B-MAX4 transmission tight?

[sosidge]

Anyone else having a few issues with the B-MAX4 transmission?

I'm a little disappointed to be honest. Seems like the tolerances on some of the plastic mouldings are way too tight, it puts pressure on the bearings and things don't spin freely.

On the centre transmission case, the lower half is fine, but add the top deck and top cap and it all tightens up. I've had to remove quite a lot of material from the inside of the top deck and from the top cap to get it to spin freely (probably a little too much in fact which is just as annoying).

On the front and rear gearbox cases, the standard shimming is way, way too tight, I can't imagine anyone getting away with it. Plus the diffs don't spin freely with a shim on each side, they jam up in the cases. I ran the car on Thursday night with the alternative setting in the manual, but it's still too tight, I've now taken a shim off the diffs to put it on the loosest setting, this is better but on the edge of being too loose.

It's almost as if the plastics used in the mouldings haven't shrunk as much as Yokomo intended and everything is a couple of tenths too big.

Anyone else found this or have I just been unlucky with my parts?

[DaveG28]

Anyone else having a few issues with the B-MAX4 transmission?

I'm a little disappointed to be honest. Seems like the tolerances on some of the plastic mouldings are way too tight, it puts pressure on the bearings and things don't spin freely.

On the centre transmission case, the lower half is fine, but add the top deck and top cap and it all tightens up. I've had to remove quite a lot of material from the inside of the top deck and from the top cap to get it to spin freely (probably a little too much in fact which is just as annoying).

On the front and rear gearbox cases, the standard shimming is way, way too tight, I can't imagine anyone getting away with it. Plus the diffs don't spin freely with a shim on each side, they jam up in the cases. I ran the car on Thursday night with the alternative setting in the manual, but it's still too tight, I've now taken a shim off the diffs to put it on the loosest setting, this is better but on the edge of being too loose.

It's almost as if the plastics used in the mouldings haven't shrunk as much as Yokomo intended and everything is a couple of tenths too big.

Anyone else found this or have I just been unlucky with my parts?

Can only speak for the one I've built, but had no problems with it in that way. The centre went together fine (I think, I'll check it again now!), and the front/rear boxes were fine on the alternative looser manual setting. I have done 3 meetings on it so far.

When I ran the Aero I had issues with it always being too tight, I ended up running in on a bench for about 30 mins after every rebuild, have you tried a long run-in? Are you using grease in the gearboxes? Also, tip from the Aero, is your pinion gear on the shafts definitely fully on and flush? I had to remove flashing from where it sat on the pin in that car?

Dave

[sosidge]

I'm pretty confident I have assembled the car right. I've had a few shaft drive cars in the past (including Yokomo SD and Kyosho Lazer ZX-5), and I have already had the drivetrain apart a couple of times to double check it.

After my mods to the centre gearbox and the shimming the car rolls very freely and silently with the pinion off. Before it hardly rolled (felt more like a belt-drive car on a tight setting) and crunched, particularly from the rear box. I'd be interested to know what yours does.

To be fair to the car it ran just fine at the meeting on Thursday night, a little crunchy at low speed, but I'd rather a free transmission than a tight one, should make for a faster, more efficient, more correct car.

I'll be adding a few more fine shims to it to get the mesh spot on without risk of stripping the gears (Yokomo shims are about 0.25mm thick, I've got some 0.1mm TOP ones coming).

[DaveG28]

I'll check mine when the motor is next out, I haven't since I put the top on the centre assembly! Just suggested the pinion input as it was a b*****d on the Aero I had!! Hope it runs ok now!

[sosidge]

Well, as I feared, taking the shim off the rear diff was a step too far, I chipped the teeth on the bevel gears. Fortunately, shimming it back up tight kept it running for the final.

Unfortunately I could not get my hands on any fine shims today but I think these will greatly improve the mesh for the future.

I'm kind of left wondering today whether I have got a bit too obsesed with the drivetrain... unfortunately I didn't see any other B-MAX4's at the NE regional today so had nobody to compare notes with!

[bigred5765]

i built up Chris cocker's for him, shimmed it up nice and tight ran it for 4 Min's in practice, checked it after and its slightly tight but nothing bad that creates to much heat, we re shimmed it so it was free, and it eats the diff and pinion gear,leave it slight tight it runs sweet.

[Rbettington]

I built a mates one of these last week and ran into the same issues, played around with the kits shims and got it a little looser. I'm hoping it will free up after the first run.

[sosidge]

Well, I took another look at the drivetrain last night, after a proper off-road race meeting. As I mentioned above I chipped some teeth from running the mesh too loose at the meeting.

Gave the gears a good tidy up, scraped out the tooth chippings, spent a little time with some finer shims, and got everything running as smooth as I could but with no backlash.

Funnily enough the shimming is getting closer now to the original kit setting. I have the front gearbox midway between the kit and alternative settings, I have the rear gearbox at equivalent to the alternative setting.

So I think I was a bit premature in my disappointment with the drivetrain (sorry Yokomo!). Give the car a few solid race meetings, keep and eye on the drivetrain, don't run it loose, and it should bed in nicely.

I was probably a bit rash in modding the top deck and centre gearbox top too. Thankfully the spur is undamaged but I'm not sure the mods were necessary at the end of the day - nobody else seems to have done them! (Note to self - must avoid late-night wrenching - tired mind + obsessive nature = silly modifications) :cry:

[Spoolio]

(Note to self - must avoid late-night wrenching - tired mind + obsessive nature = silly modifications) :cry:

Oooooohhhhhh yeaaaahhhh, I think we've all been there often enough, usually the night before a meeting :).

Wonder what the daftest example of this is.

Last time I suffered from it was when I finished rebuilding my old RC10 at 3am, then got up at 6:30 and tried a precautionary run on the street. Spent the next 30 minutes frantically ripping it to pieces - 'cos it there was no drive to the wheels - before the penny dropped that I'd not tightened the diff thrust screw :blush:.

[albertobdq]

On my bmax the transmission was terrible at first, I rebuilt it following the alternative setting suggested at the manual, it improved a bit. After a 5min break-in procedure with no wheels attached things improved a lot. Now it's really slick.