second gen fbody subframe mods

[rreichert82]

I am currently getting ready to strip, blast, paint, and install a complete PTFB comp suspension and steering setup on the front of my 79 Trans Am. It will have a 8.1L vortec 496 with a T56. I am doing the coil overs, swaybar brace, pro g brace, cowel brace, 800 series steering box, adjustable sway bar, upper/lower control arms, bump steer kit, solid subframe bushings, subframe connectors basically all new components. I did not have the budget for an aftermarket subframe but I wanted to see if there are any modifications or upgrades I can do to the subframe itself while I have it stripped down to bare metal. Any suggestions would be greatly appreciated.

[F-Body International]

PTFB Dave would be able to inform you on mods for the subframe using his suspension. There's a few additions you could weld to the stock subframe.

An option you haven't listed was solid engine mounts. This basically ties the engine into the frame and lessens flex.

[NOT A TA]

I've done several things to my stock sub frame to make it more durable and stiffen it up. You can find complete details in my project thread. Link is in my signature. Sounds like a nice setup you'll be getting from PTFB!

Increase the thickness where the lower control arms mount. Welded washers to the frame increasing the thickness, spreading the load, reducing flex. With 8 mounting points, it'll take a minute......



In the pic below you can see how the frame ends where the body mounts are has been boxed with 1/8" plate. Reduces flex and twist. I have frame connectors that fit inside the subframe. If you have an outside mount one you may not be able to box it. You can also see a large washer welded to the bottom of the cowl body mount which reduces flex.



1/8" plate welded to upper control arm mount. Reduces flex, provides a more solid base for the stud G-braces attach to. See G brace upgrades thread here https://www.pro-touring.com/threads/...or-extreme-use




Weld metal into the inside of the frame where the body mounts are then grind flat. this provides a flat surface for the solid body mounts to clamp together. Didn't matter with the squishy original rubber mounts but the solids want to tip on the uneven stock surface.



You may find a bunch of useful info in this thread about 2nd gen frames, mods, factory oprional bracing etc. http://transamcountry.com/community/...632075#msg6320

Cut off the overhang on the curve of the shock mount section of the UCA mount and fully weld to frame rail. Stiffens the UCA./shock mount. Also add welds and fix crappy welds on the whole sub frame.

[rreichert82]

Awsome information. Thanks for the help. I am hoping to have mine apart and start blasting in the next week or two then I can start some welding!

[Skip Fix]

"Increase the thickness where the lower control arms mount. Welded washers to the frame increasing the thickness, spreading the load, reducing flex. With 8 mounting points, it'll take a minute......
"
Those definitely are thin and wallowing around the flex of factory rubber bushings esp worn ones moves them all around. I've had to spread them slightly to get good bushings in then use longer bolts and hardened washers(ARP) to clamp better.

[CampbellshotrodsAZ]

It's quite interesting to see all the patches and quick fixes GM tried to do to the subframe over the years (after looking at the TACountry link). That tells me that it's actually a pretty soft piece, that leaves a lot of room for improvement, stiffness-wise. And this was before the days of sticky tires, and pro-touring! So I'll definitely be doing a lot of research in the future months here as I near this point for my Firebird. I believe the Firewall braces are a must, like the PTFB versions, or some variant, so I'll be doing that. As far as below, I'll just have to run my final headers, and just reinforce and brace whatever I can!

[MTZ28]

Since your planning on running coil overs, I'd suggest removing the upper shock tower and welding in a true upper coil over mount. Very easy mod, it will significantly stiffen up the upper control mount. Speedtech and Custom Works both make a nice kit. I used the Custom Works bracket, very nice fitment. It will also provide zero bind of the coil over and shock. This mod, along with the 1/8 plate suggested by Not A TA, would make a very strong mount.



I also installed Custom Works 2G bar on the front of the subframe. This will decrease subframe deflection with sticky tires and large sway bars. It also helps when you install a tow hook on one side of the frame to distribute the load from one side to the other. This can be bolted or welded, I suggest welding.




When it comes to front sway bar mounts the factory threaded holes can be stripped out. I installed nuts and washers inside the frame to prevent this. To do over I would weld in a plate and tap. The nuts are going to be a pain to remove when the car is put together.

Good luck with your build, sound like your going to get everything right the first time. Check out everything Not A TA is doing on his car. I'm very impressed with the work he is doing.

[rreichert82]

I like the upper shock mount idea. Looks really clean and pretty easy to install. I am thinking the PTFB sway bar brace serves the same function as the 2G Bar. I should be picking up most of the parts tomorrow and looking forward to checking out Daves facility.