JRX Pro Rebuild

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JRX Pro Rebuild

Post by Top_Billing »

Getting back into R/C after a 20+ year break. I grew up with a JRX Pro and loved it, but stupidly didn't hold on to any of my gear. Found a roller on ebay and pulled the trigger. My goal is to rebuild it so I can have some fun, see if my son is interested enough to want to build his own cars and then eventually put it on the shelf. Definitely want to update it so it can run brushless and LiPo. Read through a bunch of threads on this, but still have some questions:

-- Think I should update to the XX transmission with dual disk slipper to handle added power. Found instructions on vintagelosi.com, but I'm having trouble finding a parts list. Is this the right way to go?

-- Not sure what ESC and battery will connect to each other and fit inside the battery compartment. Recommendations?

Thanks
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Re: JRX Pro Rebuild

Post by matt1ptkn »

That's a very nice looking buggy! The stock LRM transmission is capable of handling mild brushless power. Its durability will be greatly dependent on how hard it is driven. The initial concern is to make sure that your diff is tightened properly. To help save and prolong the life of the diff, you can install a single pad slipper like on the Jrx Pro SE or LXT, or you can even adapt the XXX dual disk slipper with minimal effort. See http://www.rc10talk.com/viewtopic.php?f=27&t=42116 for some great information. Upgrading to the XX retro fit trans. is never a bad idea, but you will have some trouble locating parts and it will not be cheap. As long as you don't go overboard with your power, you should be fine. A 21.5 or 17.5 brushless setup on 2s lipo should give you plenty of speed unless you plan on racing against modern buggies.

As for electronics, see http://www.rc10talk.com/viewtopic.php?f=27&t=41105 for some battery ideas. For ESCs, you really should have plenty of room for most anything. If there isn't enough room along the side of the chassis, you can always install an ESC shelf on the rear shock tower and then your possibilities should be endless.

For additional battery and ESC mounting ideas, make sure to check out the 3d printed parts at http://www.sabulatech.com/SabulaTech/Team_Losi.html.
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Re: JRX Pro Rebuild

Post by Top_Billing »

Thank you very much for the input.

I spent way too much time looking for XX transmission parts last night and it's definitely tough. Finding parts for the dual slipper was easier. I'm thinking i'll go with the dual slipper and then pick up a separate LRM transmission for backup/parts.

Any recommendations for upgrades and other spare parts I should stock up on? I'm planning to mostly bash around the back yard so durability is most important. I saw a post that suggested using Traxxas Bandit driveshafts instead of the originals. Maybe go with some threaded shock bodies? Turnbuckles, ball cups, ball studs? I've forgotten which parts are most likely to break over time.

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Re: JRX Pro Rebuild

Post by matt1ptkn »

For extra durability, you can always pick up a set of RPM outdrives and Thorp aluminum LRM gears, but you shouldn't need them. As I said before, just be sure that the diff is tightened properly. One weakness I know about the LRM, is that if the diff is at all too loose, the diff balls will melt into the diff gear. I've purchased many LRMs that have had this happen. Bandit slider axles are supposed to fit, but you shouldn't have any issues with the Losi ones. But if you want/need replacements, Bandit's will be a lot cheaper. I've had some issues with the front bulkhead and A-arms becoming brittle, but unfortunately, there aren't too many options other than watching for parts lots/cars on eBay and stocking up on spares. Same thing with the steering bellcranks, but Sabula Tech has some nice 3D printed ones. Threaded shocks won't be a necessity for bashing and I'd spend my money elsewhere. I've never really had a problem with the Losi turnbuckles or ball ends/studs, but titanium turnbuckles are usually a good idea and RPM ball cups. Spare parts for these are usually easy to find, and with some patience, you can get some good deals versus buying the overpriced NIP parts.
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Re: JRX Pro Rebuild

Post by LosiXXkid »

matt1ptkn wrote: Thu Nov 30, 2017 7:39 am For extra durability, you can always pick up a set of RPM outdrives and Thorp aluminum LRM gears, but you shouldn't need them. As I said before, just be sure that the diff is tightened properly. One weakness I know about the LRM, is that if the diff is at all too loose, the diff balls will melt into the diff gear. I've purchased many LRMs that have had this happen. Bandit slider axles are supposed to fit, but you shouldn't have any issues with the Losi ones. But if you want/need replacements, Bandit's will be a lot cheaper. I've had some issues with the front bulkhead and A-arms becoming brittle, but unfortunately, there aren't too many options other than watching for parts lots/cars on eBay and stocking up on spares. Same thing with the steering bellcranks, but Sabula Tech has some nice 3D printed ones. Threaded shocks won't be a necessity for bashing and I'd spend my money elsewhere. I've never really had a problem with the Losi turnbuckles or ball ends/studs, but titanium turnbuckles are usually a good idea and RPM ball cups. Spare parts for these are usually easy to find, and with some patience, you can get some good deals versus buying the overpriced NIP parts.
And, courtesy of Dan @ Sabula Tech, this is what a melted JRX-2 diff looks like.....

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Re: JRX Pro Rebuild

Post by jwscab »

Matt nailed pretty much everything.

I feel the most important part of making the car tougher/last longer is definitely the slipper. The center diff gear is the weak point, so adding some protection by means of a slipper makes it very reliable.

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Re: JRX Pro Rebuild

Post by Top_Billing »

Thanks again for all the input. Here's an update on my project:

Received the car and it's in pretty good shape from what I can tell. All of the pictures below are before doing any cleaning. I'm still missing some parts so it'll be a few weeks before it's running. In the meantime, I'm going to clean and rebuild the tranny and shocks. Based on suggestions from you guys, I'll upgrade to the vintage losi dual disk slipper, but keep the original LRM. Will also upgrade Lunsford turnbuckles and ball cups -- already snapped one during the disassemble. Everything else stock for the time being.

After a bunch of searching, I found the right-sized LiPo battery: https://www.genstattu.com/gens-ace-5000mah-7-4v-50c-2s1p-short-size-lipo-battery-pack-with-xt60-plug.html. Fits perfectly, when combined with slightly longer cup from Sabula: http://sabulatech.com/storefront/index.php?id_product=2829&controller=product

Went with Hobbywing stock brushless, sensored motor/ESC combo and Savox servo.

Still have some open questions:

I picked up 3mm 1.5" and 1.875" turnbuckles and cups. The original parts are 4-40, but I think it doesn't matter. As long as the cups and turnbuckles are matched and the ball studs fit I should be good, right?

I read through so many threads trying to figure out the right wheels. I'm going to save the original wheels/tires that came with the car and run newer stuff. I was hoping to find a black spoke wheel that can fit updated tires. To summarize what I learned from various boards: B3 or B4 associated wheels should work for the front without modifications -- I'm not all that concerned about overall front end width. The most important detail for the front wheels is that they have inner and outer bearing seats. For the rear, B4 should be fine as long as it is pin driven. Hex can work too, but would require adapters. The problem is finding matching fronts/rears in the style I want. Closest I've found is JC Racing: http://www.jcracingproducts.co.uk/index.php?route=product/category&path=18

They have 5 spoke associated B2/3 wheels for the front and 5 spoke rears made for the XX4 (which should work), but the styles are slightly different. Other option is to go with dish style wheels which match:

https://www.amainhobbies.com/de-racing-borrego-2.2-1-10-buggy-front-wheels2-b4-black-pins-der-bb-afb/p215058
https://www.amainhobbies.com/de-racing-borrego-2.2-1-10-buggy-rear-wheels-4-b4-b44-black-pins-der-bb4-arb/p705674

Any tips/suggestions would be appreciated.

I'd like to add servo mounts, but drilling and countersinking holes in the chassis doesn't look all that easy. I have a buddy who has a drill press and may hit him up. Don't trust myself free handing it. Any tips?

Can't wait to get this thing running...
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Re: JRX Pro Rebuild

Post by jwscab »

Plastic ball cups aren't threaded, so new ones would be fine for both #4 and 3mm threads. The turnbuckles cut their own threads.

There are 3.5mm and also larger ones, but typically 1/8 or bigger so not relevant. The exception is lunsford makes super heavy duty 3.5 turnbuckles and rpm sells gray ends to match.

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Re: JRX Pro Rebuild

Post by matt1ptkn »

The B3 wheels will work fine on the front. You may need a few shims to clear the steering arms. You will likely be hard pressed to find a perfect matching set of wheels front and rear since so many are hex drive now. HPI used to make, and may still make, universal 5 spoke wheels for the rear that came with adapters for different pin drives, hex drives and Tamiya. They also made front wheels with various inserts for different bearing sizes. I think these were all 2.2 in. but I'm having difficulty finding them, so they may be discontinued. Anyway, depending on the rear hubs that you have, any XX or XXX rear wheels should also be options for you. Its hard to tell from the photos, but if you have losi rear hubs, XX or XXX wheels will fit, but if you have RPM hubs, you may have clearance issues.
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Re: JRX Pro Rebuild

Post by Top_Billing »

Thanks, guys. I just received some of the slipper parts I ordered and now I'm not sure if it'll work. I'm using the longer slipper input shaft (a3120) along with the rear back plate (a3121), but the back plate does not fit inside the output hole of the gearbox. i looked up some instructions: http://vintagelosi.com/Instructions_files/Friction_Slipper_A3110.pdf which say "The output hole for the top shaft has been enlarged in later production to accept the slipper backplate. If you are adapting the slipper to a previous version, the hole needs to be enlarged to a 5/16" diameter. Be sure to keep the drill bit centered in the smaller hole. If the larger hole is drilled too far off center, your transmission may not perform properly."

Wish I seen this before I started buying parts. Has anyone else done this? Is there another gearbox housing option that doesn't require modifications?
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Re: JRX Pro Rebuild

Post by Top_Billing »

Found my answer in the Losi variations thread.
aconsola wrote: Tue Jul 21, 2009 10:03 pm found another variation tonight. I was rebuilding/upgrading my VONATS racer: adding a slipper clutch and thorp aluminum BB diff gear.
When putting the whole thing back together I noticed that the inner slipper plate did not sit as far down as it should.

A little investigation lead me to find that there are 2 transmission cases (3 if you count the grey one)
The difference is in the size of the hole for the trans output shaft. The presumeably older version has a narrow opening(about1/4") while the newer one has a 5/16" hole. Not a huge difference, but enough to give clearance to the slipper backing plate.
The pictured 5/16" case was just taken out of the package for the picture. It had the original jrx-2 logo header card on it.
Saw another post that suggested using a body reamer tool. Gonna give that a shot.

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Re: JRX Pro Rebuild

Post by jwscab »

Yeah body reamer works great open it just enough to pass the collar with no rubbing.

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Re: JRX Pro Rebuild

Post by RCveteran »

RC10 Rerelease wheels work perfectly, H-arm or five link. Cheap and easy to come by, you'll need a small spacer on front axle to move it out just a bit. Rear is direct fit with pins and perfect offset.

As seen here

http://www.rc10talk.com/viewtopic.php?f=27&t=42116

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Re: JRX Pro Rebuild

Post by Top_Billing »

RCveteran wrote: Tue Dec 12, 2017 11:16 am RC10 Rerelease wheels work perfectly, H-arm or five link. Cheap and easy to come by, you'll need a small spacer on front axle to move it out just a bit. Rear is direct fit with pins and perfect offset.

As seen here

http://www.rc10talk.com/viewtopic.php?f=27&t=42116
Thanks! Will I need different pins in the rear and/or different bearings in the front? I'm assuming something like this (https://www.amainhobbies.com/custom-works-3-16-axle-shim-kit-csw7048/p701778) would work for the spacer?

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Re: JRX Pro Rebuild

Post by RCveteran »

Bearings are same, I swap back and forth on my rere RC10 and runner X2. Pins will need to be a bit shorter in rear. I can't recall if I cut some X2 ones down. Or you could simply elongate one slot on the inner wheels as it is a cross pattern.

That shim kit for the front would probably work. When you put front wheel on you'll see how much you need where it will make slight contact with knuckle and hub. A couple thin washers would work fine too. If I recall I used some of the little spacers that go on the rear axles between the pin and hub on the front axles.

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