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FJ body TRX-4 kit build

tkvtec

Newbie
Joined
Jan 14, 2019
Messages
18
Location
Wallingford
I've finally gotten my setup most of the way to where I want it and figured I'd share my progress.
Scroll to the bottom if looking for a parts list, this is a lengthy story.

I started off with the TRX-4 kit, and like many others received one with a bad 24T output gear for the transmission. Basically, the problem on many is that they never finished machining the gears out to the full 10mm needed to fit the bearing. Traxxas had a new one out to me within a couple days and I was able to complete the rest of the build. This only required a less than 5 minute phone call with support, I’m really amazed at the Customer Service.

I had a hobby night planned for Friday with a friend who just bought a Bronco TRX4, and received the kit Monday 3/18 and I was in crunch mode to get the chassis built and fit the body. Going into it knowing I was going to want a strong servo I bought a used Protek 170 TBL that popped up in the classifieds on a forum. I also ordered up the Traxxas metal servo horn to get around any issues with stripping or fitment. Thankfully Protek uses the same 25T splines as the Traxxas stock servo. I read about the fitment of aftermarket servos in the stock mount and needing to trim the servo mounting ears, so I also ordered up the Samix adjustable Aluminum servo mount so I wouldn't have to modify the aluminum mounting ears (I'm just a little funny about that, though I have no problems doing that to cheaper plastic housing servos especially when I know I can get a spare case). Ultimately, the mounting screws actually fit fine and no modification was necessary for this particular servo. My friend had to trim his Savox 1230 IIRC. I also ordered up bumpers that I was hoping to fit the body well. I swapped the front and rear bumper mounts and flipped the front at first and ultimately flipped the rear also. One arrived (rear) before the hobby night, but was really meant to fit something like the defender and was way too wide and straight.

For the transmitter, I had recently picked up a 2nd FlySky GT3C and performed the modifications necessary to reflash the firmware and get 8 Channel capability. I ordered a 6 Channel receiver from FlySky (https://www.amazon.com/gp/product/B01FXLZYMY/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1) to give me independent control of the front and rear lockers and still have an additional Channel for lighting. Now that I'm looking at possibly having multiple lighting controls or a winch, I'll probably up to an 8 Channel receiver. I find that the FlySky receivers for 6 and 8 Channels are designed for Aircraft and the antenna has a metal weight under the red heat shrink. I cut off the red heat shrink and carefully cut away at the metal weight with some small side cutters. I was eventually able to completely remove the weight and was able to slightly route it up into the antenna tube.
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I was determined to do an FJ body setup and had seen a couple other people make it happen. I ordered up the HPI FJ body and when it arrived I began my process of trimming up the fender liners with a Dremel to make the body fit. I got a decent fit, but ultimately the body was a little higher than I wanted. I figured if I could center the body a little more forward, as it sits a little too rearward using the predrilled body holes up front, I could get enough clearance to lower the body.
I ended up using a magnetic body post mount setup I had bought for a drift car build to mount up the rear while I figured out all the fitment as that gives me infinitely adjustable positioning at the rear. I ran the truck like this for a few crawls and I have 1 piece of advice... do not run magnetic body mounts (at least in the rear). The setup I had added about 60 grams of weight to the highest location you could possibly go. This made the FJ really tippy despite the body being lighter than my friend's Bronco.
I found that I was going to need to move the body forward, and I didn’t just want to keep trimming the fender liners, so I ordered up some aluminum shock towers as they were the only thing that I could get shipped quickly from a somewhat local hobby shop. I knew these wouldn’t cause any interference and I would be free to line up the body where I wanted and could figure out the body post situation. I somehow also came across some 3D printed parts designed to make the FJ body fit on the TRX4 with the stock FJ bumpers. I ordered up all the parts (Rear post, front bumper mount, rear bumper mount). I liked the idea of these bumper mounts as they would allow me to bring the bumpers much closer to the body and increase the approach and departure angles of the truck.
Early Christmas!
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And Christmas day ruined... at step 1 basically this should read 10mm
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Finished the rest of the build and just came back to the transmission at the end once I had the part.
Had some Austar Hyrax knockoffs I bought for my son and mounted them up
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Body test fit... need to do some trimming
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Fender Liners trimmed up
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Rock sliders raised with about 13mm of spacers to meet body
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3/23: Hobby night couldn’t happen, so we had Hobby morning the next day: I had some Austar Hyrax knockoffs on the truck on some cheap steel beadlocks they came mounted on. I was doing some outdoor crawling and ripping up the course and really impressed with the truck overall. I was there early and my friend showed up with his Bronco after I had done some mud crawls etc… I was struggling with getting up a certain flat faced rock that my friends Bronco just got right up and over… I was like hmmm. Maybe it’s the mud in the tread not clearing out, or maybe those Stock Traxxas tires are really just working well. I didn’t want to glue up the tires, and had planned on getting some beadlocks… well that sealed the deal for me when I found that the hobby shop had the exact wheels I was planning on. SSD D-Hole Black Beadlocks. They also had some Proline Dual Stage Foams. I figured since I was going to go through the assembly process I might as well get those now also, as I was planning to do that later, but wanted to look more into the Crawler Innovations dual stage foams. Anyways, I got the Proline Foams and the SSD beadlockas and got all the tires built and continued crawling for hours (only needed 2x 5000 mAH batteries to accomplish this). Amazed at the runtime.
Impressions: the Proline dual stage foams seem too stiff and don’t provide as much traction in most circumstances, only providing the advantage on side hills and extreme articulation. I will likely be looking into the soft and medium CI foams if I don’t just modify the Proline foams a bit.

3/24: The new new rear bumper came in, and it is a perfect fit for this body. The width and curvature at the corners is perfect. I just folded up the lower flap on the rear of the body at the crease and it was perfect. There was one other bumper out there that I found that might have been a similar design and fit. I did have to slot the mounting holes to fit with the 3D printed bumper mount designed to work with the HPI stock bumpers (40mm mounting width instead of the 43mm Axial and Traxxas uses)
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Folded up bottom flap of bumper and you can see the SSD D-Hole Beadlocks installed:
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3/25: I measured up the forward offset I wanted at the front body posts and found I needed a little under 9mm. I noticed there was an offset on the rock sliders stock that had them offset rearward by about the same amount, and using the factory predrilled holes on the FJ body, they lined right up. I swapped the rock sliders from left to right and got pretty much a perfect fit. I then modified the front posts, as you'll see in pictures, to basically cut off the bottom half of the posts and mounted them in the mount and bolted the top half to the front of them. I trimmed away material on the lower posts until the front posts were lined up where I wanted them. This ulimately worked out really well, but using this method I definitely couldn't get the body any lower, I'd have to switch to epoxy or custom 3D printed parts. I left it as is for now as the top of the body is still no higher than my friends Bronco, it just looks like the bottom of the body and fenders are really high. I also raised the rock sliders about 13mm using spacers from various plastic parts trees from other builds.
Checking body post offset for properly centering the body, just a little close. Time to modify the front body posts
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3/26: My new front bumper finally came!!! It is a perfect fit for this body for the position it currently sits. To get the bumper closer under the body and hide the winch mount brings the ends of the bumper in line with the tires under articulation. There are super narrow front bumpers that would give an even greater front approach angle, but I really like the look of this one, and I’m kind of done spending money on this thing… �� for now

3/28/19: Added Brass outer portal covers, which were an easy install. I ordered the below kits thinking I could use the various weights from the Ultimate kit and customize the weight balance front to rear and play with adding more weight overall, or just keeping it a little lighter.
Out of the box I added the portal covers front and rear and added the 47g inner weights to the front as well. This seemed a bit much and very nose heavy, also the drag brake in crawl mode was not enough to stop the truck in its tracks anymore. I removed those and liked the balance overall. After removing the 47g weights from the front, the truck has a 53% forward weight bias, which happens to be the same as the TRX-4 Sport out of the box. I'm going to roll with this a little and mess with adding weight when I can get to the crawler course again. Overall, the Brass portal covers made a big improvement in getting the tires back down to the ground. I think the truck is about 8lbs 3ozs now.
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3/29: I received the 3D printed parts!!! To my absolute joy, the person that designed the rear body posts designed them around the same “exact” offset I came up with on my custom front body posts. I didn’t have to modify anything!!! So overjoyed, as every single other part of this body fitment has been a lot of work. If I stuck with using the HPI front and rear plastic bumpers I would be great, and if I just bought the clear body and drilled my own holes up front I’d be great, but I apparently chose the hardest path.
I also test fit the rear shocks from my Kyosho Short Course truck. That’s right 46mm Velvet coating Triple Cap shocks that are just buttery smooth.
I used some E6000 Adhesive and mesh drywall tape to patch and strengthen the lower rocker edge of the body on both sides. The magnetic mounts allowed the body to flop up and snap back down when rolling over, and this caused some pinching of the body at the rockers.
I also wired up the bumper LEDs.

3/31: I wired up the remote switch for the lights to be able to turn them on and off from Channel 6. I was able to package the switch inside the radio box and just ran a servo Y adapter out to feed the bumper lights.

4/3/19: I swapped out the front shocks for matching Kyosho Velvet shocks to the ones I stole from my Short Course truck and treated it to an upgrade to the Big Bores. I just picked up softer springs to mess with tuning on the TRX-4. Currently running 60 up front and 70 in the rear, but I also have extra 60 and 65 rate springs to test. I basically just took the rears off the Short Course truck and put onto the rear of the TRX-4 for test fit and haven't changed the springs or oil in them since. I'm running Losi 15wt Shock oil in the front currently and I believe 27.5 or 32.5 in the rear. So far it seems pretty good, but again waiting to get out to the crawler course for definitive answers. The extra travel gained is huge. No loss of bump travel, and no added height due to the Treal upper shock mounts, but tons of droop travel. Of course there is also that legendary Kyosho shock smoothness and feel. Even though I built the Traxxas GTS shocks with lighter weight oil, they still seemed stiff. I messed with loosening and tightening the lower collar, admittedly didn't swap out the spacer for x-rings/o-rings, but I just didn't like the sticky feeling to them. Once you've used the Kyosho velvet shocks and Tamiya TRF shocks for on-road applications you get spoiled and nothing else really compares. My Short Course truck is butter smooth on those shocks.
Revelation: Getting the body lower would require much trimming of the body fenders, and I don’t really want to change the look of the body that much. Especially now with the articulation I’m achieving, there is no way I could bring the body lower. Only possible option for me is to see if the Defender rubberized Overfenders fit the look on the FJ, and just trim up the FJ fenders and add the rubberized ones so at least if the tires do rub them, they won’t have as much of an impact.
Fitment note... you can use the Traxxas ball mounts found in 8264 kit in the Kyosho rod ends.
…Also, there doesn't appear to be tons of extra room if you're thinking about the Kyosho big bore shocks. I will test fit once I get the ones for my Short Course built and update, but it's pretty tight. As it is I had to put 3mm spacers at the top, which gives just enough space when suspension is fully articulated at the front to not interfere with the shock towers. This only applies when using the top mounting holes, but otherwise you're likely raising your ride height with these shocks.

Have some additional body lighting and grill modifications coming…

I ultimately settled on the below for parts etc…:
TRX-4 Kit
HPI FJ Cruiser Body (pre-painted only to save time and be up and running within a week... I have 2 kids and limited time, so this was mostly just for time savings) For this build I think it would be easier to start with a clear body provided it doesn’t have pre-drilled holes.
Rear body post: LockedUp RC TRX-4 to HPI Venture FJ - Body Post
https://www.shapeways.com/product/N...mail&utm_campaign=order-shipped&utm_content=2
Front body post: custom (a clear body should allow you to put body holes where you need them, it was just a little too close to the pre-drilled holes for my liking)
Front bumper mount: Stock rear mount flipped
Front bumper: https://www.ebay.com/itm/163464228523 (This front bumper has slotted mounting holes to allow fitment for HPI Venture, Axial, and Traxxas and comes with 3 mounting types. I had to custom drill the mounting rods to get the fitment I wanted)
Rear bumper mount: Locked UP RC TRX-4 to HPI Venture FJ - Front Bumper Mount
https://www.shapeways.com/product/A...mail&utm_campaign=order-shipped&utm_content=3
Rear bumper: https://www.amazon.com/gp/product/B07DRD6JMC/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 (I had to custom drill the mounting rods to get the fitment I wanted, and the red lenses in the bumper are not red enough with how white the LEDs are. I will be replacing with Red LEDs)
Traxxas Servo Horn 8247X: https://www.ebay.com/itm/Traxxas-82...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Samix aluminum servo mount TRX4-6038BK: https://www.ebay.com/itm/Samix-RC-T...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Traxxas Body Posts and Mounts 8215: https://www.ebay.com/itm/401737967731?ViewItem=&item=401737967731
Hot Racing TRXF21HA Ultimate weight kit:
https://www.ebay.com/itm/Hot-Racing...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Hot Racing TRXF21HE Heavy 72g:
https://www.ebay.com/itm/Hot-Racing...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Treal Aluminum Rear shock towers:
https://www.amazon.com/gp/product/B078VQS9RH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Treal Aluminum Front Front Shock Towers:
https://www.amazon.com/gp/product/B078V95Z27/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Remote switch for LEDs on Channel 6 - Apex RC Products RC Remote Electronic AUX Channel On/Off Switch #9025:
https://www.amazon.com/gp/product/B07BKSGW3D/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Front and rear shocks:
Kyosho w5198 46mm Velvet shocks. Will need spacers to provide clearance to the shock towers. I had an assortment of aluminum spacers ranging from .25mm to 3mm. I believe I used 3mm in all upper locations, the lower I don’t recall exactly.

I also ended up using some spare M3 button head screws of various lengths. I’d recommend picking up a kit like below to keep on hand:
https://www.amazon.com/gp/product/B07HQC1CYF/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

***If you stick with the stock shocks or at least nothing longer, you should be able to use the factory fender liners, though with additional trimming to what I have pictured at the rear of each front and rear liner to accommodate the 9ish mm forward offset. I believe you'll also not need the Traxxas body post and mount kit. I needed it because the 3D printed rear body post was designed for that body mount location. The aluminum shock towers and the Traxxas plastic shock towers TRA8216 sit more forward where the body mount mounts. I may modify the fender liners to go on over the aluminum shock towers just to get them back.
More updates and photos to come...
 
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I'm guessing my post count is preventing me from posting photos? or they're just too large. Working on reducing the pic size. I've been lurking for some time and finally have something to contribute to the community. Hopefully a mod can see this and help a brother out.
 
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Subscribed. I'm about to do a similar build myself... "thumbsup"
 
I'm guessing my post count is preventing me from posting photos? or they're just too large. Working on reducing the pic size. I've been lurking for some time and finally have something to contribute to the community. Hopefully a mod can see this and help a brother out.

How are you putting the photos up? You'll need to use an image hosting site like Imgur, you can also use the tapatalk ap or if you become an RCCrawler supporter you can Upload unlimited attachments/pictures

I'm pleased to hear you didn't go with the Proline body, they really botched that one.
 
How are you putting the photos up? You'll need to use an image hosting site like Imgur, you can also use the tapatalk ap or if you become an RCCrawler supporter you can Upload unlimited attachments/pictures

I'm pleased to hear you didn't go with the Proline body, they really botched that one.

Using Flickr since I checked an image link in another post and figured that should work and I already had an account.
 
More photos:
new front bumper and front body post modification, trying out the rear tire mount
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Added brass portal covers and test fit Kyosho shocks in rear, check that droop advantage!
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Reinforced body and wired up bumper lights
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More photos:
Kyosho shock install, 3D printed rear body post install using Sport? body post mount from the body post and mount kit, flexing showing off the Kyosho 46mm shock travel
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4/6 Update:
Last night I realized I never vented my tires, as the stock wheels were vented and the SSD Beadlocks were not. I vented the tires with a leather punch and I get much better "squish" now. In the front I also experimented with my dremel and a narrow grinding barrel. I basically grooved the inner foams of the Proline Dual Density Foams like the Crawler Innovations Comp Cut and seem to get a bit more conformity from them now (Pics to come). The stock tires are a little shorter than the foams are built for. The foams are built for 4.75" tires, but the tires are 4.64" IIRC. The stock tires are right in the middle of the sizes offered by Crawler Innovations. I'm going to stick with the Proline foams for now, as I like the performance I'm getting from them now. I'm sure I lose a touch of side hill performance, but pick up much needed climbing grip.
 
4/9: Ok, so valuable lesson learned.
I had some plans for lighting... and I had run across a thread somewhere where someone mentioned what to use to remove paint from the inside of a body... well, for once in my life I didn't do my due diligence to verify the best method and I ended up ruining the possibility of removing the stickers and painting the corners amber and tails red with Tamiya Clear Orange and Clear Red respectively. The critical thing that I came across and ruined my chances of making this exactly how I wanted was Acetone. Of course, I could have tested on some scrap Lexan, or done some more searching. The Acetone basically ate away at the lexan to a point where the lenses will never be clear. I left all of the corner light stickers on, drilled out the headlamp holes, and cut some new headlight lenses from scrap lexan (simple circles).

Bottom line, if you don't do research on what works first, at the very least test on some scrap. Do NOT use Acetone to remove paint from a lexan body. Maybe not all lexan is created equal, so test first on scrap.

Regardless of this issue, the lighting came out pretty good. I just used some silicone adhesive to mount the light buckets as I know if I want to change anything, or swap to a new body, the silicone adhesive is relatively easy to remove.

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FJ-TRX is looking great! I have always liked the looks of these bodies. Great job on getting the inner fenders to fit."thumbsup"
 
FJ-TRX is looking great! I have always liked the looks of these bodies. Great job on getting the inner fenders to fit."thumbsup"

Thanks! I decided the single screw at the front mount point is all that's really necessary in the rear. Allows the fender to flex a little at full suspension compression. The front will be a little more challenging, but I want to try and get that front battery mount back along with the front fender liners.

The Dremel has been used just as much as the 2.0mm hex driver on this build :lmao:. Once I got over the idea that I was cutting up perfectly good parts, it's really been free reign.
 
Here is how I cut mine if it helps. I made an aluminum bracket to hold the front of the inner fender down since I had to cut all of the mounting points off to fit over the Samix shock towers.

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On the back edge, I put a zip tie on to hold it. Once everything is bolted together, it is really strong. I have not had any problem with wobbly inner fenders.

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Here is how I cut mine if it helps. I made an aluminum bracket to hold the front of the inner fender down since I had to cut all of the mounting points off to fit over the Samix shock towers.

On the back edge, I put a zip tie on to hold it. Once everything is bolted together, it is really strong. I have not had any problem with wobbly inner fenders.

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Awesome! thanks for that! Those Samix Towers look really nice. I was dabbling with the idea of a zip tie at the back of the rear fender liner, and may add one if I find it floppy.

Nice work keeping the cuts close. Really clean work. I just kind of hacked together the rear and haven't even cleaned up the edges yet. I was also allowing for a little extra room to reposition the shocks in a different mounting hole. Looks great, I'll have to check the rest of your build.
 
Awesome! thanks for that! Those Samix Towers look really nice. I was dabbling with the idea of a zip tie at the back of the rear fender liner, and may add one if I find it floppy.

Nice work keeping the cuts close. Really clean work. I just kind of hacked together the rear and haven't even cleaned up the edges yet. I was also allowing for a little extra room to reposition the shocks in a different mounting hole. Looks great, I'll have to check the rest of your build.

Hey, no problem! Yeah, these Samix shock towers are beefy. They have a really strong panhard mount. I also have these on my SCX10.2 also. I highly recommend them.

I don't have a build thread for my TRX-4 yet. I built my TRX-4 Kit last summer, but never got around to starting a thread for it. I'm hoping to get one up soon though.
 
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