JRX Pro SE "we don't do shelfers here" build

[RogueIV]

So the first ever "Hobby grade" RC I owned was a used Losi JRX Pro SE that my step father helped me purchase when I was a kid. Later I sold it off to help buy a a former racer's LXT and his entire inventory of parts, radios, electronics, and motors, batteries ect. This was decades ago but came across some bins of JRX/LXT era stuff that I had thought I lost. I've already did a nice running chassis of a JRX Pro and I have my original LXT that I recently put back onto an original molded chassis.

This time I'm going with a Pro SE, the car that started me down the rabbit hole. Starting this one off I acquired a crusty but complete LXT off of Ebay.

While complete this thing looks like it was stored outside for a portion of it's life, and the seller didn't even bother to clean up the the car at all before selling.


The rust was an added bonus, still impressed how rusted these springs are but the shock shafts aren't rusted.


At least is has mint looking hydra-drive and a diff that doesn't feel like it's been melted.


I started tearing down the chassis for cleaning


I didn't take pictures of rebuilding the transmission but I cobbled this smooth feeling transmission out of 2 separate transmissions. I'll need to source a new thrust bearing for the next transmission I build. I filled the Hydra-drive with some 10k diff lube. No seepage is evident but we'll see how it does when I drive it.


While I was taking it apart I noticed something odd. LXT apparently changed the front shock tower design for the camber links at some point during the LXT/GTX/NXT production run. Same part number but different holes.


Other observation about the LXT is both the donor LXTs I bought for different projects had similar issues with their build, the builders built the front body mounts incorrectly. I'm actually astonished these held together for any kinda driving being that he screws were attempting to thread into a part that was meant to be a through hole.


Lets fix that before I toss them in the spares bin


Man, some of these hinge pins were rusted up pretty bad. Trying to separate the pins from the rear knuckles was the most challenging part and they were stuck in there really good. After freeing them up I knocked back the rust with some 400 grit sandpaper and a drill and went over them with some polishing compound






The donor truck didn't have ball bearing steering but I had another setup in my parts bin. Love that the truck came with a nice dark grey anodizing on the drag link that matches the motor plate. Cleaned up all of that, lubed the bearings.


Assembled it up and did my typical shim job to eliminate excessive play.


For shock towers I went with these super cool carbon fiber parts from Vintage RC, as you can tell I'll be doing a 5 link car some time in the future as well.


Started reassembling the chassis into buggy form. I had a bunch of H arms around that I used for the rear. Fronts, I used a pair of RPM arms I bought from @WriteDean along with a decent pair of .6 black anodized shocks (thanks dude!) , while I do have a few original swept arms I'll save those since I plan on trying to run this car at the next Vintage Nats. Durability is a good trait to have.


Bottom of the chassis isn't perfect but is in surprisingly good shape for a car that was run off road. Not going to win any concours but that was never my intention


I decided to use some JRX2 style 5 spoke replicas made buy JC Racing in England. These things are super cool and are in modern 2.2" sizes. I had some older losi tires hanging out that I decided to clean up and just mount onto the wheels for the time being. They aren't glued on right now, it's more for display purposes for the time being till I get the rest of the parts and running gear straightened out.

[BattleTrak]

Nice restoration from a crusty truck! Interesting seeing the front shock tower variations.. I think that darker, blue tinted anodizing was late ProSE/LXT. I have some shock bodies with the same color too.

https://www.rc10talk.com/viewtopic.php?f=27&t=3171

[TRX-1-3]

Nice touch with the carbon towers.

[RogueIV]

Nice restoration from a crusty truck! Interesting seeing the front shock tower variations.. I think that darker, blue tinted anodizing was late ProSE/LXT. I have some shock bodies with the same color too.

https://www.rc10talk.com/viewtopic.php?f=27&t=3171

I put a post up on that thread for these ones. I'll probably toss this later model tower on my LXT.

[BattleTrak]

I was looking at the old Losi Tech Talks and saw this mention of the LXT shock tower change.

[HS-YZ250]

While I was taking it apart I noticed something odd. LXT apparently changed the front shock tower design for the camber links at some point during the LXT/GTX/NXT production run. Same part number but different holes.

I wonder if it corresponds to the release of the "Jammin' Jay Steering Enhancement Kit" for the Pro SE. I can't find my original shock tower at the moment to do a good side-by-side, but here is what the hole pattern on that looks like. The kit, if I recall, moved the camber link to the inner hole. The kit also came with LXT uprights which I've patterned my hex conversion uprights after. I was no good at chassis setup so I don't recall if it made much of a difference.

[asciibaron]

good stuff, i have a JRXT/2 i just started working on... it still is covered in dirt from the track when i put it in the box 30 years ago. this is a great build, following!

[RogueIV]

While I was taking it apart I noticed something odd. LXT apparently changed the front shock tower design for the camber links at some point during the LXT/GTX/NXT production run. Same part number but different holes.

I wonder if it corresponds to the release of the "Jammin' Jay Steering Enhancement Kit" for the Pro SE. I can't find my original shock tower at the moment to do a good side-by-side, but here is what the hole pattern on that looks like. The kit, if I recall, moved the camber link to the inner hole. The kit also came with LXT uprights which I've patterned my hex conversion uprights after. I was no good at chassis setup so I don't recall if it made much of a difference.


IMG_20221111_113139224.jpg

I think you're on the right track,It's probably in response to how tracks were evolving into better groomed and smoother at the time.

[HS-YZ250]

Well, if I just would have looked a little further down the Losi forum than my own posts, I would have found BattleTrak's post about the steering enhancement kit and the camber hole comparison! - https://www.rc10talk.com/viewtopic.php?f=27&p=542022#p542022

[RogueIV]

I did a little more to it over the week and it moved under it's own power, albeit just down the hallway and back.

one thing that was holding me up is I didn't have any buggy sliders to use on this car, but I did have a bunch of LXT sliders. They weren't in the greatest shape externally so i didn't have any qualms taking a saw to them so i took some measurements and did just that.


Measurements from the base of the yoke to the end on the male part is (aprox and rounded to the nearest .5mm) 25mm on the buggy and 35mm on the truck. The slotted area on this shaft is the full length on the buggy at 25mm but the truck starts 6.5mm after the yoke and ends up being 28mm in length . The female part is 25mm on the buggy and 34mm on the truck. What I ended up doing was cutting 10mm from the male slider and 15mm from the female. The result looks a little different but has about the same amount of engagement and plunge as the original buggy sliders



I was originally going to toss my old Novak SS brushless system into the buggy but I had completely forgotten that although it looked fresh it was missing a MOSFET which essentially meant it wasn't powering one of the motor poles. Sadly I can't remember where I last saw that MOSFET to solder it back on the board, so for some driving enjoyment I started digging through my old motor and electronics box for something not too over the top. Ended up with a GT7 and this nice condition Integy motor which I must have recut the comm on before putting it away because it looked pristine. I replace the way to short brushes and installed the motor and ESC





I also just got my Team Bluegroove and MCI order in.


This was for my Mini JRX and my JRX Pro but in a surprising twist TBG sent me 2 bodies, one for free and I can't really see and defects in it. While it's not a Pro SE body I think I'll still use one of these on the Pro SE, I kinda like the look better than the SE anyway, I'll still get a SE body down the road though. MCI had some difficulty with the colors I selected for the decals. They were upfront about and offered a reprint in different colors if I decided. I'm not that picky and these should be fine for that buggy.

I just realized I never mentioned my steering in the last post. I decided to go sort of a Jammin' Jay setup but a bit different, 1 I don't have the modded camber link location on the front shock tower but that still didn't seem likely to solve the really bad bumpsteer that was present when the steering spindle was centered on LXT hub. So I looked at the LXT in comparison and decide to raise the spindle all the way up and then add a large spacer, this eliminated most of the bumpsteer. I may make a 3d printed reinforcement for the spindle's steering arm to keep the added leverage from stressing the steering arm on the spindle in the future but I want to see how this handles first before bothering.



Haven't gotten to test it really yet and I still need Wing tubes so I can run a wing but I am happy that it runs under it's own power now.

[BattleTrak]

Good job on cutting down those drive shafts!

You might want to rethink your Jammin setup..that looks kinda crazy lol.. It was a specific setup & geometry for the tracks at the time. If you’re not properly centering the JRX2 spindle with 2 “B” spacers within the LXT carrier, then just use the original Jrx2 setup.

[RogueIV]

Good job on cutting down those drive shafts!

You might want to rethink your Jammin setup..that looks kinda crazy lol.. It was a specific setup & geometry for the tracks at the time. If you’re not properly centering the JRX2 spindle with 2 “B” spacers within the LXT carrier, then just use the original Jrx2 setup.

I'm going to try it and see what I think if I don't like it I'll put it back to normal. Out of curiosity you have the actual Jammin' Enhanced steering kit right? how much do the front wheels change in angle as it goes through suspension motion? This setup the Outside wheel doesn't seem to have any bumpsteer from center to full lock but the inner wheel does have a little bit at lock on par with what my RC10B6.4 has actually.

[BattleTrak]

On the Jammin setup there is some bump steer at lockup..the outside more than the inside. I see your outer tie rods are spaced up high. The Jammin only uses 2 washers like mentioned in that Losi Tech Talk.

[RogueIV]

On the Jammin setup there is some bump steer at lockup..the outside more than the inside. I see your outer tie rods are spaced up high. The Jammin only uses 2 washers like mentioned in that Losi Tech Talk.

Yeah that's how my experience was when i tried it centered with just 2 washers hence why I ended up raising my spindle and adding a bigger spacer on the arm. Maybe the bumpsteer was something Jammin' Jay was looking for in that time, but I am interested that what i have done seems to be on par with my much newer B6.4 as far as bumpsteer goes.