I purchased a 1968 bird and the rear end has flat spots on the top of the axle and just a bit outside of the spring mounts on the bottom. Is this a firebird axle? Looks like a 10 bolt GM. Thanks

The flat spots are a 69 Firebird only axle. My 67 came with one of those too. I just pulled it this week to replace with the correct 67 setup. There is a 2 letter code stamped on the tube on the drivers side of the pumpkin. You can look that up and figure out what it is

Great! I will have to change also. Thanks for your help Bob.
P.S. I am looking for a '68 rear-end if anybody has one. Also, are there options and which is the good one?

What’s wrong with that one other than it’s not correct? Does it look like this? If the cover is different it could be some sort of camaro or nova rear. If it has this cover and the flat spots then it’s a 69 bird rear

That is the same thing I have. This car has been scrambled together. Wanted everything '68 but if it did work I here it would cost 1500 - 2000 to rebuild and a new 12 bolt from eckler is 2300. Your thoughts?

If someone has to crawl under your car and look for the flat spots in order to find fault with your car which somehow makes theirs better than yours, they are the ones with a problem.

What were the flat spots on top of axle for?

The only thing I can figure is for more travel until it hits the rubber stops. I did notice there’s an L and an R stamped in the flat spot. That’s so the drunk autoworkers don’t put it in backwards

Ha now thats funny

I played college football. When I was a freshman I got a pair of team issued reconditioned practice cleats. They had on R and L written on the toes! LOL I took them back to the equipment manager and said "I can't wear these like this, it's embarrassing!" He looked at me dead serious and said... "They might come in handy!!"

Bob is right about the flat spots on 69 axle tubes. In the 69 facelift of the car they dropped the ride height a half inch with the springs and used the flat spots to retain the same suspension compression travel as the 7 and 8s. You did not mention what 9 rear you have, standard or traction lock, 4 Pinion Nodular or standard 2 pinion grey iron and what gears? Also why the rebuild just because or did you check it out? Check out these pages to get you started with identifying what you have. https://www.firebird400ho.com/nodular-rear-end-date-codes/ and http://wildaboutcarsonline.com/memb...ents/9990382806291/Pontiac_Diff_Codes.pd note that there is a mistake in the second one as the 3:36 and above traction lock rears are 4 Pinion just like the 68s.

Not sure what I have yet. Was told to change gears to lower ratio. Thanks for the info Barnbird. I will check the info site.

I have my first 68 Firebird and discovered I have the same style rear you do. I pulled the diff cover and counted ring gear teeth and also discovered I have a desirable 336 ratio 4 pinion nodular safety track.I was told they are a good rear and valuable. Good idea to change your gear oil anyway and see what condition gears are in. If you have posi make sure you add the posi additive. And in my case I also discovered seized wheel cylinders and a bad axle bearing which turned into an axle replacement.