Pumilio Design gear differential for TRF501/511 and DB01/DB01R

[Jan Larsen]

I've just taken delivery of a set of these. They're assembled from the manufacturer and filled with 5000 front and 2000 rear Ultimate oil. Their journey from Finland to Denmark did not present any leak problems. Bearings are included. No manual, so you're a bit on your own if it comes to disassembly, but if you have ever build geardiffs before, you should have no problem.
The diffs will be tested this weekend as they were delivered. The test will be on a fairly bumpy high grip carpet track - basically the biggest punishment possible. The track is known for killing off rear (ball)diffs due to several fast, on-power corners, so this will be a good test I reckon.

[mof]

I've got zero leaks so far after a couple of weeks runtime with the diffs. I have Ultimate Racing 5000 oils front and 1000 rear, seems to work fine so far

Compared to my previous setup (front one-way and a ball diff rear) I am able to drive the cars a lot more aggressively and have a lot more control over the car in the air. I realize, of course, that this partly (even mostly) due to having a front diff instead of one-way. Anyway, I have messed up zero jumps with these, which is nice.

[Jan Larsen]

Installation went without a hitch in my 511. No custom filing/dremeling needed. No shimming needed either which was a surprise. They feel great in the car but only time will tell if they perform aswell.

[Jan Larsen]

Right, first test drive completed. 12 packs of 8 minutes each, so about 1,5 hours worth of driving. And it went a bit like I expected...somewhat.

Good: Durability - These things will last a good while, but not forever (read further down to see why), awesome forward traction, consistency (wont burn out or readjust ifself like ball diffs). Apparently easy on driveshafts aswell, but I did swap the lot for new ones before the test and they showed no wear.
Drive feel was almost excatly like ball diffs, except for the forward drive. The included oils were spot on for the track (high grip carpet). 5000 front, 2000 rear.

Bad: Hard on belts if slipper isnt adjusted just right. First lap, first bit of hard braking and the horrible noise of belt skipping presented itself. Had to tighten the belt one notch. The belt is fairly new and the pulley is obviously all new, so it wasnt a wear problem. Nothing under acceleration.

Did they leak? Well.......yes. They did leak. I noticed about what seemed like half a drop(ish) of fluid on the rear diff outdrives and about the same on the front. The front I left unchanged (for comparison reasons), but the rear I decided to take apart to check its internals and see if I could fix the problem. The internals are just like any other geardiff, so nothing new in that compartment. One thing worth noting here - the spider gears does come in contact with the case, causing some rotating marks. Whether that'll mean anything in the future, I dont know. Time will tell.
I also noted a large amount of play from the outdrives when tugging it when the diff is assembled. This struck me as odd and could be contributing to the leaking.
Took it apart and put a 5x7x0.5mm Schumacher spacer in between the bearing and the o-ring to compress the o-ring a little further and also to bring the crown gear closer the spider gears. This didnt cure the problem, but it sure helped. The diff felt notchy as I reassembled it, but the slop was well and truely gone. Was a little worried about going overboard with the fairly thick spacer, but 11 packs later and the action is now smooth, so it was just a matter of breaking it in. The leaking hasnt been completely stopped but only a very small amount was found under the bearings. Something like a quarter of a drop. I can live with that. The bottom of the car is bone dry. So is the front of the car, despite the heavier amount of leaking. I estimate about 2 drops excaped from the front diff which was left completely unattended throughout the day.
The front diff will need the same solution as the rear, but I ran out of spacers (needed 4, found 3...obviously) so that'll have to wait.

So, are they worth the price? Considering the leaking and play in the outdrives, no. Slash 20-30€ off it, then yes, absolutely.
I'll be using them instead of the ball diffs, but I'll keep the ball diffs for loose surfaces since I have my doubts about geardiffs and slippy surfaces.



No oil on the chassis.

[mof]

Great to have some feedback and tips from more experienced drivers than myself.

PS. I hope you will at least try out the diffs on loose surface and see how they perform, and not just install the ball diffs without even trying the gear diffs out?

[Jan Larsen]

Of course. Trouble is though; we dont have any tracks that can be considered slippery, they're all carpet tracks.
I'm hoping to get a spot for the worlds in Finland next year. If so, then I'll try them out on dirt/clay, but until then, no.

[DaveG28]

I could almost get tempted by these but does anyone know if:

a) there is an instruction manual/exploded diagram available

b) can the individual gears/pulleys be bought separately for maintenance?

[mole2k]

I would be quite tempted by these although does anybody know how they would perform on low grip polished wood with shallow wooden jumps?

I also run the car on very high grip smooth astroturf and carpet jumps. Would you need a different oil in the diffs for this surface or would you get away with using the one set of oil. (currently running rear ball diff and one way front)

[Jan Larsen]

Dave: No manual/exploding diagram, but they're not rocket science. If you have build geardiffs before, you'll know what to do.

Parts should be available seperately, but I dont see any need for them in the near future. My pulleys on my ball diffs are 1,5 years old and still not worn. The gears are Xray NT1 gears which can be bought everywhere.

Mole: The standard oil works just fine on high grip carpet. I use it and drive the same laptimes as with ball diffs.
A video like you search for is posted on page 1 or 2 in this thread.

[mof]

Originally Posted by mole2k

I would be quite tempted by these although does anybody know how they would perform on low grip polished wood with shallow wooden jumps?

The video I posted earlier is of a very low grip track, and the car is a DB01R with 5000 oils in front diff and 1000 rear.

[mof]

Originally Posted by DaveG28

I could almost get tempted by these but does anyone know if:

a) there is an instruction manual/exploded diagram available

b) can the individual gears/pulleys be bought separately for maintenance?

a) No, since it is a custom product, but the diffs are very simple. If you were to change the pulley, though, you need to be carefull when tightening the new one so you won't bend the aluminium ring that presses on to the pulley (I am not talking about the big blue part, but there is a smaller/thinner ring on the inside), and make sure that the screws stay correctly on the threads as the thread is quite open.

b) As Jan already said, the gears are from an Xray NT1. The pulleys are standard Tamiya ones but custom machined (the center hole has been opened quite a bit). The pulley, if you would need a new one, could be customized at home or your workplace etc if you have proper tools for it, or you can of course buy a spare with the diffs.

[mof]

A slight update. The increased strain on the rear belt is starting to show, I need to replace the belt and possibly center pulley for the rear belt too, remains to be seen. Are there aluminium center pulleys available?

Other than that, the diffs are still working nicely. Only a small amount of leaking that I can live with. The chassis remains dry and clean so no issues there. I've changed to 3000/1000 oils for our track (I used to have 5000/1000), seems to work fine for me at least.

[Jan Larsen]

Finally got a chance to testfit one of these in a TRF416. Its not a drop in fit, but the modification required is actually very easy. All you have to do is put approx 1,5mm of diffspacers on each side between the diff and diffbearings. Very simple to do and it will work.

Also, as mof, I've had to replace the rear belt and center pulley recently. Both were about 6 months old.

[marco NL]

hey guys

someone has already tried a spec-r diff to make it fit for 511

or is it not possible ???


Thanks marco

[simoncrabb]

Noooo, don't buy gear diffs. Buy Lazy Balls! Put food on our table!

Actually, I love the durango gear diffs, one less thing to think about on race day.

[marco NL]

hi

I've been using Ceramic Diff Balls

[_valtsu_]

Originally Posted by marco NL

hey guys

someone has already tried a spec-r diff to make it fit for 511

or is it not possible ???


Thanks marco

It is possible, but it's not so easy. Pictures are from my car.

Front:

Outdrives are made from these.

Rear:

[marco NL]

yo mate

Thanks mate for the pictures

do you have more details what jou must change

and a part list what i need

Thanks marco

[_valtsu_]

I'll try some day, when I have more time.

[MHeadling]

Discostu on here ran the gear spec r diffs in his 501, they lasted about 2 weeks, they were only running on 13.5 motors indoors.

I would steer clear of them from what I have seen, Lee Martin seems to go well with ball diffs!