Outer Limits 4x4 Board

Just got a question, as I understand, welding etc onto the chassis rails is a big no no due to weakening the rail?

The radius arm mount on my cruiser looks as though its taken a hit from underneath and the mounting is slightly bent. This is welded onto the chassis rail.

Do they cut the mount off and weld a new one on, or get it pulled back into shape (which would probably weaken it?)

usually its cut off and a new one put on with extra bracing so it doesnt happen again (and the other side is usually good to get done at the same time). more than 50mm of continuous weld wont need to be inspected.

Its not causing any issues with the steering, suspension or anything so probably shouldnt need to be done at all?

I imagine its going to be a costly job? Or relatively straight forward?

So anything over 50mm DOESNT need to be inspected?

Smash repairers weld and pull chassis' everyday when repairing vehicles. If done correctly it is perfectly acceptable.

Its not perfectly acceptable. Smashing hydrualic rams onto steel fractures the crystalline structure of the steel, it work hardens, it becomes brittle and will lead to cracking. It might be perfectly acceptable to the laymans eyes but the steel is never the same.

Plus some vehicle cant be done this way. Look at some BMWs and Audis. You have to buy a whole new subframe because the parts are specially heat treated.,

nullack wrote:Its not perfectly acceptable. Smashing hydrualic rams onto steel fractures the crystalline structure of the steel, it work hardens, it becomes brittle and will lead to cracking. It might be perfectly acceptable to the laymans eyes but the steel is never the same.

That may or may not be true, but the fact is there are thousand upon thousands of vehicles driving around this country that have had chassis rails repaired. My workshop is right next door to a major NRMA smash repairer and if chassis rails weren't repaired or replaced in this manner 80% of crashed cars would be written off. And they don't "smash" hydraulic rams into anything - they attach them to chains which pull while the vehicle is clamped to a special rack such as a Car-O-Liner http://www.car-o-liner.com.au/caroliner ... oliner/au/

nullack wrote:Plus some vehicle cant be done this way. Look at some BMWs and Audis. You have to buy a whole new subframe because the parts are specially heat treated.

A subframe bolts to the chassis, they get replaced because they are bent. I know this because being the mechanic next door to a smash repairer we diagnose and replace a lot of subframes from Commodores to V10TT VW Touraegs. I have replaced more front and rear subframes on vehicles then I care to remember, and you would be amazed how small a hit it takes to bend them on some cars. Usually the damage isn't visible just by looking, but it will always show up to a skilled wheel aligner.

Your right, thered be many many vehicles out there repaired that way. Most people dont tow heavy objects or hammer their 4wd offroad for years on years. For those that do, even an undamaged chassis can crack and break (this happened to me in my old comp gq). What is certain is that putting tonnes of force onto a chassis dislocates the grain structure and work hardens the chassis. This fatigues the metal even further and makes it brittle. The chassis will never be as good as it was originally.

Ofcourse its never going to be as good as the day it was made, but it is still an acceptable method of repair. Driving your vehicle over corrugated roads for thousands of kilometres will also fatigue various parts, doesn't mean you're going stop driving these roads because of this does it?