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View Full Version : Frame mods for 6" backspace


Bee Jay
03-23-2009, 05:25 AM
Any one here modify their frame to fit large wheels and tires? I'm hoping to do 6" of backspacing to fit my 10.5" with 295/35-18 tires on the rear. I have the chalked area that I am concerned about enough clearance. I won't know for sure untill my 2" spacers arive, but you can see the wheels and tires mounted with 2.5" spacers. I think I have more than 1/2" clearance, but I am concerned about this area. The frame seems to have a doubler here. What is that for? If I remove the doubler, can I strengthen the frame another way. I remember Norval did this, but I can't find his thread.
Bee Jay
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mrvette
03-23-2009, 01:52 PM
Interesting you find that point being the closest on the frame, as I thought it was the point nearest the sway bar....hit that sway bar first, after the t-arms and the obvious ebrake I see you moved already...offset arms, no swaybar, then the frame in that swaybar area....I have to go look at my car again for that area....

:rain:

Yup, you right, so much for memory....it's as close as my sway bar....I don't recall any frame mod threads from Norval, but I know he did his own offset arms.....

Bee Jay
03-23-2009, 02:08 PM
The sway bar is modified and out of the way, and the offset trailing arms have the e-brake cable out of the way. My '79 had the relocated e brake cable anyways. I was surprised too, I thought the area of concern would be further up the frame. I need to look at some other frame pictures too see if that reinforcement piece is on every frame. I don't think I have to trim much, and the 35 series tire wont deflect much.
Bee Jay

mrvette
03-23-2009, 02:27 PM
BJ, I dunno how to keep the same centerline on the tire, and get anything wider than a 275/50/17 that I have on there now...I refuse to kill my sway bar, and not cutting into my frame....not now anyway, my tires are new...and so money is not growing on trees anymore....

not in THIS 'economy'.....

:bonkers:

Twin_Turbo
03-23-2009, 10:25 PM
You could either cut it away and weld in a narrower section, just check if the trailing arm has enough room (there's a good amount of excess size to that trailing arm pocket). Depending on what kind of roll bar you have (wether it reinforces the kickup or not) you could get away with a thinner section there.

How's this for clearance :)

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Bee Jay
03-29-2009, 06:54 AM
I trimmed the frame today using my sawsall and grinder. I have some welding to do. I don't think I weakened the frame, but will weld plates to cover this hole. My wheel simulator says I will have plenty of room now.
Bee Jay
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mrvette
03-29-2009, 08:07 AM
I kinda surprised that is all you need cut, on account of the bounce on the wheel, I would think you need the whole frame cut in that sort of spot....

someone was bending the sway bar in back to accommodate tires was that YOU??

Bee Jay
03-29-2009, 02:21 PM
Yep, I modified the sway bar to fit the 10.5" wheels and tires. I tried running without the sway bar and didn't like how it handled. So, offset trailing arms, modified sway bar, and notched frame to fit these big a tires. I may be able to move up to 305 or 315s next time I need tires.

I disconnected the rear spring and moved the hubs up and down thru its full travell. Surprisingly, the closest clearance/interference is at full drop, not full compression. But now I have at least 1/2" clearance thruout with 6" of backspacing. I left most of the doubled seam and will weld metal to the inside, and grind smooth. Grinding is a PITA. I checked on my adapters, they ship Monday.
Bee Jay

mlpettus
04-22-2009, 02:19 AM
Keep us updated on the finished product. I am getting ready to do the same modifications to my 68. I have a set of C5 Z06 wheels in the rear with the 2" spacers. There is a little bit of rub on the tire, but I ground away at the frame already. I also am a little bit toed out in the rear to help with the clearance.

Did you have any close clearances with the top portion of the frame? From my memory I was thinking the top side of the frame was the next closest point.

I need to get this done before the power tour comes along, and I have about 12 hrs of driving with rubbing tires:cussing:

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Bee Jay
04-22-2009, 05:13 AM
Here is what I did last weekend. I cut three steel panels about 2" square and ground them down to fit inside the frame at the front of the hole, the back of the hole, and a horizontal piece in the middle of the hole. I called them reinforcing plates. My welding is really, really, ugly. So you won't see pictures of that. But I weld, grind most of it away, weld some more, grind some more. I am satisfied that these plates are very securely welded in. I hope this reinforces the frame in that area, so that the frame is as strong as before I notched it. I'm covering the hole next, and will share pictures of that after I'm thru grinding away the ugly welds. Guess what the difference is between good penetration and burn thru?
Not much.
Bee Jay
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mrvette
04-22-2009, 09:33 AM
Dont feel bad about your welding ability, mine is much worse, and if not for my welder buddy across the river, almost none of my car projects would be pulled off.....

:rain::clobbered:

Twin_Turbo
04-22-2009, 11:11 AM
The difference between good penetration and burn through is a lot more if you remove the milling scale first :)

Looks like you're doing a good job and thought it through, not everyone has the gonads to cut up a frame LOL

MYBAD79
04-22-2009, 12:31 PM
yup, it has to be clean.... hit it with a sandpaper disc or Dremel inside the frame - can't weld dirt, paint, grease, grime - it will also reduce the fumes quiet a bit :thumbs:

Bee Jay
04-28-2009, 04:39 AM
Here is my latest efforts on my frame. I cut out two plates, ground them to fit, welded them in. Then I did my grind and weld some more dance. My welding is getting better, but I'm still not ready to share. Almost done. I think the reinforcing plates and these plates will make the notched frame OK strength wise. Comments?
Bee Jay
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Here is the passenger side:
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Bee Jay
05-11-2009, 05:03 AM
More welding and grinding this weekend, and sawing pieces. It's like piecing together a puzzle. Weld the piece in, grind it smooth, weld the next piece in, grind it smooth. I'm getting better at welding, but still not good enough to share pictures of it. I'm also getting pretty good a grinding. The left side is about done except for paint. The right side needs another piece. Maybe I'll finish next weekend.
Bee Jay
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Bee Jay
05-13-2009, 03:29 AM
I got home a little earlier today, and it was too windy and cold to do the daily walk with the wife, so I decided to weld in my last piece. It was getting dark, and my Lakers were comming on, so no grinding today. I'll let you guys see some of my welding finally. I'm no Jesse James, but if you look at the last picture, it has my practice plate that I started welding just a few weeks ago. Compare that with my current welding. My wife laughed at the before and after.
Bee Jay
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Twin_Turbo
05-13-2009, 02:21 PM
The piece you welded in is rusty, next time clean off all the rust, it will improve your welds tremendously. Also, run more heat, less wire speed and slow down the torch. Practise some more on scrap metal.

On your frame, if you grind away all the weld buildup and you had bad penetration to start with, you loose almsot all the integrity your weld had. Take a peek on the backside of the metal, see if you have full penetration. It will show as a sort of bubbled surface from where the full penetrated weld pool got in contact with air (no shielding gas there)

turtlevette
05-14-2009, 05:12 AM
Bee Jay,

i can't see that you're gaining more than 1/4 inch from all that work.

am i wrong? and if so how much are you gaining?

Bee Jay
05-14-2009, 05:18 AM
The piece you welded in is rusty, next time clean off all the rust, it will improve your welds tremendously. Also, run more heat, less wire speed and slow down the torch. Practise some more on scrap metal.

On your frame, if you grind away all the weld buildup and you had bad penetration to start with, you loose almsot all the integrity your weld had. Take a peek on the backside of the metal, see if you have full penetration. It will show as a sort of bubbled surface from where the full penetrated weld pool got in contact with air (no shielding gas there)

OK, more power, less wire speed, slow down. Yes, I need much practice.
Bee Jay

Bee Jay
05-14-2009, 05:23 AM
Bee Jay,

i can't see that you're gaining more than 1/4 inch from all that work.

am i wrong? and if so how much are you gaining?

I gained about 1/2 to 3/4" in the area I notched. I actually notched more than necessary I think. The tire and wheel would have rubbed there with the 2" adapters. They didn't touch at all and I had about 1/4" clearance with 2.5" adapters. Now I have 1/2" minimum clearance. I'm confortable with that because these 35 series tires don't flex much. I could have called it a day with 2.5" adapters, but I didn't like the tires sticking out past the fender even 1/2".
But you are right, it's a lot of work for only an additional 1/2" backspace. But I think if someone wanted to, they could cut more agressively, and notch enough of the frame in that area to gain enough clearance for 6.5" backspace, and maybe fit some 12" C6 Z06 wheels and tires. Now that would be cool.
Bee Jay

Bee Jay
05-25-2009, 05:05 AM
More welding and grinding this weekend. I've had enough of this. Welding is like finally getting your father to let you ride the riding lawn mower. After the intial thrill, it gets old fast, and then you realize "this is work".
So I sprayed it semi-gloss black and declared it finished. I think the frame is as strong here as before. The area I nothched has 3/4" clearance now. The tightest spot now is just above the shock mounts. I only have 1/2" to 9/16" clearance there. Maybe I should have been even more agresive with my trimming. Thanks Twin Turbo for your advice, more juice is great but slower wire speed made things worse.
Bee Jay
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Bee Jay
05-25-2009, 02:50 PM
Keep us updated on the finished product. I am getting ready to do the same modifications to my 68. I have a set of C5 Z06 wheels in the rear with the 2" spacers. There is a little bit of rub on the tire, but I ground away at the frame already. I also am a little bit toed out in the rear to help with the clearance.

Did you have any close clearances with the top portion of the frame? From my memory I was thinking the top side of the frame was the next closest point.

I need to get this done before the power tour comes along, and I have about 12 hrs of driving with rubbing tires:cussing:

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Hey ML Pettus, I just peeked at your pictures. Check it out. He's running C6 style wheels. Looks great. Are you running C6 Z06 wheel and tire sizes or C5 Z06 sizes like me? Where your tires are rubbing is exactly where I notched. Is that the only place you had rubbing? What does the tire look like where it rubbed? Any danger of blowing the tire? Maybe I could have gotten away with just the initial grinding in my second photo. But now I think I can move up to 19x12 C6 Z06 wheels and tires. That would require me to move in another 3/4", or 6 3/4" backspace. Not possible with only 9/16" clearance above the shock towers. I think I'll just leave it alone. Next project, RPM Air Gap intake and maybe a LT4 Hot Cam roller conversion.
Bee Jay