Best way to clean underside of car?

[Stangboy 14]

I'm in the process of rebuilding my '69. I've got all the suspension stripped off, and the motor and all the wiring removed. What would be the best way to remove 40+ years of road grime from the underside and engine bay? I have a 2 post lift so getting underneath isn't a problem. I was thinking pressure washer, but don't want water everywhere in my shop. I was thinking of hanging plastic sheeting off the body to the floor so at least the water would go straight down. Any ideas, tips or tricks? Thanks.

[JayEstes 172]

I did mine from getting under on my back.  It came out less than perfect, but its not bad.  I raised the car high enough that when I was on a mechanics creeper I had sufficient room to maneuver tools and work comfortably under the car.

 

For the most part, I started with a wire-brush on a 4in grinder.  It slings the grease and grit pretty good, so I would used a face shield a painters bunny suit (be sure you don't get a loose suit near the grinder brush - ask me how I know).  I removed most under components, brake & fuel lines, and bolted components, and went after it section by section.

 

After a relatively fast moving wire-brushing to get the big stuff, making an effort not to strip original paint and remove well-adhered undercoat minimally.  After this initial pass, I got a steel bowl and filled it about half way with laquer thinner.  I bought a 5 gal bucket of laquer thinner when I started this.  Using hand size scotchbrite pads (with some really heavy-duty gloves BTW), I would soak the pads in the thinner and work over the surface to loosen the rest of the tough greasy stuff - especially corners.  Some spots need more grinding, and in other places, you can get some shop towels soaked in thinner and finish cleaning them.  

 

I used basically a 3-stage cleaning process 1) wire-brush 2) scothbright pads with laquer thinner and 3) shop towels with laquer thinner.

 

After getting the surface clean again with towel and thinner, I got under and covered bare patches with black semi-gloss 500deg (duplo) engine paint. Once I had the whole bottom painted up, I bought spray on truck bed liner and covered it all again with that.  It came out generally pretty even and seems to have stuck really well, but I don't have alot of miles on the car to say for certain.

 

I didn't have huge rust issues to deal with, I had re-worked the floor pans (mostly from the top side) prior to getting to the bottom.  The edges where the pans had been welded, I patched up a bit with JB weld and black RTV before the paint and truck-bed liner.

 

Anyway.  it can be done working from underneath.  Doesn't take too long unless you are a true perfectionist.  If you're overly anal about stuff I recommend a rotisserie.. ;-)

 

Hope some of that helps.  since you have a 2 post lift, maybe you can work from a roll around chair instead of your back, or even standing if you have the head room in the shop.  Good luck.

 

Jay

[barnett468 418]

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You can rent a portable steam washer but you wouldn't really want to be inside a tarp tent when you use it but you could hang the plastic so it had maybe 3 feet of space between it ad the floor.

[shaun071 62]

I used the same method as described above- 4" grinder with wire brush attachment on a garage creeper.

[MikeStang 247]

I Contacted a local sand blast shop and they came to the house and I put car up on blocks about 3' in the air and the fellow climbed under the car and blasted it to the white, he then proceeded to do under the hood, behind the fender area which the fenders were off so he did those also, then the inside and the trunk area... Charged me $350.00 and took about an hour or so.

He even blew most of the sand out of the car and I finished getting the remainder of the sand out with my shop vac, and then rolled it into the shop and hosed it down with POR-15

[Rsanter 152]

I used a pressure washer with the he car on jack stands.

I had to do,it,several times.

In between I used paint scrapers, puddy knives and wire brushes to loosen up the harder stuff.

Then hit it again with the pressure washer

 

Bob

[Midlife 814]

If you want to clean everything down to factory paint, then sand-blasting and wire-wheeling isn't the way to go.  The concours folks recommended this to me circa 2000 and it worked really well.  Put the car up on a lift or high jackstands in a well ventilated area.  Dip a rag in gasoline or kerosene and use elbow grease.  For severely scraped on crud, a small scraper will do.  Be patient, but the underside will look like the factory did it without the undercoating/soundproofing, and all of the rust areas will be clearly evident.  It took me about 3 months to do the whole underside of my 66 fastback, working weekends. 

[JayEstes 172]

It took me about 3 months to do the whole underside of my 66 fastback, working weekends. 

 

I can see that working pretty well if you want to take the time.  It didn't take me that long, and I definitely wasn't going for concourse.  I just wanted it to be protecting the metal, and be ultra durable (so I don't have to do it again).

 

Good discussion from all above.

[JayEstes 172]

I used the same method as described above- 4" grinder with wire brush attachment on a garage creeper.

 

I used the wire brush sparingly, as a quick way to get the bulk of the crud off.  I specifically made an effort not to remove original paint, but if it came off in an area of rust, I cleaned a little more there, and went back with paint to seal it again.  Finally, I put the truck bed liner on to finish up the bottom. 

[RPM 1,190]

The first vehicle I stripped down to metal, a 56 F100, I used the wire wheel method. I'm too old and grumpy to lay under a car with a wire wheel. My 69 Mustang went an easier method.

 

 

 

[Stangboy 14]

Thanks guys! I'm wondering if I should try to get off the factory undercoating, or just wash it cleaning enough that a bed liner type material sticks to it. It looks like one of the above pictures, kinda spotty in places. I have new floor pans in, so I won't have to clean those much, mainly wheelwells and around the gas tank and rear quarter area.

[RPM 1,190]

On my Cali car, the only thing wrong with the factory undercoating was the looks. When I removed it the metal under it was pristine.

[JayEstes 172]

Thanks guys! I'm wondering if I should try to get off the factory undercoating, or just wash it cleaning enough that a bed liner type material sticks to it. It looks like one of the above pictures, kinda spotty in places. I have new floor pans in, so I won't have to clean those much, mainly wheelwells and around the gas tank and rear quarter area.

 

My thinking is you are better off leaving it, unless there are rust signs on either side in that area.  Like what RPM said.

[1969_Mach1 333]

+1 on leaving the existing paint unless there are signs of rust.  Then only remove paint in those areas to treat/repair the rust.  I've done both, removed paint and simply cleaned/degreased the factory paint.  Removing paint to bare metal is a last resort as now you have to prep it and seal it to prevent rust in a very short time.  Rust forms fast on bare metal.  Plus, if you ever remove original paint, you'll realize it's pretty tough stuff.

 

A long time ago I steam cleaned the bottom of a 69 Sportsroof I had.  Then followed that with Mineral Spirits, rags and a little srubbing.  Finally, Grease and Wax remover with rags to remove any film of the Mineral Spirits.  The original paint was sill in great condition after being cleaned.  I did all this with on a creeper with the car on jack stands as high as I could get it. 

 

If you can rent a steam cleaner that would be the easiest.  Otherwise, a pressure washer, Simple Green, or Purple Power and start scrubbing.  If you can, connect the pressure washer to hot water.

[machm1970 180]

I did the same as some of the others, 4" angle grinder with a wire brush attachment. After it was bare I painted it basecoat clear coat with a color that was close to the original color I found on the underside.

Matt

[fvike 173]

I first used an old paint shop heat lamp to warm the undercoating, and scrape it off. It came off easily once warmed up. Leftovers I soaked in petrolium based degreaser, and washed off with an rug.

 

I then used a steamer to wash the underside completly clean, removing any remains of the undercoating.

 

That left me with a clean underside, with the original paint intact. It is almost burned to the metal, and is the best fundation you can have on the metal. It won't ever let go if it has stuck to the car for 47 years already.