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HPI RS4 Transmission clutch.

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Old 11-25-2015, 04:55 AM
  #1  
dsmcraze
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Default HPI RS4 Transmission clutch.

I have discovered over some searching that it is fairly common having a difficult time getting these things to shift into 2nd gear. I am relatively new to the rc world let alone nitro but I've gone through 2 motors with this car and have learned a lot in the meantime. I am quite familiar with this chassis now and quite the mechanically inclined individual. Having said that I am completely stumped on this issue. perhaps it's a common seldom known issue getting these to shift. I have disassembled the transmission for the 10th time trying to figure out where the issue is. I have tried a multitude of things. All the basics are covered. The set screw for the clutch is tight on the shaft. 2 full turns out with the silver spring on the clutch adjustment screw. I have tried severial adjustments. The clutch shoe pivots freely with slight resistance. Motor is tuned and broken in correctly it rips from a dead stop and screams to high revs with no shifting. I have attached some images of the transmission clutch and bell. I am very confused. Am I missing a part? Can these simply just wear out?
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Old 11-25-2015, 10:07 AM
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Those type do not really wear out....the spring can snap or become squashed.....and the pins in the picture two piece can fall out.... Of course it should work like this» when the part in picture one reaches the correct rpm then the tooth/tang is pushed out by centrifugal force overcoming the spring tension....the tooth/tang then hits one of the pins in the picture two part thus engaging second gear. By adjusting the screw you should be able to lock it in first gear and at the other extreme it will virtually already be in second when it moves.
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Old 11-25-2015, 08:58 PM
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Thanks for the info anthoop. you may have solved the problem. I was under the impression the clutch used centripetal force to send the clutch tang out and grip the inside of the clutch bell. upon further inspection i see a pin in the bell where the tang should grab. I bought this car off craigslist about a year and a half ago so i believe the original owner may have dissembled the clutch and reassembled it backwards! thus the tang would be sliding over the pin rather than grabbing it. I see wear on both items indicating this happened, though i do believe it should still work fine. Impressive considering who knows how many times at 31000 rmp that tang has just slid over the pin. or perhaps the tang wasent extending at all because being installed backwards would put the pivot point on the adjacent side. I do mainly use this car for drift so 2nd gear never really was an issue until i put rubber tires on it with the new motor and realized it doesn't shift! Now i just need to figure out which way this clutch needs to go in as to the relation of direction it spins. kind of a brain twister.
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Old 11-26-2015, 09:57 AM
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Ah yes if that part is the wrong way around then it will not work.....there are shifting mechanisms that use a friction type clutch but what you have there is like a dog clutch.....anyways glad we got it worked out....once you figure out the correct orientation......have a look on the HPI website for amanual they are usually quite good.......have fun.
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Old 11-26-2015, 10:31 AM
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I figured out the problem!!! I was trying to figure out how both spur gears can spin the same direction. I noticed the one way bearing was pressed in the wrong way on 1st gear! So essentially it was in fact always in 2nd gear. I swapped the bearing around made sure The clutch tang was spinning the proper direction reassimbled everything and took her for a spin. It was like 28f out and about 2 am at this point so I couldn't really open her up but I'm sure it will work. Heres the bearing I'm talking about. Who would have thought.
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Old 11-26-2015, 04:32 PM
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Uugghhh still not shifting into 2nd. I'm beginning to think the spring in the clutch is not the factory spring. It seems rather stiff and honestly is absolutely the only culprite left. I took the spring out and assimbled the transmission, spun to by hand and sure enough when I gave it a good flick 2 gear engaged. I wonder if I can just use like a pen spring or something. Its looking like who ever owned this car took apart the trans and slapped it back together or something.
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Old 11-27-2015, 07:52 AM
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If the one way bearing was the wrong way around then you would not have any drive.....what should happen » pinion turns 1st spur gear. one way bearing is locked in that direction and is locked to the shaft with the shifting clutch.......as before when the shifting mech. gets to rpm then tang locks 2nd gear.....as soon as 2nd gear is locked then the shaft that the one way bearing is on is turning faster than the bearing and it should run free in that direction.

If it is any help then the engine rotates anti-clockwise when veiwed from the front ( clutch/carb end )..... You could try alternate springs but I doubt you would have much luck with that.
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Old 11-27-2015, 11:17 AM
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Well the 1st spur gear was backwards so the bearing was switched to compensate. But i did not even put that together your totally right even with the 1st spur gear backwards as long as it was spinning the shaft it should have shifted if the clutch was correct. which it is all completely assembled correctly now i know for a fact. ive tried 2 turns out - 3 turns out o the adjustment spring and still no shifting. its tuned perfect. only issue i can see feasibly possible is the spring tension is to high for the tang to extend. I will try a weaker spring and report back. Im getting really good at taking this thing apart right about now. lol
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