rooker

My Feedback: (1)

I just got this truck off Ebay. I had to replace my spur gearas soon as I got it. Now the truck jerks sometimes when idling. When this happens the spur gear is spinning. Shouldn't it be stopped when the truck is just idling. Could the problem be in the clutch or could it be idling too high?</p>

HJJFFFAA

Sounds like a high idle.

Mr Max Wheelie

try turning out the idle screw slightly.......if this doesnt help my next guess would be a broken clutch spring!

rooker

My Feedback: (1)

It will be Thursday before I can mess with it again.  It does need tuning, very sluggish on accel and cuts off suddenly after a few minutes of driving.  But, boy, does it have some power compared to Acme, even w/o being tuned well!!!

DaveG55

It is idling too high. The jerking is from the forward pawls engaging due to the high idle. As soon as they engage the internal transmission rpms fall and the pawls disengage so the truck just kind of jerks forward. You will also notice that the truck kind of revs up a bit then jumps forward when you start off from a stop rather than a nice smooth take-off.
There are ways to stop this from happening, aside from correctly setting the idle and tune. Do a search for the "no buck, constant engagement" mod if you want to keep reverse. If reverse does not matter to you then search for a 'forward only" conversion.

RIP_nitrodan

My Feedback: (1)

It could also have spools in the diffs causing it to jerk. Once you get on the throttle, does the jerking go away or does it return after you do a lap and come back to idle?

rooker

My Feedback: (1)

The jerking comes and goes.  DaveG55 described perfectly.  I hope that is what it is.

scott36

My Feedback: (54)

the jerking is NORMAL for the t maxs with reverse in them both mine do this and again its normal. if you put a forward only kit it wont do that

rooker

My Feedback: (1)

I turned the idle down today, it quit jerking.  Now, Tmaxx vs. concrete block.  guess who won.  I have lower suspension arm on order now.  The screw came out of tie rod on opposite side.  when it did that I lost control.  The truck flew into concrete block, block won!!!

scott36

My Feedback: (54)

turning the idle down will help but the jerking will still happen now and then tho. have fun fixing to.

rooker

My Feedback: (1)

Isn't it funny that you have fun working on something.  I work on equipment for a living, it is not fun at all.  I guess it is b/c I have to do it?  But do not mind at all working on little truck, in fact I enjoy it.</p>

kpm

Hello. I know this thread is old, but through researching the forums this sounds like my problem. I made a video so that it may help others identify the problem. It may also help others if they experience this problem. I am new to Nitro Trucks and just got a T-Maxx 2.5 4x4
I've followed all instructions and have only one question. The truck tends to jerk when sitting still at idle or when it first takes off. I've adjusted the slipper clutch and that produced varying results. I've adjusted the idle slightly but might need more adjusting. Some of the posts I read indicate that this is common in t-maxx trucks with the reverse gear. (if that is my problem)
Here is the video that shows what the truck is doing and my questions.
https://www.youtube.com/watch?v=FF14_ML3-vY

Thanks! Kip

collector1231

My Feedback: (1)

It sounds like you need to lower the idle speed. It can be changed through the low speed needle.

Maxximize

In watching your video, it sounded like the truck was idling higher in the first part of the video when it was jerking more. If it does it, just lower the idle as much as you can without it stalling. It's been awhile since I've ran a 2.5, but if I remember correctly they will idle quite low if tuned well. It is a normal thing for the black transmission Maxx trucks with reverse, mine did it too way back when it was a Pro .15 Maxx. It happens when the clutch inside the tranny is partially engaging due to it spinning a bit faster than it's supposed to, but not enough for the shoes to fully engage. A great way to tell if your idle is too high is if the truck won't hit reverse, if it won't your idle is way too high. If it does, but still jerks when idling try lowering your idle screw in 1/8 turn increments until it stops jerking. Sometimes even with a perfect idle it will still jerk around a bit anyways, and will also do it occasionally on slow acceleration. The idle is what will always affect how much the truck jerks around at idle, but occasional jerking is normal and is simply the nature of the design.

Here's a little info on the T Maxx classic transmission. The reverse tranny in the T Maxx classic is an ancient design dating back to the Pro .15 model release in 1999. When the original T Maxx 2.5 came out in 2002, which is now known as the T Maxx Classic, it re used the original transmission design. It is purely mechanical and relies on two gears with two spring loaded clutch shoes on each of them to engage a clutch bell to switch to and from reverse. The clutch bell is moved over the clutch shoe end of the slected gear when the reverse servo pushes it or pulls it over the shoes. If they are spinning too fast, the shoes are open and hit the clutch bell before it can slide into position. If they spin slightly too fast, the shoes are partially open and can engage the clutch slightly. As they rotate, they will open and close slightly from natural variations in the idle speed and their own rotating mass. The shoes do this most of the time, even when idle is perfect. It's only when idle is too high that it is noticed by the jerking at idle effect. Now there was also a factory reverse 3.3 T Maxx, which was the first of the gray transmission to be used. That one came out in 2006, and it wasn't used for long. It used what's called Opti Drive for it's reverse function. I'm not entirely sure how that system works, but it was electronically controlled and monitored by a small control unit installed in the receiver box and used a reverse servo as well. In 2008, Traxxas did away with reverse from the factory in the gray transmissions, but offered the Opti Drive system as a kit that could be installed by the owner.

Traxxas also offers forward only conversion kits for both reverse transmissions. It basically just eliminates the reverse clutch bell, reverse servo, and the internal clutch shoes and is the only way to fully get rid of the bucking effect on the black transmission. I did it to mine when I swapped my Team Orion Wasp .18 out for the TRX 2.5R and put Ofna Monster Pirate wheels and tires on it. The original transmission gears shredded from the extra power with the huge tires, and the forward only kit increases the durability of the tranny dramatically. It also seemed to accelerate faster and was much smoother, not to mention the weight saved. If the occasional bucking bothers you and you don't mind losing reverse, I would suggest installing the forward only kit. It's around $10 and is pretty easy to do, and you can always swap it back if you wanted to.

Hopefully this was helpful

kpm

Collector and Maxximize.
Thanks for the responses! Thanks for taking the time to provide such great details. I've been so busy this week so sorry for just checking back in. I think you guys are right and my issue is mostly going to be regulated by the idle. I've played around with it and it's much better. Thanks!!!!

Maxximize

No problem, glad I could help! Enjoy your truck