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Tubbing my Malibu

33K views 74 replies 7 participants last post by  Onebad79malibu 
#1 ·
I am starting on my tub job on my 1979 Malibu,does anyone have info on where I make my first cuts on removing the material behind seats.?Thanks for any info
 
#2 ·
I would start by cutting the inside edge off the existing wheelwell. Cut it along the trunk floor mating area, and then along the top of the curved wheelwell. You should then have a half moon shaped piece you removed.
Once you've got that out you can cut in towards the frameon each end, and then along the edge of the frame. After that the first piece you cut out can be located and tacked in at the new inside edge. Then a strip that is wide enough to span the gap can be made up and tacked to the inner wheelwell, and the relocated inside piece.
Then it's just a series of tack welds until it's all solid welds, and seam seal the welds and paint. I can usually do a mini tub in a few hours total.
Here's a tutorial that will help. It mentions drilling out all the spot welds, but I never do that as it just isn't necessary if you cut along the floor instead.
http://www.hotrod.com/techarticles/body/hrdp_0903_diy_mini_tubbing_guide/viewall.html
 
#5 ·
It will cut though the paint once you get it going.. Mine does..
But yes it doesn't like paint..
Here's a few shot's of a car I did..might give you some ideas..;)
 

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#7 ·
Here's a couple of photos from doing my Nova, the cardboard layout helped a lot. Mine looks particularly ugly because I back-halved the car as well. The plasma cutter was nice to have.
 

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#9 ·
Hi all!Well I made it home with the new mig and plasma cutter.Can someone give me some info on the size of tires I should be using on my Malibu?i would like to stuff some 31x14.50x15's under it.Im running a well built 383 stroker that I'm sure will handle whatever I put under it.Im running 295/55/15 drag radials on it now but I'm thinking I want to do my tubs to handle bigger than that.They fit nicely,but I don't like the stance,but since I already have them I'm thinking maybe just a mini tub to push them farther under the car,and with the new frame rails and rear suspension I can lower the rear down to where I want it.im going to tub and narrow it either way,but just not sure how much yet.Thanks for all the great and helpfull info!
 
#12 ·
Hard to say what you can put under it for tires until you finish the tubbing, and whatever axle narrowing you might do. Once that's all done you can measure from your hub surface and figure out what you have for clearance, plus what offset you'll need.
I use a simple piece of wood bolted across two axle studs. Make it long enough to swing inside the rear wheelwell, and it will allow you to measure the max diameter of the tire, plus measure in and out from the stick to get total tire width, and offset.
 
#13 ·
I always buy the tires I want to stuff under what ever I want to build... Set the tires in place and build everything around the tires... I learnt that from some pro chassis builder I know... But everyone does things different.. Here's a few I have done..;)

If you do it any other way then this... Make sure you do you math right.. Are you will end up with the tires to far out, Or like some people WAY to far inside the lip of the fender.. Good luck..:thumbup:








 

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#14 ·
I always buy the tires I want to stuff under what ever I want to build... Set the tires in place and build everything around the tires... I learnt that from some pro chassis builder I know... But everyone does things different.. Here's a few I have done..;)

If you do it any other way then this... Make sure you do you math right.. Are you will end up with the tires to far out, Or like some people WAY to far inside the lip of the fender.. Good luck..:thumbup:
Very good point! Nothing will ruin the look of a car more than a tire wheel combo that doesn't sit right. Some cars look better with tires tucked in, and some look better hanging out. Regardless of what you choose, it needs to be right for the car.
I've always disliked the look of cars with big tires tucked too far in, but I like old cars with some tire hanging out, if the body design works for that setup.
 
#17 ·
Tubbing my malibu

Thanks folks,I know exactly what you mean,I don't like the looks of the tires being too far inside the wheel wells.Ive just finished reading several articles on back halving g body's.With all the available wheel and tire options,wouldn't the rear end width be a determining factor in the overall width in between frame rails???Im thinking if I locate my frame rails close enough together my wheel and tire combo is almost limitless??????But I'm old so I could very well be not thinking about it right lol.Thanks for everyone's input its been very useful!!
 
#18 ·
Yes, tire/wheel size will determine axle width. Plus frame clearance also. Unless you plan to start reworking the frame rails you really need to be sure the axle width is enough to handle whatever backsapcing the wheels you like will handle, plus clearances.
I'd do the sheetmetal tubbing first. Then once it's done you can get measurements from the existing axle to see what space you have from inner wheelwell edge to outter edge. After that you can measure the hub face to see what you have for outside and backspace on the car.
Once you know the figures you can determine what wheel/tire will work. Most tire companies will give you tread width, but they also have sidewall width or cross section. That will be the true test of what clears, as it's the widest portion of the tire. I like to leave an inch inside, and about 1/2"-1" outside depnding on what side deflection your rear suspension might have. My panhard bar keeps my axle pretty solid, but normal deflection is less than 1/2", so I like 3/4" clearance to the tire for a little room.
 
#19 ·
I will also be cutting down the rear end myself and sending the axles off to be splined.We have a very large swap meet coming up in February and there is usually a massive amount of tires and wheels to choose from.Im hoping this year will be no different and am able to find what I'm looking for.In the mean time I'm going to start removing existing tubs and floor and trunk panels,I'm not sure my trunk hinges will be in the way but if I have to I can move them and pin the deck lid.Just getting anxious to start in it.Thanks everyone!!
 
#20 ·
I guess I forgot to mention I am a carpenter,business owner by trade, so I got a head start on using a tape measure and a couple son in laws that know absolutely everything from scientific engineering to having their wives figured out so I should be in good hands so I'm hoping ill just be sitting in the corner drooling on myself while they figure out how to open the trunk!!lol!!!
 
#21 ·
Picked up some 31/14.50/15's over the weekend.I got the interior removed and got the divider out behind the back seat.Im thinking of removing the trunk hinges and doing a pin on trunk????My next question is where to cut the floor out??Im assuming right at the area where the trans tunnel ends in front of backseat????I want to get frame rails cut off but I need to know how much floor to remove.Thanks guys!!!
 
#22 ·
I never cut any more than abosolutely neccessary! You can always cut more, but it's tougher to put some back! Do some measuring for tire/wheel clearance and then figure out if the frame rails need to move, and if so how much. Once you see how much they need to move you can measure from the inner existing edge and see what needs trimming. If the frame needs to be relocated in, make the cut in the trunk into the inside edge of the frame. That way the wheelwell wont be an issue for any reason.
If you want to leave your hinges just cut the down support loose from the inner wheelwell, and leave it hang while you tub. Once you've tubbed the wheelwell you can then make up metal to reattach the support for the hinges back to the new tub.
Sometimes it's easier to cut off the rear frame rails first. Then narrow them outside the car and build up your backhalf. Then you can move it under the car and jack it up to see what obstructions you have and address the wheelwells then. After cutting away the sheetmetal you can raise the frame into position, weld it in and do any gussetting. Then you can start rebuilding the new tubs where they need to be with the modified frame.
 
#23 ·
Good advice.Ill cut out the frame tomorrow.I built a heavy duty table and plan on building my rails on it.Ive built hundreds of motors,and build custom homes for a living and project managed a 5 million dollar hospital addition,but this is by far the most intimidating job I've done yet lol.Im assuming I will cut the frame toward the front of the car beyond the mounting points for rear end bracing where it connects to frame right where frame turns?If that makes sense
 
#24 ·
I would usually cut the frame before it rises for the rear axle clearance. Where to cut depends on where various body mounts are. I would also tack in a metal brace between the frame rails on the portion that will stay with the body so the frame wont move. Doesn't have to be anything huge, and some 1.2"-2" angle tacked in will keep things located so they don't spring when you cut behind to remove the back half.
Then once the back frame is removed I would build a crossmember to span the frame rails, and weld it in permanently. After that the brace can be removed. This crossmember will be what you attach your narrowed frame back half to when it's done.
This is a picture of my buddy's old '37 Plymouth coupe's frame where he back halfed it for monster tires and wheels. You can see how they built a crossmember, then narrowed the rails and reattched them. The body is still off, so I can get some other pictures if you need any further looks:


If you're going to keep the car lower, then you'll need a offset in the crossmember to give driveline clearance. His car is a gasser style, so no offset needed in the center for driveline clearance.
 
#26 ·
The thing is... Depending on if your useing a 4 link or what ever,, You need to know what your going to have in front of the rear end because this will say where your crossmember will be, then work back from the crossmember,, You can tie the crossmember into the front part of the frame,, Then set you 4 link or what ever your useing off it, Make the frame kick up's, tie back into your body in the back by the body mounts,

Really hard to give a step by step on the web,, But the car will need to be set up at ride height so you can figure everything out...

Once you have the tires under the car in place,, You can take your measurement from inside rim to inside rim.. This will be your over all measurement for the rearend,,(minus the thickness of your two hubs..)

Where people get into trouble is not setting the wheels being use under the car (IN PLACE) before starting anything.. By doing it this way the tires will end up where they need to be.. Doing a bunch of figuring without doing it this way will have your tires sitting somewheres under the car,, Might end up not being where they should be.. It's really easy to do,, When it's done the right way..Do what it takes to have the wheels right.. Are you will be sorry later when it's to late..
 
#27 ·
Tubbing my malibu

Thanks for the great info and pics.I picked up a set of 31/14.50/15's that I will be using.I guess my main question is wher to cut the floor at in front of where the back seat was located.Everyrhing Ive seen it was cut right where the. Trans tunnel ends ate the bav seat.Is this correct??That should give me plenty of space to instal crossmember.I am going with a 4 link set up btw.Thanks guys.Sorry if the questions seem like no brainers but I don't want to fabricate more sheet metal than neccassary.
 
#28 ·
Thanks for the great info and pics.I picked up a set of 31/14.50/15's that I will be using.I guess my main question is wher to cut the floor at in front of where the back seat was located.Everyrhing Ive seen it was cut right where the. Trans tunnel ends ate the bav seat.Is this correct??That should give me plenty of space to instal crossmember.I am going with a 4 link set up btw.Thanks guys.Sorry if the questions seem like no brainers but I don't want to fabricate more sheet metal than neccassary.
You really don't need to go to much ahead of the crossmember.. About three inch's should be enough to get in there and weld... Your 4 link will determine how far forward your crossmember will be..
 
#29 ·
Tubbing my malibu

Hey all!I began to start cutting the sheet metal out for my tub job.I guess I didn't realize the support bars for the rear end were bolted to the sheet metal in the floor board in front of the back seat.So the sheet metal has to be cut back to where the frame is parallel with each other before it curves underneath and rises for the shock and spring mounts?????ive got a sheet metal brake so I can fabricate a new driveshaft tunnel if I have to.Am I correct in this way of thinking???Thanks guys!!
 
#30 · (Edited)
Hey all!I began to start cutting the sheet metal out for my tub job.I guess I didn't realize the support bars for the rear end were bolted to the sheet metal in the floor board in front of the back seat.So the sheet metal has to be cut back to where the frame is parallel with each other before it curves underneath and rises for the shock and spring mounts?????ive got a sheet metal brake so I can fabricate a new driveshaft tunnel if I have to.Am I correct in this way of thinking???Thanks guys!!
We need pictures to say what to do on THAT car..Without seeing it, it's hard to say for sure.. Post pictures and it will be easier to say..

Here's a Mustang I did..Might give you some ideas..The four bar came right off that crossmember..



 

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#31 ·
Tubbing my malibu

Hey everyone.Havent posted for a while,had to change email.I have been cutting up my Malibu for the tub job and I now have old fender tubs cut out,floor cut out as needed and frame cut out.I guess my question is do I leave the contour of the old wheel tub next to panel where seat belts are molded into side panel?I would like to use the original cover and trim for this area.I have pics if I can figure out how to get them on here.Thanks everyone!
 
#32 ·
You want to leave as much as you can get away with.. If you cut to much out you may be added it back later... The inter body panel can be welded back to the fenders,, Look at the pictures I posted.... It may give you some ideas..
 
#34 ·
:eek:
Man that car would be much easier to work on if you didn't have it on it's side..LOL:thumbup:

No !!! It's looking good so far... I buy new axles from Moser Engineering,,Moser Engineering - Moser Engineering - Home

They should have a form to fill out on their web site.. You will need to know what brakes you are going to be using..

I use to get all mine cut.. But Now I just buy new one's with the new bearing ready to go.. I do all my own housing..(9'')
 
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