TXT axle modifications

Discussion in 'Tamiya RC Monster Truck Forum' started by HawnMT, Jul 3, 2010.

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  1. Jul 3, 2010 #1

    HawnMT

    HawnMT

    HawnMT

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    OK, I know this is kinda late but I finally got around to beefing up a set of axles so I could do this write up. It's funny because I've never done all these mods at once so it took longer than I had estimated.

    As most of you know, out of the box TXT axles are very strong. But when you start adding weight and/or doing serious jumping, the weak points in the axles start to show. So I figured I'd do a write of what I've done to strengthen the axles to handle the added abuse. Some of these are well known mods, some of them are things I came up with.

    WEAK POINTS

    I've numbered these in order of most important to least.

    [​IMG]

    1) Differential screws: The diff screws have a tendency to back out in high torque applications. It'll sound and act like you stripped the gears but when you open up the axle you'll see the diff has opened up.

    2) Top Link Mounts: The way they are stock each post carries the load of one link. Problem is when you land awkward or run into something, a single post can take the brunt of the force and crack.

    3) Axle "C"/ears and kingpin area. Weak point only if your truck is heavy and you do moderate jumping or if you do a lot of big air jumps. I've had them crack mid way down the "C" amd right at the kingpin hole.

    4) I've only broken the housing at this area once but I've seen it cracking in this area on a few TXTs. It really only happens when the plastic gets old and brittle. You can tell when the plastic is brittle when you screw the top cover on and the screw hole splits. If you look closely you can see post for the front screw for the top cover was cracked and I repaired it.



    HOW TO:

    Overall the lighter the better. The lighter you can get your truck the easier it will be on parts. Also not going overboard with power helps.

    1) The fix for the diff is simple, blue loctite. While it's possible to use red loctite I wouldn't recommend it. Although you can heat up the diff to loosen the loctite it's too easy to strip those small M2 screws so I would stick to blue. And since those 3-prong star shafts have a tendency to break you may have to open the diff up in the future.

    2) Top Link Mounts. The brace is a common and effective fix for this.It ties the two posts together so they share the load. Here is Yama-bro's design:

    [​IMG]

    and what it looks like mounted:

    [​IMG]

    3) Axle "C" and kinpins. In order to brace this area I use epoxy. You have two common choices, each with it's own pros and cons. The first type is the regular two-part epoxy made by Devcon, Permatex, and Loctite. It sets in about 7 minutes and dries smooth and semi clear but doesn't adhere as the other choice. The second is made by the same companies and called either Bonder or Plastic Weld. It sets in 5 minutes and dries cream colored and can be rough but it sticks extremely well. I like the regular epoxy for this area because you'll have time to work with it and get it in the places you want.

    start by sanding the area inbetween the channel braces and area around the kingpin:

    [​IMG]

    Next carefully work the epoxy in the channel and on the ear. If you lay the housing at an angle the the epoxy will "puddle" in the channel. It should look like this when it dries.

    [​IMG]

    4) Lower Link mount and canti mount perches. For this area I use the Bonder/Plastic Weld type epoxy because it sets fast and sticks well.

    First sand the corners of the boxes.

    [​IMG]

    Place the Bonder in those corners being careful not to get too close to the housing seams. If you do you'll end up gluing the housings together.

    [​IMG]

    Because it dries cream colored it's very obvious so I hit with my dremel sanding drum then paint it flat black to hide it.

    [​IMG]

    While I won't say these mods "bulletproof" the axles they do add strength to some critical areas and it's a much cheaper option to buying aluminum housings. I run my axles just like this, even in my brushless truck, plastic knuckles and all. I have never had an axle crack or fail in racing or bashing with these mods.
     
    Last edited: Jul 3, 2010
  2. Jul 11, 2010 #2

    vwhed1979

    vwhed1979

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    red loctite

    I use the red loctite. I have had even the blue loosen up on me. I used a propane torch and only had to hit the screw for a few seconds to remove it. When it is hot, it completely melts, and there is no risk of stripping the screws.

    If they do loosen up, and you dont catch it in time, you can lose the whole differential, because it wallows out the holes for the spider gear shafts, and sometimes breaks the screw holes off.

    Since those screws are so small, I would even heat them up to disassemble blue loctite. May even be worth replacing any time they need to be taken out. I found some on tower for an HPI car that are the same size, there are 10 or so in the pack for a few dollars.
     
  3. Aug 3, 2010 #3

    truckus

    truckus

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    txt woes

    Thanks for the ideas. I like the JB weld type fortifications on the axle. Perhaps I will do the same and slide some bent sheetmetal in there and paint it black after.
    I'm really stuck on fixing up #2. My truck is pretty stock save for the black tuned motors, and I've had the top link mounts break/rip out even with the suggested brace I made. In fact, I haven't run the truck since the rebuild because I'm trying to think of a way to strengthen it. I have a plate in mind that will be supported a few mm's above the screw holes by spacers, and I will either grind the original posts down and run angle aluminum/tamiya brackets on top (similar to someone's Outlaw Jugg project here), or surround the original posts with the plate by carefully drilling the appropriate post diameter into the plate. This might prove to be harder so I might go with the first option. :bang
     
  4. Aug 3, 2010 #4

    HawnMT

    HawnMT

    HawnMT

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    Yeah JoeWorks just cracked one of his top link mounts at a race and he wasn't doing anything to nuts. He ended up epoxying the two post together on a new one by filling up the space between them. I haven't broken a top mount since running lighter weight trucks. I should also add that I still run the stock Tamiya ball connectors on half of my trucks(in fact my fastest trucks all have them) because they hold up well on light trucks and only pop off under very severe crashes.

    You should come out to one of our races, we need more TXT guys.:tmb Don't need to worry about going super fast like in Outlaw, Stock and Mod Classes are a great way to "exercise" your truck. A lot of the racing tips can help with building a better basher too.
     
  5. Aug 8, 2010 #5

    truckus

    truckus

    truckus

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    thanks HawnMT,
    I might have met some of your group a long time ago, when I used to run nitro MTs at kakaako. I know Plo and remember Jimmy and Joe. I did check some of the races back at Sandy's a long time ago too. Is there a schedule of races? I can tell from the pics that they take place at Mililani or Waipio. Also, my txt is sport tuned, what class is that? Will be fixing that top link mount and remounting the shocks so it will be awhile till I come out. I want to drop the truck a little. I have 4" shocks, can I just put a rubber spacer inside the shock to lower it, is that a good idea or not?
    truckus
     
  6. Oct 13, 2010 #6

    truckus

    truckus

    truckus

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    axle mods done but...

    I finally had the time to do some of the axle mods outlined here and as well as from MonsterBrit (thanks guys). I used a dremel to scuff out some areas and also used an exacto knife blade to score areas for better epoxy adherence. a cheap brush and a bottle of semi gloss black was later used to cover things up. I used mainly Loc Tite brand gel epoxy but also used some 15 minute Mid Cure epoxy as well. To make it easier for me to fill up the top link mounts with epoxy I first super glued two pieces of lexan to each mount, then slowly filled it with epoxy. Once this was done I had extra epoxy left so I threw some on the sides as well.

    Charged up the 5000mah lipo, put on an old body and did 20 jumps off my flat ramp (only 5" high, see my video from a few months ago) and did well until I saw one wheel with excess camber. Turned out that the steering hub/knuckle? cracked and let go of the screw holding it in. Not bad but not a thorough test yet, so repairs will be in order. I'm including pics to show my attempt at the modifications.

    One question: while disassembling my axles/diff I found out the 3 prong star shafts' prongs broke off but were still "riding" in its holes in the diff and stayed in place because of the housing's molded "fin" areas. Can I still run the truck like this? Seems to drive okay and I don't know when these shafts actually broke....? The prongs centered the gear to mesh with the other gears in there so am I losing some tolerances and grinding things to death in there?
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  7. Oct 13, 2010 #7

    MonsterBrit

    MonsterBrit

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    Great to see the upper link mods working out for people. I haven't got to put a lot of mileage on the TXT-1 because of my steering issues and having to tend to a sick me and a clod with a bad leg :)

    I assume you mean the 3-prong star shaft highlighted in red below?

    [​IMG]

    If the shaft has broken free of the boss in the middle ( along the yellow line above) but is still held at the outer end the little shaft might look like it's sitting fine but under high stress, because it's not held in the centre, you'll get 'end float' meaning the shaft may move off position at the inner end. This causes uneven and/or excess wear as the teeth mesh slightly off angle. This will damage both the planetary gear on that shaft and also the two larger drive gears, which in turn wear the rest of the planetary gears. Messy.

    If it's broken I'd change it as soon as you can, they are well known for snapping I believe. I keep meaning to get a spare set for mine.
     
  8. Oct 15, 2010 #8

    HawnMT

    HawnMT

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    Jason's Store on eBay. He's in Japan but shipping's pretty fast. And it costs pretty much the same too. I recommend getting two sets.
    http://cgi.ebay.com/9445934-Tamiya-...Control_Parts_Accessories&hash=item51948d2da2

    He also sells the upper gears and other stuff which are near impossible to get anywhere else including Tamiya USA.

    http://cgi.ebay.com/9805659-Tamiya-...Control_Parts_Accessories&hash=item563d98ffbd
     
  9. Oct 16, 2010 #9

    truckus

    truckus

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    ceramic grease option?

    thanks HawnMt and MonsterBrit,
    I will be ordering these parts tomorrow. I can't wait to have fresh gears in the axles.

    One question: If I ran out of tamiya gear grease is it okay to use some automotive/marine grade grease (Bel-Ray) or lithium based grease in the gears? I know the tamiya grease would be the first choice, but I have used the others in the past with great results; but someone tell me if I am doing my gears wrong (what if the heavy grease caused my star shafts to break??).
    thanks guys :tmb
     
  10. Oct 16, 2010 #10

    HawnMT

    HawnMT

    HawnMT

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    Depending on the truck and it's application, I've used marine grease, lithium grease, rocksmith gearjelly, or the Tamiya grease. I don't think any of them have had any adverse effect on the gears but I do wonder if maybe some of them did on the plastics. It's hard to tell, since I don't know how old the housing were when I got them, if it was the grease or just time that made them brittle.
     
  11. Oct 17, 2010 #11

    MonsterBrit

    MonsterBrit

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    Does GearJelly work in plastic gearboxes? I thought it was metal gear only stuff?

    I did my WK gearbox and TXT axles with it and it's as smooth as silk, but I never used it on a plastic gearbox because I thought it wasn't any good for them? It'd be nice if it was plastic-friendly because I could use it in the clod and I've got pots of the stuff left over from my rock crawling days :)
     
  12. Oct 17, 2010 #12

    truckus

    truckus

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    HawnMT:
    Jason ebay store seems to have run out of the star shafts pack and I've had no luck looking elsewhere for this bag. He does sell the large bag full of other parts including the bevel gears and star shafts but its like $40. I did find a bag of these parts that looks similar (they use the photo you used in this thread) and the part number is 50602. Do you think this is the same exact part I'm looking for?
    thanks
     
  13. Oct 17, 2010 #13

    HawnMT

    HawnMT

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    The 50602 is for a much smaller differential like the tlt. I know it looks the same but TXTs are much larger with a different spline for the axles. The only part that is the same in that bag is the 9mm washer.

    I think that $40 bag you saw was this:

    http://cgi.ebay.com/9415812-Tamiya-...Control_Parts_Accessories&hash=item563f8931d0

    That bag contains two complete differentials(diff housings and gears w/ star shaft) as well as the top gears and some other stuff.
     
  14. Oct 17, 2010 #14

    HawnMT

    HawnMT

    HawnMT

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    Yeah it's only for metal gears. What I meant was I wasn't sure if it was good for the plastic axle housings. Seems like TXT axle housings get brittle faster than other kits. It's not just mine but other folks' trucks too. So I'm not sure if the lubricants we're using is doing it or if its the plastic itself.
     
  15. May 13, 2011 #15

    808XD

    808XD

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    to my knowledge they are the same parts
     

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