OK... WHAT Happened???

[ArmyAnt]

Hello everyone... some of you may know me already, I am relatively new to Nitro Revos.

I recently acquired a 2.5R that I upgraded to a 3.3. I replaced a few parts: Rebuilt front differential, new EZ start motor, new air filter... a few other parts. Anyway I followed the Traxxas DVD for breaking in a motor. After break in tuned the engine. Everything seemed to be going well.

My first time taking it out of my yard after break in, I took it to a local skate park. I wanted to jump the ramps and such. Things went great... Revo performed as expected. While there I spotted an area where large mounds of baseball diamond sand/dirt had been dumped. Driving it through the high grass I noticed that it seemed a bit sluggish. Didnt pay much attention to it. Got to the mounds and I noticed again that it seemed like it didnt want to go.... it growled a lot (revved) but barely moved. Reverse works awesome...quite fast, but forward it creeped even though the engine was revving loudly.

Any ideas???

[Double G]

Loose spur gear.

[ArmyAnt]

Loose spur gear.

Front or rear differential? Why does Reverse still work?? Are Revos all-wheel drive (4x4)?

[Bloody_Wheels]

He means the gear on the transmission. There is a nut that you can tighten if it is too loose.

[ArmyAnt]

My bad... I was thinking spider gears. I'll look for it on the Exploded-Views.

Thanks for the info..

[fallonguy]

The spur gear is what the clutch bell on the engine turns. So if the clutch and spur gear are turning but the truck isn't moving you need to tighten the spur.

[ArmyAnt]

The Exploded-Views helped me locate the clutch bell... but the "nut" Im supposed to tighten eludes me. Anyone have a photo handy that shows the nut? This would really help.
Before I start tightening things that may not need it.... just to clarify:

The Revo drives forward... the speed just doesnt match up with the amount of throttle pull or the revving sound of the engine... but it does go forward, only on flat hard surfaces and not full speed. If I hold full throttle, the engine revs fine, but the Revo moves slowly (as if a little less than 1/4 throttle)... it does NOT move at all in the grass. Reverse works perfectly. Hope this makes sense to someone out there.

[upbasher]

You know what the spur gear is, right? Its the bigger gear that the clutchbell turns. There is a nut on the end of the shaft that the slipper sits on. Tighten that.

[fallonguy]

The big gear in the picture is the spur gear you tighten it by tighten the nut in front of the gear.


Instruction on how to adjust it is in the manual and you can find the manual on this site if you don't have one.

[ArmyAnt]

Perfect!! Thank you.

[ArmyAnt]

I tightened it up. But it drove the same. Seems to drive slow on pavement, but very slow to almost crawling in the grass. Again, reverse is fine.

[ArmyAnt]

It seems the front differential is shot...

[fallonguy]

That could be the problem it's binding going forward but not going in reverse. Just make sure when you put it back together that you put the diff. in right side up it can be put in upside down. Then you have the front wheels turn backwards and the rear set turn forward. It is marked with up but it can be hard to see. I make mine with a white paint marker on top.

[ArmyAnt]

Someone else mentioned the same thing when I rebuilt the rear differential. I noticed the up arrow.
I know it makes no difference, but why do these differentials go bad? Abuse / neglect? Age (I think this is the 2nd Revo release, 2.5R)? Should I keep a healthy stock of gears lying around?

I bought TRA5380 Housing, TRA5381 Carrier and gasket, TRA5379X Ring gear and differential pinion, 4 bearings, and TRA5136 Diff. Oil for the rebuild.
Any tips on the removal of the front end or assembly?

Thanks

[fallonguy]

I would say most of the time it's neglect they leak a little ( It so little you don't even notice it)and if you don't check them they will run dry. You should pull them out and clean and refill them about once a year. As for disassembly it's pretty straight forward pull the bumper mount and bulkheads. you can find a digram in the products section.

[ArmyAnt]

I hope this will be the FIX I need. It just seems so strange everything was fine, then when Im about to have some fun....nothing!! Geessshh! Im sure this has been documented over and over, in the event it has not, I'll take some photos or video of the rebuild. Seems like a big deal to me... may not be to some of the seasoned veterans on this board. Oh well... Ill post an update when done. Thanks for all the help Everyone!

[ArmyAnt]

OK, so I tore apart the front end. Opened up the front differential and expected to find metal shavings or a broken tooth, but found neither. I dont think the gears are in that bad of shape to cause the problems I was having. My worst fear is that the LHS is having me buy parts I dont need. What do you guys think???
[IMG][/IMG]
[IMG][/IMG]

I already bought the parts and opened the bags, Im still gonna do the rebuild, but Im thinking this is not the problem.

[Jake C6R]

Doesn't look that bad to me. How do the gears mesh when it is all together? Is it smooth? From the pix the teeth look OK from what I can see.

[fallonguy]

You might want to take the transmission apart and have a look inside.

[ArmyAnt]

If the transmission is bad, wouldnt that affect Reverse??

[ArmyAnt]

As I was putting it back together, I notice a crack in the Bulkhead... I dont think this is my culprit. Any thoughts?

[IMG][/IMG]

[fallonguy]

Sure it could anything that would allow the differential to shift could be the problem. It could allow the differential to bind going forward but not in reverse.

[ArmyAnt]

How do the gears mesh when it is all together? Is it smooth?

I didnt want to chance it, I figured I already had everything apart...
Put it all back together... it felt very smooth.
Also, I think the diff. was leaking oil. The bulkhead was pretty grimy.

[zdragon71]

Those spider gears do look worn a bit. Also yes you need to replace cracked bulkheads. Save yourself from having to tear it all back down later.

[ArmyAnt]

Well, I rebuilt the front differential. Everything went smooth... (no extra screws leftover). Still have the same problem. Its still sluggish in Forward, but very responsive and fast in Reverse. On pavement, its not as slow as it is in the grass, but its definitely off.
When its WOT, the engine sounds like its WOT, but the Revo moves like its 1/4 throttle????

[fallonguy]

Did you replace the bulkhead?

[Snook Man]

Its still sluggish in Forward, but very responsive and fast in Reverse. On pavement, its not as slow as it is in the grass, but its definitely off.
When its WOT, the engine sounds like its WOT, but the Revo moves like its 1/4 throttle????

The Forward gear ratio is taller than the Reverse gear ratio. It is easier for the engine to pull/move the truck when it is in reverse compared to forward.
Sounds like you have a loose slipper clutch to me, the engine is overpowering the slipper and the slipper is slipping too much when in forward, but when in reverse there is not as much resistance to move the truck and the slipper is not slipping or not slipping as much.

Snug the slipper up good and snug and test, if the truck responds to the tight slipper in forward as it should, you can then adjust the slipper to where it belongs.

If that does not fix the issue, a video of it running would be helpful to diagnose the problem.

[ArmyAnt]

Did you replace the bulkhead?

Yes I did.

I will try tightening the slipper clutch and report back. Thanks

[f687s]

the classic stripped tranny gears

[ArmyAnt]

I tightened the slipper clutch snug... no results.

So... stripped tranny gears will only affect Forward??

[Snook Man]

If it is a forward gear, yes.
If the engine clutch and slipper are eliminated as the problem the next place to look is inside the tranny.

[ArmyAnt]

the next place to look is inside the tranny.

What exactly am I looking for?
Im not a big fan of taking things apart... those differentials were so tedious. Any cons to buying an entirely new transmission?

[fallonguy]

No cons in buying a new transmission. Some revos came with reverse and some came without. So if you really want reverse make sure you get the right transmission. Also the slayer transmission looks the same as the revo on the outside but are geared different because of the smaller tires.

[RC-Sakke]

Are the diffs assembled right ways in the bulkheads? If the diffs are upside down and shift servo is reversed, that would make the truck go fast on reverse and slowly forward... ?

[ArmyAnt]

Finally found the time to install the transmission I bought. I found a complete NEW transmission on ebay off of a 3.3. Relatively easy swap out. Put some fresh fuel in and charging the batteries now. Any tips or adjustments before I fire it up?

[ArmyAnt]

I got it started... let it idle for a bit. The engine is still pretty tight, being it only has about 8 tanks of fuel through it.
BUT, it only goes in Reverse. Im pretty sure this is an easy fix, something I did / didnt do, when I installed the new transmission.
Any ideas?? I already tried the obvious, its not the Reverse switch on the transmitter. Up or down, it still goes in Reverse.

[kgombe1]

if its going in reverse and not forward then it cant be anything the suggested... spur gear and diffs were a waste of time.. reverse and forward all go through the same place.. except when its shift there is a guide and also gears that help in this action... you have to take apart the transmission and look at the reverse /idler gear and all gears in your tranny.. while there i would just put in forward only and get rid of reverse....

thats the hard part.... or it could be that the servo is not pulling it quite into lock position... so look at if the servo is pulling that shaft all the way...

[ArmyAnt]

Not quite sure what youre asking me to do????

[kgombe1]

take apart your transmission

[ArmyAnt]

OUCH!!! Why? Its brand new.