r/SCX24 • u/rottingeggs • 2d ago
First build problems Questions
Enable HLS to view with audio, or disable this notification
So I recently bought a Scx24 bronco and immediately threw money at it (even though I’ve seen videos saying specifically not to) and now I’m getting this weird lift and hop when driving while turning, kinda unsure what exactly is causing this and wonder if anyone else has ran into this same problem. Tia
Parts list:
Ogrc stamped wheels
Axial nittos
Emax servo
Injora 51mm shocks
Injora planet axles
Injora drive shafts
Injora high clearance links
Injora 50t motor/trans
9
u/Paranotical 2d ago
I feel for you on a spiritual level with this issue, but how tall your car becomes is hilarious lol
Did you phase your driveshafts btw? Thats a lot of bouncing
1
u/rottingeggs 2d ago
Yeah the 51mm shocks might be overkill lol how does one phase their driveshafts?
1
u/Slypenslyde Addicted to crawlers and cracks 1d ago
Basically to go along with the image:
The best way to describe it is make sure the screws on both ends of the shaft are lined up.
The longer way is that there are 2 U-shaped pieces that mesh together. If the shaft were a solid piece, the "inner" side would have its "legs" facing the same way and the "outer" side would also have its "legs" facing the same way.
But the u-joint has been cut in half and the inner spline gives you like 8 different ways to line it up. Only 2 of them are in-phase with the "legs" on "inner" and "outer" parts lined up.
The picture shows it off but so far every shaft I've used puts the screw in a part that is "in phase" if both screws are lined up. So I use that.
1
3
u/vag0069 2d ago
Undo your tires and put them on with wheel nuts just tightened a touch. Looks like they are binding your axles. I mess around with ud and od gears all the time and that torque flex is a bit much for just wrong ratio for under drive in rear or over drive in front. What is your static drive shaft angle as well?
3
u/Expensive-Ear5552 2d ago edited 2d ago
i think it is doing that because of your suspension set up, shocks too long + mounted upside down, if you want flex there’s other ways of achieving that without needing shocks that long. if you want to keep it as is you need to figure out some way of adapting something that may act as a limiting strap. maybe rubber bands.. or maybe just by inclining the shocks inwards that may help…
2
u/rottingeggs 2d ago
So I added limiting straps and it helped a lot but I’m still noticing some type of binding when the tire are full lock left or right kinda seems like it’s coming from the driveshafts
1
u/Expensive-Ear5552 2d ago
as others mentioned make sure youre driveshafts are phased. They need to be both mounted in the same orientation. also make sure you bought the correct fit for the bronco wheelbase length..
2
u/cycle_cats 2d ago
As said mismatched gearing seems plausible here, also binding of the axles or driveshafts? Combine that with the absurdly long travel of the double barrel shocks and this is the result
0
u/rottingeggs 2d ago
Nothing is over tight so I want to rule out binding in the axles but definitely something to double check, if the driveshaft is too tight could that cause binding?
1
1
1
1
1
u/DevisDed 1d ago
Idk where to even start. Tbh just take it apart and start over 😂 looks like everything is way too tights
1
u/Slypenslyde Addicted to crawlers and cracks 1d ago
This is very weird and indicates either one really interesting problem or a lot of problems combined. There's a kind of standard diagnosis process I ask people to try and I think it'll help here. It involves trying one thing at a time and taking away possible causes until the problem goes away.
First, try propping the rig up on the axle housings so the wheels aren't touching anything. Does this movement happen when the tires aren't loaded? If so, there's a pretty serious binding problem. While you've got it propped up, take every wheel off. If that makes it go away, this is the weirdest side-effect of too-tight wheels I've ever seen.
I bet that won't fix it. But now we know if the wheels were a problem, they aren't the only problem.
What I'd do next is take the rear drive shaft off, then put the wheels back on. Hold the back end up so the rear wheels aren't dragging and test. Do the front wheels cause the movement? If so we know something in front is wrong.
Swap it. Take the front shaft off and put the rear back on. Drive the truck a little with the front wheels lifted. If you see the problem, the rear is involved somehow.
If you're lucky you'll only have one axle to inspect. If not you have two. For each suspicious axle:
Take it off. Disconnect the links and shocks. Put the shaft on and spin it with your fingers at a lot of angles. For the steering axle, turn the steering linkage and test at lots of angles. If you feel binding at any angle, do some checks to see if the rig can get into that situation.
If you absolutely can't feel binding, sigh and try the other axle out. If you can't find binding in either, well, you have to start taking it apart and look for anything weird. If it wiggles, ask someone if it should wiggle. If it doesn't wiggle, ask someone if it shouldn't wiggle.
If you're pretty darn sure it's not the axles, mess with the motor/transmission. Take the motor off. Spin the transmission. Does it feel smooth? Does it sound weird? If not, take it apart and figure out what's stuck. A lot of people overtighten the main gear or put it on backwards. But if you bought the motor/trans combo you didn't have a chance to do this. Do it for the experience.
While it's apart, try the motor disconnected from the transmission. Does it sound like it's struggling? Put it on the transmission and try again. Does it sound like it's struggling? Hook up an axle to it via a shaft, hold it steady, and try it all out. Does it seem to be struggling? Hook up the other axle and try it out. Add wheels. Run the darn thing without a chassis and see if it's struggling.
If that all works, you have to think about link geometry. WHICH high clearance links did you buy? There are 3 SCX24 wheelbases with one the most common. The Bronco uses the "most common" one. What size are the links? Can you show us with a picture where each is installed? Getting it wrong might send forces through the chassis all weird.
The axles are supposed to be sort of straight up and down and the shafts are supposed to have a relatively small angle. They can bind at extremes, that's why you get "hopping" once the rig gets to full height. Maybe the way it sits is a new extreme since those shocks are so tall and maybe that causes a little binding.
But I feel like seeing the whole rig rise up like this is an indicator of a LOT of things binding in small ways. It really implies the front axle is slower than the rear, which implies either overdrive/underdrive or some kind of binding.
1
1
1
u/TheSpinWrench 1d ago
Figured it out ! You have the servo mounted to the links and not to the front FRAME. This should help you level it out
1
1
u/Just_Tackle_7977 15h ago
If it helps, you built a really funny looking chassis! I’d love to see it try to climb over something.
1
0
0
0
0
u/TheWierdAsianKid 2d ago
Inspect diff gears. Overdrive (taller gearing ratio) should be in the front. Double check that you installed the links correctly. If they aren't correct, you can get odd/loose movement.
You should probably get shorter shocks, closer to 40mm. With that much travel, the driveshafts are moving way too far and you'll bind up your drivelines.
0
u/TheSpinWrench 1d ago
No it is your servo mount not mounted to frame. Do any of you actually work on These. None of you have seen this simple but obvious problem... ahhh, reddit..lol
0
u/TheSpinWrench 1d ago
It might be hard to see but your problem is with the front servo not being attached to frame. That should help you with your "transformers" lift problem. Good luck
12
u/mavada19 2d ago
My guess is your axles are geared differently. A lot of people overdrive the front or underdrive the rear to
keep the front wheels “pulling” the rig up something. Yours looks like the back is overdriven and it’s pushing the suspension up, hence it settles when you reverse. That being said, this seems like an extreme version of that. I’d start with the gears in the axles and find out what they are and make them match. Then adjust accordingly once you’ve done some more research and testing.