Removing the slop from a Summit trans

[TheROOSTER]

Here's a mod to remove most of the slop in the Summit trans.

Those of you that use them in your SCX-10's and other crawlers know that the worst thing about the trans is when you transition from ascending to descending and the truck rolling about 6-8 inches uncontrollably. Then after stopping, it taking a second to take up the slack before it starts moving again. After this mod your truck will be as tight as having the stock Axial trans back in it.

First disassemble the trans by removing the six screws holding the case halves together and removing the shilft lever/spring.



While keeping all the gears in the same case halve that houses the spur gear, separate the case. You should end up with this:



Next, remove the output shaft along with the 2 gears and the shift drum attached to it. Pay attention to where the shims are on the output shaft. There is a big one on one end and a small one on the other. The gear toward the front of the trans is high gear, the one toward the back is low gear. Front being the side with the spur gear.



Remove the low gear and the shift drum from the shaft. Notice that one side of the gear has 2 long slots and the other side has 8 small holes. All the slop comes from the tabs on the shift drum rotating back and forth in the 2 long slots on the gear.





Take a saw or dremel and cut about 1/3 of the tabs off the shift drum. Be careful not to take too much and to make clean and even cuts. The result you want is for the tabs to be small enough to fit cleanly in 2 of the 8 holes on the other side of the gear.



This is roughly where to cut the tabs:



The hard part is done. What you want it to look like:



Now take the output shaft with the shift drum on it and put it in a drill. While running the drill, take a dremel and sand one of the lips on the shift drum down about 2mm.



Now start reassembly. Install high gear onto the output shaft the same way it was, the shift drum with the uncut tabs facing it. Install low gear onto the shaft flipped the opposite direction so that the 8 holes face the shift drum instead of the 2 large slots.



This is how it should look assembled correctly. Notice the size difference in the tabs on the low gear side versus the high gear side.



Install assembly back in case making sure the shims are on the output shaft the same way they were.



Reassemble trans and mount back in your truck. You're done!







Now instead of the tabs rotating back and forth in the 2 large slots on the gear they are locked in any 2 of the 8 small holes.

This mod only takes the slop out of low gear. High gear could be done also by cutting the other set of tabs on the shift drum and flipping high gear over. But, I have seen no need to take the slop out of high gear since it is used for high speed driving.

My truck still shifts perfectly after months of use with this mod. And, it drives so much better when crawling in low gear.

[Grimreeper]

so that is your secret weapon. i am so temped to take the summit trans out and put it in the scaler. i guess i just need to buy another one. great write up.

[Erin]

Nice write up. I'm assuming the narrower tabs havent broken yet? That would be my only concern, but those gears are cheap.

[Cordwood]

Excellent write up. I'm gonna have to give it a try.

[TheROOSTER]

Originally Posted by Erin

Nice write up. I'm assuming the narrower tabs havent broken yet? That would be my only concern, but those gears are cheap.

No they haven't. They might if I was actually using it in a Summit running 4S, but in a scale crawler they are plenty strong.

[SMR 510RR]

Awesome mod and write up! Very clever, my summit trans will get this treatment for sure!

[AdverseCity]

Originally Posted by SMR 510RR

Awesome mod and write up! Very clever, my summit trans will get this treatment for sure!

Same here, that's the one thing I've always hated about the Summit transmission. Thanks for the mod idea and the clear instructions.

[yoda@4x4]

Nice step threw I will be doing this soon to my rig.. Thank you for the right up...

[TheROOSTER]

Your welcome guys!

[FRENCHBLUE72]

excellent WRITE UP THANKS..

[jaytet]

Originally Posted by TheROOSTER

Your welcome guys!

again, thanks, why i didnt search for this months ago....

[TSK]

Can we get a moderator in here to sticky this? This is too good to pass up. Great write up

[OllllO Fanatic]

X2 sticky this mod

[RC tinker]

Hi how about filing in some of the large holes with epoxy ,this way you all so keep the strength of the larger post

[RC tinker]

And buy the way it is a very good write up ,very easy to follow

[darkangelv24]

ooo a new part to my christmas project modifying my summit trans.

[RcSummitVXL]

Originally Posted by darkangelv24

ooo a new part to my christmas project modifying my summit trans.

Wow you were 5 minutes away from posting 12/12/12 12:12!

This is definitely worth a try. I'm guessing you would only have to replace two parts if it doesn't work and you have to go back to stock.

[TheROOSTER]

Thanks for the feedback fellas and yes, only 2 parts are modified if you want to change it back.

[RMK]

Excellent write up. How well does it engagethat gear when you do shift now that most of the slop is gone?

[crawl-o-matic]

This is THE definitive work on the subject...very nice!