Yokomo BD7 2016 Rear Diff Help

[ben5rokz]

Hi everyone,

I built the BD7 16 before christmas when I received it. I have been told countless times that the diff feels very tight compared to what it should, I am running kit 2000 oil, but it feels far less smooth/free than the others. On another diff I tried using a 0.1mm washer instead of a 0.2mm as comes with the kit and found that completely eliminates the problem, as that diff runs super smooth and feels as a 2000 diff should. I have done all the sanding of the plastic diff gears inside to make them smooth. The washer switch seems to have fixed the issue, but I dont know if there is any cons from using this fix and if there are any, a better solution would be more ideal!

I would run it as is, but the car feels very tail happy all round for the first 2-3 minutes of a run, almost coming round on itself tail happy, but it is controllable-ish. The reason I think it is the diff is because my dads car is using the washer switch (smoothing the diff) and he says he doesn't have any issues at all, but then I tend to be much more aggressive as a driver so could be just me!

Thanks all,
Ben

[neallewis]

I don't run TC, but yokomo buggies. they share diff components however.

What O-rings are you using on the outdrives? Black or red?
What grease if any was applied to them? The black molly grease doesn't really work to well with the o-rings and causes them to swell and be tight. I'd suggest you replace the o-rings and use a touch of green slime o-ring grease on them instead, as it won't react.

Removing the shim is releasing some pressure off the swelled o-ring by the sounds of it, confirming what I think.

[ben5rokz]

Originally Posted by neallewis

I don't run TC, but yokomo buggies. they share diff components however.

What O-rings are you using on the outdrives? Black or red?
What grease if any was applied to them? The black molly grease doesn't really work to well with the o-rings and causes them to swell and be tight. I'd suggest you replace the o-rings and use a touch of green slime o-ring grease on them instead, as it won't react.

Removing the shim is releasing some pressure off the swelled o-ring by the sounds of it, confirming what I think.

I did use green slime o-ring grease on it, only using a bit of the black grease on the relevant other components of the diff. shortening the shim as you say does sort the problem, do you think I'll have any shortfalls using this fix or do you think it'll be fine to use as is?

EDIT: I used the Black o-rings aswell, sorry, forgot to put that.

Thanks,
Ben

[neallewis]

Originally Posted by ben5rokz

I did use green slime o-ring grease on it, only using a bit of the black grease on the relevant other components of the diff. shortening the shim as you say does sort the problem, do you think I'll have any shortfalls using this fix or do you think it'll be fine to use as is?

EDIT: I used the Black o-rings aswell, sorry, forgot to put that.

Thanks,
Ben

Try the red ones. they seem a lot freer on the YZ2/YZ4 diffs.

I don't see an issue with removing a shim so long as its not leaking oil.

[ben5rokz]

Originally Posted by neallewis

Try the red ones. they seem a lot freer on the YZ2/YZ4 diffs.

I don't see an issue with removing a shim so long as its not leaking oil.

Will do, its weird as I have only had this problem on the new 16 diffs, the tiny ones haha. I have heard people have had to sand down the housing a little bit, but ideally i'd have it much simpler and just run with a smaller shim. And after running at 6-7 meetings it hasn't leaked a bit, just very tail-endy, annoying when you feel really fast then have a small spin because the cars doing weird things and clipping a corner haha. Thanks for the help though, will try a different o-ring as you said, if not i'll have to rely on the shim fix.

[Robocop]

I had a similar problem on a bd7 14 model it was one of the gears was slightly warped,I put a new set of gear in and problem went.

[qatmix]

As above, I rebuilt a diff for my yok (14) and the new gears were warped (It confused the hell out of me at the time, I didn't expect that). I bought a new set and I managed to gather enough good parts out of the two packs to rebuild the diff.

Look forward to hearing how you get on with the 16. My friend loves his (I am tempted to try one) The only thing he has replaced was the plastic steering arms which he replaced with the alloy parts. They didn't break though, he just thought the steering felt iffy on fast corners and transitions (he was convinced they were bending under load)