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Old 05-04-2010, 12:13 AM
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Frame re-enforcement

I got a 1970 nova and want to re-enforce the frame to prevent it from twisting. Reason is because the new engine cracks my tranny because the body twists just enough at take off causing it to crack. I've haven't done one on my own yet. Always had shop do it. I want to do my own on this project.

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JD

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Old 05-04-2010, 01:17 AM
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First thing to do is to install solid aluminum body mounts, where the front subframe bolts to the body. This is the first place twist happens as the old rubber mounts are shot after this many years. if this is more of a cruise or street car you could use polyurethane mounts instead but they aren't as tight as solid mounts.

Next would be to add weld in subframe connectors to connect the front subframe with the rear unibody structure.

Next would be a 6 or 8 point roll bar or an 8, 10, or 12 point roll cage depending on how far you want to go with stiffening and safety.
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Old 05-04-2010, 10:12 AM
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I am no experianced drag racer or something but this isn't making sense to me. The motor and trans sit on a sub frame, a VERY STRONG sub frame. They move with each other, something just doesn't sound right.

Where is the transmission breaking? How many have broken? WHEN do they break?


Brian
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Old 05-04-2010, 05:16 PM
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Brian, that subframe isn't so strong as you think back where the trans bolts up, the 4 body to subframe attachment points do quite a bit to keep this rear section of the subframe straight. This can get really bad when worn out bushings or rust gets into the attachment points and gets things rusted out.

Subframes like this are strong as hell whem welded into a street rod or old truck frame, but mounted on rubber they can get twist in them from the power put into the back axle twisting the rear of these frame horns in a unibody car. This is a known problem point with Novas and Camaro/Firebird.
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Old 05-04-2010, 10:44 PM
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Quote:
Originally Posted by ericnova72
Brian, that subframe isn't so strong as you think back where the trans bolts up, the 4 body to subframe attachment points do quite a bit to keep this rear section of the subframe straight. This can get really bad when worn out bushings or rust gets into the attachment points and gets things rusted out.

Subframes like this are strong as hell whem welded into a street rod or old truck frame, but mounted on rubber they can get twist in them from the power put into the back axle twisting the rear of these frame horns in a unibody car. This is a known problem point with Novas and Camaro/Firebird.
I'm with you, the mounting to the body allows movement. But BETWEEN the motor and trans, I don't believe there could be that much movement to break transmissions. I picture the whole assy twisting the body, but the motor and trans would be going along for the ride. Again, I have ZERO experiance with a super high horsepower car and some serious traction with slicks or that sort of thing. And this is the only way I can imagine any damage to the tranny. That being 5-600 horsepower with SUPER sticky large slicks for instant hook up, anything less than that I just don't understand how the tranny could get broken.

Brian
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Old 05-05-2010, 01:34 AM
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Tail cracks

The tranny tail cracks. I have broken 2 of them. Only happens if I decide to gun the car. I got a dyno sketch build that rates block at 468 torque and actual torque from shop was 516 torque. I cracked (2) TH350's. My next one is a TH400 but want to stiffen the car up a little. I don't have slicks but I do have rims that are wider from the rear than the front ones. I got them as wide as I could get them.

You guys have a schematic for welding frame?
Thanks,
JD
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Old 05-05-2010, 08:31 AM
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I believe it's possibly rear end spring wrap that is causing it. Is the drive shaft the correct length? Look and see if the yoke is bottoming out in the tail-shaft of the tranny.

Has the rear axle been changed? Is the pinon angle correct?

I am not saying I am RIGHT, but you should be looking for what ever is causing this and not focusing on one thing. If the motor-mounts are all good (are they?) and the motor isn't moving a great deal then look at other possibilities.

Brian
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Old 05-05-2010, 05:51 PM
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Good advice Brian^^^^

Also look at driveshaft run-out and balance along with the things mentioned in the above post.
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Old 05-06-2010, 12:38 AM
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Checked!

Drive shaft is an aluminum brand new and does not hit. Reaer end has not been changed or modified yet. The car didn't do this until this engine went in it. There is no noises or anything like that. I have brand new motor mounts and the are stiffer than the stock ones but not solid.
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Old 05-06-2010, 09:01 AM
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Quote:
Originally Posted by 355Nova
Drive shaft is an aluminum brand new and does not hit. Reaer end has not been changed or modified yet. The car didn't do this until this engine went in it. There is no noises or anything like that. I have brand new motor mounts and the are stiffer than the stock ones but not solid.

Ok, cool, did the drive shaft go in when the motor did?

Brian
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Old 05-06-2010, 09:09 AM
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What do you have to prevent spring rap?

Listen, you are building a hot rod and stiffening up the structure will be in the plans, that's cool. But for THIS problem, it sure doesn't hurt to look outside the first thoughts and see what you find.

Brian
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Old 05-10-2010, 11:45 PM
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Frame work done!

I did as you told me eric and no more cracking! Thanks a bunch!! I didn't do it all myself. I had a buddy come over and help me out. It was alot more difficult than I thought. Only thing now is the car spins tire on first 2 shifts. Is there a way to adjust this so I don't wear out tires so fast?

Thanks,
JD
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Old 05-11-2010, 12:08 AM
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What exactly did you do?

Brian
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Old 05-11-2010, 11:21 AM
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Frame work done!

We welded on subframe support like eric suggested. I also went ahead and replaced the rubber mounts under the 4 bolts that hold the car together. The end part was the most difficult. My friend Mike and his friend Steven worked on the rear end area, and built a frame that keeps the car from flexing. They got the idea from a local shop and decided to give it a shot. As for roll cage I bought a kit from MT's Machine shop down here and welded it into place.
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