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Volksbury

Grand Hauler Gearbox Problem

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Hello.  After building a couple of cars, I’ve taken the plunge and started on my first 1/14 truck, a Grand Hauler in Matt Black.  All is going well until I hit a problem with the gearbox.  I was getting a grating sound when engaging 3rd gear, as the shift rod was not being pulled far enough by the servo.  A longer servo horn seems to have resolved the issue, but all gear changes (with the exception of 2nd to 1st) are clunky and result in a grate/grinding noise on changing.  I’ve taken the gearbox out and rebuilt it in case I’d got something not quite right, but this doesn’t seem to have made any difference.  When the gearbox is out of the truck and just attached to the motor, manual pushing of the shift rod is much more efficient although still a bit clunky in and out of 3rd gear.  

Does anyone have any suggestions as to what might be the cause as I’m starting to run out of ideas?

Many thanks

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Hello,

The MFC manual should have instruction how to set the gears to stop grating. You will need to read it 5 times before understanding.

Basically set 2 certain trims to max on the transmitter and then power the truck up. It will enter 'teaching' phase.

Then you can move transmitter leaver to engage first gear and SET that position...then you do 2nd ands third gear.

 

Once finished, when you move the transmitter sticks it will make the servo move the amount that you programmed.......

Of course you need to make sure the servo can throw all the way to first and third. So suggest extending the rod or move it to outer hole on the horn. even if it initially binds, and then do the programming.

When you do the programming you will stop it from binding as you will have told it when to stop for each gear.

 

Sorry to ramble, and good luck

Russ

 

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you might find it could be the steering servo horn as it has notches in it for ajustment i think i had the same prob with my grand hauler as it turned out to be that take note of e6 and e7 in the manual

IMG_20180630_074936.jpg

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Thanks very much for the responses.

Topforcein - I figured that was a problem so I’d changed the parts for some spare ones I had in order to make a longer ‘throw’ from the servo.  Alas, no joy though.

Dafinity - I’ve read the manual again and searched online, but couldn’t find anything about this ‘learning’ activity.  There is the standard 6 steps that are in the manual, that I’ve done, but nothing that I could find about maximising the trims.  Don’t suppose you have any more information?

Thanks again for your help.

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16 hours ago, Volksbury said:

Thanks very much for the responses.

Topforcein - I figured that was a problem so I’d changed the parts for some spare ones I had in order to make a longer ‘throw’ from the servo.  Alas, no joy though.

Dafinity - I’ve read the manual again and searched online, but couldn’t find anything about this ‘learning’ activity.  There is the standard 6 steps that are in the manual, that I’ve done, but nothing that I could find about maximising the trims.  Don’t suppose you have any more information?

Thanks again for your help.

have you checked that the gearbox build was done correctly as i did manage to chuff that up also and ended up rebuilding it. some parts need to go on in a certain way i think i spent a good hour on building it and following the instructions to the tee as this was my first 3 speed build also.did you put the gear shaft in the right way 

have you left the little plastic jobbie that it tell you to use while building

even the rear axles pulled me up when i installed them i noticed the drive shaft was offset i ended up takeing them out at least 5 times and even taking it to my lhs to ask what i did wrong but it turned out it was meant to be like the and the only thing my lhs pointed out was the fifth wheel was'nt built right as it was sitting level and not facing up

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Topforcein - Thanks again.  I’m pretty sure that it was built correctly, as I did pay extra close attention on the re-build.  Got the little plastic jobbie in as well.  I did wonder if I’d got the 3rd selected gear the wrong way round, as that was the one causing the problem, but it really only goes in one way.  I refitted it back to the truck and it runs fine with the extended servo horn.  Now, whether that is because you don’t hear anything above the noise of the truck moving, I don’t know, or whether it is the fact that there is some movement from the road wheels turning that is helping to equal things out?  

I too had problems with the driveshafts, and had to remove the edge from one of the metal casings, as it was hitting the plastic cover.  I also lost drive to the rear wheels before realising that the little grub screw had come out from the rear axle, so the cone was just literally turning on itself!  Alas, my 5th wheel is also sitting flat, so sounds like I’ve got to look at that again.  Trouble is, with one set of instructions with the truck, one with the MFC and another set for the support legs, it’s a little confusing!

Thanks again.

Martin

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A common gear shifting problem of the Tamiya Tractor Truck gearbox is caused by using too many ball bearings! 

Some sell / buy ball bearing sets for these models with the best intentions, including bearings to replace absolutely all the bushings. However, in the gearbox, part J7 should not have the bushings replaced with ball bearings. There is no rpm-difference between J7 and the shaft it's sitting on, but J7 needs to glide freely along the shaft. The included bronze bushings cause low friction in the linear movement of J7 on the shaft (when lubricated), whereas the hard steel of the ball bearings causes high friction, hampering gear shifting. Probably not the problem in your case, but it doesn't hurt mentioning it, because it happens quite often.

Untitled 2.jpg

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Thanks Mokei.  Initially, I hadn’t glued those bronze bearings in place, but I did on the subsequent rebuild, although they were a tight fit anyway and getting them in place without getting instant glue all over me was a little tricky!  I believe that the only ball bearings in the gearbox are the ones in the 2 metal end plates (4 in total) where the 2 gear shafts sit.  All of the bearings in the plastic cogs are bronze ones, although it is only the J7 ones that have been glued; I assume I’ve read the instructions correctly that this is correct?

Thanks again

Martin

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One more thing to check - do you have the shift forks the right way round & also all the springs + spacers on the shifter rod in the correct places. 

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the fifth wheel is just down to the spring  not located properly or the wrong way round

plus if you can give us a video of the problem

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Tamiya big stuff - Thanks, I’ve checked the forks but all looks OK as does the rest.  Have got springs etc all OK. 

topforcein - Will try and get video over the next few days - thanks again.

 

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Have you managed to get the MFC into setup mode and set the servo positions for the transmission?  I'm sure there's a way to do it but I don't have my manuals right now.  If you don't set that right then you may have problems regardless of what changes you make to the servos and shift rods.

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Dafinity - Thanks so much for the instructions, they are certainly not in the manual that I have, so I’ll give them a go.  

Thanks again.

Martin

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Transmission teaching is only for the MFC-03, if you have the MFC-01 it is not used. 

Sometimes when using an analog transmitter (all trims must be centered) and the steering and shift servos are centered you may not get the desired effect with the gearbox or the truck running straight. This is when you may need to adjust the servo horns or tie rods away from factory settings to make the truck operate correctly. If the truck selects 1st and 2nd fine, but 3rd is a little graunchy or it pops out sometimes, then a simple extra 'one turn lengthways' might be all it needs to stay in gear (or track straight). 

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Thanks berman for the info.  I’ve got a new higher spec servo coming for the steering, so when that arrives and I’ve got it apart again, I’ll try the tweaking to the gear change servo as well.  I’ve noticed that the servo is pushing/pulling the shift rod to the end of the travel OK, so maybe the graunching is still from inside the gearbox itself? 

Thanks again

Martin

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If the shift rod is moving to the end of its travel but still not engaging gear correctly that would imply a minor assembly error.

Check the 3rd gear shift fork is the correct way round on the shift rod again.

The 3 shift forks do not all go the same way round.

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Ok as Tamiyabigstuff says if the shift rod is being pushed to both ends by the servo it will be an internal error. 

Quite a few first time builders miss the fact that the manual has a 'rotate shaft' arrow to build the other side of one of the gear shafts so it is possible one of the constant mesh selectors could not be on correctly or another possiblity is one of the splined nuts that the gears sit on is on backwards.

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Apologies for the delay in replying, but I think I’ve managed to solve this issue as a side effect of fitting a slower motor to the truck.  The standard motor was far too quick for the truck, so I fitted a 55T motor in it’s place.  By slowing everything down, I no longer have any crunching or grating noises.  I’d previously tried swapping around part BD12 (Long Gear Hub), as this has a small lip on one end and the instructions aren’t totally clear as to which way they should go on, but this made no difference.  So, not only does everything seem OK, it’s much easier to drive, particularly indoors now.  Many thanks to all who have taken the trouble to help over the last few weeks.

Martin

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