|The CEN CVD is great but the diff cups are not holding up. Today the diff cup in the front of my savage gave out. I still want to run CEN CVDs in the front of the savage, so I will need to find a way to make the diff cups stronger.
I tried a few differential cups that are made by different companies and/or car models. Each of them had their own weakness.
Here in the picture below is a Diff cup from a Losi 8ight / LST. Like in the past in my brushless LST XXL the diff cup always snapped where the pins goes through.
Next up I have the Hot Bodies D8T diff cups. These lasted a few minutes longer but not much more. Instead of breaking where the pin hole is, it looks like the actual diff cups just ripped right off.
In the front of the Savage I used a older model diff cup that used a smaller dog bone. But the inner hole was still 1mm larger than what is suppose to be. These diff cup are the non heat treated version (HPI part number 86064) that I heat treated myself. I got about an month of use out of it until it broke too. It is hard to say if this cup is an better than the rest because the 2 diff cups I used above was in the rear end of the savage. We all know that the all the weight shifts to the rear of the car when accelerating and that it is a lot more stress in the rear drive train.
Here is a picture comparison to the different HPI diff cups. Starting from the left: HB D8T with a 8mm inner hole, HPI Savage with a 9mm inner hole, HPI Savage Flux with a 11mm inner hole.
My first attempt to create a stronger HPI diff cup is to make a sleeve that goes over the diff cup. If you even owned a HPI Baja 5B/5T/5SC you would have heard of a company called Dark Soul. They make a hopup part called toobz. It is a steel sleeve that is pressed over the diff cups to reinforce the outer edge. From the looks how the diff cups break on my savage it think this might help.
Unlike Dark Soul I will be using aluminum instead because I hate working with steel. Here I have a 7075 Aluminum rod that is about 16mm in diameter that I will make the sleeve with.
In this picture you will see the aluminum rod on the lathe after I finish making the inside of the rod a press on fit for the diff cup.
This is the diff cup sleeve before I installed it.
On the right is the sleeve pressed on the diff cup and right next to it is same cup without the sleeve.
Here is a view from the back.
Once again all three different diff cups right next to each other. Starting from the left: HB D8T with a 8mm inner hole, HPI Savage with a 9mm inner hole, HPI Savage Flux with a 11mm inner hole.
After my first test fit I found out a made the sleeve too wide and it will rub against the plastic bulkhead. In the picture below you will see the modified sleeve on the left, with the edge trimmed off. And in the middle is the non modified sleeve. On the far right is the stock diff cup.
Here is the diff with the sleeves over the diff cups. If this works out I might knurl the edge of the sleeve and but a rubber boot on it too seal in the grease inside the diff cups.
Test fitting the diff in the bulkhead, making sure it does not rub against anything.
- HPI Savage TCS Flux 5T (Super Flux 5SC Bumper)
- HPI Savage TCS Flux 5T (Differential Cup Reducer)