Runaway help

[BadWill]

Hi guys. I am new to nitro and I bought a gently used tmaxx from a friend. He took it to a local rc shop for a tune up a few months ago, and he said it was running badly after he got it back. He said was shooting fuel out of the exhaust and running really rich. He messed with the the high speed needle and got it running better, but was running a bit lean when he sold it to me. I richened the hsn about 1/4 of a turn and did a few high speed runs and it seemed to be running decent, based on videos I've watched.

Since it was running decent I took it for a few runs around the back yard. I drove thru a small leaf pile and up and down a few hills. Stopped it right beside me and attempted to pull a wheelie, but when I let off the throttle, it took off! Full throttle hitting second gear and I hit the brakes but it was still going strong. It hit a tree @ 30+ mph. Broke the upper and lower control arms, tie rod, bulkhead, drag link, and the steering servo connectors.

I've checked the action of the throttle servo and the action of the carb and everything seems to be working as it should. I can't explain what happened. Does anyone have any ideas? Or has anyone had this happen?

 

[cbaker65]

Hi guys. I am new to nitro and I bought a gently used tmaxx from a friend. He took it to a local rc shop for a tune up a few months ago, and he said it was running badly after he got it back. He said was shooting fuel out of the exhaust and running really rich. He messed with the the high speed needle and got it running better, but was running a bit lean when he sold it to me. I richened the hsn about 1/4 of a turn and did a few high speed runs and it seemed to be running decent, based on videos I've watched.

Since it was running decent I took it for a few runs around the back yard. I drove thru a small leaf pile and up and down a few hills. Stopped it right beside me and attempted to pull a wheelie, but when I let off the throttle, it took off! Full throttle hitting second gear and I hit the brakes but it was still going strong. It hit a tree @ 30+ mph. Broke the upper and lower control arms, tie rod, bulkhead, drag link, and the steering servo connectors.

I've checked the action of the throttle servo and the action of the carb and everything seems to be working as it should. I can't explain what happened. Does anyone have any ideas? Or has anyone had this happen?

It could have been just a fluke were the throttle & brake linkage jammed up ,or a faulty servo!
I don't know what type of radio gear you have ,is it 2.4 or the old 27 AM radio?

 

[BadWill]

It could have been just a fluke were the throttle & brake linkage jammed up ,or a faulty servo!
I don't know what type of radio gear you have ,is it 2.4 or the old 27 AM radio?

2.4ghz. I am not sure what happened. I've tried to recreate the same scenario, except stationary, but the servo seems to respond normally. I need to replace the steering servo, and plan to go with a better setup, might swap the throttle servo too. Any suggestions

 

[cbaker65]

2.4ghz. I am not sure what happened. I've tried to recreate the same scenario, except stationary, but the servo seems to respond normally. I need to replace the steering servo, and plan to go with a better setup, might swap the throttle servo too. Any suggestions

Like I said ,it could have been a fluke ,as in the linkage jammed or weak servo !

That system should have a fail safe in which is intergrated into the receiver which detects low voltage an will shut everything down ,....
But does not detect a weak servo or jammed throttle rod ,....LOL...that get folks all the time thinkin they are safe on run aways!....

A simple spring on the carb. will be better!.....

 

[BadWill]

Like I said ,it could have been a fluke ,as in the linkage jammed or weak servo !

That system should have a fail safe in which is intergrated into the receiver which detects low voltage an will shut everything down ,....
But does not detect a weak servo or jammed throttle rod ,....LOL...that get folks all the time thinkin they are safe on run aways!....

A simple spring on the carb. will be better!.....

Yeah spring on the carb was my plan, which will probably require a stronger servo. Thanks

 

[cbaker65]

Yeah spring on the carb was my plan, which will probably require a stronger servo. Thanks

Yea ,radio fail safe systems only detect low voltage an loss signal ,but do nothing for mechanical failure ,such
as servo failure or any linkage mechanical or damage wire to the servo failure!... ....lol ,have folks that preach to me about
using a fail safe system in the radio gear ,I laugh at them an say I got the best fail safe system ,........A 10 cent carb. spring!....

Most of your chassy stock parts like a-arms ,knuckles ,an tie rods are cheap to replace on e-bay ,so it
should not cost no more than a few dollars to fix!

Do recommend a better throttle servo an a carb. spring to be installed!...

 

[BadWill]

Here's the damage. I forgot to mention it busted two shocks

 

[cbaker65]

OOOOUUUCH!.......

 

[badboy2]

as i was reading your post i kinda laughed as i know whats gonna happen!i can just see your face ! heheh anyway cbaker is right throttle spring will help close the carb
in times like those..TREE-1 TMAXX-0 ..oh and because that happened dont go with alum parts..stay plastic imo

 

[BadWill]

as i was reading your post i kinda laughed as i know whats gonna happen!i can just see your face ! heheh anyway cbaker is right throttle spring will help close the carb
in times like those..TREE-1 TMAXX-0 ..oh and because that happened dont go with alum parts..stay plastic imo

Yeah. I didn't even have the car 24 hours and boom. Was devastated, was like it happened in slow motion.

My friend told me not to buy all aluminum for that purpose. He only has an aluminum chassis. I figured the only other parts I would get in aluminum would be the bulkheads

 

[Shakey_Nitro]

I have a Tmaxx 3.3; 4908 model...no reverse. I just had mine disassembled to replace my clutch and I noticed (from your pic) one difference between yours and mine. Yours doesn't have a throttle return spring like mine. I attached a pic of mine. I would think you should be able to the same parts as mine to add a return spring. On my model, my throttle will not return to idle without the spring.

 

[BadWill]

I have a Tmaxx 3.3; 4908 model...no reverse. I just had mine disassembled to replace my clutch and I noticed (from your pic) one difference between yours and mine. Yours doesn't have a throttle return spring like mine. I attached a pic of mine. I would think you should be able to the same parts as mine to add a return spring. On my model, my throttle will not return to idle without the spring.

View attachment 94020

Thanks for the picture. I have already installed a throttle return spring after replacing the servo with a hi-tec. My spring doesn't fit the way yours does due to my servo being offset, but I've rigged up something to make it work.

As an update, I did manage to fix everything. With the new servo and all the replacement parts, it set me back about $100. I've since tuned it and got it running decent, and so far have not had anymore issues. *knock on wood*

I have reason to believe the runaway problem could have been caused by a really bad tune on the carb.

 

[olds97_lss]

Be careful with a TRS if you have it directly on the carb. The traxxas carbs are composite body which doesn't hold up well to the side load a spring would put on it if you have it directly on the carb. You will end up with binding in a short while due to the extra wear inside the slide, then you end up with a runaway even with the spring.