So I'm under the car replacing the brake compensator rubber hose and the e-brake cable. Generally the underside is ok but I wanted to scrape off some of the messy tar/whatever it is and then clean up and maybe spray with truck underbody coating or something. Assuming I don't want to take everything apart (eg. remove all the steel brake lines, remove the rear axle, etc...) what's the best process for this? Is it worth doing?

I'm thinking.
- use grinder or wire wheel and remove old crap off underbody and wheel wells and maybe bottom of gas tank
- sand with a rough grit sandpaper (200?)
- treat with POR-15 (I still have a quart left from the interior floor work)
- spray on underbody truck paint but be careful to cover surfaces I don't want treated.

Here's a few pictures of the underbody.





Here's a picture of the current black crap that's on there.

I know for a fact that if you coat it with oil it will get soft and release form the body and pull of in large pieces. This happened to me this summer when I had a cam box gasket fail on a 700 mile trip and was losing a quart of oil per 100 miles. I had oil dripping off everything. What a mess to clean up, but that junk under the car came off real easy. I would say spray with diesel fuel and see what happens.

grinder or wire brush is not a good idea. This stuff gets soft with heat. better off to try to chisel it off when it is cold and stiff.

the small needle gun from harbor freight will take that crap off and it doesn't mark the sheet metal (at least mine doesn't). It doesn't make a lot of heat either so it won't soften it up while you do it.
http://www.harborfreight.com/compact-ai ... xVt64XY_X4

20% coupon:
http://www.harborfreight.com/20off-coup ... 17547.html

I noticed in your pictures that your brake line has surface cracks in the rubber you may want replace them while you have things apart. I took mine to the local hydraulic line shop and they made me a set of all five in stainless braid for 100 dollars.

Ptoneill wrote:I noticed in your pictures that your brake line has surface cracks in the rubber you may want replace them while you have things apart. I took mine to the local hydraulic line shop and they made me a set of all five in stainless braid for 100 dollars.

Yep. Brake hoses already done. That's just an old picture.

I haven't done the underside, but did do my wheel wells. First, I used a power washer. A putty knife to get the loose, failing undercoat. Degreaser and a dish brush and a final rinse. I used brush on Rustoleum to coat a few areas where minor rust was beginning to show. Finally, hit the entire area with a spray on undercoat.
Prior to the final step:


The underside will be a filthy job, not one I would want to do on a creeper. Maybe touch up the few needed areas. For an entire coating, I would take to a shop that has the lift, steam cleaner, etc to do the job well.

I tried using tall 6 ton jacks to lift the body up about 30 inches to clean under it in the driveway....it sucks!! I was able to spray it with POR's Marine Clean and I used a long handle brush to get the heavy stuff but it was a lot of work, I can't imagine trying to remove all of the undercoating without a proper lift or rotiseree.

Your wheel wells look great!

Hey Richard

I picked up one of these at Princess Auto for nothing, it was a great help when working underneath. Also wore a garbage bag like a poncho and the stuff wont stick to you

My 5 cents since I've been doing a LOT of this - sadly time and a wire wheel on the angle grinder has been the best approach for me. It's slow but the heat from the wire wheel semi-melts the area you're working on and it comes off OK. I've also tried the heat gun + scraper approach which is even slower and less complete. I'm told that oxy torch burns it off but I don't have one of those, only the MIG. The drawback of my technique is that you will end up with little black specks ALL OVER YOU. wear overalls and zip them up as high as you can - the faceshield looks like a great idea too (I have protection goggles so I end up looking like a panda)

For me, if the original undercoat is still in good condition and theres no rust hiding underneath it, just give it a decent degrease, sand back any rusty spots then coat it with underboady deadener/sealer. I did this in my wheel arches too and underneath my coupe and it looks great! Even though its something you rarely see