View Full Version : TR4/4A sandblasting TR4 chassis won't remove rust inside

06-06-2005, 04:46 PM
Hi all,

I'm about to have my chassis sandblasted, and I'm worried of the creeping rust inside the box sections, that I can see from every opening (from the rear end for instance). The sanblast will obviously only remove a very small part of it, so what's the use of a newly coated chassis if it continues to rot from the inside ?

Do you consider that some cavity wax is a good-enough protection, and more generally what are your opinion about this, is it a real concern ?


06-06-2005, 05:01 PM
I've just finished sandblasting my own frame and am very pleased with the results. While this does nothing for the rust growing inside the frame it sure makes for a presentable restoration and to be rid of all that gunk and crud which used to coat my tools and car jack, yahoo! Now, for the inside of the frame I'm spraying a rust killing (rust-off?) concoction available from home depot. This is basically phosphoric acid + some additives that converts existing rust into a zinc phosphate (inert) structure. Then I plan to spray a coat of waxoyl etc. to provide further protection. You have to be careful because the more you spray on these cars the higher the probability you are simply creating an estuary for future rust growth. Be sure to clear all drain and evaporative holes so that ventilation is maximized.

06-06-2005, 07:18 PM
Hi Phillipe,

It is possible to have a frame "dipped" to strip old paint and rust away. However, the chemicals get into every crevice and are hard to completely remove, might cause more problems later by seeping out and damaging the new finish after the frame is back under the car. The chemicals might "thin" the metal too (an old racer trick to lighten their cars), and can leave the now-bare metal inside even more vulnerable to new rust!

Short of dipping, there really is no way to completely eliminate rust from the inside of the frame. Just have is sandblasted and check that no areas are too thin and weak, might need some repair.

With that done and the outside refinished to your liking, the inside should be treated with something like Waxoyl, as 71tr says. That product is sprayed inside the frame through 1/2" holes. It's a mist and settles on all surfaces, sealing the surface. The holes are then closed up with plugs. It should be re-done every few years.

The point about being sure all drain and evaporation holes are clear is a very good one, too. Internal frame rust is probably 80% from condensation, 20% from water intrusion. Air circulation to allow it to dry is important and will go a long way to preventing or slowing rust.

Any accumulated mud or dirt buildup inside the frame should be cleaned out too. Underneath this is where rust really gets going, when moisture is trapped.

Finally, one place to look at very carefully is the diagonal brace that goes from the shock/spring tower to the main frame rail. These did not have a drain hole drilled by the factory and are very susceptible to internal rust. If your car is all apart for frame work is a great time to drill a 1/4" hole on the inside of this brace (toward the engine), just above the weld at the main frame rail. I'll bet if you do that a bunch of powdery rust comes out! If not allowed to drain, it's common for this brace to eventually fail, rusting from the inside out. In extreme cases, the rust can extend to and destroy the main frame rail immediately adjacent, too.


06-07-2005, 01:21 AM
Hi Philip I have sandblasted, paint removed, and dipped a couple of tr3s. I have even use 70 weight sand on body panels with a 5/16 orifice and maybe 100psi air with good results and I think the Wax Oil is great stuff. I cut a couple of small re-sealable access panels in the rear body tub to get sandblaster in and the wax oil in later. But what I wanted to mention is I have recently been experimenting with an electrolyses dip. Look under (Rust Removal) on the internet. Out in the North West and Canada there are a couple of shops that dip the whole car. They use DC voltage and water with soda in it. It is really trick. The whole car comes out of there bare naked metal and unmolested by any kind of blasting. The process basically breaks the bond on a molecular level. I built a small one in my back yard in about two hours and cleared a couple of crappie rust air cleaners (I bought on eBay from a xxx) to bare metal just by dipping them in using a battery charger. It really works check it out.

Regards George

06-10-2005, 02:20 PM
Dipping for weight reduction is different than the dipping used to remove rust. The old racers trick was an acid dip. The acid did thin the metal which of course removed weight. The last time I heard any rumors about acid dipping was in the early 70's.

The modern rust removal process used by Redi-Strip franchises and various independant shops is a electrolitic process. I believe he liquid is alkaline. The liquid is electrically charged. The metal piece is also charged, the opposite of the bath. The metal gives up its rust to the bath. I can never remember which is the anode and which is the cathode. Think of it like gold plating. The gold bar is charged and the object to be plated is charged (opposite). The gold bar gives up atoms while the piece being plated attracts them. In this case the part give up its rust. The rust is attracted to the liquid.
This modern dipping does not eat into the base metal. Atleast not ferrous metals. I think it will eat a piece of aluminum.
It's a much better process for cleaning an engine block that the standard hot tank. Although it's good practice to hot tank then dip. I mention engine blocks because they have internal areas that are not accessible like a frame. My experience with dipping has yeilded absolutely clean parts. Engine blocks look like a fresh casting. Even in the water jackets which had to be viewed with a penlight.
The fenders and hood from my '51 Ford truck were perfect. My only concern is the thorough flushing of the parts to insure there was no solution left in the weld joints. If your stripper does a good job of washing the parts after the process You should have a perfectly prepared frame to seal with whatever you want.
The first blosk I had done still had rust in the water jackets. I insisted they run it again. They did so and it was perfect. Apparently the number of wires and the choice of the connect points have a big effect on the outcome. The stripper re-did these before the second run.
You can always run a test piece to see the results.