!!HELP!!Twin hammers shifting problem

[tomb0118]

Hello,
I have been having a TON of shifting problems with my twin hammers V2. Before you say its my servo, i have made sure it wasnt my servo, the only modification i have done to my tranny is steel gears all around. No matter what i do, rolling or not, the servo never has enough power to actually shift the transmission, and i even would have to take a screwdriver and shift it manually, which is still really hard, it feels really sticky and hard to move. when i dissembled it, it felt like the selector fork was binding.. cant figure out any way to fix it and i really need some help.

[lonleycreeper]

You probably didn't get the trans back together square. I fought the same problem when I first built my twin. I know you don't want to hear this but take the trans back apart and when assembling make sure everything is smooth. The shifting should not take much force at all.

[tomb0118]

i cleaned the whole gearbox when i re assembled it with the steel gears and everything seemed to run smooth, the shifter arm feels like its binding when it tried to move the selector fork in between the gears though... i will take your advice since i have it all apart already haha thank you and i thought some marine grease might help the situation? opinions on putting grease in there?

[fyrstormer]

If the shift servo arm is bending the selector shaft sideways even a tiny bit, it will bind like crazy. You might need to cut a slot in the shift servo arm so the bolt that attaches the selector shaft to the servo arm can move in a straight line while the servo arm itself moves in an arc.

[lonleycreeper]

Originally Posted by tomb0118

i cleaned the whole gearbox when i re assembled it with the steel gears and everything seemed to run smooth, the shifter arm feels like its binding when it tried to move the selector fork in between the gears though... i will take your advice since i have it all apart already haha thank you and i thought some marine grease might help the situation? opinions on putting grease in there?

I am going off memory here, but I remember the trans running smooth except for the shifting The screws do not pull the housing together straight and the shift shaft binds just slightly. But its enough that the little servo doesn't have a prayer.
I use marine grease on most transmissions and axles my self.

[Bart458]

Did you fix this problem? Mines doing the same thing after changing to metal gears

[fyrstormer]

Get yourself some Tamiya Molybdenum Grease and use that to lube the splines that the shift puck slides on. Also, shim the spring in the shift servo-saver so it can transmit more force. I shimmed mine about 1.5mm.

[new2rocks]

x2 on all the other advice. I bored out the shift shaft hole in the t-case slightly in my Ascender (same tranny as TH) and it helped. Good luck!

[Bart458]

What do you mean by shim the servo?

[fyrstormer]

I just took apart my Ascender transmission and did some work on it, because it still wasn't shifting quite as smoothly as I wanted. When I opened it, I found scratches on the square shaft that the shift puck slides on. I knew that the shift puck sometimes tilted on the square shaft when the shift fork pulled the shift puck to one side or the other, but I figured the hardness of the metal and the grease would make sure it didn't bind too much. I was wrong.

So, I washed everything and then went to work with a small diamond-coated file. I smoothed-out the square hole in the middle of the shift puck, paying special attention to the edges where there were mold-lines from the sintering process. Then I got some 400-grit emery paper and laid it on a flat surface, and smoothed the surfaces of the square shaft. Then I polished the square shaft with a 3000-grit sanding sponge, and polished the inside of the square hole in the shift puck with a small strip from that same 3000-grit sanding sponge. Then I washed everything, greased everything, and put it all back together. Now it works perfectly.



Also, regarding shimming the shift servo-saver spring, this is what I mean:



The shims preload the servo-saver spring so the servo-saver can transmit more force to the shift linkage.

[Bart458]

Thanks mate I'll give it a try

[meatmonkey]

Don't forget to give the "shift shaft" the same polishing as the rest of the mechanism.

Just so people looking at your pic get it, the second washer fits around the plastic of the servo saver so it adds preload to the spring.

I like your dust booties on the ball studs. Got a part#?

[fyrstormer]

Tamiya 53980

You are correct about the preload washers. They are Traxxas 5mm x 0.5mm Teflon washers and they fit around the plastic stud in the center of the servo-saver, so they compress the spring when the retaining screw is tightened.

I didn't actually polish the shift linkage shaft, I only greased it. When I tested the parts individually, the only binding was between the shift puck and the square part of the output shaft. However, I was careful when tightening the screws that hold the transmission together, testing to see if tweaking the two halves of the transmission case one way or the other would make the shift linkage shaft move more easily.

One last thing: You may find that the shift servo-saver binds against the plastic case of the servo when the retaining screw is tightened. You can fix this by inserting 3mm circular shims into the socket where the servo's spline hub fits into the servo-saver. I had to use 0.5mm of shims in this location to keep the servo-saver from binding against the servo.

[Richterat83]

Rebuilding a rig i picked up 2nd hand and am having something similar. It'll shift into high no problem, but the low gear requires the shift locator to be 100% tight at full lock and even then it'll slip out of gear into "neutral". Going to take the trans apart and see if it was put back together incorrectly previously.

[Richterat83]

Originally Posted by Richterat83

Rebuilding a rig i picked up 2nd hand and am having something similar. It'll shift into high no problem, but the low gear requires the shift locator to be 100% tight at full lock and even then it'll slip out of gear into "neutral". Going to take the trans apart and see if it was put back together incorrectly previously.

Small. Update, whoever put the trans together put the gears in backwards. Flipped them and it works perfect

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