SUBJECT: 2nd Gen Subframe Differences

At 11:03 PM 4/10/99 -0400, Andrew K. Mattei asked:

Will all my 79 f-body control arms, spindles, steering linkage,
etc bolt on to the 73 f-body?).

And Phil (B.), did you ever put that later model subframe on your

=================================================================== The following answer is thanks to Ken Carothers and Phil Boylan.

At 05:48 PM 10/27/1998 -0600, Ken Carothers wrote:

Okay folks, I measured a few things. The HPP (High Performance Pontiac) article appears to be right, they (early and late 2nd gen f-body subframes) are different. All measurements were taken at the location where the tranny crossmember bolts up. The subframe & crossmember are still under the Bird, so my measurements are approximate, but I think I'm within an 1/8".

'73 Subframe:

Outside to outside dim: 37"
Inside to inside dim: 29"
Tranny X-member bolt holes: 30-3/4" Centerline
Distance between holes: 2-1/2"

'79 X-member:

Tranny X-member bolt holes: 32" Centerline
Distance between holes: 2-3/4"

Then from Phil we have:

Thanks Ken, I believe that clears up the mystery. My numbers off the '78 subframe pretty much agree with your numbers from the '79 cross member:

'78 Subframe:

Outside to outside dim: 36.5"
Inside to inside dim: 28.5"
Tranny X-member bolt holes: 31.5" Centerline
Distance between holes: 2-3/4"

The bolt hole centerlines were taken measuring from the top of the subframe(easier because the holes are much smaller on top). I had interpreted theHPP article to say there was a significant difference in the distance between the frame rails, but as you can see we found only a 1/2" difference. But the X-member bolt centerlines are more problematic. Probably the easiest thing to do when mounting a TH-400 in a later subframe is to convert a later TH-350 X-member by flipping the trans mount from rear-facing to front-facing (while being careful to maintain the drivetrain centered between the rails).

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