MALIBU 78 with frame rust

[4elatemodel]

Hey all,
Just picked up a 78 malibu 4 door last week. I've been crawling around under it every chance I get. I happened across some frame rot around one of the reat body bushing mounts (a week spot I know).

Is there any reason I can't cut it out and re build it with fresh metal? I've seen some people wanting to stay away from the frame seam why?

Thanks

 

[Sweet_Johnny]

You can source different rails and weld those in or you can try and fix it, just do everything you can to avoid and prevent cracks. A crack can turn a corner but it can't take a roundabout. What I mean is if you're going to cut, remove, and replace rectangular shapes (or fix a crack) then drill a hole at each corner (or end) before welding. It relieves the stress- a crack will not continue once it encounters a circular hole. Having a hole pre-drilled also provides a very clear reference point of where to cut and when to stop. Given the size of that rust hole I imagine the frame is currently in a bit of stress due to a loss of structural integrity.

Be mindful of warping or work hardening these frames, as they're comprised of substandard steel. I guess it's not really "work hardening" but when you weld steel you change the microstructure of the entire Heat Affected Zone, and that makes it harder and therefore more brittle.

It's never fun to weld on top of another weld- it's considerably different than the surrounding metal and therefore requires a change in technique... mid weld. It's not uncommon to have poor penetration.

If things crack later, it's most likely to happen at the edge of a weld.

So it's possible to ruin the temper of the frame, warp it, and send a new crack down an old seam all while having a weld that didn't penetrate well enough to begin with.

 

[78Delta88]

Reason for most shying away is catastrophic failure to include death. Imagine going down the highway and back bumper falls off and into the car behind you or spring perch collapses and into the on coming lane at highway speed.

If the repair is in front of or after the connection area of the "coach" is not as bad as if it is in the long span in between the axles. You have to remember the vehicle is two structures of sprung and unsprung weight joined together by the frame and has to stay in balance as well as proper geometry.

Then if done by a shop you run the risk of the repair entered to DMV and you end up with a vehicle that has a "salvage" or "non-rebuildable" title. This can cause the vehicle to be unsalable or not be able to plate and insure it once the restoration is done.

Late 70's to mid eighties the steel was garbage. USA steel production was being killed and large influx of overseas steel coming in. Notice where the rust is and certain areas with a black coloration? This was due to poor quality control of the manufacture process and removing the slag from the steel.

GM also had trouble with soft cams, spring sag, body panel rust. All due to poor quality steel.

If you can do the repair and do it right, it's basically a non issue..., mechanics from model T days have been repairing frames.

 

[4elatemodel]

Thanks for some of the tips guys! I might look into sourcing a rear rail. I think I found one that will work. It starts just behind what I'll call the axle bump? So it's behind the rear wheel and goes all the way to the bumper mounting. It's fairly cheap. Not a small peice of 12 gauge cheap but peace of mind cheap. Well see. For now she's holed up for the coming winter.

 

[Sweet_Johnny]

Right on. What exactly did you find? There are lengths of the stock frame for sale on eBay- people salvage them before crushing the rest. Pay close attention though, as the car, wagon, and Camino frames differ in the rear. There are also universal frame rail kits available from places like Summit. Perhaps Trick Chassis has something you'd like. Maybe check with Wild Rides. Have a look at A&A Manufacturing too before you commit to anything.

Most importantly check out UMI because they have all the braces and suspension parts you need and they make a damn fine product. Returning it to stock condition without adding their parts still leaves you with an unsatisfactory frame.

 

[SS_Malibu]

That's a very common spot for rust on these vehicles. My far rear frame rails need replaced also. I call that my crumple zone until I can get to it. I'll make a template, cut it out and weld in a new piece of 3/16 steel in its place.

 

[4elatemodel]

Right on. What exactly did you find? There are lengths of the stock frame for sale on eBay- people salvage them before crushing the rest. Pay close attention though, as the car, wagon, and Camino frames differ in the rear. There are also universal frame rail kits available from places like Summit. Perhaps Trick Chassis has something you'd like. Maybe check with Wild Rides. Have a look at A&A Manufacturing too before you commit to anything.

Most importantly check out UMI because they have all the braces and suspension parts you need and they make a damn fine product. Returning it to stock condition without adding their parts still leaves you with an unsatisfactory frame.

I bookmarked all those sites to check out. Was originally thinking umi but I'll poke around and see if there's any other parts I'd like to add.

As for frame rails I found these that claim fitment for a 1978 malibu. Granted a 2 door and not 4 but I think it should work?

Frame Rail, Rear Section, 1978-88 G-Body 2dr exc. El Camino @ RESTOPARTS.com

Frame Rail, Rear Section, 1978-88 G-Body 2dr exc. El Camino. Fits 1982 Buick Grand National, 1984-1987 Buick Grand National, 1978-1987 Buick Regal, 1983-1987 Buick T-Type, 1978-1983 Chevrolet Malibu, 1978-1988 Chevrolet Monte Carlo, 1978-1988 Oldsmobile Cutlass, 1978-1986 Pontiac Grand Prix.

www.restoparts.com

 

[Sweet_Johnny]

Here are some links to discussions about frame interchangeability.

G Body frame Interchangeability for 2 door and 4 door swap

I've searched and have found many contradicting answers. To start, I would only like to discuss the difference in the front frame horn section. I realize we can compress the 5 mph shock or lengthen the frame horn by cutting and welding. There also appears to be different 5 mph shocks.It would be...

gbodyforum.com

Malibu frame swap 2dr vs 4dr

The frame is all rusted out on this '78 Malibu 2 dr. I picked up a really clean 4dr frame off a I think was a 1980 Malibu years ago and best I can tell they are the same. Is this true? Does anyone know of anything that is different before I start putting everything over on the 4dr frame?

gbodyforum.com

Not all G Body frames are the same

I am trying to pinpoint EXACTLY what year make and model the G Body FRAMES have an OVAL HOLE in the frame where the lower rear trailing arm attaches to the frame. Most everything cross references as being the same but they are NOT THE SAME! So far my list includes ONLY the following as having...

gbodyforum.com

frame interchange

I searched some but didn't find the answer I was looking for or I just overlooked it...will say a 4dr malibu, Lemans etc g body frame work on a 2dr g body malibu, Lemans from 78-80 ? Thanks

gbodyforum.com

4door to 2door frame swap

Can I put my 79 monte carlo body on a 4 door cutlass frame? Also does anybody build a reasonably priced aftermarket tube chassis for these cars? Thanks! Dave

gbodyforum.com

And you can't go wrong with any UMI part.

 

[gnvair]

The 2 and 4 door Malibu frames are identical. The wagons and El Camino frames are different. Wagons have some differences at the back. El Caminos are also different at the back and have a longer wheel base. All of the 78-88 A/G bodies have a 108" wheel base. The El Caminos are 117"
Also, if swapping frames.....the Monte Carlo, Cutlass, Regal and Grand Prix frames are longer in the front which can result in the front bumper being too far from the body.

 

[57 Handyman]

When it involves frame rust, the best and ONLY option is to find a replacement. The frame on my 87 El Camino had visible flaking but what worried me most was not knowing what was happening inside the rails.