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Old 07-30-2012, 12:00 PM
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1978 firebird subframe question

I'm doing a restoraton on my 78 finally, not total since its not very rusty, but i need some guidance. I want to replace the front subframe-body mounts but i dont want to completely remove the subframe. Can i just put a jack under each side, remove the bolts, lower it down, change out the mounts, then rais it back up and connect it? I also want to take a wire wheels to it to remove any surface rust and give it a coat of paint. Will this method work?
Also, what body mounts should i use? I see jegs has aluminum but i dont want any crazy vibrations or anything.
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Old 07-31-2012, 07:10 AM
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Yes, that method works just fine.

Ames Performance sells the correct body biscuits for the Firebird. No need for anything else. "Hard" mounts will increase road shock and transmit vibrations throughout the car.

Jim
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Old 07-31-2012, 09:33 AM
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Quote:
Originally Posted by bigdog7373 View Post
I'm doing a restoraton on my 78 finally, not total since its not very rusty, but i need some guidance. I want to replace the front subframe-body mounts but i dont want to completely remove the subframe. Can i just put a jack under each side, remove the bolts, lower it down, change out the mounts, then rais it back up and connect it? I also want to take a wire wheels to it to remove any surface rust and give it a coat of paint. Will this method work?
Also, what body mounts should i use? I see jegs has aluminum but i dont want any crazy vibrations or anything.
There are several types to choose from, from stock durometer rubber, to polyurethane, to delrin (like a hard plastic material), to aluminum. Unless you're serious about racing and/or handling, the hard mounts are rougher riding/noisier compared to the softer stock type bushings.

I was lucky and had no rust but if you do, there are subframe hole repair 'washers'. I was able to slide my Chassisworks aluminum bushings into place w/only one side of the subframe loose at a time (also they don't use the bottom bushing).

If you loosen both sides of the subframe at the same time you will need to be careful that the alignment between the subframe and body is maintained. Make note of the subframe alignment hole position before removing both sides. There are alignment pins that can be bought or you can make them.

You'll want to do the radiator core support, too. Luckily there are replacement core support brackets, core supports, and even the entire subframe if needed for the F-cars.
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Old 07-31-2012, 12:13 PM
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Cool, thanks for the responces. I'll stay away from the metal and only do one side at a time so i dont have to mess with alignment. The car only has a little rust on the body and floor, none on the subframe.
Will i have enough room to sand/wire wheel the top of the frame and paint it or is it too tight under there?
The car will be almost 100% street driven (daily driver). I dont expect to take it to the track nore than once a year, and thats probably still an exageration. Which type of mount would be best for it? I've heard good things about polyurethane for suspension, does the same apply here?
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Old 07-31-2012, 11:38 PM
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Originally Posted by bigdog7373 View Post
Cool, thanks for the responces. I'll stay away from the metal and only do one side at a time so i dont have to mess with alignment. The car only has a little rust on the body and floor, none on the subframe.
Will i have enough room to sand/wire wheel the top of the frame and paint it or is it too tight under there?
The car will be almost 100% street driven (daily driver). I dont expect to take it to the track nore than once a year, and thats probably still an exageration. Which type of mount would be best for it? I've heard good things about polyurethane for suspension, does the same apply here?
If it will be a dd and not a serious handling effort (lowered suspension, springs, control arms, subframe connectors, etc.) I would recommend stock-type rubber. Or polyurethane at the most.
Ideally you would ride in a car that had urethane mounts and see if you can deal w/them. But the amount of harshness is like exhaust volume- what's unacceptable to one guy is OK w/another. That's why I can't recommend poly mounts outright. I'm sure if you do some searches you'll get other opinions.

It's kind of funny though- if the mounts you have now are really shot, the ride and harshness can be as bad as new poly mounts because the stockers will have collapsed and become basically useless.

Hard mounts like delrin or aluminum have zero 'give' to them so they transmit a lot more harshness and noise into the interior, even more so than worn out stockers. I wouldn't recommend them unless handling was the main point.
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