for the pontiac rear end
there is a break-in procedure for brand-new gears. I dont remember what it is exactly, but you might check with richmond gear. you aren't supposed to drive them for long, or very fast, before letting them cool. I think after 100 miles or so they should be seated. For towing it might take longer.
My Eaton posi also said not to use synthetic lube.. probably because the clutches can chatter.
69firebirdman, I'm not swapping the axles. I have an entire 8.5 rear end. It is brand new and only cost me $600. I priced a posi unit and gears for my BOP and it was going to run me $1200 including labor. I have also heard that the 8.5 10 bolt is almost as strong as a Chevy 12 bolt. I'm not knocking the BOP. It all boils down to $$. This is the cheaper way to go to get where I want to be.
Let a pro shorten your driveshaft - he'll be able to balance it - you won't. Most of the shops around here want the vehicle on site as they don't trust amateur gearheads with a measuring tape.
I realise that I don't do well with what parts are what, but I didn't know that GM made an 8.5 rear. I thought that was a Ford deal.
As far as doing it correctly, GM 10 bolts, whether or not they are posi, are the weakest rears, compared to other rears of that era. A 12 bolt, or an 8.5 is a much better selection than the skimpy 10 blot rear.
I have a 3:23 12 bolt pois from a 71 Nova donor car in my 9. Sure, it's not correct, and some people know that 12 bolts are incorrect in f/g/f. Even so, it makes a nice statement because it belongs in the family, and compared to GM's 10 bolt, it's bulletproof.
If you have a drum to drum from a Nova, even if it's an 8.5, it will bolt up. I had to have my driveshaft shortened because the yoke or housing is about 1/4" longer than the 10 bolt.
Amervo, the 8.5 ten bolt is supposed to be almost as strong as a 12 bolt. It's supposed to be significantly stronger than the BOP 8.2 ten bolt. The rear end shop I talked to recommended moving away from the BOP for the simple fact that parts are getting hard to find and are more expensive. I would love to keep my car all BOP but the realities are that this rear is stronger and less expensive to repair. The engine is an exception to that rule for me. It will always be a Pontiac. No way will I put a Chevy in there.
bastereo, I saved $$ for several months and watched the various forums like a hawk for months. When this rear showed up I was in a position to be able to buy immediately. I had to pass on several very good deals on other stuff. I kept focused on what I wanted. I know there are more out there. It just takes time for them to show up. When they do you have to be ready.
bastereo, I watched this page, the Performance Years page, which is down right now, Classical Pontiac,the Pro Touring page and Ebay. You just have to decide on what you want and in my case, start to save money. I had to really stay focused because I had an opportunity to buy a 400 long block a week or so ago. If I had I wouldn't have had the $$ for the rear. I knew what I wanted and knew one would come up sooner or later. It did and it was local. Just be patient.
There is one thing 2 be aware of when switching rearends, I have a friend who put a chevy 12 bolt in his 69 and while it bolts right up we found that it is 3/4 of an inch shorter on both sides for a total of an 1 1/2. F.Y.I.
Yes, the width is very important. The 8.5 ten bolt out of a Nove is 1/4 inch wider per side for a total of 1/2 inch wider over all. I think I can live with that.
