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Old 06-23-2008, 06:32 AM   #1
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Default Kyosho ST-RR Diffs

I was wondering if anyone out there is smoking diff gears on their ST-RR's?

I am really getting bummed out, and broke from buying gears at every race.

My latest attempt were Hot Bodies gears. They worked for awhile, but gave during a 45 minute main.

Any tips or advise on what has been working for you would be great.

Thanks
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Old 06-23-2008, 07:40 AM   #2
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You have to shim them, I'v had mine for about 3 mouths an only had to shim it one time. just shim tight.
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Old 06-23-2008, 07:41 AM   #3
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They need to be shimmed such that they are notchy when new. They will break in and smooth out.
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Old 06-23-2008, 07:47 AM   #4
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Default ST-RR Diffs

I feel that I have them shimmed correctly. 2 right now. I am afraid to shim any more as the diff doesnt feel like it moves free. Thanks for the input.
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Old 06-23-2008, 08:41 AM   #5
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Quote:
Originally Posted by mxtoeknee View Post
I feel that I have them shimmed correctly. 2 right now. I am afraid to shim any more as the diff doesnt feel like it moves free. Thanks for the input.
Like the guy said below. You HAVE to shim them to the point where they are notchy, I learned the hard way. I know I have more than two shims in mine.

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Old 06-23-2008, 08:38 PM   #6
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YOU ARE NOT THE ONLY ONE WHO IS HAVING DIFF PROBLEMS THERE IS MORE OF A PROBLEM THEN JUST SHIMS YES YOU CAN PROLONG THE GEARS IF SHIMED CORRECTLY I HAVE TWO TRUGGIES AND I HAVE REPLACED AT LEAST 6 RING GEARS AND PINIONS IN THE LAST 2 TO 3 MONTHS I HAVE TRIED EVERY WAY TO SHIM THEM AND STILL DAMAGE RING GEAR EVERY RACE OR TWO IT WOULD HAVE TO HAVE SOMETHING WRONG WITH DIFF CASE MATERIAL OR THE MATERIAL THE GEARS ARE MADE OF.LOVE THE WAY THE TRUGGIES HANDLE BUT I AM LIKE YOU DONT KNOW IF I CAN AFFORD TO RUN THEM MUCH LONGER I WISH THEY WOULD TRY TO IMPROVE SOMETHING BECAUSE THEY KNOW THERE IS A PROBLEM LOOK AT HOW MANY TIMES DIFFS HAS GOT LUTZ
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Old 06-23-2008, 09:31 PM   #7
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Wow! I thought they had fixed all teh diff gear problems and I was almost kinda considering a ST-RR until this thread
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Old 06-24-2008, 12:12 AM   #8
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i decided to use the msr 72 tooth center spur, and buggy ring and pinions to keep from stripping out gears. i had to use huge blocks under the diff mount and throttle servo. as well as a different brake plate but so far so good. all from msr. i was thinking that it keeps some of the torque out of the diff case, and makes the whole ratio change at the center. lower cg vs $$$ and dnf's. any mechanic thats rebuilt a 1/1 rearend knows how important it is to shim it properly but no where does it say to shim it till it binds.
you shim the pinion till it rides in the center of the ring gear then you shim the ring gear for back lash or slop. in the st-rr's case shim the ring gear side until there is minimal slop between the ring and pinion. but you end up with the mysterious cvd pop at full suspension compression due to offset diffs.
good luck.
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Old 06-24-2008, 04:54 AM   #9
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I had the ST-R and now an ST-RR. I've got over a gallon on my ST-RR and my buddy has over 2 gallons on his with ZERO diff issues.

What I learned from my first ST-R where I only blew only one ring and pinion was that it wasn't only correct shimming, but ensuring the chassis wasn't "over-flexing".

I noticed that with the stock rear chassis brace, that over time the plastic ball-end would "stretch" allowing the chassis to over-flex lengthwise. This would momentarily jam the ring and pinion into the diff gear.

On my ST-R, I went with the KH rear brace and only used one screw on the chassis to allow it to flex laterally but not longitudely. After that, never had a problem with diff gears...

On my ST-RR, I just check the plastic ball-end on the rear brace. So far haven't had to change it....
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Old 06-24-2008, 06:17 AM   #10
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I don't think this was mentioned yet, but if you built your truck new or replaced the diff housing then you will need to check your shim job after the first race day. You will need to add more shims as they tend to get loose.

When I built the truck I used 2 shims and my diff was nice and tight. After 1 race day I had to add 2 more shims to make it tight again. So far my diffs have remained tight after the initial re-shimming.

A friend of mine had to add 1 extra shim after his 2nd run.

So you really need to check there is no slop in the diffs after each race day.

Also change the plastic ball end for the chassis braces like bushyar15 said, they stretch out rather quickly and are cheap to replace.
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Old 06-24-2008, 08:19 AM   #11
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Quote:
Originally Posted by too fast 55 View Post
YOU ARE NOT THE ONLY ONE WHO IS HAVING DIFF PROBLEMS THERE IS MORE OF A PROBLEM THEN JUST SHIMS YES YOU CAN PROLONG THE GEARS IF SHIMED CORRECTLY I HAVE TWO TRUGGIES AND I HAVE REPLACED AT LEAST 6 RING GEARS AND PINIONS IN THE LAST 2 TO 3 MONTHS I HAVE TRIED EVERY WAY TO SHIM THEM AND STILL DAMAGE RING GEAR EVERY RACE OR TWO IT WOULD HAVE TO HAVE SOMETHING WRONG WITH DIFF CASE MATERIAL OR THE MATERIAL THE GEARS ARE MADE OF.LOVE THE WAY THE TRUGGIES HANDLE BUT I AM LIKE YOU DONT KNOW IF I CAN AFFORD TO RUN THEM MUCH LONGER I WISH THEY WOULD TRY TO IMPROVE SOMETHING BECAUSE THEY KNOW THERE IS A PROBLEM LOOK AT HOW MANY TIMES DIFFS HAS GOT LUTZ
I can 100% honestly say that everytime I have had a diff go out it is because I neglected to 'maintain' it for a extended period of time. When I shim it properly (Zero-side to side play) with a slightly notchy finish when new I have had no problems. It is when I don't reshim it after hours of use that it has come back to bite me in the butt on occasion.

Also some people change the screw that they put in through the chassis into the bulkhead. If you put a machined screw up through the chassis then you must use a 4x15 size and not a 4x20. If you use a 4x20 you will create flashing inside the diff case. That flashing can either tear off or get caught in your gears and destroy everything in the gear box.
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Old 06-24-2008, 08:22 AM   #12
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4th gal now on my truck. used to have this problem with my ST-R
till the day my LHS tells me that it could be due to the bulk heads tends to "open ups" w/o u realising it, thru impacts of hard landings or heat generated from inside the bulk head....u'll never know...
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Old 06-24-2008, 08:28 AM   #13
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hope this may help. supplementary instructions regarding shimming from Kyosho. i shimmed mine with reference to this copy.
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Kyosho ST-RR Diffs-shimkyoshosupp.jpg  
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Old 06-24-2008, 11:20 AM   #14
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Default ST-RR Diffs

Hey guys,

All good stuff! Thanks. I am a maintenance freak. I want to go to races and not have to worry about my equipment being 100%. I see where I am going wrong. I was shimming for smooth movement. At this point I am going to grab a wad of shims and get to work. IF I still have problems, I will send the truck packing. Its not like I am a team Driver, this is getting expensive and effecting my results in becoming a sponsored. I think the most frustrating part about ALL of this, is that the truck is so unbelievably good, but if it is not durable, it is no good to me. Thanks again!
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Old 06-24-2008, 11:45 AM   #15
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once you reshim you should be good to go!!
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