Gearbox Crack: Causes and Solutions

Hello.

I have a T4 gearbox (DQR) here with a crack in the housing.
The seller doesn't know (or perhaps prefers not to know...) how the crack occurred.

There are marks on the transmission that suggest external mechanical damage caused by an accident, but these marks could also be due to improper storage or similar issues.

Now the question for me is whether disassembling it would be a good idea or not. What could have happened inside if the damage originated from there? Could something have become stuck and rotated within the housing?

I know that you can never be 100% certain what the problem was without disassembling something, but I hope someone with experience might be able to offer a pretty good suggestion.

Upon close inspection of the grinding and pressure marks near the crack, it is likely that the transmission, without the engine being moved forward approximately 10 cm, was forcibly jammed against the left chassis rail.
Or, in a mishap, the drive shaft struck the housing.
It could also be a faulty bearing.
It's difficult to say exactly what the problem is, as you mentioned, without disassembling the transmission.

Aunt Edith: It could also be a problem with the constant velocity joint boot needing to be replaced; forcing the outer joint forward can put pressure on the transmission housing.

Sieht wie ein Treffer von außen aus. Eine Beschädigung von innen ist unwahrscheinlich da ich keine Haarrisse oder Erhebungen nach außen erkenne. Späne im Öl? Funktioniert alles noch? GeräSure?

Behind the position is the relatively large gear for reverse.

Beim Wechseln des Getriebegehäuses müssen Antriebs-, Abtriebswelle und das Differenzial neu eingestellt werden. IIt's a huge amount of work.

We've had something like this welded before, and it can be done using AC TIG welding with a high amperage setting (which requires an expensive machine). It might even be possible to do it from the outside.
I'm looking for a company that welds aluminum. I can recommend one near me.

Simplest solution: Liquid metal adhesive .

Quote:

The simplest solution: liquid metal adhesive

It might not last very long due to thermal expansion. Additionally, the adjacent bearing (if it's a tapered roller bearing) will be under pre-tension, which can disrupt sleep.

Welding would be the best solution.

Quote:

The seller doesn't know (or perhaps he doesn't want to know...) how the crack occurred.

The issue is unknown – it might be defective. Is there an alternative to the current transmission?
If not, disassemble, overhaul, and have it welded.

Right off the bat: Any kind of liquid metal solutions or similar are out of the question; this part is intended for personal use only.

Unfortunately, there is no oil left in it anymore, as it was purchased by a recycling company.
So far, everything seems to be working normally when it comes to switching and rotating.

The thing is, I bought it either to have a replacement part on hand, or because I actually wanted to build something custom out of it. The latter would be my preference, as even the standard DQR feels a bit too short for me.
"I spoke with the gearbox company; in case I can't fix it myself, but only after I've made sure everything is okay beforehand, they will accept it as a core even if it has cracks, but it must be assembled. Therefore, the motivation to disassemble it for 4 hours isn't very high, because there's a risk that everything could be scrap, and then it would take another 4 hours to reassemble it so it can be used as a replacement part."

I finally had the time and motivation to finish it today.

The cause is now clear: The bearing of the driveshaft has failed, which caused grinding noises within the housing even when shifting into reverse.