Chassis/Underside - What's your approach to surface rust removal on complete underside?

[SMLE]

HI folks,

I appreciate this issue may not be an issue for many of you in North America (besides those wetter areas!), however in the UK rust is a huge issue for us on these due to salt on our roads during winter etc. Avert your eyes if you're of weak constitution when it comes to crusty undercarriages!

My 2004 100 series is considered 'solid' by UK standards despite having quite substantial surface rust throughout the entire underside. There is one small area on a rear crossmember which will need cutting out and replacing however the rest is at the surface rust/scabby rust kind of point which I'd really like to address after this winter before it gets too much worse and hopefully treat so it takes a good time before it starts the 'clock' again.

I'm trying to avoid this becoming a mammoth job which I inevitably end up taking it off the road and turning it into a light restoration, so I'd appreciate people's thoughts.

I'm replacing components like control arms etc with new OEM stuff so won't need to sort those, but on the rear axle and the rest of the chassis/underside of the body it's pretty ready for some love.

I've seen people use a dry ice blasting method, but I'm open to suggestions, I just don't want to be painting over badly prepped surface rust areas, and would much rather properly remove the rust, treat and paint it, I just feel like the lengthy part will be the removing of the rust. I plan on keeping this for a long time so I don't want to do a bad job on it. I know you can get a wirewheel on a drill/brush by hand but I feel like there has to be a better way (something like sandblasting feels like it'll cause more issues than it's worth!).

A couple of random pictures, probably the best examples as some areas are better, some are worse.

Any thoughts/guidance/experience with this is appreciated!

Thanks

 

[riffman12]

thoughts and prayers for whoever has to remove the nut on that body mount.

 

[SMLE]

thoughts and prayers for whoever has to remove the nut on that body mount.

That'll be a cutting job for sure I imagine! Just want to salvage the rest of it

 

[OwnerCS]

It can be done with a lot of effort. This is not a small job.

I've used a high pressure wet blaster to take rusty surfaces down to the bare metal.

Additional items that will be beneficial are a mini-induction heater for rusty bolts.

Phosphoric acid is used to treat surfaces before priming and/or painting with rust-inhibiting paint.

 

[SMLE]

It can be done with a lot of effort. This is not a small job.

I've used a high pressure wet blaster to take rusty surfaces down to the bare metal.

Additional items that will be beneficial are a mini-induction heater for rusty bolts.

Phosphoric acid is used to treat surfaces before priming and/or painting with rust-inhibiting paint.

View attachment 3797039

View attachment 3797042

Thanks for the insight!

I'm not sure how feasible that would be in close quarters for the underside but definitely an option to consider.

Thanks

 

[plainjanefjc]

I don’t know how you rust belt folks do it.

 

[SMLE]

I don’t know how you rust belt folks do it.

Sadly no other option if we want to run an older vehicle, except a JDM import (big bucks) but then we're back to square one down the line!

To put things into context, this is a solid example for over here, I looked at a few before this that were absolutely rotten and the sellers wanted £8K+ for them, a lot of the time they are undersealed within an inch of their lives so buyers have no idea what they are getting.

 

[reconranger]

I live in Maine so I'm acutely aware of the issues of rust. Your pics show more than surface rust. Those are some serious flaking. This is going to take lots of elbow grease. I had to use a combination of needle scaler, air chisel, phosphoric acid and sander for some of my frames. I'm more concerned about the insides of those channels and crossmembers. I'd be spraying fluid film/old transmission fluid into those channels ASAP.

 

[delz05]

Something I deal with on a weekly schedule... If you can put the truck up on a lift of some sort, begin with removing the wheels, exhaust (muffler/tail pipe at least), drive shafts, fuel tank, spare tire, as much of the suspension as possible (AHC?) including the rear axle assembly if able. Remove both bumper covers, running boards, plastic splash shields/fender liners, support the transmission, drop the tranny crossmember, spare tire carrier, exhaust heat shields, skid plates etc... Basically, everything you can remove from the underside of the vehicle. I wrap the CATS with paper or foil, same for the exposed electrical connectors and as much of the remaining drive line as possible.

Begin prep by blowing/vacuuming every crevice that can catch debris. Blow out the remaing crossmembers and both frame rails. Using a medium duty needle gun, attack, attack, attack like crazy, every bit of oxidation and corrosion you can access and follow up with a 36g or 40g grinding disc. It is very common that I will spend 20-25 hours just on these 2 phases. At this point we determine what has to be repaired on the frame (prep for welding) if anything, then acid wash (spray on and brush) all exposed areas. While this treatment times out, I re-vacuum the inside of the frame rails, using a blow gun to force out the rust scale and debris (hello mouse-house!) I also blow out the rocker panels and the rear body reinforcement support in prep for internal soft coating (Woolwax).

After the acid wash is complete and dry, I scuff the frame with fiber pads and spray rust kill primer (2 coats minimum). This needs to properly cure (24 hours) so while this is timing out, I repair and clean all the removed components as needed, and attack the floor pan and floor supports, repeating the process. I spray the Woolwax into the body cavities, lower doors, upper/lower hatch areas and anywhere water, dirt and debris will be able to accumulate.

Semi-gloss black paint is next for the frame if the owner chooses to NOT do an exterior coating, or a seal coat as prep for a Rusfree rubberized exterior coating over the entire reconditioned frame, which goes a long way in keeping the reconditioned frame in "as-new" shape. In either case, I next apply the Woolwax inside each frame rail and crossmember. Too much is NEVER too much! I apply liberally, using 3 to 4 quarts per vehicle. (I use 4 to 6 quarts of external coating as well). Some customers have chosen to have me paint the floor pans, others have chosen hard coat, and others just Woolwax. In any case, the underside now looks better than new. I will add some 2012 4Runner images tomorrow... just finished that job today! All told I have about 35 hours into the reconditioning of the frame, which includes the dis-assembly/re-assembly.

Re-assembly now begins with reconditioned components or brand new, at the customers request.

Here is a Tacoma frame just completed. We chose to drop the frame, as it is a simple process and easier to recondition on the ground. First 4 images, cleaned prepped and primed... Last 3 external/internal coatings completed...

 

[hoser]

@delz05 Your photos came out a bit small. But can't see a spec of rust!

 

[SMLE]

I live in Maine so I'm acutely aware of the issues of rust. Your pics show more than surface rust. Those are some serious flaking. This is going to take lots of elbow grease. I had to use a combination of needle scaler, air chisel, phosphoric acid and sander for some of my frames. I'm more concerned about the insides of those channels and crossmembers. I'd be spraying fluid film/old transmission fluid into those channels ASAP.

Would spraying e.g. old transmission oil into those channels/cross members address existing rust? I'm aware people spray the undersides with old oil to protect from rust, but not sure about the insides of the channels works.

Thank you for the suggestions, greatly appreciated

 

[reconranger]

Would spraying e.g. old transmission oil into those channels/cross members address existing rust? I'm aware people spray the undersides with old oil to protect from rust, but not sure about the insides of the channels works.

Thank you for the suggestions, greatly appreciated

As far as I know, the existing rust is not affected by spraying fluid film or old transmission fluid. However, I've read several web sources that transmission fluid has rust inhibitor. It should at least stop further rust.

Other option is to spray phosphoric acid into the channels. There are several caveats that you should follow when using phosphoric acid.

I usually have an air compressor and spray fluid film:transmission fluid (9:1) into the channel every 1-2 years. The key is to do the spray regularly. I usually buy used cars from Maine. Most of these are cheap because of rust issues. I've been able to keep the underside rust issues to a stable minimum. My 1999 Acura and my 2006 LX look like AZ cars.

Key is to regularly apply the spray.

 

[Kabanstva]

That ain’t no surface rust lol

 

[SMLE]

Something I deal with on a weekly schedule... If you can put the truck up on a lift of some sort, begin with removing the wheels, exhaust (muffler/tail pipe at least), drive shafts, fuel tank, spare tire, as much of the suspension as possible (AHC?) including the rear axle assembly if able. Remove both bumper covers, running boards, plastic splash shields/fender liners, support the transmission, drop the tranny crossmember, spare tire carrier, exhaust heat shields, skid plates etc... Basically, everything you can remove from the underside of the vehicle. I wrap the CATS with paper or foil, same for the exposed electrical connectors and as much of the remaining drive line as possible.

Begin prep by blowing/vacuuming every crevice that can catch debris. Blow out the remaing crossmembers and both frame rails. Using a medium duty needle gun, attack, attack, attack like crazy, every bit of oxidation and corrosion you can access and follow up with a 36g or 40g grinding disc. It is very common that I will spend 20-25 hours just on these 2 phases. At this point we determine what has to be repaired on the frame (prep for welding) if anything, then acid wash (spray on and brush) all exposed areas. While this treatment times out, I re-vacuum the inside of the frame rails, using a blow gun to force out the rust scale and debris (hello mouse-house!) I also blow out the rocker panels and the rear body reinforcement support in prep for internal soft coating (Woolwax).

After the acid wash is complete and dry, I scuff the frame with fiber pads and spray rust kill primer (2 coats minimum). This needs to properly cure (24 hours) so while this is timing out, I repair and clean all the removed components as needed, and attack the floor pan and floor supports, repeating the process. I spray the Woolwax into the body cavities, lower doors, upper/lower hatch areas and anywhere water, dirt and debris will be able to accumulate.

Semi-gloss black paint is next for the frame if the owner chooses to NOT do an exterior coating, or a seal coat as prep for a Rusfree rubberized exterior coating over the entire reconditioned frame, which goes a long way in keeping the reconditioned frame in "as-new" shape. In either case, I next apply the Woolwax inside each frame rail and crossmember. Too much is NEVER too much! I apply liberally, using 3 to 4 quarts per vehicle. (I use 4 to 6 quarts of external coating as well). Some customers have chosen to have me paint the floor pans, others have chosen hard coat, and others just Woolwax. In any case, the underside now looks better than new. I will add some 2012 4Runner images tomorrow... just finished that job today! All told I have about 35 hours into the reconditioning of the frame, which includes the dis-assembly/re-assembly.

Re-assembly now begins with reconditioned components or brand new, at the customers request.

Here is a Tacoma frame just completed. We chose to drop the frame, as it is a simple process and easier to recondition on the ground. First 4 images, cleaned prepped and primed... Last 3 external/internal coatings completed...

View attachment 3797150

View attachment 3797151

View attachment 3797152

View attachment 3797154

View attachment 3797157

Thank you for this really detailed response, I think I'll have to take an approach like this to sort it out otherwise it's going to go too far for me to manage it longer term.
Funnily enough, I've never come across a needlegun before or the acid so it looks like it'll be a great solution - I feel like I've been living under a rock

Thanks so much

 

[SMLE]

That ain’t no surface rust lol

I need positivity please

 

[baltistyle]

As extra reinforcement for Delz’s post, do not use any films or coatings before dealing with the rust. Deal with the loose rust, treat the rust with acid, paint, and then do a lanolin. Otherwise you’ll never be able to get that coating off well as a diy, in order to treat later.

 

[SMLE]

Thank you all!

We are moving more rurally in the coming months and I'll have a proper designated workspace for this, so I'm thinking that next summer I'll take it off the road for a few weeks so it can be fully sorted properly.

I'll be getting myself a nice big compressor and the required bits to sort this out!

Is anyone aware of the required % for phosphoric acid? If I'm just buying pure acid then I would be good to know what strength is required. I'm also curious to know if this will affect factory coatings underneath on areas where there is very little rust but would still use this.

Thanks!

 

[delz05]

I typically use a 25% ratio (1 pint acid mixed with 3 pints water) or just purchase pre-diluted 30%

ALWAYS add acid to water... greatly reduces spills and splatter.

There are plenty of "general use" rust converter solutions on the market (BEEST rapid rust converter, Rustoleum, Naval Jelly etc...)

Work slowly and safely, the end result is well worth the time and effort you put forth! Good luck!

 

[Kabanstva]

Spend a few hours with a needle gun before you use any chemicals or rust converters or any other BS like that.

 

[SMLE]

Spend a few hours with a needle gun before you use any chemicals or rust converters or any other BS like that.

Planning to get the rear half of the car stripped underneath of components as suggested by @delz05 in their first post on this thread next summer to address the rust as described, reinstall and then do the same for the front half (I may do it all in one go, it's purely down to time so will have to see, especially as the annual roadworthiness inspection (MOT) is due in June 2025 and I'd ideally like it sorted by then so it's not going to fail etc.