any difference between second gen subframes?

[zamora7]

like the title says, os there any difference between subframes in second gens? I have 1980 t/a that i have done a pretty good amount of work done to it and about to buy a clean 1981firebird, but its a v6 car. Is there any difference.between subframes/motor mounts that would mak swapping these a pita?? Any help is appreckated.

[Skip Fix]

I think the earlier than 75-76 were a different width-why their TH400 crossmembers don't fit. Most subframes have all the motor mount holes drilled.

[Randy67]

The subframe is the same for a V8 & V6 so no problems swapping them, the subframe will have all the holes so you can put the motor mounts in the right spot.

[LeighP]

70-74 and 75-81 F-Body subframes are the two basic groups.
The frames are the same physical dimensions in both early and late frame, the difference lies with the location of the rear body mount holes. Starting in 1975, the rear body mounts on both sides were moved forward approximately 2". Along with this change, the gearbox crossmembers were redesigned to mount further forward on the frame rails, ahead of the depression pressed into both upper inner frame rails where the earlier crossmembers had been mounted. These changes were to accomodate the altered floorpans due to the position of the catalytic converter.

Some things I've found.....
1. you can use late frames under an early body (and VV) by cutting new rear mount holes and plating over the old holes.
2. 70-74 body shells require the use of 70-74 gearbox crossmembers, the floorpan does not allow the clearance to fit the 75-81 crossmembers.
3. later frames are drilled for all engine mount combinations, Pontiac (early and late frame mounts), Chevrolet and Oldsmobile.
4. early 2nd gen frames have small diameter lower control arm bolt holes, requiring the use of early control arm bushes only.

I have a late 2nd gen Camaro frame in my 71 Firebird. I use 79 Trans Am control arms and a 71 TH350 crossmember. Other than having to locate and drill the crossmember mounting holes and the rear body mount holes, everything lines up and bolts in fine.

[David Pozzi]

74 & later upper control arm bushings are larger, & the idler arm bolt hole spacing in the frame rail is a different spacing. I think there are 3 different idler arms listed for 2nd gens.

[badazz81z28]

The lower control arm bolts are actually Metric (14mm) vs SAE (1/2"). I found out the hard way installing the Hotchkis Arms. They come pre-installed with the smaller bushing sleeves.