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Hobao Hyper 7 wheel jammed

My Hobao Hyper 7 wheel jammed recently. It was a used purchase from eBay and when I came to check it over before its first run, I noticed it wasn’t rolling freely. It wasn’t completely stuck, but would only go for about 1/4 of a turn of the wheels before stopping.

Picture of a Hobao Hyper 7 1/8th scale nitro buggy

Investigation: why is the Hobao Hyper 7 wheel jammed?

I started by trying to find the location of the problem. I did this by putting the car down on a hard surface, then lifting each wheel off the ground in turn and spinning it to see if it rotated freely.

In my case, this led me to finding out it was the front left wheel that was stuck. Having found this, I checked for a twig or stone jamming the driveshaft. I didn’t find anything like that, so it was time to start taking it apart!

Tools to repair the Hobao Hyper 7 Jammed Wheel

I used the following tools for diagnosing and repairing the problem.

Dismantling the front drivetrain to find the problem

Here are my instructions for dismantling the front left wheel hub / axle assembly.

Remove the wheel

Start by removing the wheel nut. Most of the standard RC cross wrenches or spanners have a 17 mm socket for this job. With the nut undone, the wheel can be removed. Use the wheel to prop the side of the car up if you wish, so it isn’t resting on the ground.

Remove the front driveshaft

With the wheel removed and the steering turned all the way to the left, I could see the cause of the problem: the pin in the joint on the driveshaft had come loose and was jamming against the steering knuckle, stopping the driveshaft turning. I was glad the problem was at the outer end of the car, as I was hoping to avoid dismantling the differential.

Picture showing Hobao Hyper 7 wheel jammed by loose universal joint pin

Use the same 17mm wrench to stop the wheel hub turning. Hopefully yours has a hole in the middle, to allow you to insert a 2.5 mm Allen / hex key through and into the hub to undo the grub screw in there. This can just be loosened or removed completely. I chose to remove it completely to avoid it falling out and being lost later.

Picture showing removal of the hub pin grub screw on a Hobao Hyper 7

Removing this grub screw allows removal of the pin locking the hub to the driveshaft. Sometimes it will fall out and sometimes it needs encouragement. Some gentle taps with a suitable drift should remove it. I used an old bicycle spoke and my smallest hammer!

Picture showing using a bicycle spoke to remove the hub pin on a Hobao Hyper 7

Next, use a 3 mm Allen / hex key to remove the upper and lower steering knuckle screws. Remember to catch the metal collars that allow the hub to rotate in the hub carrier.

Now you can remove the steering knuckle, along with the driveshaft. Pull the driveshaft out of the knuckle. The inner wheel bearing might come out with the driveshaft. This is an ideal opportunity to change the wheel bearings if they have too much play, don’t spin freely or feel like they’re full of sand.

Picture showing a Hobao Hyper 7 steering knuckle
Steering knuckle showing inner wheel bearing still in place.

With the driveshaft in my hand, I could push the pin back into position and tighten up the grub screw holding it in place. This is a 2 mm hex. Before doing this, I decided that having got this far, I’d give everything a clean (brake cleaner and rags) and apply some fresh grease. It comes apart as shown in the picture below:

Picture showing a dismantled Hobao Hyper 7 front driveshaft
Front driveshaft dismantled for cleaning.

Reassembly and testing

Reassembly is fairly straightforward, just remember the driveshaft needs to go through the hole in the hub carrier first, before refitting the steering knuckle. Getting this back in with the metal collars in the right place can be tricky as they tend to fall out. Use some tape to hold them in place if needed.

I didn’t use any thread lock in this case but if I was doing this job again I think I’d put some thread lock on the grub screw holding the driveshaft universal joint pin in place.

With everything back together, it was time for a test: starting with a simple push along the tarmac. It kept rolling this time, so I moved on to a test under power and at speed. Everything was fine – a successful fix!

Other causes of a jammed wheel

In my case, fixing the problem was fairly simple, but what else could cause a jammed wheel?

Debris

Stones or twigs stopping a wheel, the drive cogs or brake disc from turning is still a likely culprit, so I’d check for this first.

Checking the centre differential

If none of the wheels will spin when lifted off the ground individually (i.e. with the other 3 held still on the ground), the problem is likely to be at the centre differential or in the brake, clutch or drive gears.

Checking front and rear differentials

The front and rear differentials can be checked by:

  1. Lifting both front or rear wheels off the ground together.
  2. Stopping the main drive gear from turning with a screwdriver / finger (careful!).
  3. Spinning one of the lifted wheels. The other wheel should turn in the opposite direction. If this doesn’t happen or doesn’t feel smooth, this is pointing towards a problem with the differential being checked.

I hope you manage to fix your jammed wheel. Let me know how you got on in the comments below!

Watch me fix the Hobao Hyper 7 Jammed Wheel

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