What Baja Rey 1/10th centre diff fluid?

[Cuiken]

Hi,
First, I appreciate there is a dedicated Baja Rey 1/10th thread and plenty of discussion about diff fluid n the Rock Rey but I wanted to ask a specific question.

I just bought a Baja Rey 1/10th and am blown away by it. I replaced the servo straight out of the box (since it is terrible) and shoo goo'd the panels. Other wise it is stock and, I think, runds really well on loose/dusty surfaces.

My only complaint is the 'pizza cutter' tyre deformation when cornering. I doesn't seem to do any real harm but it looks terrible

I was thinking of increasing the weight of the centre diff oil a bit but wonder if that would spoil other aspects of the truck's handling. Additionally, I guess the 'release' of power via the spinning front wheel reduces the loading on the rear diff under hard acceleration so maybe it helps to improve reliability too?

Has anyone else experimented with the centre diff and what did you learn?

Thanks.

 

[Panther6834]

It's a bits of a PitA to get to the center diff, considering everything you have to remove in order to remove the trans (the center diff is inside the trans), but it can be worth it. Right this moment (brain not entirely working, yet, as I just woke up), I'm blanking whether I put 200K in the front & 500K in the center, or the other way around (at least I DO remember I put 2.5M in the rear)...but, whichever I do, I can tell you or works great.


~ More peace, love, and kindness would make the world a much better place

 

[Speedy-Triple]

as mentioned its quite a bit of work ... basically rebuilding the truck completely in order to get to the center diff. I waited around for maintenance after 15-20 packs after i got it new to do some bling upgrades. once the stock servo burnt it was time to tackle all the upgrades and performance. other than a savox servo and a hot racing steering bellcrank the diff maintenance did wake up the baja rey incredibly. i changed all the fluids and greased everything and i went with 200k front 500k center and 2mil on the rear (also did the traxxas screw mod to all 3 diffs) take your time doing the diffs correctly so they dont leak the fluids... with the changes the truck comes off the line way faster and much more controllable with the avc off. well worth the work IMHO.

 

[Cuiken]

Thanks guys. I'm aware it's going to be a ton of work to get in there but I've got an SSD bulkhead and third member to install so I'm going to do that at the same time.

Looking at the exploded parts diagram for the truck I wasn't sure the rear diff would actually hold oil.

http://www.losi.com/ProdInfo/Files/LOS03020T2-Manual-EN.pdf

There also appears to be a mistake where the front diff part number is the same as the rear diff but the outdrives appear different.

Either way, good to know they are all sealed units.

Seems that there are some wildy different approaches to setting this truck up. I spoke to Horizon to find out what the stock oils are and they swore blind that all three diffs use simple grease rather then silicon oil as the stock setup (pulled up a service document to show me). Only oil listed was 35wt for the shocks.

Other guys seem to say that 30k in the centre, fully locked rear (the older version of the truck had a locked rear setup) and fully open in the front.

I'm actually prety happy with the truck as it stands, really love the manouverability and the way it slews about. Only thing I'd like to change is the way that all power (like all of it) finds its way to the inside front wheel when cornering. I just want to temper that behaviour a bit. To that end, I guess I'm probably only really interested in adding weightier oil to the centre diff? I'd reckon adding heavy oil to the front and rear might reduce the sharpness of cornering at low/mid speeds (which I like).

Cheers

 

[Cuiken]

Just found @Panther6834 's comments here:

http://www.rccrawler.com/forum/losi-rock-rey/622424-what-diff-fluids-do-you-run-why.html

The comment below makes sense given my own observations on the rear diff from the exploded diagram:

'The other part of the 'problem' is that the diff isn't a sealed diff - it's "open". Use too thin of a diff fluid, and it can/will leak out, into the axle housing. I had initially solved this by "plugging" the ends of the diff with a thick marine grease before filming the cup with diff fluid, which worked extremely well...but, again, the rear wasn't "limited" (as it is now).'

Baiscally, you're sort of forced into using a thick oil in order to help avoid leakage.

@Panther6834, forgive me for crossing the streams but on the comment below:

'Initially, I replaced front/center/rear with 10K/15K/80K (the majority of my vehicles prior to getting my Baja Rey have been off-road race). After running a few times, and realizing I needed to go MUCH heavier, I replaced with 100K/500K/2.5M.'

What behaviour from the truck led you to thinking that you needed to go heavier?

Thanks.

 

[Panther6834]

What behaviour from the truck led you to thinking that you needed to go heavier?

It was a combination of a couple things. First, I was getting a bit too much left/right 'freewheeling', and I wanted the left/right "power" to be more equal. Second, I wanted the front/rear "power" to be more equal, especially considering the mostly-flat & lightly-rough terrain I usually run it in (ex. a fried lake bed South-East of Las Vegas, an area just south of the San Mateo Bridge (SF Bay Area, CA), and an area in the northern end of the Santa Cruz Mountains).

Third, related specifically to the rear, as I didn't want to return to 'grease' (what Losi had in there), and knowing the rear diff isn't sealed, the only realistic "solution" was to go with a MUCH thicker diff fluid. I figured 1M might not be think enough, and 20M would probably be way too thick...so, 2.5M it was (those were the only three viscosities I could find in the 1M+ range). I haven't been running it long enough to know if the 2.5M will stay in the rear diff (initially, I thought the 80K was, but it didn't), so I'll have to wait until I have approx a dozen runs before removing the third-member, and checking. If the 2.5M is still completely (or almost completely) in the rear diff, then that'll be the "answer"...and, if an 'excessive' amount has come out, then I'll need to decide whether to switch to the 20M, or switch to a locker. Hopefully, the 2.5M is the "answer" I'm hoping for.


~ More peace, love, and kindness would make the world a much better place

 

[Cuiken]

Thanks man. Appreciate you taking the time to explain.

Yeah, that rear diff is an issue. It's kind of weird to me since the original Baja Rey had a fully locked rear diff but the way they've changed it to a 'semi sealed' diff means you end up completely open instead. Somewhere in between probably does make most sense.

My own preference would probably be to have it around 300k (based just on a the way I've set up my other SCT type trucks) but that's just going to leak.

I run over a rage of terrains including quite a bit of grass and scrub so I don't think I'm losing so much left/right power on the rear axle.

My thinking will be to keep it pretty light. Maybe 10k in the front and ~50k in the centre just to reduce the 'pizza cutter' effect and reduce the loss of power when cornering.

That sounds pretty different to the approach you've taken but I think the terrain around here is very different to yours. The stock setup works pretty well out of the box so I'm probably lookling to tweak reather than revolutionise the way the truck handles.

Thanks again.

 

[521BBF]

One of the first things I did to mine was to lock the center diff. This made the truck almost twice as fast as it allows so much more power to get to the rear wheels. I may try a really heavy oil in it at some point... I just wanted to go from one extreme to the other at first. I think I have 6K in the front, but it doesn't seem like enough.

I just put 1,000,000 oil in the rear because I wanted to to be able to steer with the throttle. I have only run it on pavement so far, but let me tell you, it's even faster now. I can be cruising along at 20-30 mph, punch it, and it will pull wheelies. If you're not careful, it will flip over, but if you use the throttle, you can ride them for a bit. And this is without the weight of the spare tire on the back. It's a total animal now.

 

[Panther6834]

One of the first things I did to mine was to lock the center diff. This made the truck almost twice as fast as it allows so much more power to get to the rear wheels. I may try a really heavy oil in it at some point... I just wanted to go from one extreme to the other at first. I think I have 6K in the front, but it doesn't seem like enough.

I just put 1,000,000 oil in the rear because I wanted to to be able to steer with the throttle. I have only run it on pavement so far, but let me tell you, it's even faster now. I can be cruising along at 20-30 mph, punch it, and it will pull wheelies. If you're not careful, it will flip over, but if you use the throttle, you can ride them for a bit. And this is without the weight of the spare tire on the back. It's a total animal now.

First, 6K is WAY too low for the front. Even when it ran 80K up front, that was too low. Right now, I'm running 200K up front (along with 500K in the center), and that seems to be about perfect.

As for the rear, IF it were a sealed diff, 1M MIGHT have been enough...but, the rear is NOT sealed. You might want to remove the third member, same take a look to see how much of that diff fluid has leaked into the axle. I'm willing to bet a considerable amount of it already has...and, if you continue to run it as-is, sooner or later, that rear diff will not have ANY fluid.

The "problem" lies in the design of the diff gears. Whereas most diffs use gears at each end having 'posts' that exit the diff, which are sealed through the use of O-rings (and then have outdrives attached to those gears from the outside of the diff), the gears used in the Baja/Rock Rey have square 'holes' in them, to which the rear driveshafts slide into each side of the diff, and into those square 'holes'. That is why Losi packs the rear diff with grease.

In switching to diff fluid, the ONLY way you're going to keep that fluid in is to use an INCREDIBLY viscous fluid. That's why, in rebuilding the diffs a second time, I went with 2.5M...and, truth-be-told, I haven't yet team out long enough to find out it the 2.5M will completely stay. There's still the possibility that I'll need to 'bump' it up to 20M, or even go back to a super-thick grease (which I'm hoping I won't have to do).

Again, I'd HIGHLY suggest removing the rear axle's third member, and checking things out. When I ran 500K (what I had originally filled the rear diff with), after 3-4 runs, it appears ok...but, after 7-8 runs, that's when I realized the 500K diff fluid wasn't staying in the rear diff. Upon removing the diff, and opening it up, I discovered that almost all of the diff fluid had "escaped" into the axle housing, and that there was only a minimal amount remaining in the diff, itself. Alternately, you can continue running it exactly as your currently have it...and, at some point, be it 3-6 weeks, or 3-6 months, you'll destroy the gears in the rear diff, due to there being nothing in there.


~ More peace, love, and kindness would make the world a much better place