A or G-Body Rear Suspension

[BBPanel]

I have a project vehicle with the oem triangulated rear end. How do I tell whether its A or G-body and what years it came from? Are the upper and lower arm lengths unique, etc? -Bob

[Ben@SpeedTech]

Hey Bob- can you clarify a little? Is this just an axle you have or a whole car?

A bodies were from 64-77. G Bodies were first introduced as the Monte Carlo in '70 and the Grand Prix shortly thereafter. The Riviera may be an early G body too? The early G bodies were basically an A body platform with a longer wheelbase, the difference was between the front suspension and the firewall. In 78 the A body platform was downsized to be lighter weight and to get better MPG. Technically a 78-80(?) G body is actually labeled by GM as an A body and in 81 or 82 they were officially labeled G bodies from then on. Generally G body guys call 78+ cars G bodies because they're all the same new smaller platform. Mine is a 79 and I've always referred to it as a G body rather than an A body so people know what I'm referring to. Clear as Mud? ;)

78+ G bodies axles/ suspension are easy to identify, they come with the puny 7.5" rear 10 bolt axle. The earlier A/G cars had the 8.5" 10 bolt or a 12 bolt. In the later years only the Turbo Regals and the Cutlass 442/ Hurst Olds can be found with an 8.5" rear, and they're pretty rare. To put an early A 8.5 10 bolt in a later G body requires custom offset upper arms because the later upper arm ears are in a different location on the axle housing than the early upper mounts. If using G body lower arms I believe they will line up with the lower brackets on the early rear. The Early rear is about 2" wider than the later 7.5".

Rear control arm lengths are different between early 4 links and '78+ 4 links. The later G bodies also have metric sleeves and bolts in the bushings.

Front suspension is totally different between the early and later cars, I don't believe anything at all interchanges, including suspension, springs and shocks.

Hope this gives a little insight.

[Carl @ Chassisworks]

Measure the upper arms from bolt to bolt.

A-Body
12-7/8" centers, 64-67
10-5/16" centers, 68-72

G-Body
11-1/8" centers, 78-87

Source: http://www.cachassisworks.com/c-334-...y-vehicle.aspx

[BBPanel]

Measure the upper arms from bolt to bolt.
A-Body
12-7/8" centers, 64-67
10-5/16" centers, 68-72

G-Body
11-1/8" centers, 78-87

Source: http://www.cachassisworks.com/c-334-...y-vehicle.aspx

Ben, yes the rearend/suspension has been transplanted into a 56 Chevy Panel. Carl, appreciate the details and digging out the info - I'll measure now and see what I have. I need to move the axle back ~1.5" to center the wheel in the opening and will have to relocate some of the brackets (they have been done very poorly) but with this info I now have quite a number of combinations I can consider. Thanks. -Bob

[Ben@SpeedTech]

Sounds like a great project! If it helps any Bob I've got a bunch of pics of my G body frame's details, check out page 13-14 for old rusty frame pics and 18 for shiny new ones. Maybe you can see the details and compare to yours? Click here...

I doubt hardly anyone would transplant a weaker 7.5" rear into anything, so here's a possible quick way to tell. The lower tabs on the 8.5" and the 7.5" are different. 8.5's have a beefier tab while the 7.5s tab is quite small in comparison. If you have a 7.5" rear it's a good chance you have G body frame.

Notice in THIS PIC the 8.5 lower triagular tabs are pretty beefy.

Notice in this 7.5 pic the tabs look like little fangs dropping down.

The covers are different shaped too. Notice the later G body 7.5 cover is more "square" and doesn't have the ring gear bump. Hope that helps!

[raustinss]

70 monte Carlos are a bodies...not g bodies

[Ben@SpeedTech]

Check out the first couple paragraphs. I had my years wrong, the GP came first.

https://en.wikipedia.org/wiki/GM_G_platform_%281969%29

[BBPanel]

Thanks again - I'll take a look at those references. I do have an 8.5" diff so that narrows it somewhat.
On another note - since I will be basically redoing everything what would be the best driver quality bushing(s) type? Should I run stock stuff or go with something more performance oriented like polyurethane/delrin, etc? I have the oem sway bar (attaches to side of lower arms) and will probably retain it and the lower arms (but box them) but the uppers are open to change.

[Carl @ Chassisworks]

Happy to help!

Personally, if I was building a cruiser style truck I would just stick with rubber. But, if it's going to have a reasonable amount of power (450ish or more) you should consider going to a poly-bushed control arm with boxed style construction. That will be a considerable upgrade for a truck and still be low maintenance. Or, you could get a little more aggressive... There's lots of options at the link I shared above.

Our arms have greasable bushing housings and the bushings are channeled so they don't squeak like a poly bushing in a stock arm.

[raustinss]

I stand corrected the Monte is a bit of a hybrid...I've always treated it as a A body ..

[Ben@SpeedTech]

Lol! I think we all thought the early Montes were A bodies until we come across someone who has come across the correct info. That's where I was until I bought my 79 A, er, G body a few years ago and looked into the names.

Speedtech arms, for street or race applications use greasable Delrin. Personally I don't mind driving on them in my daily driven car. Whether they make more noise or make the ride more uncomfortable I can't really tell and I think how much a control arm bushing contributes to that is a bit debatable anyway. A good stiff low profile sidewall tire will beat you up more than a control arm bushing I would think. As has been said rubber is what the factory used for all out comfort, and 215-70-15s too. Poly comes next and work well but they still have flex, can deform in time and if you haven't got enough grease on 'em can squeak too. I like the Delrin because there's basically zero flex when it comes to "spirited" driving, they're not going to wear out, and they'll help give a firmer more responsible feel over the other choices. Some hard core guys run spherical bearings but I'd reserve that for the race car stuff, not so much for a cool cruiser.

[BBPanel]

UPDATE: Looks like I have an 8.2" diff - measured the upper arm and got 10-5/16". Looking at the lower arm bracket it would appear, for whatever reason, the PO retained one side of the bracket and made the other side (nice sawtooth finish!). Only thing I can figure is the lower control arm was wider than original bracket. Looks like I may have a hybrid of different parts.

[Ben@SpeedTech]

Forgot to mention the 8.2's, used on the earlier A Bodies.

Some real interesting stuff about casting numbers, dates, identifying axles, ect. ...

http://chevellestuff.net/qd/rear_axle_info.htm