M05 Differential Weak Spots?

[TurboTimmy]

After running my NSU TT for about 30 minutes, the gearbox began to make noises unlike a gearbox should. Now when the throttle is applied, the wheels do not turn and I hear a buzzing type noise from the car. Does the M05 have any weak spots in the gearbox? I have a Torque Tuned 540 in it-and it has been fine until now. It also has the upgraded cv joints and axles. I guess I'll have to tear the whole thing down. Anyone out there have any ideas or possible causes?

[OCD]

Is it a gear differential or ball?

The M transmissions are simple things, so it shouldn't take much to troubleshoot.

What happens when you turn the wheels individually by hand?

[TurboTimmy]

It is the stock out of the box gear differential. When I turn the wheels,normally they would turn in opposite directions. Now they seem to only be halfway attached to each other and before when you turned them forward at the same time, you could feel the motor turning. Now there is no feeling of being hooked up to the motor pinion at all. When the thing broke, the car was making gear whine noises and slowed down considerably, then stopped altogether. The pinion is tight-I checked that first. It is also in its proper 20 tooth mounting position.

[markbt73]

I'd bet anything your pinion set-screw came undone. Put it back in, with a dab of threadlock, and you should be good to go.

[TurboTimmy]

Well, I checked the pinion-it is now tight (thanks markbt73). I reinstalled the motor and when the throttle is applied, both wheels will turn-but the diff makes a horrible sound and I also noticed that when you turn the wheels under power, both will spin turning one direction-but only one will spin turning the other direction. The car will move under its own power, but is REALLY noisy.

[OCD]

I would have guessed it was the pinion as well, but it definitely sounds like a deeper issue

At this point I would just do a tear-down and get a good look at the diff and counter gears. It's a pain dis-assembling everything, but the M05 has a decent reputation for durability and such labor should be a rare occurrence. Look at it as a chance to do a little maintenance or upgrading that you might benefit from. Did you include bearings on the initial build? Now might be a good time to order some if you haven't already

 

[markbt73]

Huh. Yeah, those diffs are more or less bomb-proof (it's the exact same gears as several monster truck models), so a failure would be unlikely, but possible I suppose. One thing to check: when you built the diff, did you install the thin shim washers behind the side gears? If those are missing, it's possible that there could be enough slop to let the diff gears start skipping a tooth. An once gears start skipping, they just get worse from there (ask any Blackfoot/Monster Beetle owner).

[TurboTimmy]

As far as I know, I assembled it exactly according to the manual. I guess I'm going to have to tear it down tomorrow and look. By the way-I noticed that before the diff started making nose, one of the front tires started to come off the rim on the outside and some foam was exposed. I assume this would cause quite a vibration....Would that do anything to perhaps start a failure?

[ncpantherfan71]

I raced the M05 several years.  The gears are pretty strong and I never had any problems with any of the gears except the spur gear, it  can be damaged when you hit something with the front wheels.  If your pinion cam loose it also could have damaged the spur when it shifted. Also, if you are still using stock pinion keep an eye on them, they can wear pretty fast too.

[TurboTimmy]

As a matter of fact, I did hit something before the thing got noisy. Which one is the spur gear?

[ncpantherfan71]

Its the largest diameter kind of thin gear.  It is the gear the pinion mates to.  If you pull the motor again and slowly spin the tires you can kind of see the teeth through the hole in the chassis where the pinion fits into.

[TurboTimmy]

Well, I think I found the problem.......How far does the pinion gear have to be on the shaft? Apparently it was not properly lined up with the spur gear......The entire inside of the teeth are shaved off.

Now that I have the diff out, is it worth the money to upgrade to a ball differential? I just like to race this thing around little cones in parking lots. Just curious as to what difference it will make to a basher like myself....Thanks, everyone, for all the assistance.

[ncpantherfan71]

I didn't have a lot of luck with the ball dif, to me it was more trouble than it was worth and just stuck to the gear dif. 

If you bought the kit new,  there is a pinion hood in the kit used to set where it mounts on the motor shaft.   Your spur probably was damaged when your pinion came loose.   Use the hood and as long as the pinion doesn't move you will have good mesh. 

[TurnipJF]

Ah, that would do it!

Not much benefit to a ball diff for bashing, best stick with the gear diff as it needs less maintenance and no adjustment. 

[OCD]

Well that's not so bad!

 

Maybe you already know, but here's a guide cup thing in the kit that indexes where you need to have the pinion located on the motor shaft:

 

 

 

 

[TurboTimmy]

Thanks all-perhaps I should have paid more attention to the instructions.......Luckily, I still have the little pinion stopper. My local hobby store can order the Tamiya #50794 parts bag-cheap!!!

Everything else looked fine. The diff appeared to be in perfect shape.

[berman]

Now would be the time to get a steel pinion also.

[Juls1]

I would forget the ball diff if you want durability. It’s a racing item only really. 

A steel pinion gear isn’t a bad idea if your installing a new gear set. The steel gear won’t slowly disintegrate and coat all the gearbox with aluminum shavings.

Juls

[TurboTimmy]

Thanks again everyone. How about the Robinson Racing #1420? 20 tooth 48 pitch steel pinion.

[TurnipJF]

In order to prevent premature wear to your spur gear, you need the pitch of the spur and pinion to match.

 

The M-05 uses a 0.6 Module spur, so you'd want a 0.6 Module pinion to go with it.

[TurboTimmy]

What do you recommend?

[TurnipJF]

A 20t 0.6 module steel pinion from the maker of your choice. I use RW Racing ones myself.

[TurboTimmy]

Thanks TurnipJF !!!!