Differential Distress

[Zaytri]

I have a nice HPI nitro MT.

Then, I bought and put in an OS .18 CVRX

I broke it in, started to tune it for some power :boxing:

Then the rear differential stripped DEAD on the 3rd run with some power

Shimmed the diff, stripped again 3/4 into the next run.

Trip to the LHS, complete differential rebuild with new plastic, gears, everything except the bearings. x alot

Around the 5th tankon new diff, stripped AGAIN! :arrr:

Shimmed it AGAIN! 2 tanks later... Click click click :argue:

Trip to the LHS, purchased HPI's heavy duty final gear for 3$ and that too stripped.. albeit after 9 tanks.. but I'm to the point where I can't keep spending money to replace these damn diffs!

Does anyone have any advice? Or know of a 3rd party company that fabricates gears for this particular car? I'm afraid to know what would have happed if i put the .18TM into the truck.. almost did :hammer:

Thanks in advance! <did a search.. and found the info on shimming and general diff maintenance.. couldnt find anything on diff hopups for this car though>

 

[FastEddy]

I would first ask myself why they are striping. Yes the parts are made of plastic but should hold up much better then that. When gears mesh together properly they become strong. I find it hard to believe that your putting out so much power that its flat out just destroying gears.

This is one of those times where your going to have to think and re-think about whats going on. Throw some brain power at it rather then money. If you can, please post a detailed photo of BOTH gears involved. It would help for us to see all the gears that have blown out as well.

Sometimes issues like this aren't even gear related. Mounting brackets, loose screws, broken or tweaked gear housings, and even bent chassis can cause this to happen.

Is this the dif?
http://www.hpiracing.com/graphics/instr/nmt2/MT2_16.jpg

 

[beason]

maby shim befor your run ??

 

[Zaytri]

Thanks for the reply

Gears are actually metal, not plastic, in the diff. I replaced all the screws and the differential case and the metal parts that the dog bones go into <can't think of the name of the part at the moment>. I didnt replace the chassis, didnt think that would cause this problem. Ill post photos of the gears when I get home tonight. Thanks again for the advice!

Do you think putting in a slipper spur instead of the stock spur would put less stress on the drivetrain?

That link is esentially the diff, i have the MT1 not the MT2.. It's page 7 on the instructions at the HPI website. I dont have access at work to copy links

I would first ask myself why they are striping. Yes the parts are made of plastic but should hold up much better then that. When gears mesh together properly they become strong. I find it hard to believe that your putting out so much power that its flat out just destroying gears.

This is one of those times where your going to have to think and re-think about whats going on. Throw some brain power at it rather then money. If you can, please post a detailed photo of BOTH gears involved. It would help for us to see all the gears that have blown out as well.

Sometimes issues like this aren't even gear related. Mounting brackets, loose screws, broken or tweaked gear housings, and even bent chassis can cause this to happen.

maby shim befor your run ??

I have it shimmed. If I add anymore shims, I wont be able to put the satan-clip on the gears to hold them in place.

 

[FastEddy]

Your stripping the METAL gears?

Are the tips of the gears rounding off?
If so, you need to shim it so you make the two gears closer together. There should only be a itsy bitsy amount of play in the mesh.

You are doing something terribly wrong we just need to find out what it is.

 

[.21Rc10GT]

Yeah, something is wrong... The gears shouldnt strip like that... I really dont know much about the vehicle, but, i know that the engine you are running doesn't put out enough power to destroy a well shimmed diff...

 

[Zaytri]

Yes, they are rounding off. I went to HPI's website and did exactly what it said to do in the added notes at http://www.hpiracing.com/graphics/instr/nmt/mtdiff.jpg

I think that's the only place I can shim that will help. It's really pissing me off that they are stripping. The bottom of the chassis is pretty beat up, could it be that I landed a bad jump and bent the chassis to the point of it messing up the drivetrain?

The only other thing I can think of is that maybe the bearings are not smooth enough on the diff and possibly at the tires, causing extra resistance and stress on the diff itself.. Any other ideas?

I bought another set of diff gears tonight, the standard 5$ ones. I'm gonna rebuild the whole diff again tomorrow, re-shim it, and check to see if there is any play in the diff.

Thanks for the advice!

Your stripping the METAL gears?

Are the tips of the gears rounding off?
If so, you need to shim it so you make the two gears closer together. There should only be a itsy bitsy amount of play in the mesh.

You are doing something terribly wrong we just need to find out what it is.

 

[FastEddy]

If your rounding off the tips its 99% shimming issues.
Take your time. Look, think, look, think, shim, look.....
You will get it right.

 

[Doggie]

Do you think putting in a slipper spur instead of the stock spur would put less stress on the drivetrain?

Absolutely. Get the slipper clutch set for NMT2 for about $12 (comes with 52T spur).
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFYP4&P=7
It drops right in to NMT1, despite the warning from tower hobbies.
You have to take it apart and clean it periodically though. The slipper plates tend to get stuck together after a while.

I have OS 15CVRX on my NMT1 with std. gears and NMT2 slipper clutch. It's doing fine, but the people with NMT2 18SS (with HD gears as standard) have been stripping their diffs front and back. I'm guessing that they set the slipper clutches too tight, because some people have done .21 conversions and they held up.

The heavy duty final gears should cost heaps more than $3. Are these the ones you got?
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTB54&P=7
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTB55&P=M

Or did you strip the bevel gears?
Anyways, try the slipper clutch and see.

 

[Zaytri]

Ok, after about an hour or two of studying the drivetain, i came to the conclusion that my lower arm brace, and the rear end of the chassis were slightly warped. I also found out that one of the bearings on the diff was a little tight. Lo and behold, after taking a pair of pliers to the chassis and replacing the lower arm brace and bearing, the diff seems to be holding up so far.

Thanks alot for all the advice!

Absolutely. Get the slipper clutch set for NMT2 for about $12 (comes with 52T spur).
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFYP4&P=7
It drops right in to NMT1, despite the warning from tower hobbies.
You have to take it apart and clean it periodically though. The slipper plates tend to get stuck together after a while.

I have OS 15CVRX on my NMT1 with std. gears and NMT2 slipper clutch. It's doing fine, but the people with NMT2 18SS (with HD gears as standard) have been stripping their diffs front and back. I'm guessing that they set the slipper clutches too tight, because some people have done .21 conversions and they held up.

The heavy duty final gears should cost heaps more than $3. Are these the ones you got?
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTB54&P=7
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXTB55&P=M

Or did you strip the bevel gears?
Anyways, try the slipper clutch and see.

 

[rbmaxxbasher]

try MIPs they are a whole lot stronger.