Gbody 8.5 Question

[pontiacgp]

took me a year to find my 8.2 posi, the G body rears are too narrow

What are the 8.2's usually found in? Bolt in deal for a g-body or mods needed?

you can find them in Chevelles 64 to 73. The 64 to 67 rear is 2.5" wider than the G body rear. You need the upper conversion arms and for the lowers the brackets on the rear end are closer to the center of the rear end even though the rear is wider than the G body rear. UMI helped me out with the lowers by adding a roto joint to a set of lowers pick up the angle. (picture below). The spring perches sit more to the front of the axle tube instead on on top in the G body but that didn't affect the spring. For the 68 to 73 the rear end is 4.5" wider than the G body rear. You need the conversion upper arms and for the lowers I think the stock ones works. JBrue helped me out with my installation and he have the 68 - 73 version and he never mentioned he had any problems with the lowers. JBrue has the 12 bolt rear but those rears are the same width as the 8.2 though out the years in the Chevelle.

The reason I went with the 8.2 over the 12 bolt is the price and the 8.2 is good up to 500 hp which I'll never get to. In addition to being wider than the G body rear I can easily find clutch disks for the Eaton 8.2 but for the Eaton 8.5 in a G body rear they are very hard to find. There was a recall on the 8.2 rear cause the thrust washers would prematurely wear out. They were originally brass. The rear I bought still had the brass thrust washers which were very worn but I was able to find the GM upgrade thrust washers. without much difficulty

 

[G-Body_Vet]

took me a year to find my 8.2 posi, the G body rears are too narrow

What are the 8.2's usually found in? Bolt in deal for a g-body or mods needed?

you can find them in Chevelles 64 to 73. The 64 to 67 rear is 2.5" wider than the G body rear. You need the upper conversion arms and for the lowers the brackets on the rear end are closer to the center of the rear end even though the rear is wider than the G body rear. UMI helped me out with the lowers by adding a roto joint to a set of lowers pick up the angle. (picture below). The spring perches sit more to the front of the axle tube instead on on top in the G body but that didn't affect the spring. For the 68 to 73 the rear end is 4.5" wider than the G body rear. You need the conversion upper arms and for the lowers I think the stock ones works. JBrue helped me out with my installation and he have the 68 - 73 version and he never mentioned he had any problems with the lowers. JBrue has the 12 bolt rear but those rears are the same width as the 8.2 though out the years in the Chevelle.

The reason I went with the 8.2 over the 12 bolt is the price and the 8.2 is good up to 500 hp which I'll never get to. In addition to being wider than the G body rear I can easily find clutch disks for the Eaton 8.2 but for the Eaton 8.5 in a G body rear they are very hard to find. There was a recall on the 8.2 rear cause the thrust washers would prematurely wear out. They were originally brass. The rear I bought still had the brass thrust washers which were very worn but I was able to find the GM upgrade thrust washers. without much difficulty

I completely forgot that those 10 bolts were 8.2". I was familiar with the 12 bolt changes needed for a g-body bolt in though. What kind of backspacing are you running to accommodate that rear end? I kicked around the idea of a 12 bolt years ago, but I like to be able to lower my cars with the rear wheels tucking.

 

[pontiacgp]

I have 4.5 BS with 255-50-17 tires.and had to roll lip a little for the 255 tires, I like to run 245 but the torque thrust rims I bought last summer were a package deal. I had 245-50-16 on the car before these rims and the 245 tires did not rub the fenders. I found the car more stable around corners with the wider rear.

 

[cutloosecutlass81]

Pontiacgp I had a 81 cutlass before I got my 87 and I ran a 255/60/15 in the rear with a 3.750 back space on a 8 wide rim with no clearance issues at all but for my 87 after I swap the 7.5 for my 8.5 imma get torque thrust 2's now could you answer this for me I wanna run a 255/60 or a 275/60/15 on the rear on a 8" wide rim what bs should I run? My 81 had 275/60's on the rear when I got it with no issues I just don't know the bs on the old rims before I sold them. And imma run a 15x7 in the front with a 235/60/15 with a 4" bs is that alright? I don't want my tires to poke out the fender wells and I'm trying to do everything without rolling the fender lips but if I have to that's no big deal either

 

[pontiacgp]

Pontiacgp I had a 81 cutlass before I got my 87 and I ran a 255/60/15 in the rear with a 3.750 back space on a 8 wide rim with no clearance issues at all but for my 87 after I swap the 7.5 for my 8.5 imma get torque thrust 2's now could you answer this for me I wanna run a 255/60 or a 275/60/15 on the rear on a 8" wide rim what bs should I run? My 81 had 275/60's on the rear when I got it with no issues I just don't know the bs on the old rims before I sold them. And imma run a 15x7 in the front with a 235/60/15 with a 4" bs is that alright? I don't want my tires to poke out the fender wells and I'm trying to do everything without rolling the fender lips but if I have to that's no big deal either

the G body 8.5 is the same width as the G body 7.5 so the bs you ran will work with the 255-60. the 275-60 tire is a little more than 3/4" wider so if you had more than 3/8" clearance with the 255-60 tire it'll fit. For the front you won't have any problem with the fender with the 4" bs but it may come close on the inside at full turn.

 

[88hurstolds]

Spoke to a guy last night, was looking for an 8.5" rear for his 260 powered '80 Cutlass.
I asked why and he didn't know, just knew they were good rears and wanted one.
I get calls all the time for people wanting them for the El Camino with a 350 etc. and I ask them why... and they usually are clueless about why or haven't done their research.

8.5" rears are truly over rated.

How many stories have you actually heard of people braking their 7.5" rear with a street driven car?
The only stories I've heard are of people bracket racing with a 500hp/500ftlb setup and most on here build their cars to enjoy them.
Remember Torque and hooking up at the track will break a rear end, not HP and most Chevys are just that, HP and rely on spinning the crap out of them to get the power needed.

There is only a small window where one would really need an 8.5" rear and I can guarantee 80% of those that are looking for them do not need them for their 350/383 stroker etc. crate motor or are not running 11/12's at the track bracket racing on a regular basis.
A 7.5" will do just fine for running 13's and a couple visits to the track a year.
In fact there is less rotational energy required to move a 7.5" rear and it can only benefit you unless you are making gobs of power to where it's negligible.
I beat the living snot out of a 7.5" rear in my '88 with a 455 that was putting out 350hp/510ftlbs at the flywheel and took it to the track 3 times a year.

If you are running over 400hp 500ftlbs AT THE TIRES then yes you will need one but most are only making 350hp 400ftlbs at the tires with their setups and a nicely built 7.5" will run you the same money a roached out high mile 8.5" will cost you.


Anything over 550-600hp /ftlbs forget it, sink your money into a Ford 9".

Also, just because the dyno says it's 450hp doesn't mean that's what you will see at the tires...

 

[cutloosecutlass81]

Yeah I get what you're saying I got mine because I was looking for a posi and I figured if I found one might as well be a upgrade from the 7.5 can't complain to much I paid $400 and it came with a new set of gears. No one likes a one wheel peel