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I have a 51 Pontiac Business coupe I am building. I had the axle and springs mounted but it didn't sit or fit right. Looked at a Chevy and it is a whole different frame, much lighter and easier to work on. Question I have is whether to cut off as much as I can and put some 4x3 tubing in the existing frame at the firewall bring it forward, add crossmembers, then cut rest of old frame off or just cut it back completely to where the X frame starts and build from there. This is my first gasser build and I am doing it by myself. I have a 74 GTO that I run as Pro Bracket car, mid11's, so building a car is not new to me just doing a gasser is a whole new thing for me.
Thanks for any help you can give me , I can post some pics if it will help.

Butch
 

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Hi Butch, Best way that I have found is to take a ton of measurements. Block and level the front and rear to the angle you want if any. If the car can remain at one location during assembly, mark the floor with the axle location, centerline , hub location. Find a fairly level location in the frame just forward of the firewall and measure from there to your radiator support or anything else that will need to be repositioned after you cut off the front frame rails. All there is left is to cut off the rails, try not to use a cutting torch. Put at least 6-8 inches of your new frame rail inserted in to the old frame, drill rosette holes in the frame top, bottom and both sides. Weld her up, make sure everything is square and level. You may or may not need to put fish plates on the sides. Hope that helps, just my 2 cents.
 

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Can't add much to Mike's great info, but I would only say I usually leave the frame stubs longer than needed by a few inches so I can build up everything between the rails first, and then cut them to the exact length after all the crossmembers are done.
I'm very familiar with the Chevy frames, but not the Pontiacs, so not sure what size box tubing you'll need to fit inside it? I found this picture over on the HAMB site and it appears to be a very complicated frame compared to a Chevy!



I would cut it off where the supports come into the side from the center, but try to leave as much material on those two inside supports to be able to weld them to the boxed tubing also. As Mike said, if you can level up the existing frame first, and ensure it stays level during the time you cut the stubs off, and build the new stubs, then it should go well. Just make sure you measure it all up and write it all down. Then as you tack the tubing in, be sure to take measurements often to ensure nothing is moving as you weld it all together.
PS-Don't be afraid to slice and weld your rectangle stubs a little to make them slide back into the original frame, and allow them to be leveled. Sometimes the frame rails curve down and wont allow the stubs to slip in as far as you want. So pie cutting the donor tubing until it slips in is needed. Then once it fits you can weld up the pie cuts and grind them smooth before weling them into the frame.
 

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You just got some expert advice from two very knowledgeable guys. If you follow it you'll probably be very happy with the outcome and your final build.
 

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If you come forward from the firewall you better plan where you leaf spring and axle mount perch will be. Make sure you will be able to turn the tires without hitting the leaf springs. So I would get the axle setup first and plan the frame on the needs for positioning everything up front. Just a thought.
 
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I have a 51 Pontiac Business coupe I am building. I had the axle and springs mounted but it didn't sit or fit right. Looked at a Chevy and it is a whole different frame, much lighter and easier to work on. Question I have is whether to cut off as much as I can and put some 4x3 tubing in the existing frame at the firewall bring it forward, add crossmembers, then cut rest of old frame off or just cut it back completely to where the X frame starts and build from there. This is my first gasser build and I am doing it by myself. I have a 74 GTO that I run as Pro Bracket car, mid11's, so building a car is not new to me just doing a gasser is a whole new thing for me.
Thanks for any help you can give me , I can post some pics if it will help.

Butch
Good morning and Happy Holidays,

Only if this might help and add to your gasser theme: I use the 57-64 Olds/Pontiac differential in an old A/SR I have and collected some back up stuff. I have a ladder bar housing out of an old Pro Stock car (yeah, I know) and some complete differentials. If you're the least interested, I will take a couple pictures. I assume a possible problem would be getting it to you - they're not light. What neck of the woods are you in? I'm in Akron, Ohio - Near Summit Racing.
Either way, I hope your project works out - it should be a neat car.

Best regards,

LS
 
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