Reasonable DIY rust repair on a vehicle subframe, unibody, or frame.. Repairing a subframe by cutting out the rust, welding patches, then painting.
Although this subframe is from a Saturn S-Series car this information is univeral for all subframes across various vehicle brands. This subframe was from a rusted out vehicle that I purchased for the engine. Upon examination I found that my 2nd subframe (replaced 5 years prior) was rusting out AGAIN. So this one looked decent, I decided to clean and paint it. Sandblasting revealed 2 minor rust spots, both on the drivers side.
In this video you will see me cleaning the frame, cutting out the rust, and welding in patches then painting the subframe with a rugged coating of Rustoleum truck bed liner.
Some subframes can be repaired on the vehicles while extensive damage may require removal. The reason is that it may be hard to reliably access certain areas for a quality repair. Subframe failure can result in loss of control, very dangerous. If you discover sub frame damage you should not drive the vehicle unit it is replaced or repaired.
Some people say that sub frames or engine cradles should not be repaired at all but I see no reason why minor rust like the one shown in this video cannot be patched with quality welds and material. I used scrap metal that's strength exceeded the original material. If your subframe is as bad as the picture in the beginning of this video then I don't feel it should be repaired.
The first time I did a subframe I had no prior experience and it took me a weekend. Mostly dealing with rusty and broken components.
Sub frame removal should be similar for most cars but will vary a bit. Here is the general procedure.
1. Jack up the front end, secure it behind the subframe on jackstands or something secure so it won't fall. I typically also shove the wheels under the car for extra insurance in case the car falls it will land on the wheels hopefully saving anyone underneath.
2. Support the engine & transmission (you can lay lumber across your fenders and chain to it). I used a chainfall from the ceiling of my garage.
See photo here: http://mainejunker.com/dosumpthin/saturn/pics/satchain.jpg
3. Support any other items (Probably just your radiator) with ropes, bungee's, or zip ties. Get creative.
3. Disconnect everything from the subframe (engine & transmission mounts, control arms, steering rack, brake lines, sway bar, etc.)
4. Drop the subframe out. Installation is the opposite.
NOTES: Pre-soak rusty bolts & be prepared to replace any old rusty exhaust parts that may break. I have found that old exhaust systems, once disturbed, tend to have issues.
The large subframe to body bolts can be a chore. They are often retained by captive nuts in the frame which often break free if they are old and rusted. Pre-soak these heavily with good penetrating oil like PB Blaster, days ahead of time, and repeatedly. Sometimes to avoid breaking the nuts a high speed high power pneumatic impact wrench is the best option (fast & furious). If the captive nuts break do free and spin then you have some options:
You may need to drill a hole to access it of there are no holes nearby:
1. Tack weld it in place
2. Wedge something in next to to keep it from spinning
3. put a wrench on it if you reach it
4. Cut the bolt off (torch or saw) then shove the remains up into the frame and install new nut.
I also highly suggest joining a forum specific to your vehicle for specific help.
To see the horrible condition of the car this came off of:
Saving a rusting oil pan:
Here is some info on the tools I am using:
Harbor freight model 68992 40 lb sandblaster like the one I used:
Really cheap Harbor Freight model 95793 $20 sandblaster
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