Granite BLX Diff Maintenance Trouble

[Adamator]

Hey all

Due to me being in uncharted territory here more than usual, I want to mention up front that not only I have only been into RC's in general for about 3 months now, accessing and working on a diff is even more new to me.

In doing some light maintenance on my Granite the other day, I had the motor mount and the wheels off. I was spinning the drive shafts on the wheels and I noticed the opposite side spinning was kind of sluggish on my back wheels. Figuring I can't avoid learning about the diffs and how to perform work on them forever, I thought I would open up my truck and pull out the rear diff to take a look at things.

Getting the diff with the drive shafts out was easy enough, but here is where my problems began.

Once I figured out I needed to put a screwdriver through the drift shaft in order to get the little screw off, I was able to get one drift shaft removed from the yoke. However, somehow, I stripped the screw on the other side and well... it ain't coming off.

So my first questions are to do with that stripped screw. Is there anything I can do, any technique I can try to get that screw off?

When I realized what had happened and there was nothing I could do at the moment, I decided to put everything back together as it was the best I could. However, I now have a new problem that appeared once I slid the motor mount back on. Now when I turn the rear wheels, everything is very stuff and almost wont even move. Furthermore, the driveshaft through the motor mount is no longer spinning at ALL.

I'm sorry to ask for help when I am probably not giving all the information, but what could I have possibly done to cause everything to seize up like that? I'm planning to open things back up to see if something seems obviously off but wanted to get some ideas of what might be going on first.

Back to the topic of the stripped screw. My initial thought was I would just buy a new diff from Jenny's RC. But then it hit me: they have the diff by itself. So I would potentially need a new diff, new yokes, and at least 1 new drift shaft all because I can't get that screw off. Unless of course I can make this diff work again, even though it's impossible for me to open it.

Thanks!

Edit: One more thing. Before I messed with my diffs, I had most recently taken my motor mount apart just to see how the insides were. Everything seemed fine so I put it back together with no alterations. The thing is, if I spin the spur gear, it seems to have quite a bit of resistance from the pinion gear on the motor itself. I can't for the life of me recall if it's always like that. Usually when I open it up, my focus is on my mesh and don't really spin it other than to make sure I have a good mesh. But I'm wondering if my problem could lie on the motor mount. Just wanted to mention that.

 

[FlipSide]

Somewhat of a silly answer, but are you 100% sure the little screw is stripped? Sometimes you need to pull quite hard on the driveshaft for them to come off the splined output drives.

If it is indeed stripped, I'd get rid of the driveshaft so that you can to access the stripped screw (probably destroying the driveshaft in the process) and I'd do whatever is needed to get the little screw out. Then your diff would be saved and you'd only need to buy new driveshafts. I'd suggest waiting for other idea before doing this...other members may have a better solution that would not involve destroying anything.

For the rest not spinning freely anymore, it will be difficult to help you. You will need to isolate where is binds first. Maybe you overtightened the diff yokes, causing binding between the input gear and the diff crown gear? Maybe you assembled the power module wrong, or the motor? Some resistance to spin the motor shaft is normal (it comes from the magnets in the motor), but a certain amount of force should overcome the magnet resistance. Maybe post a video? First, take the power module off and isolate where the resistance comes from.

 

[Adamator]

Somewhat of a silly answer, but are you 100% sure the little screw is stripped? Sometimes you need to pull quite hard on the driveshaft for them to come off the splined output drives.

If it is indeed stripped, I'd get rid of the driveshaft so that you can to access the stripped screw (probably destroying the driveshaft in the process) and I'd do whatever is needed to get the little screw out. Then your diff would be saved and you'd only need to buy new driveshafts. I'd suggest waiting for other idea before doing this...other members may have a better solution that would not involve destroying anything.

For the rest not spinning freely anymore, it will be difficult to help you. You will need to isolate where is binds first. Maybe you overtightened the diff yokes, causing binding between the input gear and the diff crown gear? Maybe you assembled the power module wrong, or the motor? Some resistance to spin the motor shaft is normal (it comes from the magnets in the motor), but a certain amount of force should overcome the magnet resistance. Maybe post a video? First, take the power module off and isolate where the resistance comes from.

Hey there. Yeah it's stripped and stripped bad. I was not able to get it even remotely loosened. The screw is still fully tightened in there.

I spend time time breaking off the drive shaft in order to get to it, but even still I just can't. I'm fairly confident I need to say it's a lost cause and unfortunately I'll likely need to replace the diff itself, a drift shaft, and and the yoke set. Ugh! I took a week off from my Granite for the first time since getting it and had not had any problems for a good while. I guess this is my reward!

Another thing I realized is when I took it apart and put it back on earlier today, I somehow completely lost a washer that goes between the yoke and the gear. (Part R709052). I don't know how important that is but luckily I'll get a new one if I get my Diff itself from Jenny's RC.

Even though it doesn't matter much until I get my new parts, you brought up something I was not aware of regarding the diff yokes. Those can be tightened too much? I had just put them back together and tightened the screws on either side. I wasn't even aware I could tighten it too much. Do I need to think of the mesh on the input gear and the case like the mesh on my motor? Or is it not that finicky? (I sure hope it's not.)

Appreciate your help. May need to pop back on when I get my parts. Hoping the new diff kind of fixes my issues on it's own, or I will need to further investigate what may be causing my resistance.

 

[FlipSide]

The diff yokes on new cars can be too tight and cause binding when fully tightened. It's unlikely this is your issue, because it goes away as the gears get some wear.

I had to loosen the diff yokes on my vorteks when it was brand new because of the gear binding. I was able to tighten them back after a few packs.