Whats the difference between 7.5 and 8.5 rear end??

[hoodfellas1987]

Whats the difference between a 7.5 posi and an 8.5 posi? and which one is better??
My buddys friend is selling a 7.5 posi and I see online everyone wants an 8.5? whats the difference?
thanks!

 

[bill]

Whats the difference between a 7.5 posi and an 8.5 posi? and which one is better??
My buddys friend is selling a 7.5 posi and I see online everyone wants an 8.5? whats the difference?
thanks!

depends on your intentions....7.5's are fine for the street...but they have there limits. Most people who want to run their cars hard and do 1000ft burn outs opt for the stronger 8.5 or the ford 9inch rears. Alot also depends on the HP and torque of the engine...and the rear gear you are running.

 

[hoodfellas1987]

ok i see i wanted to drop that in a monte carlo i have running a 454, i bought the car like that and it doesn't have a posi and this guy only wants $300 so i thought it was a steal its basically completely rebuilt new bearings and new Richmond gears detroit locker unit he said so i don't know if thats good?

 

[beermonkey9417]

...about 1"... :lol:

 

[Phoenyx]

It's a hard call. Seems like a good deal, but then again. Seems almost to good. I had my 7.5 rebuilt drum to drum, and it was around the $2000 mark (Yes I know I wasted my money, but in my defense that was before I found this site). So $300 seem really low.

Then there's the whole issue of it being behind a big block. I think I have broke 4 7.5s behind what were basically stock 305s and a 301. But those were also 25 year old rears. At the same time there are members on here who run their 7.5s at the track and they are holding up. It's a gamble, but for $300 it's not to bad.

If your car isn't gonna see the track or be abused to bad, I would go for the 7.5... for now. But start saving and looking for a beefier replacement.

 

[LS1GN]

The 8.5 is considered the "holy grail" of G body parts. They came in later Buick Grand Nationals and are stronger than the 7.5s that practically everyone has.

I'd love to come one across one in a junkyard. I always look under any Monte Carlo I find - checking too see if someone else had done the swap.

 

[CHRIS.O]

For 300 bucks I wouldn't pass it up. You could make a few bucks off the rear end if you don't end up using it. If you do then don't do mile long burn outs and don't launch it off of sticky tires. So pretty much no serious drag strip action.

 

[mobileaudio25]

I would grab it. If its posi, works well and has been rebuilt why not? Hopefully you get as lucky as me and come across a 87 g national rear end with 373 gears for 500$ and I paid him an extra hundred for new bearings, seals and fluid

 

[bill]

Still...the question remains ...how do you know a posi is any good without installing it first :?: