GPM diff gears

[Savage030]

Posted this a while back on one18th so might be old news but GPM released their diff gears for the mlst and the few that have them so far are punishing them and their holding up well so far! Our prayers might have finally been answered, once again thanks losi for sticking it to us all that rushed to buy one just cause it was a losi product and we wouldnt have doubted someone like losi...boy were we stupid.
Almost a year later it took GPM to save this truck cause I was just about to unload it on ebay and buy a AE rig or something else.

In yellow now also! lol
http://img.photobucket.com/albums/v187/savage03/Mini%20LST/GPM/ml65.jpg

[carmatic]

ok lets continue the discussion of these gears over here....

ive got one of them put together (put fullforce rc ball bearings and stock outdrives on) , and the spider gears are very very grindy.... they wont even spin smoothly, im worried that if i run the truck like this im gonna melt the spider gears or something....

did the same thing happen to any of you guys? i was hoping that this new gear and the new bearings will sort out that veering to the left problem i was having....

[Natedog]

That 'grindy' is just some very nice and tight spider gears...break em in gently with some figure eights and easy driving...just like new built 1/8th scale diffs. Good grease is essential. I'm so glad that GPM is finally making these diff gears!

[Savage030]

Yea Nate was over last night and checked out my newly installed gears and we commented on the tightness of the gears. They have a bump sorta feeling as you turn them but like Nate said I think some very easy running at first so tehy can get seated and broke in. Might be the cause of some of the breakage reports. Also watch that pinion screw, you can easily overtighten the screw and split that pinion.
The plan is me and Nate will take our trucks out tomorrow afternoon and I will get a chance to see how these gears work out.

[carmatic]

yeah but its so tight to the point where the sides of the diff gear which holds the screws wont go in properly, before the drivecups were installed they sat flush with the rest of the gear but now theyre sorta sticking out... as the gears are worn in wont they sort of get thinner and i have to open my truck up to tighten this part of the gear in...

[Savage030]

Oh, are you using stock cases or GPM cases? Stock cases wont work without trimming the back of the pinion, its better to just use gpm cases imho, less flex and stripping of the screws.

[carmatic]

no not the case, the diff itself, like the ring gear.... you know where the outdrives actually attach to? those parts wont go in all the way into the ring gear, they stick out abit

[Savage030]

Go here, I have info about the case posted there, I had it at one18th but we all know that deal.
http://www.rebelrc.com/forums/showthread.php?t=895

Ah posted same time, hmm not sure whats the deal with yours...take it apart and double check everything closely, no burs and whatnot. I'm super tired so I;m not thinking real clear, lol.

[carmatic]

I'm super tired so I;m not thinking real clear, lol.oh boy its almost 7am here, i gotta kick this habit of being nocturnal... like yeah i took it apart again and again, everything checks out, it seems to only be a problem when the drivecups are installed, i dunnoe maybe the position of the hole of the drivecups dont match up to what gpm was designing their gears to, theres only one way to find out if this things gonna break on me or not...

im also gonna buy a ball diff, that would spell the end to any accelerate steer problems caused by the diff...

[Savage030]

What drivecups are you trying to use? I have a new set of stock Losi ones in the rear and I bought a set of the GPM alloy ones for the front and did'nt have any issues but could be a freak thing. Got another set to try? The diff itself once its screwed together is nice and tight ? Just tossing things out there...

[Natedog]

Yeah as Savage said, I'd take it apart and double check everything...his went together real nice.

Carmatic...7am??!??!! Dude you're worse than me...lol!

[carmatic]

something else's up... when i put the pinion gear in, theres a massive slop, and im already using the gpm gearboxes.... so yeah i think im just unlucky or something

my idea of slop is that when the ring gear and pinion gear is installed and the gearbox is put together, you can pull and push at the center drivecup because theres space in front and behind of the pinion gear...

the square bit that holds the ball bearing and the drivecup and the outdrive gear sticks out abit, but its half of the screwholes seem to sit flush with the other half of the screwhole that is on the ring gear... im not sure if its how i damaged it when i tried to screw it in, or it came from the factory this way....

ok, shimmed the pinion gear (1X losi jrx-s 4mm shim) , and the ring gear feels decidedly.... oval.... you turn at the center drivecup, and it feels tight-loose-tight-loose-tight .... good thing ive got a 3racing ball diff coming my way, im definitely keeping the pinion gears from the 2 gpm gearsets i got just cuz everyone seems to like them so much, i'll just have to see how sweet a ball diff + gpm pinion will actually be...

[Natedog]

Carmatic, A pic or two would help us to help you. :D Yesterday when Savage and I ran our trucks, he split a GPM pinion right away...we're not sure why...maybe the screw was too tight, maybe the plastic, maybe the fit of the pinion on the input drive drive cup.

We put a stock Losi pinion on the MIP center dogbone input in place of the split GPM pinion. At first it seemed that the pinion wasn't going on the MIP input piece all the way, so I shaved the little ridge off back of the pinion with a knife...this made it worse. :D LOL...

Because I trimmed the back of the pinion, we had to shim it with about 1.25mm behind the pinion which was a little tight on the pinion bearings...but otherwise it was very loose and I could pull the pinion input in and out quite a bit. 1.0mm would have been about right if I hadn't shaved the back of the pinion. Since we didn't have any other shim combo with us and nothing to lose, we tried it. :p It held up just fine for the rest of our bashing...don't remember how many batteries we put through this particular truck though. The rear GPM was not a problem though...and the GPM rear pinion held fine.

Maybe Savage030 will chime in as I don't recall the number of battery packs and we finished up late last night. BTW, another fun afternoon of running.

[Savage030]

Heh yea a pic is worth a thousand words....
I got 2 lipo packs ran through the truck after the pinion split and no issues for those 2 packs, so I'm lost as to why it split. It will be interesting to see what MIP has in the works also and the rumors of metal gears being made by 3R or GPM...
http://img.photobucket.com/albums/v187/savage03/Mini%20LST/99e6df70.jpg

[alfred]

I wanted to get a MLST but did'nt because of the gear problems, now im thinking of getting one since theres better gears and now a balldiff out for it.:D

[carmatic]

well just had a little run on the mlst, and the front diffs are working smooth as silk now, it doesnt grind anymore...

check to see if you can push the outdrive around sideways, thats what i found was happening with my b&s pinion in the rear, so i tightened it down and it fits snugly now.... the pinion gear was being pushed sideways when im accelerating hard or braking hard, and it caused the gears to skip and make a barking sound, maybe if the pinion was a gpm pinion (b&s gears have a different mesh to all other gears) it would result in a split pinion

[carmatic]

ok i have a strange new problem with the gpm gears up my front... at first i wasted my center mini t mip ball diff, then when i installed the mini lst version of the ball diff, it still behaved like the ball diff was slipping , like the spur gear shaft is spinning but the outdrives underneath the spur gear arent... well, at least the rearward center outdrive wasnt spinning....but i didnt spot that straight away

when i was trying to tighten my new mlst ball diff, the screw side was at the rear (so the rear has to stay still) and the nut side was at the front, so when i turned the front wheels to tighten the diff it felt like it was doing something,it felt like it was driving a screw against a nut, but when i looked closely the front center dogbone wasnt even spinning , i thought to myself huh? the diff action was still there, and turning the center outdrive turns the front wheels, but turning the front wheels does not turn the center drivecup when theres something pushing against it (like a ball diff being tightened),i couldnt tell if a tooth was definitely missing from the pinion or not, or if anything has broken ...i put the mini lst on my table so i could get a close look at it, held it down tight and apply throttle and the gpm gears slip under torque, the only thing that moved on my truck was the center tranny gears and the front center dogbone... now i dont know whats causing this to happen, it makes no sense to me at all , like the pinion gear is slotted onto the center drivecup and held there by a screw, it drives the ring gear, which is fixed to the spider gears, which seem to mesh properly with the side gears, which are fixed to the left and right outdrives by hingepins.... somewhere along the way , something's come loose, when i put power thru the drivetrain its just leaking thru the front diff...i'll have to open it up tomorrow, cuz its tomorrow already (5am) and im sleepy

ok opened the front gearbox up, and im greeted with this sight...
http://img179.imageshack.us/img179/3350/dsc05296zw0.th.jpg (http://img179.imageshack.us/my.php?image=dsc05296zw0.jpg)
hmm, doesnt look that bad, but on closer inspection
http://img179.imageshack.us/img179/155/dsc05306ah1.th.jpg (http://img179.imageshack.us/my.php?image=dsc05306ah1.jpg)
hmm it cant be, can it?

http://img183.imageshack.us/img183/3388/dsc05308ln2.th.jpg (http://img183.imageshack.us/my.php?image=dsc05308ln2.jpg)
oh well looks like it is a problem with the gpm gears after all....

this is the pinion gear on its own http://img161.imageshack.us/img161/6772/dsc05321ce5.th.jpg (http://img161.imageshack.us/my.php?image=dsc05321ce5.jpg)
you can see from this picture
http://img179.imageshack.us/img179/9708/dsc05320aw8.th.jpg (http://img179.imageshack.us/my.php?image=dsc05320aw8.jpg) that the socket of the gpm pinion is a weak point , as compared to the teeth on the stock gears... perhaps , shimming these gears will be a bad idea because the force of the shaft it sits on is concentrated on a smaller area and increasing the likelyhood of the the plastic around the socket splitting like this

[carmatic]

ok these gears are just a joke... took out the old split pinion, put in a new one, gave it some gas, yay my mini lst can almost wheelie with a ball diff! did it again , ooh thats fast... gas it one more time, and the front pinion starts slipping....the ball diff may be tight enough for a quick start but with a totally unloaded side of the drivetrain it still diffs out and merely pushes the truck around at a snails pace... i dont know what im doing wrong at this point, personally these gears are the most overhyped item ive ever bought , ever....they failed on me within 10 seconds of another rebuild of my truck, at least with the stock pinions this doesnt happen! ive been running that one single stock pinion at the front for who knows how long already and not a single problem... now i have to wait for a few hours for the epoxy to set before i open up my gearbox again, i dont know what im going to replace the gpm pinion with...... oh i forgot to mention, those screwholes in the gpm gearboxes strip out, man now i have first hand experience of just how $h177y gpm really are.... i coat the screws with epoxy before putting them in, the epoxy sets to a plasticy substance but isnt strong enough to hold the screw a-la threadlock ,and it ends up coating the walls of the screwhole so i have 'freshly threaded' screwholes to work with once it dries up...

[Savage030]

Send your pics and issues to GPM, should here back from Clara. Man I will be ticked if my cases strip!

[carmatic]

well i hope it doesnt strip for you, but my hopes are slim... i was about to buy new gearboxes but i thought i could just fill in the screwholes with epoxy instead and keep on using them that way, hopefully nothing goes wrong like this (i.e. the screws get epoxied in permenantly)

ive just sent an email to chinngai@netvigator.com , with a link to one of the pictures , i dont know how this is gonna help tho...

back to stock pinions it is then, i guess... these gpm gears were exciting up to the point when i actually ran the truck

[Savage030]

I may replace my screws with longer ones if they will fit and use a grade better screw.

[alfred]

it seems to me that there are still issues with the diffs.....i was really hoping it was resolved, maybe in a couple of months when someone decides to make them in aluminum or steel.:rolleyes:

[carmatic]

I may replace my screws with longer ones if they will fit and use a grade better screw.

get the rcscrewz screws, they are the exact same screws on the gearboxes except they are the correct length

only the screwholes holding the shock tower and the front skidplate have stripped, the screwholes holding the bulkhead seems to be OK... i think they stripped because the gearbox has suffered a couple of collisions and those screws are in the direct path of the shock

well, the epoxy has dried and the screws came out like they were screwed into tight plastic...the epoxy i used was Araldite, by the way...personally i think its a good idea to coat screwholes in metallic components with epoxy, it forms a barrier between the 2 metals...when it sets its like plastic, so hopefully its as if a plastic screw was used in the metallic screwhole, or the metallic screw was used inside a plastic screwhole, and both of them last much longer...

[Savage030]

Well hope you can get it sorted out, Im waiting for a few parts for mine. I ordered one of those T bone bumpers, HR slipper disks, mip lightweight top gear shaft, something else but I cant remember. I decided to go back to the original slipper only with the hR disks and pads, I couldnt get the stock gear cover on with the mini T dual slipper and when I got home I noticed my spur was getting chewed up.

[carmatic]

yes the 60t spur gear and the shaft is too big to fit into the gear cover... but if you have a rotary grinding and drilling tool its easy to fix, all it takes is a hole for the shaft to go thru, and the spur gear does actually fit under the gear cover if you made the areas where it touched thinner... the same goes for the pinion gear now that you pushed it further to the side, some areas will be razor thin and there will be almost nothing left of the original thickness, but the gear cover doesnt get exposed to alot of wear and its function for me seems to be to protect your wiring from being chewed up by the gears....

i have opened up the gearbox and had a look at the pinion gear... this one isnt cracked, but there are alot of blue plastic filings all around the shaft.... when i took it off it slid right off, and what i find at the back is just a round hole with 2 smooth sections where the round edges of the slot originally were... hmm if i applied some epoxy to stick the gear firmly onto the shaft as well....

[Savage030]

lol your havin fun with that epoxy heh...

Yea I tried that with my gearcover and I kinda sanded to much and it went through the plastic, since theirs a real slipper setup for the stock gear I will just go back to that, only reason I switched was for the slipper pad setup.

Hey Alfred, 52 posts and my avatar has'nt showed up..

[carmatic]

if you only went thru the plastic of the gear cover at a few places (like i did) , then you can use epoxy to cover the holes and thicken up the plastic on the outside