New FJ build, diff not turning

[Elmo]

I received a new FJ kit for my birthday and have spent the last two days building the kit at a leisurely pace. I got the truck built but the front diff is very difficult to spin. Are the screws that hold the diff case together supposed to be flush? I have bottomed them out and I fear that it may be binding there. I am using Fast Eddy bearings in the build so I know that that is not the problem. Any ideas what the problem could be?

[canadianbacon]

Do you mean difficult to spin when it's installed between the bearings in the front case section, or difficult to make the diff actually work if you didn't lock it?

In my Pajero the front diff is locked, but it was sort of hard to spin when installed in the front between my Fast Eddy bearings too, but when all the other gears are installed and everything buttoned down it spins fine.

[monkeyracing]

Be sure you installed the correct screws. They're smaller than most in the kit and will sit quite flush. The regular screws bind inside the chassis. I did this once. Oops.

[Elmo]

I have locked the diff internally. I meant that the diff doesnt spin in the bearings; I should have been more clear on that. I will pull the diff out and check the screws. I may have overlooked that during the build.

[Elmo]

Got it figured out. Turns out it was a hex binding on the hub. Runs smooth as butter now. These FastEddy bearings are so smooth its amazing. Im waiting on the plasti dip to dry on the servo now and I hope to test drive it soon.

[Elmo]

I took the truck out today for its maiden voyage. I am having a little trouble with some popping in the front end and I'm not sure where it is coming from. I'm going to pull the truck apart tonight and see if a gear is stripped. the truck definitely needs a GRU. are there any options that allow me to retain the stock battery location? the ones that I have seen place the motor through the battery wall and require moving the battery. I would like something that place is the motor above the battery and electronics tray.

[mojo2]

Hey dont install a gru rather get a strong 55t motor and a 16t pinion, i promise you it is slow and strong enough

[lonleycreeper]

In my opinion a 55t is to fast, GRU' s are the way to go to really slow these down.

[Elmo]

I tried an Integy 45t I had lying around and it was still too fast. It has the 16 t pinion in it already so I can't gear down anymore. If I can find a way to mount the gru above the battery tray I will mount a 2 or 3:1 unit there. Idon't mind the extra noise so that's not an issue.

[K.O.M.]

Originally Posted by mojo2

Hey dont install a gru rather get a strong 55t motor and a 16t pinion, i promise you it is slow and strong enough

If you want to have a mediocre rig, then be my guest. A high-turn motor is a band-aid fix to a gear reduction problem. The motor will still run hot, and you still will not have the low-speed control that a properly geared driveline will have.

O.P., if you don't want to hack the battery tray area, the only option you have is the GD600 reduction unit modified to fit.

Read this page THOROUGHLY:

schlabinski's CC-01 FJ Cruiser (updated 3/4/2014) - Page 3 - Scale 4x4 R/C Forums

Alright, I did the research for your. Now go and build.

Edit: I don't really know why people worry about a little trimming in the battery area, as you can get any LiPo battery you want to fit wherever you want with some velcro straps.

If it were me, I would just get the RC4WD 4:1 reduction unit--which has the advantage of keeping the gearbox sealed--the other reduction units require you to hack the cover a bit which exposes the internals to the elements.

[Elmo]

I have heard a lot of horror stories about GD600's grenading so I think I will just bite the bullet and trim the battery tray. I guess my hangup with cutting the tray is hacking on a brand new chassis. Thanks for the link. Regarding the rc4wd unit, I like a little wheel speed and wonder if i should go with the 4:1 unit or the 3:1? I would like to be about as fast as a stock scx10.

[monkeyracing]

Originally Posted by K.O.M.

If you want to have a mediocre rig, then be my guest. A high-turn motor is a band-aid fix to a gear reduction problem. The motor will still run hot, and you still will not have the low-speed control that a properly geared driveline will have.

Why would it run hot? I'm using a cheap 55t motor. Run for 45 minutes solid, creeping over rocks, chasing the dogs around the yard, barely gets warm. Low speed control is good, top speed is a little quicker than a jog.

I did have a 4:1 gru for a while. I liked it for the amazing low speed control, but it was a waste otherwise. Couldn't get any wheel speed at all. I'd like to have tried a 2:1 or 3:1 though.

[K.O.M.]

Originally Posted by monkeyracing

Why would it run hot? I'm using a cheap 55t motor. Run for 45 minutes solid, creeping over rocks, chasing the dogs around the yard, barely gets warm. Low speed control is good, top speed is a little quicker than a jog.

I did have a 4:1 gru for a while. I liked it for the amazing low speed control, but it was a waste otherwise. Couldn't get any wheel speed at all. I'd like to have tried a 2:1 or 3:1 though.

Hey, if you're happy with it, more power to you. In my experience, the control is awful without a GRU--and that's running a 65t lathe motor. Forget about driving it in any type of slow, scale manner (which is how my motors before the GRU heat up), let alone keep up with what SCX10s are walking up.

If it's built as a single track trail rig, stock is fine, but you're not easing up to an obstacle and smoothly drive over it.

Speed? 3s.

[Elmo]

K.O.M. I will do some research to see if the stock brushless ESC can handle 3s; hopefully it does. I think that the 3:1 GRU may be a good compromise for me. It should have the slow speed control and torque and still allow some wheel speed. My only concern is whether or not the RC4WD GRU can handle the power of the stock motor on 3s. I may make the switch later on to a 55t with the GRU if that is necessary. I like the little Mabuchi sealed cans since they're as durable as claw hammers and cheap if they do go poof. I think that I can make a simple mount to supplement the body mounts that I built for the front to hold the battery using a stock axial scx10 battery mount and Velcro straps. Should I look into throwing a 55t turn along with the GRU or will it hold up to the silver can on 3s? Thanks guys!

[Elmo]

I got a chance to run the truck today in the driveway and popped a dogbone while making a small (not full lock) turn. I'm going to have to upgrade to universals before I can run the truck again. The grinding is back, this time in the idler between the spur and front diff. I have had a total of two minutes of run time so far. Ugh... I will have to order a GRU next week and then the universals after that. I cant wait to drive this truck in the dirt.

EDIT
I drove the truck after fixing the dogbone, which turned out to be a missing o-ring in the outdrive, and within two minutes of driving on concrete to set the trims I broke a lower 4 link and stripped a gear inside the transmission. I am afraid this is going to turn into a lengthy project. And by the way, it still hasn't seen dirt...

[Elmo]

I tried running the truck again and all seemed well until I got the wheels in a bind. And by bind i mean running from asphalt onto grass. There was the same loud pop from before and the truck lost power to the rear wheels. The "transfer case" gear is where the pop and ensuing grinding comes from. Am I missing something here?

[Wraith1985]

When i have had this problem it has always been the pinion not seated all the way in the housing, hope this helps.

[Elmo]

I just put an hpi gru in and changed the motorplate. I use the tool from the kit to set the pinion depth. Could the motor mount be moving? Also when using the 16t pinion I have to mount the motor in the 20t holes. Am I missing something?

[Elmo]

Woo hoo! I finally figured out where the problem is coming from. I drilled a 1/4in hole in the cover over each gear and used that to see where power was going and which gear was slipping. It turns out to be the bevel gear in the front end. I shimmed it a little tighter and all is good now. I have some aluminum sealing tape that i will use to seal up the holes. I cant wait to get this thing out on a trail. After some research I discovered that the esc is limited to 2s so that will have to be changed if i need more wheel speed.

[Elmo]

Took the truck out this evening and stripped the spur and the bevel gear in the front gearbox. I guess I will shelve the truck until I can source some gears in steel or at least aluminum. I have seen a few pieces made by GPM but the alloy and plastic spur looks a little suspicious as far as strength goes and the steel gears i have seen only replace ones that are still good in my truck and not the weak points. The truck was climbing a ledge that was about 3" and as soon as the tires hit the face of the ledge the dreaded sound started and the run was over. Any suggestions for some more resilient gears? Thanks for all of yourbhelp!