the reason they break is because you are forcing both wheels all the time, a job that the spider gears were not meant to do. but if you can jam them locked in all four corners, both sides and weld a sustantial bead over that, its the best you can do and when done properly will be hard to bust.

if you want to keep your drivetrain in one peice, sell your twin turbo fuel injected a15 and stop doing burnouts.

yeah well, i picked up a spare centre when i welded it, cause i knew it was a good chance i'd need it

im not exactly suprised it went...

meh

i think yeah, need to make up plates to weld in there and really go crazy with it to ensure it wont break, and all will be well

but id prefer an open centre for winter anyway, i think welded would catch me out too many times in the wet

ah well im going to pull the box out while im feeling inspired (doesnt happen often)

It's a shame that you didn't get any photos of the gears in a million pieces..

I'd love the laugh..

Good work. Go the turbo(s) and injection!

While we're getting technical (Datsik).......
When you weld your diff centre you are far from annealing the metal. The problem is that gear steel is relatively high in carbon which means that it must be cooled slowly to avoid causing a martensitic transformation which basically means it becomes very brittle. Secondary heat treatment is necessary to restore the steel back to close to the original properties.

So 1200rallycar had particularly brittle gears which are much more prone to cracking and braking than they were before he welded it. I wouldn't go near brazing a diff up! Brass is too soft. For a proper locker you really need someone to TIG weld it and cool it appropriately.

if you allow a steel to cool in air, is that not annealing?

As for the brazing.....I did say that I wasn't sure..I know that welding it, is likely to result in failure.

now about the steel properties.. annealed steel has a brinell hardness (tungsten ball) of about 177.

Steel which has been heat treated (like axle steel) has a brinell hardness of about 417.

In this example, the hardness also means a higher Ultimate Tensile Strength. (UTS)
Rough figures...annealed UTS 85,000 psi, Heat treated axle 194,000 psi.

Now, not going of any knowledge here...please correct me if i'm wrong...The gears in the diff are probably ORIGINALLY made to a similar strength and hardness as the axles?

By welding...no matter which type of welding is used...if allowed to air cool..you end up with the diff gears in an annealed state.

This is why I suggested that maybe brazing may be better as it is less likely to change the state of the steel. Although brazing maybe weak..I would use it, only to hold a washer in place. The washer is what would cause the diff to lock.

I know that there is a company out there, that fills the diff center with some kind of resin, which also prevents the steel from being annealed. This maybe the way to go?

Bring it on Daveman

You want to change the states of the steel, brazing is like using a glue, versus melting to hold things together. I think the washer would get "squashed" though the gears, if the blazing surfaces were to let go.

Annealing is normally done in some hot bricks, and let to cool slowly over several hours. Air cooled is a good way to reduce brittleness, but not the best way, when you are wanting a nice even grain structure.

The gears would be surely harder. I know that many axles are not heat treated, nor are they anything special other than a slightly harder than normal steel (can't remember the numbers).

A good low temp tig weld would be the go. Pentetration is the name of the game. Cockysh!t (Cockatoo sh!t) welds don't cut the mustard

This isn't a common problem for welded diffs. I've used arc welded centres for years and never had any gear failures. Putting 200bhp through them on sticky Yokohama A032R's, and do lots of standing start events, including hillclimbs where you're permitted a tyre warming burnout each run.

Side gears would be the last thing I'd expect to fail in a welded centre anyway - they're welded to the carrier itself so the side gear's teeth aren't really transferring the torque anymore - the welds are.

Quote:=Spot on!

Firstly lets start with annealing! There is a key factor you seem to have missed and that is the steels critical temperature. For steel its around 723degrees C. Once you heat the steel above this (say when you weld it!) it actually changes state from Body Centred Cubic to Face Centred Cubic and allows the Carbon into the solution meaning the iron and carbon are all mixed together evenly. If you cool this at the correct rate and allow the carbon out forming carbides then the steel will return to it's original state after being welded.

The problem is that with a high carbon steel the time period you have to cool it down is so large that even air cooling it will not allow the carbon out trapping the carbon in solution forming "martensite". Like I said before this is significantly more brittle than the steel was beforehand. So you see if you are only heating it up to 400-500 degrees then letting it cool in air then you would actually be annealing it. Unfortunately when you weld you are going well above this. Annealing is a form of heat treatment. It allows the grains to recover from things like cold working and depending on temperature allows grain growth making the metal softer and more ductile.

It's already Brought Datsik!

i had my names mixed up sorry, it was actually the "spider" gears

which means i should be able to reuse this centre by welding a plate back in there and try again if i want a locked centre... i beleive?

Your mostly right.

To anneal a metal you need to raise its temperature..ABOVE the austenite transition temperature. As you rightly said..that is 723 degrees.

Brazing can be done at temperatures above 450 degrees and below the melting point of the parent material. So if brazing is carried out at say 600 degrees. There will be no change in the properties of the parent metal. This is why I suggested that this may the way to go.

But the metal close to the weld, the metal which does not melt, but reaches say 800 deg. this metal ends up annealed. So you end up with a hard weld and a small surrounding of hard, brittle metal. But surround that...You have soft, annealed metal.

It does not matter if u tig, mig whatever..you still end up with this soft zone..the only difference will be it's size.

As for not heat treating axles....Are these "switched on" type people?? I swear black and blue that somewhere, sometime, I read somthin on the matter and if my failing memory is correct..it said the heat treatment should be done on axles? The material they begin with, would have been heat treated (annealed) to make it soft. This would allow for better machining and reduce tool wear. After the axles are made..they should be heat treated to harden em???