it's a quick ring of weld and a quench, no way does the pin structure change, numerous drag days and welded pins are up to the job, real world experience wins for me The weld just needs to be strong enough to counteract the centrifugal forces of the diff pins, there's no real stress on them, it's the pins moving which does the case damage...........

 

Does anyone know how much the pins/service is by itself? I know it's best to have it done while putting a clutch in but I did my Exedy Twin over the winter. Maybe Burscher or Shep could chime in. . .

Why do I feel like every time I read a thread on here I am more nervous about my car falling apart

 

^x2 Anyone mind giving us a ball park how much the pin upgrade costs?

 

$250 through shep trans. He does something extra too besides the pins.

 

is that labor and pins?

 

I don't think Shep replaces the pins...they do something else to keep them from popping out.

 

I spoke with evodave, he had shep replace his pins and torrington bearing.

 

And why do the pins move??

Cause and effect.

The pins move because the gears that run on them pick-up on them. This in effect tries to spin the the pin and this torque is transmitted to the small 6mm retaining pin.

After a while, this constant movement wears the 6mm retaining pin. The more wear, the more movement allowed, which makes it wear faster. In the end the retaining pin wears right through and the diff pin is free to migrate out of the centre diff housing.

Welding in the pins is a complete bodge. This will not solve the cause of the problem. The centre diff gears will still pick-up on the pins, causing wear. As the wear increases the gear will be able to rock more and more on the pin. The position of the gears mating together will change, causing wear to the teeth. In the end the centre diff will not work correctly and all this time all the metal that is wearing off the gears and pins will be moving around the gearbox in the oil, like a metal paste.

All the earlier Evos 4-9 have exactly the same design centre diff without any problems. The problem is caused by an incorrect material specification, hardness and coating of the centre diff pins. The only way to solve the problem is to replace the pins with a new design with the correct spec material and coating.

 

What you say is generally correct, but there probably is a pre-cause and after-effect to all of that.
The picking up on pins by the gears may well be because of the play of pins inside the case and gears and this play causes exessive friction and destruction of retaining pins. I have Shep trans pins installed in my diff and I have examined them after 1000k miles. Ths shafts (big pins) have no signs of wear, but the retaining pins do have signs of wear albeit very small (so far). Which indicates that there's micro movement which eventually will lead to wear of the retaining pins.
Second, if you put strong shafts and they will be stronger than gears, they will start eating the gears and what you described will occur anyway.
Therefore it may be a good idea to do both, upgrade the pins AND weld them up to remove any play from day 1. I heard that laser welding can be used for this kind of application.
What do you guys think?

 

Upgrading the pins and welding seem to be a bit much...I just did the pins, so hopefully that does the trick.

 

......the small pins shear, diff pins migrate outwards due to centrifugal force and put a hole in the casing, how is stopping that by actually doing something and not just waiting for a failure a bodge? I'm not pretending this is all anyone ever needs to do to make a bulletproof box, but the proof is here, launches and abuse and mine's fine. When it was stripped recently (engine failure) there was no signs of wear, just because a mod is cheap/free doesn't make it a bodge/useless!!

 

No problems yet and at 18k miles. Have around 300 to the wheels and street driven.

I will be switching out the pins once I need a clutch install tho.

 

What I have detailed are the facts. I have removed and inspected the centre diff components in minute detail. I have hardness tested all the components, measured all clearances, and compared the design and tolerances to the centre diffs from earlier Evo's 4-8 (which don't have any problem), and are near identical in design, but with different material specifications.

The wear on the big pins is a combination of too large a clearance, but mainly caused by the lack of a special hard coating on the pins. The hardness of the pins is 55 rockwell C scale, and the gears around 60. Any engineer worth his salt (and I've been one for 27yrs) will know not to run two surfaces together with similar harness. And this is what has been done. With adequate lubrication there shouldn't be a problem, but if starved, the gears and pins pick-up which causes damage to both and a torque on the main pin which then damages the small retaining pin. This then accentuates the wear.

The pins from the earlier boxes which suffer no problems have an extremely hard ceramic coating with a very low coefficient of friction (0.65) which means even with a lack of oil, the gear will not pick-up on the pin. It looks like Mitsubishi have cut costs and omitted the coating which has caused this problem.

The strength of the components have nothing to do with it, it's the hardness that counts. If you put two components together with differing harnesses, the least hard will wear, but they will not pick-up on each other, which is something completely different, and the components picking-up causes a big torque load on the main pin.

If you replace the pin with one which has the correct tolerances and coatings, you don't need to do anything else. As I said before, earlier boxes have a near identical design and have no problems. I've stripped 15 year old boxes which have only miniscule wear of the pins and absolutely no pick-up. Any welding is a bodge, pure and simple.

 

Can anyone answer this?

 

It's a bodge because it's not addressing the cause of the problem, the gears picking up on the pins. The only way to solve the problem is to fit pins that have the correct tolerance and coatings.

You said you stripped the box and checked for wear. How can you see the wear on the pins if you cannot remove them? That's the ony way to see. Guaranteed there will be wear on the pins and gears causing friction and heat, and also distributing small particles of metal which will be floating around in the oil of the gearbox, accentuating wear on all the other components. And the more wear there is, the worse it will get, and the quicker it will wear.

I'm trying to help you here, I'm not having a go at you I have a lot of experience as an engineer in the Aero industry, and my hobby and passion is Evo's. I only post facts from my own findings and experience, not conjecture, rumours or BS.

Check out the Evo I built Here to see what I normally do in my spare time