Some things I found interesting in the manual:
Step 1: Same suspension arms and spacers as TB03...
Step 2: The suspension blocks don't have any shims under them, unlike the TB03.
Step 3: The differential gear box parts tree is the same part number between the TB03 and TB04 (51351), so I think that opens the door to using the TB04 gear diffs in a TB03 chassis.
Step 4: Ah, gear diffs! The metal cup joints are appreciated as the TB03 used plastic cup joints with the ball diffs. The ring gear looks like it could be used with either the gear diff or with the ball diff. I'd hop up these diffs with the metal gears and metal cross pins while building them. I don't see recommendations for diff oil weights.
Step 5: Building the spur shaft and rear gearbox prop shaft...
Step 6: For the TB03 it was important to check the gear meshes and adjust with shims as necessary. Since the TB04 is using the same diff gear boxes, I'm assuming this has to be given the same consideration again. This involves fully assembling the gearbox, then checking for lash and binding, then disassembling and adding/removing/shifting shims around to get it just right. I think you really have to pay attention to this step to get the best result.
Step 7: Again, I'd check for any lash and binding, and adjust shims as necessary.
Step 8: New rear stiffeners...
Step 9: Same rear hubs as before...
Step 10: Since the TB04 is using the same gearbox, suspension arms, hubs, and axles as the TB03, I assume the same CVDs can be used instead of the dogbones supplied in the kit.
Step 11: One of the front suspension blocks needs to be filed a little...
Step 12: Same front arms and spacers as the TB03. Also note the same base suspension blocks -- 1XA, 1D, 1A, 1A.
Step 13: No shims under the front blocks either.
Step 14: Front gearbox...
Step 15: I find the steering very interesting here... The arms and bridge are still plastic, but the bridge now uses 730 ball bearings instead of flange tubes. This is like my TB03 steering bridge mod where I drill out the holes with a 15/64" drill bit and install flanged 630 bearings. Also, something else of interest is the longer tie rods now connect to the center bridge instead of the individual arms. The total slop across the steering from knuckle to knuckle should be very low. The ball bearings should reduce the slop between the arms and bridge. Then the final bit of slop will be in the servo saver and servo. All in all, a big improvement over the TB03 steering setup.
Step 16: The PRO kit is also including ball bearings for the steering arms...
Step 17: Front gearbox... Same thoughts about binding/lash/shims apply here. Note the spring in the front cup joint instead of a urethane sponge...
Step 18: The front stiffener is a new part with a new sprue parts number, but it does essentially the same thing as K1 on the TB03.
Step 19: Nice, front CVDs! I'm ok with front CVDs and rear dogbones. I like how these CVDs have a retaining clip for the cross pin instead of a grub screw; I've seen this in other makes/models over the past year or two.
Step 20: Same front assembly...
Step 21: Whoa, this is interesting! The center prop shaft can be installed and removed without removing a gearbox! That's what that spring in the front cup joint is for!
Steps 22/23/24: I was looking for more O-rings based on my DB01R dampers, but it looks like the only O-ring is for the threaded collar for ride height adjustment. I hope there isn't much play between the piston and e-clips on the shaft. All the V-parts are common with just about every other high-end Tamiya car (TRF415, TA06, TA05V2R, etc.)
Step 25/26: The carbon damper stay is pretty nice with all the mounting hole options. There should be more options for fine-tuning this way. Of course you could also use the older TB03 stays and dampers if necessary; maybe the TB03 parts are in the base TB04 kit?
Step 27: Well, this could be the most polarizing aspect of this kit. The T5/T7 parts surround the pinion and limit how large a pinion can be used. Later in the manual there is a table showing 21T to 30T pinions with gearing ranges from 7.86:1 to 5.50:1. For all the guys running 25.5T, 21.5T, or 17.5T motors this might put them off as they're typically striving for lower gearing. This seems like an area for experimentation with the largest pinion and a smaller spur gear with the motor positioned as close to the spur as possible. The TB03 could go as low as 4.58:1 per the manual.
Step 28: Upgraded servo saver compared to the TB03...
Step 29: Trade off here... For the TB03 you would have to cut part of a servo case to make room for the center prop shaft... For the TB04 it looks like there is no need to cut the servo, but now the servo link is more difficult to adjust without a turnbuckle.
Step 30: Pretty normal electronics installation.
Step 31: Typical tire installation. The kit includes wheels but no tires; that's ok as you'd want to pick the tires for the conditions anyhow.
Step 32: Fancy blue wheel nuts, but plastic drive hexes. I've used clamping wheel hexes in the past and they are worth it. They look good, the cross pin never falls out, and the wheel mounting surface runs true.
Step 32/33/34/35: Pretty much the same bumper, body post, and battery strap parts as before. The front of the battery strap is held in place with a screw instead of a post and body clip now.
Step 36: Tamiya is calling out the TA06 sway bar set for the TB04; they listed the TA05 sway bar set for the TB03. Anyone know if there is any difference between the two sets?
Things I like:
- Lots of parts commonality with the TB03, which means TB04 gear diffs could be used in a TB03, or TB03 parts could be used on a TB04. The new TB04 front one way/spool could be used in a TB03. I like the suspension parts commonality between TB03, TA05, TRF416, TRF417, TB04.
- New gear diffs provide some durability and low maintenance. Put the metal gears and cross pins in the gear diffs to start; the parts are cheap. It would be easy enough to run 100k or 500k oil up front for a pseudo-spool effect and run 1k or 2k in the rear. The metal cup joints are appreciated.
- The new steering rack looks like a big improvement over the TB03 rack with much less slop anticipated. I like the ball bearings in the bridge.
- New 6 degree caster hubs should make the steering a little less sensitive.
- The retaining clips on the CVDs are nice.
- This will sound kind of silly, but I like the spring-loaded center prop shaft. It just makes maintenance and changes easier as I don't have to line up the shaft while I'm trying to reinstall a gearbox on the chassis.
- The carbon damper stays won't flex like the stock TB03 plastic stays, the short shocks should lower the COG just a little, and the traditional front setup won't be as sloppy as the IFS setup. The IFS setup is nice for using low body shells like the LaFerrari and other Autobacs TB03 shells, but it's not the performance solution with all the extra moving parts and tolerances.
- Better stock servo saver.
- Don't have to cut a servo mounting ear to make it fit.
- Flat battery tray.
- Molded-in AMB transponder mount.
- I should be able to reuse some of my non-Tamiya TB03 bodies from HPI and Protoform with the same mounting holes.
Things I'm questioning:
- The T5/T7 motor spacers really restrict the pinion options. I wish Tamiya would have put the motor mounting plate on the other side of the spur. I would think a lot of sales would come from 17.5T and 13.5T customers, so gearing is important.
- Plastic internal diff gears by default. Maybe this is helpful from a rotating mass perspective, but I'm wondering about durability. At least there is a metal gear option available.
Minor whining:
- Shimming all the bevel gears for minimal lash and best wear will still take some work with iterative assembling/disassembling of the gear cases.
- Filing the front 1A suspension block to clear the steering. This seems to imply filing an aluminum mount, too, if I wanted to install one.
- Cutting the ball cups for the steering servo linkage is another small hassle like filing the front suspension mount.
That's all, folks!