Originally Posted by TeamT

Hi guys,

I am hoping someone will be able to help me with a problem I have.
Firstly, thank you to Racer 53 for your diff rebuild videos. They are excellent. I've subscribed to your channel.
I've just gotten back into RC after a 25 year break. To get back in I bought a T4 second hand. The owner told me he had just re-built the diff.
When it arrived I fitted the electronics and went for a drive. It turns out the diff had never been set.
So I set about stripping out the gearbox as the diff was built with the cover over the head of the thrust bolt, which I removed then re-assembled. I then followed the videos to set the diff. I just could not get it right. It would be fine a few minutes, then loosen right up. After a few re-tightens I realised I had the diff the wrong way round (head of the bolt was on the left, looking. From the rear).
I then stripped the entire thing and re-built it as per the videos.
I struggled quite a bit with getting it right in terms of how tight and I think I was virtually at the bottom of the spring. If I look at the plastic T nut holder for the thrust bolt it seemed like it was really being pulled concave a bit. But if I put screwdriver shafts to hold the diff outdrives (outdrives?), if I really twisted hard I could move the diff, but only just and I really had to twist hard. I backed off the bolt a little bit, then re-assembled everything (the right way round this time).
I then set about doing the run-in. As I was getting to the end of this I heard a pop and saw the T nut holder had shot out and hit the dogbone (this was the pop sound). I opened up the opposite side where I saw the head of the thrust bolt had snapped off.
So, I started again from the beginning, went through everything as above. I ended up getting the same result only this time a little further into run-in.

There was another symptom I noticed. When the gearbox was assembled but out the car, when I twirled the shaft that the slipper and spur attach to it wasn't completely smooth. It felt like every 1-2 turns there was some imperfection that the gears had to roll over. I can't see this affecting the diff, although I don't know enough to tell.

I'm a bit at my wits end. I don't know what I'm doing wrong. My sense of it is I'm over-tightening the thrust bolt and the pressure is simply ripping the head off.
I'm now out of thrust bolts so will have to get more.
Are there any pointers anyone could suggest. I really want to get this right.
Maybe I should start with a really loose diff then tighten up? I think I'm starting too tight.

Thanks for the help.