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jk6672

jk6672

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RC Driving Style
  1. Bashing
  2. Racing
I bought a 2.5 tmaxx for my son and I need some help. I've just ran one tank through it following the break in procedures and something needs adjusting. It seems like something is catching in the transmission and its bucking forward even with slight throttle. It's not a slow creeping forward that would be fixed by adjusting the idle speed.
 
It is a common issue with the 2.5 TMaxx with reverse.

There are a few modifications you can do to the internal gears to eliminate the Buck, or you can install the forward only conversion and do away with it once and for all.
 
I finished the second tank and adjusted the idle speed because it started creeping. Still bucking. If this is a common thing for the 2.5 does it cause problems? I don't think I'm going to wrench on this one for a while, like I said this ones for my son, he is 12yrs old and this will be his first R/C. I think he might need reverse until he's got some experience, then will do the FOC.
 
jk6672 said:
I finished the second tank and adjusted the idle speed because it started creeping. Still bucking. If this is a common thing for the 2.5 does it cause problems? I don't think I'm going to wrench on this one for a while, like I said this ones for my son, he is 12yrs old and this will be his first R/C. I think he might need reverse until he's got some experience, then will do the FOC.
Click to expand...

The best experience is without reverse. It'll teach him to crash less. The more time he spends running back and forth to move it, the more he learns. That's how I taught my son, and most of the kids at the track I know learned the same way. Actually, at the track reverse is forbidden, so you learn fast that you don't need it.

Personally, I'd do the forward only conversion.
 
sound like wise words.
 
Man, I was on the fourth tank and the wheel fell off, so off to the LHS tomorrow for parts to finish the break in. I should of check the wheel nuts before starting, but I didn't.
 
If/when you need to open the transmission for repairs(and you will:))You can modify the output gears to stop the bucking. It’s not that difficult to do but the FOC will make the transmission more reliable.

All that’s needed is to replace the pin that holds the gear pawl in place with a grub screw pin like the one that attaches the drive shafts to the differential.

The gear on the left is stock, the gear on the right has been modified with the grub screw pin and the pawl removed (leave the pawl installed to prevent switching from forward to reverse while the truck is in motion).
You can do the modification to just the forward gear or both the forward and reverse.

forwardreverseoutputgears.gif
 
Its still bucking. I'm going to put the FOC in the granny. Should I do the above too? BTW- I have have. A 3.3 revo and I'm pretty impressed with the 2.5 tmaxx.
 
opps, darn phone spell check. I don't think I'd FOC the granny LOL.
 
The above mod isn't required with the FOC installed as it replaces those gears with 1 gear I believe.

Having the FOC makes for a much smoother operating truck and takes the strain off the drive train that the bucking provides.
 
I have a question. I went through three glow plugs during the break in and they looked like they had been dipped in dirty motor oil. Is this an indication of way too rich? I've started leaning out the LSN and the HSN some, and I'll keep turning clockwise if that's the problem
 
3 glow plugs? And they look like dirty motor oil? If they're wet it means your engine was either flooded or rich.
If there's any dark color then you've been running way lean.
Look at the top of the piston, you shouldn't see anything but the color of your fuel after a few tanks.
 
They were wet, and it was dark. I'll check out the pistion today after I run a tank because it's sitting BDC and oiled. There is a lot off smoke when you get on the throttle, and from what I understand that's also an indicator of too rich. (i think)
 
You probably are running rich now, or just plugging the exhaust to shut it off. That will force fuel into your engine making you think the plug looks rich.
The dark color comes from being too lean, but I'm sure you've corrected that by now.
 

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