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Old 02-02-2013, 08:59 PM   #1
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Default Ofna DM-1 problems right out of the box, HELP

I just bought an Ofna DM-1 1/7 scale RTR. I have a problem and I can't figure out what it is. If I roll the car on the ground in a straight line I can feel a "lope" in it, almost like it's running over a pebble every rotation, if I turn the front wheels either way and push it, it doesn't roll smooth at all, almost like it's wanting to bind up. It feels a lot like putting a car in 4WD with locked differentials and turning on concrete, it "hops". I thought maybe the spur gear wasnt meshing right so I took the engine out and it still does it. This is a brand new car and hasn't even been run yet, I'm scared to until I find out whats wrong.

What can I check on this car???

Also, if the hold the front wheels the rear wheels will not roll and vis versa....
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Old 02-03-2013, 09:40 AM   #2
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My friend has a DM1 pre-asembled kit version. He also thought it was ready once put all the elec. on it and ran. And only took him 10mins to feel a similar problem as yours. After dissembled we found out the center diff. was loose and also found out some places did not put thread lock as well. So I think you might check the all the diff.s esp the center one. Hope this helps.
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Old 02-03-2013, 09:57 AM   #3
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Originally Posted by GregUnd View Post
if I turn the front wheels either way and push it, it doesn't roll smooth at all, almost like it's wanting to bind up. It feels a lot like putting a car in 4WD with locked differentials and turning on concrete, it "hops".
well with the 2 speed it is not a diff like a buggy it is a center spool arrangement so any driveline binding when rolled on a circle is normal under power there is enough tire slip that it is not a issue
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What can I check on this car???
1 Ofna tires notorious for not being round
2 you way may have alittle runnout in one of the 2 speed gears which is common and normal
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Old 02-03-2013, 10:00 AM   #4
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well with the 2 speed it is not a diff like a buggy it is a center spool arrangement so any driveline binding when rolled on a circle is normal under power there is enough tire slip that it is not a issue

1 Ofna tires notorious for not being round
2 you way may have alittle runnout in one of the 2 speed gears which is common and normal
You know, that makes a lot of sense becuase the "lope" or binding happens in the same spot everytime. I marked the tires and when the mark is at 12oclock, is when the lope happens, every time. I think I'm just going to run it and see how it acts.
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Old 02-03-2013, 10:51 AM   #5
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I took it out and ran it a little, it runs and steers great. I guess it's just normal.

Thanks all!
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Old 02-03-2013, 11:50 AM   #6
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Default 'binding in a rolling chassis'

Before you operate this car too much the problem needs to be addressed.
Isolate the problem :
1. Place the chassis on blocks and ensure that each wheel rotates freely, forward, reverse and in opposite directions. Together and independently
2. check each of the 4 drive (CVD and dogbones) axles for binding.
3. check the transmission and gear mesh (pinion/spur gears) for smooth engagement.
4. Check the front, rear and center portions of the driveline by removing or disconnecting the drive shafts and checking rotation.

I have a couple of these cars and they rotate smoothly. If you dicsover a defective wheel or tire, discard it because it will cause problems with other parts.

Ken
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Old 02-03-2013, 06:34 PM   #7
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Originally Posted by CurveTracer View Post
Before you operate this car too much the problem needs to be addressed.
Isolate the problem :
1. Place the chassis on blocks and ensure that each wheel rotates freely, forward, reverse and in opposite directions. Together and independently
2. check each of the 4 drive (CVD and dogbones) axles for binding.
3. check the transmission and gear mesh (pinion/spur gears) for smooth engagement.
4. Check the front, rear and center portions of the driveline by removing or disconnecting the drive shafts and checking rotation.

I have a couple of these cars and they rotate smoothly. If you dicsover a defective wheel or tire, discard it because it will cause problems with other parts.

Ken
I broke the engine in today and I have to agree that there's something funky with it, it's not so bad that it's real noticable while running the car but there's still something not quite right with it. It still does this "lope" that I keep describing even if I take the engine out so I know it's not the clutch bell meshing to the transmission incorrectly. I do think that the tires are crap though, not round and not near balanced. I'm going to try the things you say to see if I can figure this out.

How can I get all four wheels to move at the same time in the same direction if it's on a stand?
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Old 02-03-2013, 07:54 PM   #8
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It could be the shoes in the 2 speed. too much air gap. Hense the shoes rub. Turn each set screw counterclockwise alittle the same amonut. See if its better.
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Old 02-03-2013, 08:29 PM   #9
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It could be the shoes in the 2 speed. too much air gap. Hense the shoes rub. Turn each set screw counterclockwise alittle the same amonut. See if its better.
I did feel a scrape in the 2 speed clutch when I spun it in my hand. Thought that was it, so I installed the 2 speed without the clutch shoes and it still does the exact same thing. What in the heck could it be, I can't figure it out for the life of me...

It only does it when the wheels are turned and all 4 wheels are rolling on the ground, the further you turn the worse it gets.....

There is a note in the instruction manual in the differential assembly that says you need to remove the 30776 washer if the gear mesh is too tight....

I can also hear the gears in the diffs as I roll it, I'm sure it's the diffs I'm hearing and not the spur gear. Maybe those washers need to come out?

Last edited by GregUnd; 02-03-2013 at 08:56 PM.
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Old 02-04-2013, 11:07 AM   #10
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So Dave Starks at ofna says that this is normal and is due to not having a center diff and the lope comes from the front universals.

Guess all is well...
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Old 02-04-2013, 12:43 PM   #11
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Quote:
Originally Posted by CurveTracer View Post
Before you operate this car too much the problem needs to be addressed.
Isolate the problem :
1. Place the chassis on blocks and ensure that each wheel rotates freely, forward, reverse and in opposite directions. Together and independently
2. check each of the 4 drive (CVD and dogbones) axles for binding.
3. check the transmission and gear mesh (pinion/spur gears) for smooth engagement.
4. Check the front, rear and center portions of the driveline by removing or disconnecting the drive shafts and checking rotation.

I have a couple of these cars and they rotate smoothly. If you dicsover a defective wheel or tire, discard it because it will cause problems with other parts.

Ken
Agreed! I have two of these cars and everything is smooth.
I would pull the diffs and check them - rebuild if neccessary - and while you do this you can check the ring/pinion mesh.
I would also rebuild the two speed completely.
Along with the items on the above mentioned post that is all that could cause it.
One other thing - balance your tires always!
Check your drive shafts and make they are straight and not rubbing on your chassis brace.
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Old 02-04-2013, 05:30 PM   #12
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Ill start taking it apart tonight. What should I look for when checking the mesh on the differential gears??

I know my rear drive shaft rubs against the brace.
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Old 02-04-2013, 06:26 PM   #13
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Originally Posted by FastPete View Post
It could be the shoes in the 2 speed. too much air gap. Hense the shoes rub. Turn each set screw counterclockwise alittle the same amonut. See if its better.
+1
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Old 02-04-2013, 07:55 PM   #14
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+1
I have the 2speed clutch taken out and it still does it
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Old 02-04-2013, 09:29 PM   #15
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I took out the front diff and everything looks fine. A little bit if slack in the pinion gear and some horribly un-round and balanced tires is all I could find.
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