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Old 09-08-2010, 11:31 PM   #1
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Default Losi 8ight-t 2.0 rear diff skipping teeth

Hi. Please forgive me if I use the wrong terms for the parts. I'm not used to the English words for all the parts.

Last time I was at the track with my 8ight 2.0 truggy the rear diff started to skip teeth at the end of the 2 hour session.
I have to explain what happens with the "skip teeth": When I throttle it hard I can hear something really bad, something like two sprockets/gears that don't align right. If I take the car and put it on the starter box and then apply full brake and then grab both back wheels and turn them the same amount I can hear the rear diff crunching.
So I come to the conclusion it is the small gear at the end of the drive shaft that don't hook up enough on the largest gear on the diff.
I'm talking about these two:


After that happened I took the rear diff apart completely and looked for any damage but there was no damage and no excessive wear. I put it back together with new oil (2000) and new fresh grease on the outer gears. I also moved ONE shim from one side to the other so the large gear would get closer to the small gear.

Last evening I was at the track again and everything seemed to work fine until about the 1.5 - 2 hour mark. Then it all started over.
We tested again, my brother held full brake and I grabbed both wheels and I could get the gears to skip.
The front wheels get the same treatment but I can't turn them over unless I want to break something.

Why does this happen and more important, how can I fix it?
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Old 09-09-2010, 03:09 AM   #2
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sounds like it needs more shiming, get some of these for the rear diff i had the same thing going on till i put these in
http://www.amainhobbies.com/product_...ing-Inserts-20
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Old 09-09-2010, 03:25 AM   #3
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Another thing to check is that you diff case isnt warped-which could cause some movement and it then having the play to skip teeth.. but to me sounds like a shim issue of case is creating play..
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Old 09-09-2010, 03:50 AM   #4
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All good information but I would also check the following:
Is the internal diff gears o.k as worn diff inserts can cause the diff case to wobble and cause the diff gears(small planatery gears inside diff) to wear prematurley..just hgappened to a friends buggy EU model and he replaced diff inserts and all good now.
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Old 09-09-2010, 05:36 AM   #5
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Check the two bearings on the diff as well. Anytime a bearing gets sloppy or wears out, it can cause the mesh to seperate and cause your problem.
Several things to check but it's quick and easy. If the gears aren't damaged, use them again.
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Old 09-09-2010, 10:00 AM   #6
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The best thing to do is replace the ring and pinion gear, diff inserts and bulkhead once the diff starts to skip it stretches the bulkhead, sometimes you can fix the problem with more shimming but it's better to replace the parts if it has been doing it for a while
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Old 09-09-2010, 10:26 AM   #7
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replace plastic bearing holders with alum..... replace diff case, check bearings.. reshim..
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Old 09-09-2010, 11:30 AM   #8
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I really listen to you and I will check everything once again.
I will move some more shims from one side to the other.
But how would the diff feel when I turn it by hand? Should it move absolutely free without ANY resistance or is a little resistance OK.
I will also swap out the bearings in the diff case.
The internals of the actual diff is in excellent condition.

This diff has not yet reached 2 gallons.
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Old 09-09-2010, 12:10 PM   #9
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No more time than is on the diff, I wouldn't worry about replacing the gears unless the teeth are wore bad. I would re-shim and try it. I haven't shimmed any diffs for 2 years but I'm running the D8T. I hear several Losi's clicking and clacking from the drivers stand.

I wouldn't buy anymore than I had to at first. It's senseless and expensive. I would shim it tight and apply grease. It should mesh in fine.
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Old 09-10-2010, 06:43 AM   #10
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I had this problem on my Mugen MBX6T and it turned out to be my pinion having a bit of play moving in and out of the gearbox. I don't know how the Losi's connects to the CVD, but mine was with a set screw that I loosened, pushed the pinion back into it and tightened again. It happened on both the rear and front. I bought it used and the rear was so bad that it ground two teeth down that was causing an intermittent popping sound. I did shim it at the same time that I did all the other repairs/fixes as well.
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Old 09-10-2010, 07:01 AM   #11
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I had the same problem when the truck just came out, and continued to have the problem during my whole summer race season, the diff would not last more than two weekends, and it's because I would only replace one thing at a time, later on, I realized and after doing some research, that only answer to my problem, was to change all the parts needed at the same time, and shim it properly and them reshim after a couple of gallons:

This is what solved my problem, and have been running a couple of years without anymore diff issues:

Replace:

Gearbox

Flanged bearings

Swapped plastic inserts for aluminum inserts

Ring and pinion gear

Shimmed enough to have a gritty diff (no problem because gears will wear in)

With time reshim, because:

1) gears wear, and more slop

2) gearbox wear and creats slop in the inserts


*********Don't forget that the rear center CVD must be pushed all the way back on the gearbox bearing, absolutly no play should exist!!!!******

Hope this helps......
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Old 09-10-2010, 11:26 AM   #12
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First off guys, THANKS!
This means a lot to me, that you help out.
I was totally lost for a while but you got me back on track and I think I have figured it out.
I want you to take a look at something for me.
I took the rear apart and made this little short clip so you could perhaps tell what parts I need to replace.

http://www.youtube.com
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Old 09-10-2010, 12:07 PM   #13
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I don't own a Losi but first of:

There shouldn't be any forward/backward play on the pinion, so resolve that by loosening the cvd and push it up the pinion and fasten again - maybe the pinionbearings needs replacing aswell.

The diff itself seems far too loose in the diffcase aswell. Maybe the bearings are shot or the plastic bearing holders and case are worn out...maybe all 3. Aren't there alu bearing holders available from Losi? I would suggest to get those. Anyway i think other Losi 2.0T owners can probably help you a lot better (hands on experience with the car).
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Old 09-11-2010, 05:30 AM   #14
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can anyone tell me if the 8ight t 2.0 rtr comes with grease or oil in the diffs,also what is the best setup for diff oil,what about 7000wt in front,5000wt in centre and 2000wt in rear,thanks guys...........
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Old 09-11-2010, 09:29 AM   #15
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Quote:
Originally Posted by jon9e View Post
can anyone tell me if the 8ight t 2.0 rtr comes with grease or oil in the diffs,also what is the best setup for diff oil,what about 7000wt in front,5000wt in centre and 2000wt in rear,thanks guys...........
Thats the standard setup for buggy and truggy. Seems to work good based on the setup guides i've seen so far. I heard the rtr comes with grease, so i'm in the process of clearing those out and filling with oil. I did the rear last night and will work on the center and front today. I'm also in the process of replacing all the bearings, which imo is money well spent. For $24 you can get a complete set of avid revolution bearings for the 8b or 8t. Never hurts to change those out at the same time you refill the diffs.
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